The Anatomy of Dorsal Ramus Nerves and Its Implications in Lower
University of Adelaide...2 TABLE OF CONTENTS LIST OF FIGURES................. LIST OF...
265
23'5'15 ¡t Cephalometric Evaluation of Mandibular Relapse followirg Vertical Subsigmoid Osteotomy Martin Ching, B. D. Sc. (Melb.) Oral and Maxillofacial Surgery Faculty of Dentistry The University of Adelaide South Australia 1.995 fir"o¡''ioc( l.1i;{
Transcript of University of Adelaide...2 TABLE OF CONTENTS LIST OF FIGURES................. LIST OF...
23'5'15
¡t
Cephalometric Evaluation of
Mandibular Relapse followirg
Vertical Subsigmoid Osteotomy
Martin Ching, B. D. Sc. (Melb.)
Oral and Maxillofacial Surgery
Faculty of Dentistry
The University of Adelaide
South Australia
1.995
fir"o¡''ioc( l.1i;{
2
TABLE OF CONTENTS
LIST OF FIGURES.................
LIST OF TABLES...................
1..1 Oaeraiew.......
1.2 Vertical ramus osteotomy.
T REVIEW OF THE LITERATURE.............
CIIAPTER 2. Manilibulør prognøthism...
2.1 Definition
2,2 Classification of mandibulør prognøthism......................
2.3 Incidence of møndibular prognathism............
2.4 Surgery for the treatment of mandibular prognathism
2.5 Complications of aertical subsigmoid osteotomy
2.5.1 Intraoperatioe complications..........
2.5.2 Immediate postoperatiae complications..............
2.5.3 D elay ed postoper atiae complicøtions.............
8
11
74SUMMARY.........
STATEMENT.........
ACKNOWLEDGMENTS.........
I INTRODUCTION.........
CIIAPTER 1. Cephølometric eztøluøtion of reløpse following
o ertic al sub sigmo iil o ste of o rny ............
18
19
1,6
77
27
22
23
23
23
27
30
36
38
42
45
48
79
2,5.4 Complications øssociated with extraoral approach.....
3
CHAPTER 3,
Intr oducti0n.................
Orthodontics and occlusion..
4.2.1 Postoperatiae mønagement.
Magnitude of mandibular setback..
Reløpse f ollowing zt ertical sub sigmoid
o steotomy ............... 51
3.L Defining postsurgical relapse 51
3.2 Measurement of postsurgical relapse .........53
3.3 Early, intermediate and long term relapse...... ...........56
CIIAPTER 4, Føctors øssociøted with postsurgical relapse
following oerticøl subsigmoid osteotorny..................,.......... 60
4.1
4.2
4.3
4.4
4.5
..60
65
66
Condylar position .......67
Proximal and distøl segment positioning ......77
4.5.1 Rotational et'fects between fragments .................72
4.5.2 Medial displacement ot' proximal segment... ....73
4.5.3 Wire osteosynthesis between the proximal and
distal segments 74
4.6 Maxillomandibular fixøtion... 76
4.6.L Period of maxillomøndibulør fixation 76
4.6.3 Wires 79
4.6.4 Skeletal fixation... 79
4,6.5 Nutritional aspects ot' healing. 80
4.7 Muscular interactions........... 82
4.7.1 Tongue pressure after reduction of tongue space.................,..........82
4.7.2 Bite force and its aector componenús............ 87
874.7.3 Masticatory muscles........
4.8 Vascular considerøtions of osseous segments. .........89
4
4.8.L Healing of osseous segments..
4.8.2 Viability ot' osseous segments
4.9 Growth
4.9.L Normal growth
4.9.2 Hemimandibular elongøtion
hy p erplasia ..............
Single jazo aersus bimnxillary procedures.....
Cor onoidect omy .............
High angle mandibles
and hemimandibular
89
90
90
90
95
96
97
97
99
99
' CIIAPTER 5. Cephø\ometry..........
5.1. Introduction............
5.2 Eruorsofprojection.............,.
4.10
4.11
4.1.2
5.3
101
Errors of superimposition....
5.4 Eruors of landmark identification
5.5 Errors of digitising.............
103
105
1,07
5.6 Enors of measurement.........
5.7 The selection of a suitable line of reference...
III MATERIALSANDMETHODS...............
CHAPTER 6. Eaaluation of postsurgical rclapse..
6.L Selection of patient records......
6.2 Radiographic technique.
6.3 Tracing and digitising procedure....
6.4 Reference points and lines
6.4.1. Hard and soft tissue points
6.4.2 Cephalometric lines
6.4.3 Calculation of linear ønd angular oariables.,
6.5 Statistical analysis
108
1,09
't72
113
113
776
779
722
722
125
127
130
5
CHAPTER 7. Erors of the method
7.1 Materials and methods... 732
132
737
147
1,42
742
1,42
1.45
145
IV RESULTS 736
CHAPTER 8. Early, intermeiliate anil long term dentoskeletal effects
following zterticøl subsigmoiil osteotottty ...........................737
8.1 Intr o duction............
8.2 Analysis of aariables by gr0ups............... ......737
8.2.1. Horizontal mandibular mooement at Point 8................................739
8.3 Analysis of aøriables 739
8.3.1 Mandibular mooement............. 1,40
8.3.L.1. Horizontal set bøck and re1apse.............. ....740
8.3.1.2 Vertical moaement and relapse........
8.3.7.3 Angle SNB
8.3.2 Proximal and distal segment ølteration.
8.3.2.1 Condylar displacement (S-HA)
8.3.2.2 Posterior facial height ................143
8.3.2.3 Anterior føcial height
8.3.2.4 Mandibular plane angle ( SN-Go-Me)............ ............ 1,44
8.3.3 Segmental inter-relationships
8.3.3.L Gonial angle (Ar-Go-Mù.............
8.3.3.2
8.3.4 Dentoskeletal changes
8.3.4.L
8.3.4.5 Oaerbite.
1,46
Maxillary incisal ang1e........ .......746
8.3.4.2 lnterincisal ang1e........ 1,46
748
8.3.5 Sex of patients.... 1,49
6
8.3.6 Períod of maxillomandibulør fixation
8.3,7 Age of patient at time of surgery
8.3.8 Orthodontics aetsus no orthodontics
8.3.9 Influence of maxillary surgery
8.3.9.1 Horizontal moaement and relapse
8.3.9.2 Vertical moaement and reløpse.....
8.3.1-0 Influence ot' hyoid position
8.3.1.0.1, Horizontal moaement and relapse
8.3.L0.2 Vertical mor¡ement and relapse......
8.3.1-1 Pharyngeal depth (AP-PP)...
8.3.11.1 Horizontal mooement and relapse
8.3.1,1.2 Vertical mooement and relapse...
8.4 Complications following aertical subsigmoid osteotomy
8.4.1- Intraoperatiae complications
8.4.1,.1, Haemorrhage.........
8.4.2 Immediate postoperatiae complications...........
8.4.2.L Condylar dislocation
8.4.3 Deløyed postoperatiae complications............
8.4.3.1 Postoperatiae int'ection..
8.4.3.2 Sequestration of proximal segment
CIIAPTER 9. Results: Errors of the method
9.L Error ot' the method
150
151
151
1.52
1,52
153
153
1,il
1,54
155
155
156
1,56
1,57
757
757
757
757
158
158
158
759
759
7
V DISCUSSION.........
CH,APTEIR 1.0, Discussiott...............
10.1 Patient selection
10.2 Materiøls and methods
11.9 Growth.......
11.10 Single jaw as bimaxillary procedures.
7L.12 High angle mandibles
vr coNcLUSroNS........
CIIAPTER 1.2. Conclusions.
VII APPENDIX.....
Appendix - Intraoral vertical subsigmoid osteotomy.........
VIII BIBLIOGRAPHY.
776
173
774
774
194
795
197
798
204
205
CH,APTER 77. Discussion - Factors in reløpse of zsertical
subsigmoiil osteotoffiy....,...... ...............778
Ll.L Definition of relapse.. 778
LL.2 Orthodontics and occlusion...........¡....... ........778
11.3 Møgnitude of mandibular setback 180
1-1-.4 Condylar position 181
11.5 Rotational effects between fragments.. 183
11.6 Wire osteosynthesis between the proximal and distal segments 7U
LL.7 Møxillomandibular fixation... 185
LL.8 Muscular interactions................... .1,87
789
11..11 Coronoidectomy....... ......792
.792
192
B iblio gr aphV ..........
8
LIST OF FIGURES
Figure 2.1
Figure 2.2
Figure 2.3
Figure 2.4
Figure 4.1
Figure 5.L
Figure 6.1
Figure 9.1
Figure 9.2
Calculation of the enlargement factor for points lying
on the mid-sagittal plane.
Figure 6.2 Hard and soft tissue points listed in order of
digitising sequence.
Figure 6.3
Figure 6.4
Figure 7.L
Variations of skeletal pattern of Class III malocclusions.
Surgical techniques performed in the vertical rami
of mandible to correct mandibular prognathism.
Mandibular divergence angle.
Panoramic radiograph showing anterior dislocation
of the right mandibular condyle....
Average growth curves for males and females..
Reference lines.
Differences between digitised double determinations
for nasion (N). ..........
Differences between digitised double determinations
Cephalometric lines.
Angular and linear variables used to evaluate
dentoskeletal changes following vertical subsigmoid
osteotomy. .............. ...........129
Hard and soft tissue points listed in order of digitising
s€quence. 133
26
31
34
4't
93
111
118
727
126
1,63
763
.764
Figure 9.3 Differences between digitised double determinations
for orbitale (Or)......
Figure 9.4 Differences between digitised double determinations
for condylion (Co)... 764
9
Figure 9.5 Differences between digitised double determinations
for hinge axis (HA). 765
Figure 9.6 Differences between digitised double determinations
for articulare (Ar). 165
Figure 9.7 Differences between digitised double determinations
for gonion (Go)......... 766
Figure 9.8 Differences between digitised double determinations
for menton (Me)...... 1,66
Figure 9.9 Differences between digitised double determinations
for pogonion (Pg). ...1,67
Figure 9.10 Differences between digitised double determinations
't67
Figure 9.11 Differences between digitised double determinations
..168
Figure 9.1,2 Differences between digitised double determinations
for ANS. 1,68
Figure 9.L3 Differences between digitised double determinations
for PNS... ..........1,69
Figure 9.L4 Differences between digitised double determinations
for upper incisal tip (IS). 1,69
Figure 9.L5 Differences between digitised double determinations
for upper incisal apex (AS) ...............770
Figure 9.L6 Differences between digitised double determinations
for lower incisal tip (AI). 770
Figure 9.L7 Differences between digitised double determinations
for lower incisal apex (II). .................777
Figure 9.L8 Differences between digitised double determinations
for upper molar crown (MS). 171,
10
Figure 9.19 Differences between digitised double determinations
for lower molar crown (MI).......... ....172
Figure 11.1 Mandibular relapse identified on clinical review ........,..191,
77
LIST OF TABLES
Table 1.1 Synonyms used to describe the vertical subsigmoid
osteotomy. ...... 2"1
Table 2.1
Table2.2
Table 2.3
Table2.4
Table 2.5
Table 2.6
Table 4.1
Table 6.1
Table 6.2
Table 6.3
Table 7.1
Table 8.1
Table 8.2
Table 8.3
Table 8.4
Table 8.5
Table 8.6
Table 8.7
Prevalence of Class III malocclusions (Iacobsen et al. 1974)...........29
Prevalence of Class III malocclusions (Lew et al. L993)...................2g
Historical review of surgery to treat mandibular
prognathism................. 35
Percentage of complications with mandibular surgery .................. 36
Incidence of neurosensory deficit - sagittal split
osteotomy of the mandible
Incidence of neurosensory deficit - horizontal
42
osteotomy of the mandible 42
Table 3.1 Amount of mandibular setback and landmarks
used for measurements.... 53
Period of maxillomandibular fixation ..........76
Procedures performed in conjunction with vertical
subsigmoid osteotomy........... ...........115
Age at operation
Statistical analysis of mandibular relapse following
vertical subsigmoid osteotomy....... 130
Statistical analysis of the experimental error. 734
Comparison of relapse at point B(x) for group I...............................138
Comparison of relapse at point B(x) for group II.............................138
Comparison of relapse at point B(x) for group III............................139
Comparison of relapse at point B(x) for group IV...........................139
Comparison of relapse at point B(x) between groups.....................140
Comparison of relapse at point B(y) between groups............... ......140
11,6
Comparison of relapse at point B(x) - pooled data. 741
72
Table 8.8
Table 8.9
Table 8.L0
Comparison of relapse at point B(y) - pooled data...........................741,
Comparison of relapse for angle SNB - pooled data. .....'1.42
Comparison of relapse for distance S - HA(y)
143
Table 3.1L Comparison of relapse for distance S - HA(x)
- pooled data................
Table 8.12 Comparison of relapse for distance PFH
- pooled data..................
Table 8.13 Comparison of relapse for distance AFH
- pooled data...... 1/1 Á
743
7M
..1,49
Table 8.14 Comparison of relapse for mandibular plane angle (SN-Go-Me)
Table 8.15 Comparison of relapse for gonial angle (Ar-Go-Me)
- pooled data................
745
145
Table 8.16 Comparison of relapse for ramal angle ( SN-Ar-Go)
- pooled data.................. 746
Table 8.17 Comparison of relapse for angle Mx 1 SN
1,46
Table 8.L8 Comparison of relapse for interincisal angle
Comparison of relapse for angle IMPA - pooled data......... ............147
Comparison of relapse for overjet - pooled data.......... ...748
Comparison of relapse for overbite - pooled data............................749
Comparison of diffe¡ences in relapse at point B(x)
for sexes.
Table 8.19
Table 8.20
Table 8.21
Table 8.22
Table 8.23 Comparison of differences in relapse at point B(y)
for sexes
1,49
Table 8.24 Period of maxillomandibular fixation 150
13
Table 8.25 Comparison of relapse with different periods of
maxillomandibular fixation.
Comparison of relapse at point B(x) for age and sex...........
Comparison of relapse between orthodontics aersus
no orthodontics....
150
151Table 8.26
Table8.27
Table 8.28
Table 8.29
Table 8.30
Table 8.3L
Table 8.32
Table 8.33
Table 8.34
Table 8.35
Table 9.1
Comparison of relapse for point A(x) - pooled data................
Comparison of relapse for point A(y) - pooled data................
Comparison of relapse for angle SNA - pooled data..............
Horizontal movement of hyoid bone and
subsequent relapse
752
153
153
754
...754
155
155
1.56
1,56
762
Comparison of relapse for point H(x) - pooled data.........
Comparison of relapse for point H(y) - pooled data.........
Comparison of relapse for pharyngeal depth
tAp - PP(x)l - pooled data..........
Comparison of relapse for pharyngeal depth
lAp - PP(y)l - pooled data..........
Error for hard tissue points (horizontal axis) by double
determination..................
Table 9.2 Error for hard tissue points (vertical axis) by double
determination............
1.4
SUMMARY
A retrospective cephalometric study was undertaken to evaluate the long term
relapse potential following surgical setback of the mandible using the technique
of intraoral vertical subsigmoid osteotomy.
The investigation involved a detailed analysis of 24 sets of serial cephalometric
records consisting of 72 males and 12 females, in the Oral and Maxillofacial
Surgery Unit, The University of Adelaide. Of the 24 sets of patient records, 19
had longitudinal radiographs which had been taken a minimum of two years
following surgery. This series was studied for long term relapse.
The 24 records were assigned to one of four groups:
Group I: consisted of bimaxillary osteotomies in which a standard Le Fort I
maxillary osteotomy was performed in conjunction with the
intraoral vertical subsigmoid osteotomy (n = 1.4).
Grouo II:+ consisted of bimaxillary osteotomies in which a segmental Le Fort I
maxillary osteotomy was performed in conjunction with the
intraoral vertical subsigmoid osteotomy (n = 6).
Group III: consisted of bimaxillary osteotomies in which a quadrangular Le
Fort II maxillary osteotomy was performed in conjunction with the
intraoral vertical subsigmoid osteotomy (n = 2).
15
Group IV: consisted of intraoral vertical subsigmoid osteotomies only (n = 2).
Relapse was measured over the short, intermediate, and long term and
correlated with selected cephalometric variables. The results of the short term
study showed that minimal relapse occurred. The long term results showed a
further setback of the mandible occurring at the skeletal level, measured at point
B. The occlusion was maintained and was clinically acceptable. In one patient
only, significant relapse did occur and this was attributed primarily to surgery
being undertaken prior to the completion of growth.
In correlating factors which were associated with skeletal relapse following
mandibular setback, muscle forces, in particular the tongue, were identified to be
an important secondary factor. The hyoid bone was investigated to determine
its role in the relapse potential of the mandible following surgery as its position
reflects the position of the tongue which has been implicated as a causative
factor in relapse. A general trend was found whereby the hyoid bone position
initially moved down and backwards with the setback of the mandible,
presumably to maintain airway patency, but this slowly returned towards its
former position, although only in the horizontal direction. In the vertical
direction, the tongue occupied a more superior position and this was
maintained in the long term analysis.
76
STATEMENT
This thesis is submitted in partial fulfilment of the requirements for the degree
of Master of Dental Surgery. I declare that the text of this thesis has not been
previously published or written by another person except where due reference is
made. The findings are the result of my personal investigations. No part of this
work has been previously submitted for a degree in any University.
I give consent to this copy of my thesis, when deposited in the University Library,being available for photocopying and loan.
Martin Ching, B.D.Sc. (Melb.)
The University of Adelaide,
January 1,995.
77
ACKNOWLEDGMENTS
I wish to acknowledge the opportunity, given to me by Professor Alastair N.
Goss in 1989, to pursue a career in Oral and Maxillofacial Surgery. I thank you
sincerely. He has devoted considerable time and effort to ensure that I complete
my training in the specialty of Oral and Maxillofacial Surgery and I am very
appreciative of his leadership and guidance. To Dr. R.H.B. Jones, I thank you for
fostering in me all your surgical and clinical skills and expertise (1989-7993). My
sincerest thanks also go to Professor Tasman Brown whose assistance was most
valuable in collating and formatting the computer data.
I wish to also thank the Consultant Surgeons who have taught me so much
clinically and personally and to all the surgical Registrars with whom I have
been associated. In particular, I am indebted to Dr. Richard Hing for giving me
the impetus to pursue this topic as my Masters degree.
To my mother and father, I am gratefully indebted for all their trust and support
over all the difficult and trying years.
To all the assistants who helped in this research, I thank you
And finally to my grandmothers, Mrs. Lee Shee Ching, to whom I promised I
would complete medicine, passed away on 23rd April 1979 and Mrs. Siu King
Cheung, who passed away on 10th December 7993, during which time I was
preparing this thesis:
" This one's for you ! "
18
I
INTRODUCTION
CHAPTER 1,
CEPHALOMETRIC EVALUATION OF RELAPSE FOLLOWING BILATERAL
VERTICAL SUBSIGMOID OSTEOTOMY
l.L OVERVIEW
The prognathic mandible is a deformity which can display a variety of
functional and cosmetic disadvantages. Chapter L outlines the incidence and
nature of the prognathic mandible. The vertical subsigmoid osteotomy is a
proven surgical technique used to correct deformities associated with the
mandible. In particular, its usefulness is praised in the treatment of prognathic
mandibles. Relapse associated with this technique was initially unquestioned
and intensive assessment of the long term results since then has revealed
analyses supporting its stability. Many variables are implicated when relapse
does occur and Chapter 4 details these factors. Although the vertical subsigmoid
osteotomy is a user friendly technique with minimal morbidity some
complications can occur and these are presented in Chapter 2.
Relapse is a term which necessitates clarification on how it is defined. Chapter 3
discusses the use of this term. The most appropriate method for analysing
relapse is by cephalometric evaluation. Cephalometry is a subject encompassing
much information and a discussion of this subject is presented in Chapter 5.
Review of the literature identified a number of variables which provoked
thought and consequently several aims were established for investigation.
20
1
The objectives of the study were:
To retrieve data from the files of the Oral & Maxillofacial Surgery Unit on
patients who had mandibular setback using the vertical subsigmoid
osteotomy.
2. To quantify the amount of relapse of the mandible following setback using
the vertical subsigmoid osteotomy.
3. To establish whether patient sex or age influenced relapse
4. To establish the degree of association of the reported variables and the
amount of mandibular relapse.
The investigation involved a detailed analysis of 24 sets of radiographs, each
radiograph being assigned to one of four groups, with all groups having either
vertical subsigmoid osteotomy only or in combination with other surgery. The
material and methods are outlined in Chapter 6 and the methodology for
examining the error of the method is discussed in Chapter 7.
Student's f-test for unpaired values showed no statistically significant
differences for relapse between the groups, hence all the groups were combined
for analysis. These results are presented in Chapter 8.
The findings of this study are discussed in Chapters 10 and 11 and some
interesting results were noted.
2't
.],.2 VERTICAL RAMUS OSTEOTOMY
The term "vertical subsigmoid osteotomy" is widely used in Australia to
describe a procedure for mandibular setback. This term, however, is not
commonly used in the literature. Consequently, surgery of the ramus of the
mandible in the vertical plane has resulted in a number of synonyms, derived
either from anatomical landmarks or from the direction of the osteotomy or a
combination of the two. Table 1.1 summarises the terms used to describe the
vertical subsigmoid osteotomy. There are only minor variations in all of these
procedures covered by this list. In this thesis the term "vertical subsigmoid
osteotomy" will be used exclusively.
Table L.1 Synonyms used to describe the vertical subsigmoid osteotomy
Oblique osteotomy
Vertical ramus osteotomy
Subcondylar osteotomy
Vertical subcondylotomy
Overlapping vertical osteotomy
Oblique osteotomy
Oblique sliding osteotomy
Vertical oblique osteotomy
Oblique sliding osteotomy
Vertical subcondylar osteotomy
Oblique subcondylar osteotomy
Transoral vertical ramus osteotomy
Vertical subsigmoid osteotomy
1925
7954
1958
1958
1959
7967
7967
19æ
1970
1970
1981
79tß
1988
Limberg
Caldwell & Letterman
Hinds
Robinson
Robinson
Thoma
Shira
Nordenham & Waller
Robinson
Hebert et al.
Egyedi et al.
Phillips et al.
Quinn & Wedell
SYNONI}ÎvfYEARAUTHOR
22
II
REVIEW OF THE LITERATURE
23
CHAPTER 2
MANDIB ULAR PROGNATHI SM
2..]. DEFINITION
Historically, John Hunter in 7778 (Palmer, 1935) described mandibular
prognathism as being "the lower jaw projecting too far forwards so that the fore
teeth pass before those of the upper jaw, when the mouth is shut; which is
attended with inconvenience and disfigures the face". Hogeman (1951)
elaborated on this definition by describing mandibular prognathism as being
"the projection of the lower anterior teeth to a position in front of the upper
anterior teeth and concomitant anterior positioning of the mandible to cause
disfigurement of the facial profile when the teeth are in contact with the
articular condyles in the rest position within the articular fossa".
Joffe (1965) and Kelsey (1968) have similarly defined mandibular prognathism as
a disorder of craniofacial growth in which the facial profile is marred by an
undue prominence of the mandible. Horowitz et al. (7969) identified another
criteria and added that this deformity is characterised by an Angle Class III molar
and/or incisor relationship in which the lower molars or lower incisors are
further forward than normal.
2.2 CLASSIFICATION OF MANDIBULAR PROGNATHISM
Despite the various classifications available, the pathognomonic feature in all
cases of mandibular prognathism is that the lower incisors close in front of the
upper incisors. Although prognathic mandibles may look very much alike,
24
several subgroups have been identified, each differing in aetiology and more
importantly in the treatment required.
Biederman (1967) classified mandibular prognathism into four categories:
1. Mandibular overgrowths which consist of two subgroups:
(a)
(b)
one in which the excessive growth is vertical; and
the other group in which the growth is horizontal.
3.
2. Maxillary undergrowths or insufficiencies.
False mandibular prognathisms where mandibular closure is achieved by
forward condylar translation.
4. Dental Class I, type 3 where there is no skeletal discrepancy and the first
molars are in Class I but the canines are in Class III with an edentulous
distal the canine
Sanborn, in L955, classified Class III malocclusions more comprehensively into
the following categories using facial profilograms (Figure 2.7) and reported that
45Vo of Class III cases had a normal maxilla and a prognathic mandible:
Group A: maxilla within normal range
mandible beyond the normal range
Group B: maxilla below normal range
mandible within the normal range
25
Group C: maxilla within normal range
mandible within the normal range
Group D: maxilla below normal range
mandible beyond the normal range
Hirose et aI. (7976) added a fifth group to account for Asian profiles:
Group E: maxilla beyond normal range
mandible beyond the normal range
26
Figure 2.1 Variations of skeletal pattern of Class III malocclusions
(modified from Hirose et al. 19Z6)
Group A Group B Group C Group D Group E
N,,
,,
It
t
I
J
.l
tat.
Ia
Ii
a
aI
!¡lr
a
Ia
I
4rr rY ì
\i A
B
Pascoe et al. (1960) included another group in which the madlla is normal; the
occlusion and alveolar process are also normal but the prognathic appearance
results from prominence of the mental protuberances. Jacobsen et al. (7974)
agreed with Sanborn that the most common feature of a Class III malocclusion
was prognathism of the mandible rather than a deficiency of the maxilla in the
anteroposterior dimension, found in 50% of his adult sample. Ellis and
McNamara (1984) divided Class III cases into those with and without anterior
open bite and found a retrognathic maxilla in 67Vo of cases. In summary, there
exists three entities which comprehensively defines mandibular prognathism:
27
(i)
( ii)
(iii)
occlusal;
skeletal; and
postural.
Treatment for mandibular prognathism is dependent on a number of factors
which include:
(i)
(ii)
(iii)
degree of dentofacial deformity;
patient perception of the problem; and
treating clinician(s) perception of the problem
no treatment at all;
orthodontic camouflage;
surgery alone; and
surgery in combination with orthodontics
Treatment options available to correct mandibular prognathism include
(i)
(ii ¡
( iii)
(iv)
2.3 INCIDENCE OF MANDIBULAR PROGNATHISM
The literature on the incidence of mandibular prognathism is sparse although
an approximation can be gained by determining the incidence of Class III
malocclusions which typically reflects the size and shape of the mandible. Ag",
genetic and racial variations are primary determinants of Class III
malocclusions. Rarely is mandibular prognathism a problem of infancy. Its
onset is often apparent in the mixed dentition phase and true prognathism is
quite evident during and after puberty, the period of rapid growth. A recent
review by van Vuuren (1991) reported that the incidence of Class III
malocclusion varied usually between 1.To and 4.2% of the sample populations
28
studied although a high incidence of Class III malocclusion was noted in a
review by Huber and Reynolds (1946) who reported an incidence of 72.2Vo. A
separate study by Rakosi and Schilli in 1981 reported that 787o of their study of
2000 pre-school children showed a Class III relationship in the primary dentition
which subsequently reduced to an incidence of 3Vo in the first phase of the
mixed dentition. Propensity for racial groups to manifest jaw deformities is not
uncommon. Nordenham and Waller (1968) reported that the most common
jaw deformity in Scandinavia was mandibular prognathism. More informative
reviews detail sample sizes and incidence of prognathism (Tables 2.'I.. and 2.2).
29
Table 21 Prevalence of Class III malocclusions (facobsen et aI. 1974)
Table 2.2 Prevalence of Class III malocclusions (Lew et aI.1993)
4.2
1.35
1,2.2
4.0
2.7
2.2
7.2
9.4
2.97
7.6
18.0
American Caucasians
School children
Students
Swedes 21y.o.
Swedes 72y.o.
Caucasians-males
Caucasians-females
Children 14-18 y.o.
Children 7-15 y.o.
Children 15-18 y.o.
Preschool children
several thousand cases
4,770
500
737
474
not stated
not stated
2,759
2,956
1,473
2,000
7907
7925
7946
7946
7946
1951
1951
1951
7957
1965
1985
Angle (7907)
Ainsworth
Huber & Reynolds
Seipel
Seipel
IGogman
Krogman
Massler & Frankel
Goose et al.
Ast et al.
Rakosi
PREVALENCE
oF CLASS rtt (%)
ETHNIC GROUPSAMPLE SIZEYEARAUTHOR
5.5
10.0
4.0
4.0
8.7
16.8
11.0
33.0
29.0
70.6
12.6
American Caucasians
Eskimo
British
Swedish
American Blacks
Kikuyu Kenyan
Indian
Chinese
Malay
Egyptian
Chinese
718
100
1,000
301
445
s05
42
154
151
501
1,050
1970
1977
7974
7974
1985
1985
1989
7989
1989
7990
7993
Horowitz
Wood
Foster & Day
Ingervall
Garner & Butt
Garner & Butt
Woon et al.
Woon et al.
Woon et al.
El-Mangoury et al
Lew
PREVALENCE
OF CLASS III(%)
ETHNIC GROUPSAMPLE SIZEYEARAUTHOR
2.4
30
SURGERY FOR THE TREATMENT OF MANDIBULAR PROGNATHISM
(Figure 2.2)
The first deliberate surgical intervention for the correction of an acquired jaw
defect was performed by Hultihen in 1849 to rectify an anterior open bite which
resulted from a burn contracture of the neck. Half a century passed before
Berger pioneered the surgical correction of prognathism in 1,897. Berger (1,897)
and Jaboulay and Berard (1898) first performed a bilateral condylectomy via a
preauricular approach to push the mandible back. The subcondylar osteotomy
was first described by Kostecka in 1928 in which the condylar neck was divided
with a Gigli saw by a blind external approach. This technique fell into disrepute
because of complications encountered. Intraoperatively, damage to the
maxillary artery was a serious problem with this technique because of its
position just medial to the condylar neck. Postoperatively, the occurrence of
salivary fistulae and facial paralysis was noted and anterior open bites often
resulted following release of maxillomandibular fixation. Smith and Johnson
(1940) described a minor modification of this operation which involved
removal of a section of bone from the region of the sigmoid notch to allow
posterior repositioning of the mandible. The horizontal ramus osteotomy
above the level of the inferior dental foramen via an external approach was
described by Blair (1907) and Babcock (1909) early this century. Later, this
osteotomy was performed intraorally by Aleman (1.92'I) and is sometimes
known as the Swedish approach. Obwegeser (7957) described the original sagittal
split procedure in which greater bone to bone contact is achieved and various
modifications of this operation are very popular today. The vertical subsigmoid
operation was first described by Caldwell and Letterman in 1954. Here the
ascending ramus is divided vertically from the sigmoid notch to a point just
anterior to the angle of the mandible. This may or may not be combined with
31
coronoidotomy and was approached as an extraoral procedure. Trauner and
Obwegeser (7957) reported the logical extension of this procedure.
Figure 2.2 Surgical techniques performed in the vertical rami of mandible to
correct mandibular prognathism (modified from Alling, 1965)
a. Condylectomy
o
b. Subsigmoid notch osteotomy with sliding condylotomy
\
b
I
32
c. Horizontal osteotomy
t
I
c
d. Subcondylar osteotomy
TI
e. Operations between rebomolar area and gonial angle
d
\ r-t
e
33
f. Triangular oblique ostectomy
UI
ì'
g. Vertical osteotomy
h. Oblique sliding osteotomy
1
f
II
g
\tI,I
(
h
34
With the introduction of the intraoral approach, extraoral scars could be
avoided. Winstanley in 1968 and Wilbanks in 7977 terrned this technique the
double oblique osteotomy. The name of the technique is derived from the fact
that the bone cut is oblique in two directions, that is, from the anterior region of
the sigmoid notch down to the gonial angle (a superior - inferior obliquity) and
simultaneously a biased cut from the lateral cortex to medial cortex (a lateral -
medial obliquity). In 7970, Hebert and associates reported the correction of
mandibular prognathism in seven patients via an intraoral approach using a
Stryker oscillating saw which allowed a cut to be made similar to the extraoral
technique. However, the method had disadvantages of poor visualisation and
difficulty in access. Massey et al. (1974) and others refined the case selection by
excluding patients whose mandibular morphology presented an access problem.
Their basis for selection of cases was to exclude mandibles that presented with
mandibular divergence angles less than L30o (Figure 2.3) as these were deemed
to introduce a high degree of difficulty (Akin and Walters,7975).
Figure 2.3 Mandibular divergence angle - submental vertex view
(modified from Massey, 19741
t58.5. t57.5.
35
More recently, a new osteotomy, termed the intraoral vertico-sagittal ramus
osteotomy, has been introduced by Choung (7992) for the correction of
mandibular prognathism. The rationale behind this technique is an attempt to
decrease the incidence of condylar displacement by virtue that the osteotomy is
theoretically parallel to the plane in which the mandible is repositioned. It
claims to combine the advantages of both the vertical ramus osteotomy and the
sagittal split osteotomy as well as reducing the incidence of neurosensory
disturbances. Table 2.3 summarises the various surgical techniques which have
been used to treat mandibular prognathism.
Table 2.3 Historical review of surgery to treat mandibular prognathism
(modified from Hinds 1957)
Osteotomy in body of mandible
Bilateral ostectomy in body of mandible
Bilateral condylectomy
Ramus osteotomy for recessive mandible
Ramus osteotomy for prognathism
Ostectomy posterior to last molar with preservation
of nerve and artery
Subcondylar osteotomy for open bite
Subcondylar osteotomy for prognathism
Two stage bilateral ostectomy
Subsigmoid ostectomy
Vertical osteotomy
Intraoral subcondylar osteotomy
Inhaoral vertico-sagittal ramus osteotomy
1849
7897
1898
1905
1909
791,2
1928
7947
7944
1,954
7954
1968
7992
Hullihen
Blairjaboulay
Blair
Babcock
Harsha
Kostecka
Schaeffer
Dingman
Smith & Robinson
Caldwell & Letterman
Winstanley
Chounq
SURGICALTECHNIQUEYEARAUTHOR
The technique used in this study was that of Winstanley (1968)
36
2.5 COMPLICATIONS OF VERTICAL SUBSIGMOID OSTEOTOMY
Although the vertical subsigmoid osteotomy is now perceived to produce a low
rate of complications and these are considered to be only minor in nature (Van
Merkesteyn et al. '1,987; Wang and Waite, 7975) some complications associated
with any surgical procedure are inevitable. It must be remembered that there is
a learning curve for individual surgeons. Modification, refinement of the
technique and improved instrumentation have popularised the vertical
subsigmoid osteotomy and minimised the complications since its inception in
7954 by Caldwell and Letterman. Van Merkesteyn et al. (1987) highlighted the
various complications that can occur and reported the incidence of
complications with the use of the vertical subsigmoid osteotomy to be low
(1,7.8%) when compared with the sagittal split osteotomy (25.8%) (Tabte 2.4).
Table 24 Percentage of complications with mandibular surgery
11.8
25.8
Vertical subsigmoid osteotomy
Sagittal split osteotomy
% OF COMPLICATIONSSURGICAL TECHNIOI.'E
Tornes (1987) reviewed and compared the perioperative and postoperative
complications between the intraoral and the extraoral technique of vertical
subsigmoid osteotomy of the mandible. Although both techniques were
considered to be safe and satisfactory, the extraoral approach was favoured
because it resulted in less operative time, less blood loss, less swelling and a
significantly shorter stay in hospital.
37
Review of the literature suggests a number of technical and biological problems.
The reported complications known include:
Intraoperative complications
(a)
(b)
(c)
(d)
(e)
(f)
(a)
(a)
(c)
(d)
(e)
(f)
Immediate postoperative complications
(a) neurosensory deficit involving the inferior alveolar nerve;
(b) postoperative infection; and
(c) sequestration of the proximal segment.
Delayed postoperative complications
haemorrhage at the time of surgery;
inadvertent bone cut and incomplete bone sectioning;
displacement of the proximal segment;
inability to set the mandible back;
condylar dislocation; and
herniation of the buccal fat pad.
anterior or lateral open bite;
reduced mouth opening i.e. residual trismus;
temporomandibular joint dysfunction;
ankylosis of the coronoid process to the zygomatic arch;
Frey's syndrome; and
Eagle like syndrome.
Further complications are encountered when the vertical subsigmoid osteotomy
is performed via an extraoral approach and these include:
38
Complications associated with extraoral approach
(a)
þ)
(c)
facial nerve palsy - marginal mandibular branch;
keloid scarring; and
parotid fistula.
2.5.1. Intraoperative complications
(a) Haemorrhage at the time of surgery
Haemorrhage associated with mandibular osteotomies, especially to the extent
that it becomes life threatening is a rare occurrence and its risk is less than that
following maxillary surgery. Lanigan et al. (1991) provided a comprehensive
review of haemorrhage and its management following mandibular surgery.
The two vessels commonly involved in intraoperative bleeding during the
vertical subsigmoid osteotomy are the inferior alveolar artery and the maxillary
artery. Bleeding from the inferior alveolar artery with its concomitant
neurosensory involvement is not considered to be problematic as this vessel is
more accessible to ligation or cauterisation. However, laceration of the
maxillary artery can be quite a serious event with a rapid amount of blood loss
in a very short period of time. The difficulties arise because of the blind
approach in performing this technique. Tuinzing and Greebe (1985) reported a
series of three cases out of 150 in which bleeding from the maxillary artery
occurred. Astrand et al. (7973) detailed profuse bleeding intraoperatively from
the cancellous bone in 11 of 55 patients undergoing vertical subsigmoid
osteotomy. These were controlled with compression. To the more extreme,
Quinn and Wedell (1988) reported problematic haemorrhage in a case which
necessitated ligation of an unspecified branch of the external carotid artery.
Other vessels may be involved and include the buccal artery which may be cut at
the time of incision and may not present any problems until the vasoconstrictor
39
effects of the local anaesthetic solutions have been expended. Generally, this
procedure can be performed safely with minimal bleeding (Akin and Walters,
797s).
ft) Inadvertent bone cut
Very little literature is available on the problem of placing the osteotomy cut in
the wrong position. Van Merkesteyn et al. (7987) reported one case of an
erroneous bone cut. Anecdotal experience particularly from teaching Units
where trainees are involved in the surgery indicate that aberrant osteotomy cuts
are not uncommon. The reason for aberrant placement of the osteotomy cut
may be due to incorrect positioning of the Le Vasseur Merrill retractor. If the
retractor is allowed to "sag" an osteotomy cut is placed very close to the posterior
border of the mandible resulting in a very narrow proximal segment. If the
"Iedge" on the retractor is not utilised (ie. the saw is not resting on the ledge),
then a very wide proximal fragment may result with possible damage to the
inferior alveolar neurovascular bundle.
(c) Displacement of the proximal segment
Incorrect position of the proximal segment has been reported by Hall et al.
(1975). Correction was necessary in one patient. In the series by Van Merkesteyn
(7987) displacement of the proximal segment occurred in three sites, two of
which were surgically repositioned. Medial displacement of the segment has
been reported to occur in about 3Vo to 8Vo of cases according to various authors
(Tuinzing et al. 1983; Tuinzing and Greebe,1985; Rosenquist, 1990).
(d) Inability to set the mandible back
Difficulties in retropositioning the mandible using the oblique sliding
osteotomy due to the sfrength of the masticatory muscles has been reported by
Willmar et al. (1.979). These authors favoured the sagittal split osteotomy since
40
extensive stripping of muscle aids in mobilisation of the segments. Flowever,
Johanson et al. (7979), indicated that this problem can be easily overcome by
careful dissection of the insertions of the pterygoid and masseter muscles on the
proximal fragment. Furthermore, this method has been used to correct
prognathism with even as much setback as 21 mm.
The coronoid process is thought to restrict the posterior movement of the distal
segment of the mandible as it is rotated anteriorly in open bite cases. It also
impinges on the condylar process as the mandible is set back, therefore, it is
sometimes considered desirable to section the coronoid process during the
vertical subsigmoid procedure in order to facilitate repositioning of the bone
fragments. This is especially so in more severe cases of prognathism and
anterior open bite (Hinds and Kent, 1972).
Difficulty in setting the mandible back may be due to other bony hindrances.
Braun and Sotereanos (1983) reported a case in which a right styloidectomy was
necessary to complete a mandibular setback following vertical subsigmoid
osteotomy. It has also been suggested that the configuration of the medial aspect
of the mandible may be a hindrance in performing larger mandibular setbacks
and this can be overcome by making the cut more oblique (Tuinzing and
Greebe, 1985).
(e) Condylar dislocation
Macintosh (1981) stated that "the two potential difficulties of most lasting
significance in the sagittal split osteotomy are improper condylar positioning
and improper application of the fixation wires". Undoubtedly, the same
principles apply to any osteotomy of the mandible. Freihofer (7976)
recommended that intraoperative radiographs be taken to ensure the correct
positioning of the condyle and although theoretically it has merit, in practice
41.
this is difficult. Mechanical aids have been described to assist in stabilisation of
the condyles (Leonard, 7976; Zecha et al. 7978) but the technique of vertical
subsigmoid osteotomy does not lend itself to these devices. Quinn and Wedell
(1988) reported one case of condylar dislocation with consequent ankylosis of the
condylar head anterior to the articular fossa. Subsequently, avascular necrosis
resulted necessitating total temporomandibular joint replacement.
In one unreported case in the South Australian Unit, a trainee of the Unit
inadvertently dislocated the proximal segment anteriorly on one side (Figure
2.4). This required a second operation to reposition the fragment via a
preauricular approach.
Figure 2.4 Panoramic radiograph showing anterior dislocation of the right
mandibular condyle
42
2.5.2 Immediate postoperative complications
(a) Neurosensory deficit involving the inferior alveolar nerve
Neurosensory changes to the inferior alveolar nerve have been reported and are
likely to occur in most types of operations of the mandible, however the
incidence of these changes are variable. These injuries are particularly common
in operations which utilise the intraoral sagittal split osteotomy (Table 2.5).
Table 25 Incidence of neurosensory deficit - sagittal split osteotomy
of the mandible
Neurosensory changes are also frequent for the horizontal osteotomy of the
mandible (Table 2.6).
Table 2.6 Incidence of neurosensory deficit - horizontal osteotomy
of the mandible
76Vo
44Vo
677o
37Vo
87o
7965
7969
7978
1986
7997
Kohle
White, Peters, Costlich & Page
Pepersack & Chausse
Coughlan & Irvine
Læira & Gilhuus-Moe
INCIDENCE OF NEI.'ROSENSORY DEFICITYEARAUTHOR
38Vo
757o
55%
1951
7962
19æ
Hogeman
Fromm, Nordh & Nordstrom
Nordenham & Waller
INCIDENCE OF NEUROSENSORY DEFICITYEARAUTHOR
43
The intraoral vertical subsigmoid osteotomy probably carries the lowest risk of
inferior alveolar nerve injury for ramus procedures. Although the operation is
performed blind, the position of the neurovascular bundle is determined by
locating the antilingula, a very slight rounded prominence on the lateral side of
the ramus of the mandible (Caldwell and Letterman, 79il), and then performing
the osteotomy behind this landmark. Identification of the antilingula does not
ensure the prevention of damage to the inferior alveolar nerve. Yates et al.
(1976) investigated the reliability of the antilingula as an anatomic landmark
during oral and maxillofacial surgery. They found a high variability in its
position. The antilingula was situated considerably more anterior and superior
to the inferior alveolar foramen. It was suggested that if the osteotomy cut was
made 5-10 mm distal to this landmark and only if this landmark was found
(antilingula present in <50% of dried mandibles), then the inferior alveolar
nerve would be spared during operation.
Wang and Waite (1.975) considered paraesthesia to be a rare complication.
Massey et al. (1974) reported no cases of permanent paraesthesia or anaesthesia
in his study of 'l..4 patients. Akin and Walter ('1,975) demonstrated minimal
numbers with only two cases of nerve injury in their series of 38 patients, one
which was severed at the time of operation and the other case arising
consequent to medial displacement of the proximal fragment. Zaytoun et al.
(1986) compared the long term neurosensory deficit following intraoral vertical
subsigmoid osteotomy and the sagittal split osteotomy and found that in the
study of 26 patients, an incidence of 28.87o of neuropathy of the mental nerve
occurred. All incidences were associated with the sagittal split osteomy and
none involved the intraoral vertical subsigmoid osteotomy. This highlights the
point that the vertical subsigmoid osteotomy produces less nerve morbidity.
Hall et al. (7975) also experienced medial displacement of the proximal fragment
causing neurosensory problems and hence identified another factor to be the
M
close proimity of the bone cut to the mandibular canal. Astrand et al. (7973)
also reported only two cases of transient paraesthesia (3.6V") with full recovery
whereas Rakosi and Schilli (1981) reported an unusually high incidence of
neurosensory changes (637o). Hall and McKenna (7987), in refining the surgical
technique of intraoral vertical subsigmoid osteotomy by extending the inferior
portion of the cut anteriorly to improve the vascular supply to this region,
reported acute nerve damage to an incidence of 36Vo of operated sides of which
747o recovered fully within one year.
(b) Postoperative infection
Hinds and Kent (7972) reported the possibitity of postoperative infection but this
complication is rarely seen since the institution of sterile techniques (1890) and
prophylactic antibiotics (1950). Hogevold et al. (7997) demonstrated in their
study that over a 50 year period of performing mandibular osteotomies,
fluctuations in the frequency of postoperative infections were evident. A cause-
effect relationship could not be determined for these infections. Flowever,
plausible explanations included the patients being warded in the same hospital
unit as the urology patients, no prophylactic antibiotics being used and salivary
contamination of the operative field (surgery performed by an extraoral
approach).
(c) Necrosis of the proximal segment
Necrosis of the proximal segment has been documented by Shepherd (1980).
Prolonged fixation without loading, coupled with decreased blood flow
contributed to the degeneration. Quinn and Wedell (1988) experienced two
cases of avascular necrosis necessitating total prosthetic replacement of the
temporomandibular joint. Hall et al. (7975) reported on necrosis of the distal tip
of the proximal segment and suggested several factors may be involved. Firstly,
they noted that very little tissue acted as a pedicle for blood supply to the
45
Proximal fragment. This was confirmed by Bell et al. (7974), using animal
studies, hence the necrosis results as a consequence of ischaemia. Hall et al.
(7975) offered an alternative explanation for necrosis. They postulated that
necrosis resulted from bacterial contamination from the intraoral incision
overwhelming the marginal blood supply. The bacterial contamination
produced osteomyelitis and subsequent necrosis. The pedicle for blood supply to
the proximal fragment does not differ from the sagittal split osteotomy
(Grammer et al. 1974). Secondly, necrosis of the distal tip only occurred in those
patients with long proximal segments. This complication may be prevented by
cutting off the most distal and presumably the most ischaemic part of the
proximal segment (Hall et aL.7975).
2.5.3 Delayed postoperative complications
(a) Anterior or lateral open bite
Postoperative open bite following vertical subsigmoid osteotomy has been
recorded and to some extent is to be expected. Baumrind et al. (1,974) found that
the tendency to open bite in their series of 22 patients surgically treated to correct
mandibular prognathism proved to be of lesser magnitude than had been
anticipated. The incidence of postoperative bite opening has been variable.
Hinds (1958) and Nordenham and Waller (1,968) found no opening of the bite in
their stud/, whereas Astrand and Ridell (1973) found minimal bite opening.
Robinson (1959) suggested that a posterior open bite should be planned to
compensate for the anterior open bite. Hall et al. (7975) also experienced six
cases of anterior open bite in their series of 42 patients. They concluded that the
reason for the anterior open bite may at least be partially related to condylar sag
since it occurred about twice as often in patients without firm wire fixation of
the condylar segments.
46
(b) Reduced mouth opening
Decrease in function immediately following any operation of the mandible is
inevitable usually as a result of pain, psychological concerns of the operation
and muscle guarding. An initial reduction in mouth opening is not
uncommon after maxillomandibular fixation. Astrand et al. (7973)
demonstrated that, in a few cases, the maximum opening at six months was
only 20 mm but normal opening was regained within two and half years.
Edlund et al. (1979) confirmed that the maximum opening of the mouth
decreased following operation and in their study an average of 10 mm reduction
was noted although masticatory efficiency was not adversely affected. Stacy
(7987) showed that the maximum mouth opening recovered to presurgical
limits without the use of mechanical devices and this was achieved within nine
months following release of maxillomandibular fixation. The effect of physical
rehabilitation on mandibular function after ramus osteotomy was assessed by
Storum and Bell (1986). The results indicated that function was not altered after
vertical sigmoid osteotomy whereas sagittal split osteotomies resulted in
reduction of mandibular opening and bite force. This was corrected with
physical rehabilitation.
Masticatory function was studied by Shiratsuchi et al. (7997) with elaborate
techniques consisting of measuring the use of adenosine triphosphate granules
(ATP) by means of a spectrophotometer, measuring the bite force and the
amount of occlusal contact. The findings were that masticatory function tended
to improve gradually postoperatively although masticatory efficiency was still
judged to be inferior to those with normal occlusion even 12 months after
operation.
47
(c) Temporomandibular joint dysfunction
Surgical correction of prognathism will undoubtedly improve both the
occlusion and the profile but adverse effects on the temporomandibular joint
may result as a consequence to this correction. Astrand et al. (7973) reported that
most patients had tenderness and discomfort in the region of the joint in the
initial period after release of maxillomandibular fixation but these symptoms
subsided. At the six month follow-up, seven of 55 patients still experienced
temporomandibular joint problems. Five patients were treated successfully
with occlusal equilibration or bite splints and the remaining two patients had
symptoms prior to operation. Hogeman (1951) presented his findings of
temporomandibular joint symptoms in 2'1..2 7o of cases and found the frequency
higher among those patients that had been followed up for longer periods of
time. In contrast to temporomandibular joint symptoms developing after
correction of prognathic mandibles by vertical subsigmoid osteotomy, this
procedure has been historically used and still is being used for the treatment of
symptomatic internal derangements of the temporomandibular joint (Hall et al.
7993; Bell et al.7990; Nickerson and Veaco,7989).
(d) Ankylosis of the coronoid process to the zygomatic arch
Troyer (7977) reported a case of ankylosis in which the temporomandibular joint
was immobilized subsequent to surgical correction of mandibular prognathism.
The ankylosis of the coronoid process to the zygomatic arch resulted following a
coronoidotomy being performed concurrently with the vertical subsigmoid
osteotomy.
(e) Fre/s syndrome
Frey's slmdrome, also known as gustatory sweating, may result following any of
the surgical procedures to the ascending ramus of the mandible as the nerve
involved in this complication, the auriculotemporal nerve, may be damaged as
48
it passes posterior to the neck of the condyle. Following damage to the
auriculotemporal nerve, its component parasympathetic fibres reanastamose to
innervate the sweat glands instead of the salivary glands. This would lead to
gustatory sweating in the temporal and auricular regions triggered by appetising
food (Hinds and Kent, 7972). This syndrome has also been observed in patients
treated with horizontal osteotomy of the ascending ramus of the mandible
(Hogeman,7957).
(Ð Eagle like syndrome
Eagle's syndrome is characterised by pain laterally in the throat with radiation to
the ear and along the mandible. It is due to an elongated styloid process. There
is also commonly a sensation of a foreign body in the throat which necessitates
frequent swallowing. A case of Eagle's syndrome following mandibular setback
has been reported by Tuinzing et al. (1983). The treatment recommended for
patients with Eagle's syndrome consists of fracturing the styloid process and
removing it (Glogoff et al. 1981).
2.5.4 Complications associated with extraoral approach
(a) Facial nerve palsy
Last (1978) described the facial nerve, the seventh cranial nerve, as two roots (a
motor root and a small sensory root) emerging from the anterior surface of the
hindbrain between the pons and medulla oblongata. It then passes into the
acoustic meatus with the vestibulocochlear nerve. Thereafter, it enters the facial
canal, expands into the geniculate ganglion and turns sharply backwards to run
posteriorly and then inferiorly across the medial wall of the middle ear cavity. It
emerges from the base of the skull at the stylomastoid foramen. Before the
facial nerve exits from the stylomastoid foramen, it gives off three important
branches; the greater superficial petrosal nerve, the nerve to stapedius and the
49
chorda tympani nerve. These nerves supply secretomotor fibres to the lacrimal
gland, motor fibres to the stapedius muscle and taste fibres to the anterior two
thirds of the tongue respectively. After it emerges from the stylomastoid
foramen, the facial nerve gives off the posterior auricular nerve which supplies
the occipital belly of the occipitofrontalis muscle. A muscular branch is next
given off and this supplies the posterior belly of the digastric and stylohyoid
muscles. The facial nerve then divides and rejoins to form a plexiform
arrangement known as the pes anserinus before it finally divides into the five
main branches which supply motor function to the muscles of facial expression.
The five branches are:
(i)
(ii)
(iii )
(iv)
(v)
temporal branch;
zygomattc branch;
buccal branch;
marginal mandibular branch; and
cervical branch.
Intraoral surgical methods carry only a negligible risk of facial nerve injury as
the nerve is positioned well lateral to the operative site (Behrman, 1972; Kohle,
1965). Damage to the facial nerve is a known complication of the vertical
subsigmoid osteotomy when performed via an extraoral approach as the
dissection must pass the nerve to reach the mandible. The marginal
mandibular branch of the facial nerve is the nerve most commonly
encountered when the vertical subsigmoid osteotomy is performed by an
extraoral approach. Astrand et al. (1973) reported injury to the mandibular
branch of the facial nerve in one patient in a study of 55 patients and this
resulted in partial paralysis which spontaneously resolved after two months.
Martis (1984) suggested that facial nerve paresis may occur indirectly following
posterior repositioning of the distal segment in mandibular setback procedures
50
and is due to pressure on the nerve trunk by the posterior border of the distal
segment. When the osteotomy is performed via an extraoral approach, the
marginal mandibular branch of the facial nerve is at risk of being damaged.
Hogevold et al. (7997) reviewed 898 orthognathic surgical cases presenting with
mandibular prognathism and/or asymmetry since 7939. In all cases mandibular
surgery was performed extraorally and a high incidence of temporary facial
nerve palsies was found, numbering 15 patients in all, with one patient
experiencing permanent postoperative paresis.
þ) Scar formation
For the extraoral approach, the scar is usually inconspicuous, but does occur.
For some patients who are predisposed to adverse healing, hypertrophic scarring
or keloids may form and it is in these patients that skin incisions should be
avoided particularly in certain racial groups e.g. Negroes. The refinement of the
intraoral technique obviates the need for any skin incisions.
(c) Parotid fistula
Postoperatively, the occurrence of salivary fistulae was noted with the Kostecka
(1928) procedure of high and blind condylotomy. This may be a possibility
whenever surgery is performed in the region of the parotid gland or duct and
glandular tissue is accidentally damaged.
Hogevold et al. (7997) detailed their experience with 31 cases of saliva retention
over 14 years following extraoral ramus osteotomy in 280 patients. They
reported that routine treatment for this complication consisted of repeated
aspiration and radiation with doses of 4.00 Gray daily for three days to the
parotid gland to reduce saliva production for 3-4 months.
51
CHAPTER 3
RELAPSE FOLLOWING MANDIBULAR SURGERY
3.1 DEFINING POSTSURGICAL RELAPSE
Reitzik (1988) defined relapse as being the tendency to "return to the
preoperative position". Long term stability of mandibular orthognathic surgery
is complicated by relapse. Reitzik (1988) divided relapse into three categories,
each with its own anatomy, pathophysiology and time period. Firstly,
immediate relapse occurs upon release of maxillomandibular fixation and is
due to the malposition of the mandibular condyles or condylar sag induced at
the time of surgery. He emphasised that this only occurs when the proximal
fragment is secured to the distal fragment and only when maxillomandibular
fixation is used.
The second type of relapse is long term relapse due to interfragmentary
instability. The third type of relapse results from a flexural drift causing a
change in the shape of the mandible. Reitzik (1988), in his summary, reported
that stability is primarily determined by the degree of interfragmentary stability
or instability and the best parameter to measure this is the gonial angle. This
angle will increase if the distal fragment rotates clockwise (lateral head
cephalogram facing to the right) and/or the proximal segment rotates
anticlockwise.
Whether an extraoral or intraoral approach is undertaken, the vertical
subsigmoid osteotomy has established itself as a safe technique with a reasonably
predictable result although some relapse after removal of fixation must be
52
anticipated. Franco et al. (1989) defined relapse as "forward movement of
pogonion during the postoperative period".
Petersson and Willmar-Hogeman (1989) defined relapse as "postoperative
displacement of the mandible". Their assessment of movement was made
easier by the use of a tantalum pin being inserted into the midline of the
mandible using the method of Björk (1955).
Michiwaki et al. (1990) arbitrarily defined skeletal relapse as the postural change
of the cephalometric point "gnathion" between the time immediately after
surgery (within seven days) and at some time more than one year later.
Paulus (cited by Lindorf, '1,986) considered relapse to be present whenever
changes in the occlusion (..g. such as open bite), occurred during the
postoperative period. Although these definitions describe changes at the
occlusal level, Reitzik (1988) interpreted relapse to mean "a return to the
preoperative state". This broader definition encompasses skeletal and occlusal
changes, but to further define this statement, the horizontal shift of point B
toward the preoperative state will be used throughout this study to assess
relapse.
Surgical setback of the mandible for correction of prognathism varies in amount
from study to study. Reported measurements for mandibular setback have been
in the range of 3 mm to 10 mm (Table 3.1).
53
Table 3.L Amount of mandibular setback and landmarks used for
measurements
Pogonion
Gonion
Gonion
Gonion
Pogonion
Point B
Gonion
Point B
Gonion
1,0.2
9.1
5.1
8.96
8.4
8.4
2.4
6.6nn
1981
7990
1990
7979
1986
7990
1990
1997
1980
Egyedi et al.
Allen & Rosenquist
Greece et al.
Johanson et al.
Kobayashi et al.
Lew et al.
Michiwaki et al.
Proffit et al.
Reitzik
LANDMARK
USED
AVERAGE MANDIBULAR
SE-IBACK (mm)
YEARAUTHOR
Reports have shown either no correlation or only weak correlation between the
amount of surgical setback and postoperative relapse (Astrand and Ridell,7973;
Johanson et al. 1,979; Rosenquist et aL. 7986; Pepersack and Chausse, 7978).
Contrary studies have found that the magnitude of mandibular setback does
have a bearing on relapse potential (Kobayashi,7986; Reitzik, 1980a).
3.2 MEASUREMENT OF POSTSURGICAL RELAPSE
Comparisons and measurement of relapse is arbitrary and variable depending
on the method of assessment. The literature is replete with a variety of
methods of presenting statistics on relapse. There is a need to consider
orthodontic and occlusal movements as well as skeletal movements when
measuring relapse. Some studies emphasise relapse in terms of occlusal
changes (Freihofer and Petresevic, 1,975; Pepersack and Chausse, 1,978;
Macintosh, 1,987; Lello, 7987) whereas others represent the changes in
cephalometric detail (Poulton et aL.1979; Lake et al. 1981; Van Sickels et al. 1988).
il
Macintosh (1981), although favouring the assessment of relapse by the clinical
method of measuring changes in occlusion, found that cast analysis was difficult
and therefore eventually abandoned this type of study.
Relapse may be studied on both cephalometric radiographs or on dental casts
$ohanson et al. 7979). Early longitudinal studies have reported a relapse in the
horizontal direction ranging from 2-3 mm whereas the positional changes in
vertical direction have been less pronounced (Astrand and Ridell, 1,973).
Inconsistencies in the method of studying relapse makes comparisons with
other investigations difficult. Poulton and Ware (1973) and Huang and Ross
(7982) measured mandibular changes from articulare to gnathion. The resultant
effect of this type of measurement pertains to the combining of horizontal and
vertical changes and reporting them as one set of data. Hence one needs to
measure relapse in both axes as well as in detailed vector and rotational changes
as opposed to collated relapse changes.
One of the problems encountered when using cephalometry to locate and
identify dental landmarks is in the location of the hinge axis (Worms et al.
1980), especially when a splint is removed and rotation of the mandible is
necessary in order that complete intercuspation occurs. Commonly, the rotation
of the mandible occurs from a fixed axis of rotation at the centre of the condyle.
Flowever, Grant (1,973) has shown that the use of an instantaneous centre of
rotation is more akin to the natural kinematics of the mandible. The
significance of this changing centre of rotation is in the interpretation of
cephalometric studies that utilise an arbitrary centre of rotation. Data
interpretation may be misleading in that using an arc of rotation scribed with its
origin at the centre of the condyle may be incorrect. On the contrary, use of the
instantaneous centre of rotation may reveal that the closure of the mandible is
directed vectorially in a different pattern. The implication of this in
55
cephalometry is that relapse of mandibular setbacks may be overestimated. This
is especially the case if rotation of the mandible following removal of a splint is
directed in a more vertical vector rather than a horizontal vector when using
the instantaneous centre of rotation as opposed to using a fixed arc. Fixed arc,
more often than not, has a greater horizontal or "x" vector, implying greater
relapse.
Some authors prefer to measure relapse specifically by using single landmarks
only. Proffit et al. (1997) analysed their results of mandibular setback and
reported on the changes of chin position only, whereby the intraoral vertical
subsigmoid osteotomy was found to be more stable than the bilateral sagittal
split osteotomy. They cited muscular and condylar influences in concluding
this outcome. This, however, is a simplistic approach to a complicated analysis.
Lake et al. (1981) used 15 cephalometric variables to assess dentoskeletal relapse.
Sandor et al. (1,984) used a simpler method of analysis consisting of horizontal
mandibular advancement, horizontal incisal tip advancement and increased
mandibular length. Reitzik (1988) measured relapse by assessing the skeletal
changes in each of the fragments and relative to each other. This method
presents problems in that the surgical technique employed must result in
minimal remodelling and minimal resorptive changes of the landmarks used,
otherwise longitudinal comparisons are invalidated. This is the case with the
vertical subsigmoid osteotomy technique where extensive resorption occurs in
the lower portion of the proximal fragment.
The timing of relapse has been divided into a number of phases based on the
release of maxillomandibular fixation which also represents the time of
physiological bone repair (Spiessel, 1974). Generally speaking, early,
intermediate and late relapse are the designated phases where significant
changes would be expected. Many authors have their own interpretation of
56
these phases. Kraal and Valk (1981) considered these phases relative to
maxillomandibular fixation, ie. during maxillomandibular fixation, within a
few months of release of fixation and a considerable time after surgery. Sesenna
and Raffaini (1985) added an additional stage, that being at the moment of
release of maxillomandibular fixation. Other authors (McNeill et al. 7973; Ive et
aL.7977; Schendel and Epker,7980; Van Sickels et al. 1988) identified early relapse
to be within the first two months of surgery prior to release of
maxillomandibular fixation. The intermediate period covers the next four
months and long term relapse occurs after six months.
This study interprets relapse in the same manner as used in a thesis published
by Hing (1989) in which early relapse is designated as the period prior to release
of fixation and the intermediate phase being arbitrarily assigned to the period
from 2 to 72 months. Long term changes are noted after 72 months at which
time postsurgical orthodontics should have been completed. Relapse values,
relative to the constructed line seven degrees below Sella-Nasion with its origin
at Sella, are assigned a negative value throughout the text, whether in the
horizontal or vertical vectors. This would mean that mandibular setback and
upward movements of any designated points are assigned negative values.
3.3 EARLY,INTERMEDIATE AND LONG TERM RELAPSE
Skeletal stability following surgical manipulation of the mandible, whether
advancement or setback, has been well documented and the spectrum of
stability has been diverse (Schendel and Epker, 1980). It has been suggested that
most of the relapse occurs during or immediately following release of
maxillomandibular fixation (McNeill, 1973; Rosenquist et al. 1985). The
immediate postoperative condylar ascending ramus position and the tension of
the paramandibular connective tissues are important aetiological factors
57
dictating skeletal stability. The paramandibular connective tissues include skin,
interstitial connective tissues, periosteum and muscles attached to and
surrounding the mandible (Wessberg and Epker, 1981).
Epker and Wessberg (1982) elaborated on the effects of postoperative condylar
ascending ramus position and the tension of the paramandibular connective
tissues in mandibular advancements and these factors could easily be applied to
mandibular setback procedures. As is the case with condylar distraction causing
relapse in mandibular advancements following release of maxillomandibular
fixation, forced posterior seating of the condyles could have a similar effect in
mandibular setback procedures. This skeletal relapse occurs because a
discrepancy is created between the functional occlusal position and the terminal
hinge position.
In reviewing the influence of muscles on relapse, Wessberg and Epker (1981)
showed that suprahyoid muscles alone do not significantly affect skeletal
stability when the mandible is advanced, especially when less than 30 per cent of
the muscle length is stretched. So it is thought that the musculature acts as only
one component of the paramandibular connective tissues in concert with the
skin, interstitial connective tissues and enveloping periosteum to exert a
relapsing force on the surgically positioned mandible (Solow and Kreiborg,
ßn).
Animal studies by Goldspink et aI. (7976) and McNamara (7979) supported the
concept of the paramandibular tissues playing a key role in skeletal relapse and
specifically implicated the periosteum as the primary aetiological factor. As a
result of these findings, it has been recommended that the periosteum at the
osteotomy site be incised to reduce the tension on the bony segments. Berman
and Behram (1978) suggested that skeletal stabilisation be maintained longer
58
than the traditional six weeks to alleviate the relapsing potential of the
paramandibular tissues. According to McNamara (7979), skeletal stabilisation of
12 weeks maintains the desired osseous relationships while the connective
tissues adapt to their new environment.
Some authors (Pepersack and Chausse, 7978; Astrand and RideII, 1.973) have
postulated that the cause of relapse in some of the surgical cases may relate to a
failure of the musculature to adapt to the new form created by surgery. It was
suggested that electromyographic studies would be an aid in assessing whether a
reduction of mandibular length would result in a change in muscle activity and
whether the pattern of muscle activity would be associated with relapse. Moss
(1990) undertook this investigation and found changes in the pattern of muscle
activity before and after surgery. He postulated that patients who do not show
an increase in activity of the anterior temporal and posterior masseter muscles
at the end of the post retention period would tend to relapse. The
accommodation of the tongue in the space available was also an important
determinant of whether or not relapse would occur.
Epker and Wessberg (1.982) detailed the clinical applications of the
biomechanical and biological principles mentioned above in minimising
relapse of mandibular advancements and specified that prolonged skeletal
stabilisation (up to 1.2 weeks) with control of the proximal segment of the
mandible is advocated to ensure stable and predictable results. The principles
advocated were used in the context of mandibular advancements and therefore
applying these same principles to mandibular setback procedures would be
inappropriate.
Degeneration of the mandibular condyles following mandibular ramus surgery
in children or adults is rare but can also contribute to relapse. This type of
59
relapse masks the changes that normally occur at the osteotomy site. This
phenomenon has resulted from avascular necrosis, degenerative arthritis or
condylysis (Phillips and Bell, 1,978; Weinberg and Craft, 1980).
There is controversy in the literature regarding the concept of solely using
dental fixation to control skeletal stability. The dentition can be bodity
repositioned within the alveolar process and as such relapse following an
operation could be masked by compensatory changes in axial inclinations of the
teeth (McNeill et al. 7973; Ive et al. 7977; Schendel and Epker, 1980).
Consequently, skeletal fixation has been trialed and its effects have been
compared to studies utilising dental fixation only with inconclusive results
(Rosenquist, 1985; Stella et al. 1986). Johanson et al. (7979) reported in a study of
112 patients, that even though relapse was greatest in the first six months, it was
observed during the whole control period. He suggested that positional changes
during the first year might be due to muscular forces during the healing of the
osteotomy. The relapse occurring after this period might be explained by the
development of new intercuspal relationships. Grinding of teeth
postoperatively may facilitate sliding into an anterior position. Kobayashi et al.
(1986) and Kahnberg and Ridell (1988) also confirmed and supported the idea
that the major part of relapse occurs within the first six months following
surgery and minimal relapse occurs thereafter (Johanson,1,979). Johanson et al.
(1979) reported that relapse is so minimal after two and a half years that clinical
follow-up after that period does not seem to be necessary. However, many
authors (Astrand and Ridell, 1.973; Johanson et al. 7989; Rosenquist et al. 1,987)
have suggested that long term stability should be carefully observed as
displacement of the distal segment has been found as late as two to two and a
half years after surgery, although this decreases with time.
60
CHAPTER 4
FACTORS ASSOCIATED WITH POSTSURGICAL RELAPSE FOLLOWING
VERTICAL SUBSIGMOID OSTEOTOIVTY
4.1. INTRODUCTION
Treatment of mandibular prognathism now entails a multidisciplinary
approach using the combined skills of the Oral and Maxillofacial Surgeon,
Orthodontist and Speech Pathologist. The role of Oral and Maxillofacial Surgery
and Orthodontics in the treatment of facial deformities is well known. The role
of the Speech Pathologist is to assess, diagnose and treat problems associated
with the voice, fluency, speech, language, eating and swallowing disorders. The
Speech Pathologist has been integrated into the overall treatment planning to
assess and determine the functional status of the orofacial musculature and to
determine the potential effects, both positive and negative, on orofacial function
after orthodontic treatment and orthognathic surgery alone or in combination.
The role of the Speech Pathologist is also to determine if there are any effects on
dental and skeletal relapse. Reliability of surgical procedures in association with
a combined approach has yielded quite good results with few complications.
However, despite these advances, long term results of treatment are not yet
uniformly satisfactory. The current main factor contributing to success is
dependent on the postoperative stability of the maxillomandibular structures.
While early studies reported minimal relapse following vertical or oblique
sliding osteotomy (Caldwell and Letterman, 7954; Nordenham and Waller, 1,968;
Hinds and Kent, 7972) subsequent publications showed a higher incidence of
relapse (Astrand et al. 'J,973; Astrand and Ridell, '1,973; Hall et aL. 1975; Isaacson et
aL.7978; Johanson et aL.7979; Egyedi et al. 1981). Most of the relapse is thought to
67
occur after release of maxillomandibular fixation but skeletal relapse has been
reported to occur during the fixation period (Astrand and Ridell, 7973;
Rosenquist et al. 7982; Jonsson et al. 1983).
The aetiology of relapse is considered to be multifactorial since univariate
analysis of relapse by some authors produced insufficient results for predicting
relapse potential (Pepersack and Chausse, 1978; Kurihara, 7984; Kobayashi et al.
1986). Although the contribution of each individual factor causing relapse is
undetermined, certain factors are more reliable the others. Michiwaki et al.
(7990) reviewed the literature and suggested that aetiological factors in relapse
must include:
(i)
(ii )
(iii)
(iv)
condylar growth;
postoperative tension or pressure of the pterygomasseteric sling;
immaturity of bony union; and
tongue pressure after reduction of tongue space.
In order to understand relapse in its vector components, changes in the position
of the mandible after setback gives insight into what is expected. These changes
appear to be of two types and apparently have not always been separated in
previous investigations (Astrand et aL.1973). The two types of changes are:
(i) A rotation of the mandible with superior shift of the chin which occurs
mainly in the fixation period followed by
(ii) An anterior gliding of the entire mandible which occurs mainly between
the fixation period and the six month control period.
62
Following these early positional changes, a generally accepted expectation is the
tendency to continue relapse for up to one and a half to two and a half years.
Hall et al. (7975) reiterated that, in general, there is an eventual one to two
millimetres forward movement and slight backward rotation of the mandible
from the immediate postoperative position following mandibular setback via
an intraoral vertical subsigmoid osteotomy.
4.2 ORTHODONTICS AND OCCLUSION
Among the factors mentioned affecting stability of orthognathic surgery,
presurgical orthodontics has been reported (Welch, 1989). Although there are
no control studies of skeletal stability after mandibular setback in samples with
and without orthodontics, presurgical alignment and decompensations have
been greatly emphasised as an adjunct in orthognathic surgery (Bell et al. 1980;
Henderson and Poswillo, 1985; Epker and Fish, 1985; Proffit et al. 1997). It has
also been shown that vertical and horizontal dimensions can be altered by the
mechanics of presurgical orthodontics resulting in varied intermediate
mandibular positions due to occlusal interferences (Vasir et al. 1,991.). Greater
stability of mandibular setback procedures is thought to be associated with a
better postoperative occlusion (Phillips et aL. '1,986; Wisth, 1981). Astrand and
Ridell (1973 ) found in their study that the entire dental arch was subjected to a
tooth regulating effect during rotation of the mandible with retroclination of the
incisors as a result, the reason being that cap splints were used for fixation. The
return of the incisors to their previous position at the six months control period
may therefore be interpreted as relapse. In a separate paper which analysed
relapse by studying the occlusion, Astrand and Ridell (7973) noted that occlusal
relapse was found to be '1,'l.,% of the surgical retroposition at 6 months,1.5Vo at 18
months and L9% at 30 months. They also stated that the degree of occlusal
relapse tended to be greater in cases with lack of intercuspation. Johanson et al.
63
(1979) reported an average relapse in overbite of 1.5 mm over five years and
emphasised that the relapse occurred during the whole postoperative control
period with 0.2 mm relapse occurring between the two and a half year control
period and the five year control period. The importance of good intercuspation
to reduce the risk of relapse has been pointed out by Becker (7966). Bell and
Creekmore (7973) also state that although gross skeletal changes take place
postoperatively, the occlusion generally remained stable.
Extrusion of the lower incisors has been recorded during the period of fixation
after horizontal osteotomy of the ramus and this effect has also been shown in
vertical osteotomies of the ramus by Astrand and Ridell (1,973). Hovell (7964)
and Nordenham and Waller (1968) have confirmed such extrusion in
horizontal osteotomy and Ahlen and Rosenquist (1990) have supported this
finding in vertical osteotomies of the ramus of the mandible. Other research
has failed to find any correlation between fixation and extrusion in vertical
subsigmoid osteotomy of the ramus (Nordenham and Waller, 1,968).
It has been suggested that presurgical orthodontic treatment may actually
predispose to postoperative dental and skeletal alteration. Poulton, Taylor and
Ware (7963) found in a study of five cases of mandibular prognathism without
open bite that surgical treatment by vertical subsigmoid osteotomy without
presurgical orthodontics resulted in minimal relapse. Bell and Creekmore
(1973) also found less tendency for relapse with the same treatment methods.
With this in mind, these researchers advocate the use of orthodontics at the
completion of surgery when the mandible has stabilised They also support the
idea of overcorrection of the mandibular setback when orthodontics is used
adjunctively. Astrand and Ridell (1,973) detailed conflicting results and stated
that in their material the degree of relapse did not vary with preoperative
orthodontics. Johanson et al. (7979) confirmed this when they compared surgery
64
with orthodontic (n=32) and without orthodontic treatment (n=55) and found
that the relapse tendenry were of the same magnitude in both samples. Isaacson
et al. (7978) remarked that the tendency for skeletal relapse of anterior open bite
due to condylar displacement during the fixation period is masked and
compensated by extrusion of the anterior dentition as much as 1-3 mm during
the six weeks of maxillomandibular fixation.
Kahnberg and Ridell (1988) found in a study, treating open bite and concomitant
prognathic deformities by oblique sliding osteotomies, that a compensatory
mechanism in incisor angulation occurs which maintains the occlusion even
though relapse occurs skeletally. The angulation between the upper incisors
and the nasal plane increases as does the lower incisor angulation to the
mandibular plane. They also found a decrease in the interincisal angle as a
result of dental compensation during skeletal relapse and also, probably, as a
result of continued tongue thrust habit. Willmot and Moss (1984) found similar
upper incisor angulation changes but noted lower incisor retroclination when
the mandible was setback horizontally only with no vertical changes involved.
Kahnberg and Ridell (1988) reasoned that a pure closure of an open bite by
vertical ramus operation only would certainly experience considerable relapse.
However, when the closure is combined with a backwards movement of the
mandible, the mechanics are altered such that they facilitate stretching of muscle
fibres both in the suprahyoid and in the masseter and pterygoid group of
muscles.
Moss (1984) found in his electromyographic investigations that the upper
incisors had proclined further in the postoperative period following mandibular
setback and related this to an increase in the activity of the anterior temporal
and posterior masseter muscles. This increased muscle activity was a consistent
65
finding following setback procedures. Contrary to these findings, Ahlen and
Rosenquist (1990) found in their study, using anterior skeletal fixation, that the
changes in angulation of the incisors to their skeletal bases was minimal. They
reported that the maxillary incisors were essentially in the same position at 18
months as they were preoperatively and that the mandibular incisors
reÍoclined during the entire observation period. It was suggested that this effect
may be the result of relapse of an overcorrected lower incisor proclination
during the orthodontic phase of treatment. Simpson (7974) alluded to the role
of the tongue in occlusal stability and found that the maxillary incisors
remained stable following surgery whereas the lower incisors proclined. It was
postulated that this was due to the effect of tongue pressure. He also noted that
the intercanine and intermolar widths had increased and this supported his
notion that the tongue was active in the postoperative phase. The literature on
the stability of lower incisor proclination following presurgical orthodontics is
controversial and although some reports confirm that lower incisor
retroclination following surgery is inevitable (Artun et al. 7990; Mills, 'J,966),
other studies have shown that dental decompensations in Class III surgical
correction can be stable (Vasir et al. 1991).
4.2.1, Postoperative management
The role of postoperative management in contributing to or preventing relapse
has not been determined. It is possible that postoperative Class III elastics may
prevent anterior movement of the mandible and cause the muscles and their
attachments to better adapt to the new position. Hirose et al. (7976) trialed the
use of elastics as well as the wearing of a chin cap for as long as six months in an
attempt to avoid relapse and downward displacement that might occur as the
result of renewed mandibular function. They found that this adjunctive
treahnent aided stability of mandibular setback procedures.
66
4.3 MAGNITUDE OF MANDIBULAR SETBACK
Franco et al. (7989), in a study of single jaw procedures, found that the only
influence resulting in relapse of the mandible was the magnitude of the setback.
The amount of correction at surgery has been cited by other investigators as one
of the possible causes of relapse (Abe et al. 1980; Reitzik, 1980; Astrand et al.
1,973). Kobayashi et al. (1986) stated that a significant relapsing potential may
exist when the amount of correction exceeded 10 mm. On the contrary,
Johanson et al. (7979) found no correlation between the degree of posterior
positioning or closure of open bite at the operation and relapse tendency in a
review of 772 patients treated by oblique sliding osteotomy. Pepersack and
Chausse (7978) and Sorokolit and Nanda (1,990) found no correlation between
amount of surgical setback and the amount of anterior relapse in a study of
mandibular setback procedures with rigid fixation. Astrand et al. (7973)
identified a positive correlation between the tendency to anterior open bite and
the degree of surgical retropositioning and likewise Reitzik (1980) observed
frequent postsurgical vertical relapse manifest as an open bite among 50 Class III
patients treated by a variety of techniques. Rosenquist et al. (1985), using a
stereomeÍic methodology to study relapse in three planes of space, reported that
there was no correlation between the amount of surgical setback and the
amount of displacement of the mandible during maxillomandibular fixation
and reasoned that suprahyoid muscle tension was reduced. They found weak
correlations between the amount of surgical setback and anterior relapse after
removal of maxillomandibular fixation. Moss (1990), in identifying the tongue
as a cause of relapse, reasoned that one would expect that the degree of relapse
would be related to the degree of mandibular setback.
67
4.4 CONDYLAR POSITION
Emphasis has now been placed on mandibular condylar position in the pre-
treatment assessment of dentofacial deformities and during intraoperative
manipulation of the mandibular fragments since it has been shown that
distraction of the condyle occurred during surgery (Schendel and Epker, 1980).
This resulted in immediate relapse following release of maxillomandibular
fixation. Relapse of surgical and non surgical cases may be related to pre-existing
pathology in the joint (Doyle,7986), adaptive changes of the joint (Le Banc et al.
1.982; Doyle, 1986; Moore et al. 199'1.), condylar resorption after orthognathic
surgery (Merkx and Van Damme, 1994) or inadequate positioning of the condyle
in the fossa (Kohn, 7978; Lake et al. 1981). Fish and Epker (1986) hightighted the
possibility that orthognathic surgical procedures involving the mandible
especially may cause minor displacement of the mandibular condyle in relation
to the mandibular fossa. Attempts have been made to control this with a
variety of devices (Leonard, 7976; Leonard, 1985) and techniques (Hall et al. 7975;
Hall and McKenna, 7987; Ware and Taylor, 7968). Rotskoff et al. (7991) have
even trialed the use of a geometric splint during the healing phase to
compensate for the magnitude of condylar displacement. This splint replaces
the original splint during the healing phase and holds the distal segment in an
overcorrected position to prevent anterior open bites when the condyle re-
establishes its preoperative position. Some surgeons believe that the proximal
segment should be surgically repositioned before bony union occurs to
minimise post fixation occlusal and osseous changes (Hall et al. 7975; Bell,
Proffit and White, 1980). Kundert and Hadjiangelou (1980) hightighted the fact
that condylar displacement occurs in three dimensions with rotation and tilting
of the condylar head following surgery. The final position is dictated by the
position of the tooth bearing fragments and occlusion, by the mutual
relationship and adaptation of the fragments, fixed either by wires, screws or left
68
unsecured and finally by the musculature. Aberrant condylar position (also
known as condylar sag) is considered by many to be a major factor in relapse
with all types of mandibular surgery whether advancement or setback (Edlund
et al. 1979; Flase, 7988; Hollender and Ridell,7974; Rosenquist, 7988; Sund et al.
7983; Will et aL.1984; Wisth and Tornes,1975). Tendencies to relapse after ramal
surgical procedures have commonly involved clockwise rotation of distal
segments that had been surgically rotated counterclockwise i.e. relapse of
surgically corrected anterior open bites. For an anterior open bite to relapse, the
healed segments would have to rotate as a single unit in a clockwise direction.
For this to occur without a change in mandibular morpholoçy, the condyle
would have to move superiorly in the fossa as the anterior open bite relapsed
around a fulcrum of molars in contact. With the use of the vertical subsigmoid
osteotomy technique, the condylar fragment is separated from the distal
segment and its position is dependent on muscle pull during the period of
maxillomandibular fixation. Condylar sag typically occurred when the masseter
and medial pterygoid attachments to the proximal segment were removed.
With modification of surgical technique, which maintained adequate medial
pterygoid muscle attachment to the proximal segment, condylar sag was avoided
(Hall and McKenna, 1,987). Displacement of the proximal segment during
surgery has been reported with displacement occurring in an anteroposterior
direction usually (Astrand and Ericson,1.974; Isaacson et al. 7978). The degree of
condylar displacement following mandibular surgery varies between different
surgical techniques and imaging techniques, tomographic methods being far
superior to plain radiographic techniques (Eckerdal et al. 1986). Sund et al. (1983)
reported an average horizontal condylar displacement of 3.2 mm following
oblique sliding osteotomy and Wisth and Tornes (1975) reported a significant
downward and forward displacement of about 1 mm whereas an average
postoperative condylar displacement of less than L mm was found after sagittal
splitting of the mandibular rami (Edlund et al. 7979; Will et al. 1984). Rotskoff
69
et al. (7991) believed that the cause of condylar sag was a result of the pull of the
lateral pterygoid muscle.
If the segments of the vertical subsigmoid osteotomy did heal with the condyles
in a displaced position, an immediate posterior translational relapse of the
mandible would be expected to occur at the time of release of the
maxillomandibular fixation as the proximal segments would return to the
fossae in a posterosuperior direction. Isaacson et al. (1978) stated that this does
not occur as the proximal segments return to its original position during the
period of maxillomandibular fixation if the segments are not secured together by
osteosutures. The study by Rosenquist et al. (1986) confirms that this is the case.
Petersson and Willmar-Hogeman (1989) also found no correlation between
mandibular relapse and the degree of immediate postoperative condylar
displacement.
The variability of skeletal remodelling has been reported as between 7-80%
following oblique sliding osteotomy of the mandible (Wisth and Tornes, 7975;
Eckerdal et al. 1986). Remodelling of the condyle by bony apposition may be an
attempt at normalisation of the loading of the joint altered by surgery. Previous
studies corroborate the finding that a morphological adaptation of the condyle
occurs after altered position of the mandible but it is important to note that
these changes were primarily occurring in young experimental animals who
were able to adapt and compensate for these new positions (Boyne, 1,966;
McNamara and Carlson, 7979; McNamara et al. 'I.,982; McNamara, 7980;
Schneiderman and Carlson, 1985). Ware and Taylor (1968) concluded that
distraction of the condyle within the fossa may serve as a stimulus to
compensatory condylar growth and could be the cause of the double contour
formation seen on radiographs. Hansson (7977) concluded that an increase in
biomechanical loading of the temporomandibular joint was the reason for
70
stimulating the undifferentiated mesenchymal cells to proliferate with
subsequent cartilage formation and possibly this was followed by endochondral
ossification. Further skeletal remodelling also occurs in the roof of the fossa in
the posterior surface of the fossa, a functional adaptation to condylar
displacement. Eckerdal et al. (1986) confirmed this finding in the temporal part
of the joint and the corresponding value was a mean bony apposition of 0.9
mm. Hall and McKenna (1987) have advanced a method for rectification of
condylar sag whereby the medial pterygoid muscle attachment is retained
allowing this muscle tone to position the condyle.
Most surgical methods of the mandible involve the risk of changing the relation
between the condyle and mandibular fossa. Such a change after horizontal
osteotomy is due to anterior rotation of the upper fragment. Lundberg (1972)
found that this change did not produce any subjective symptoms of the
temporomandibular joint. Fromm et al. (1962) agreed with this even though 14
cases (327o) had clinically demonstrable temporomandibular joint signs.
Hogeman (1951) reported temporomandibular joint symptoms ín 27.2% of the
patients who had been followed up for a long time. It would be presumed that
temporomandibular joint symptoms would occur with greater frequency
following vertical subsigmoid osteotomy for a number of reasons. Firstly,
lateral angulation of the proximal fragment relative to the distal fragment
results in a change of the condylar head position in the glenoid fossa. Secondly,
presumed stretching of the lateral pterygoid muscle associated with the lateral
rotation of the proximal fragment may further increase myofascial symptoms
but remodelling of the condylar head is known to occur and this possibly
accounts for the lack of symptoms.
Plain radiographic examination of the segments following vertical subsigmoid
osteotomies have a number of disadvantages in that it is usually difficult to
77
identify defined points in the joint at consecutive examinations as the condyle
may rotate about its sagittal and vertical axes. Remodelling of the joint may also
make identification of defined points difficult. In an attempt to resolve this
dilemma, Astrand and Ericson (7974) used frontal radiographs to study the
lateral angulation of the condylar segments while Sund et al. (1983) used lateral
tomography as well as frontal and axial radiographs to obtain three dimensional
configurations of the joint. Even then it was difficult to determine the accuracy
of their results although the results did yield changes in the condyle to fossa
relationship. The x-ray stereometric method devised by Selvik (7974) improved
the scientific examination of mandibular segment movements. Rosenquist
(1988) used this methodology and was able to report with more accuracy that the
condylar head displaced in a medial/superior direction with a weaker tendency
to displace posteriorly during the period of maxillomandibular fixation. He
reasoned that the inferior part of the condylar segment becomes displaced
laterally by the postoperative oedema resulting in a medial translation of the
condylar head. He also explained that the superior and posterior movement of
the condylar head lies in the assumption that "there was decreased tension in
the muscles that displace the condyle anteroinferiorly as the muscular
equilibrium was disturbed during surgery". After release of fixation, condylar
displacement tended towards a lateral translation as well as an inferior and
anterior direction as most other studies have shown as noted above.
4.5 PRO)OMAL AND DISTAL SEGMENT POSITIONING
Interfragmentary movement occurs between the proximal and distal segments
following surgery of the ramus of the mandible. These rotational movements
have been thought to be unfavourable and consequently have been implicated
as one of the many factors involved in surgical relapse following mandibular
surgery (Isaccson, et aI.7978).
72
4.5.1. Rotational effects between fragments
Positional changes of the proximal and distal segments after surgical correction
of mandibular deformities have been reported. Clinical observations and
several reports have remarked that the proximal segment does not always
remain in an unchanged position following surgery whether the segments are
left free or are intraosseously fixed (Hall et al. 7975; McNeill et al. 7973; Ware and
Taylor, 7968). One cause of these positional changes is the presence of only
small contact areas between the fragments. When the contact areas are small it
may take much longer for the fragments to stabilise and during this period the
position of the mandible may be altered by muscular forces. Caldwell and
Letterman (7954) stressed that the osteotomy should end anterior to the
mandibular angle. The rationale for this anterior extension of the osteotomy
cut was to provide a better bony contact between the fragments. Tornes (1989)
however, showed that no significant correlations could be demonstrated
between postoperative stability and osteotomy length or overlapping bony area
and concluded that the osteotomy length appears to be a factor of minor
importance for postoperative stability.
Franco et al. (1989) identified in his study of rigidly fixed mandibular setbacks
that muscular interactions played a definite role in relapse. He reasoned that
there is a tendency for the proximal segment to rotate clockwise with
mandibular setbacks. Unless the attachments on the medial aspect of the
proximal segment are detached and measures taken to prevent rotation, then
the further the distal segment is setback, the greater the tendency for the
proximal segment to rotate. When the distal segment is positioned posteriorly
without detachment of muscles in the proximal segment, the medial
attachments are placed under tension. Consequently, clockwise rotation of the
proximal segment elongates and stretches the lateral attachments. Both these
73
effects will result in a tendency for the mandible to relapse back towards its
original position. Komori et al. (1989) supports this contention and confirmed
in a study of mandibular sagittal split osteotomy setbacks with
maxillomandibular fixation and skeletal fixation, that the degree of inadvertent
anteroposterior rotation of the proximal segment at the time of surgery, rather
than extent and pattern of surgical repositioning of the distal segment, was
significantly correlated with the degree of shift. The finding in this study
confirmed the importance of preserving the proximal segment in its exact
presurgical anatomic position without rotating the segment either backward or
forward.
Astrand and Ericson (1974) reported that the morphologic changes between the
proximal and distal fragments varied with the immediate postoperative relation
between the fragments. In cases with a good adaptation of the fragments only,
small remodelling changes occurred whereas in cases with greater lateral
angulation of the profmal fragment, extensive remodelling occurred.
4.5.2 Medial displacement of proximal segment
The technique of vertical subsigmoid osteotomy requires that the proximal
segment be positioned lateral to the distal segment. In the extraoral approach to
the vertical subsigmoid osteotomy the proximal segment is easily maintained in
the lateral position, however, with the intraoral vertical subsigmoid osteotomy,
medial displacement of the segment has been reported to occur in about 3% to
8To of cases (Tuinzing et al. 1983; Tuinzing and Greebe, 1.985; Rosenquist, 1990).
Rosenquist (1990) further brought attention to the implications of medial
displacement of the proximal segment. Medial displacement can occur during
surgery but in most instances the displacement occurs postoperatively.
Calderon et al. (7992) described a number of methods to retrieve the medially
74
displaced proximal fragment so that it can be repositioned laterally and uses
manipulative, as well as dedicated instrumentation, to achieve this. Burk (1968)
published a variation of the vertical subsigmoid osteotomy whereby the
proximal segment was placed medially to the distal segment out of mechanical
necessity. Substantial postoperative displacement of the proximal segment has
been reported (Hollender and Ridell, 7974; Rosenquist, 1988; Wisth and Tornes,
7975). Rosenquist (1990) elaborated on this problem by suggesting that medial
displacement of the proximal segment had no influence on relapse and even
suggested that, in fact, it could lead to increased stability of the osteotomy as less
angulation of the proximal segment increased its contact area with the distal
segment. Contrary to this suggestion, Poulton et al. (1963) in a much earlier
statement remarked that if the proximal segment is not placed lateral to the
distal fragment of the mandible a non union may result and relapse would be
inevitable.
4.5.3 Wire osteosynthesis between the proximal and distal segments
Osteotomies of the mandible may be performed through an intraoral or through
an extraoral approach. Only through an extraoral approach is it possible to apply
wire osteosynthesis to approximate the proximal and distal fragments. Wiring
of the proximal segment to the distal segment was thought to cause more drastic
changes and relapse potential following mandibular setback. The fact that the
proximal fragment is placed lateral to the distal part of the ramus will make it
impossible to reposition the condylar head in its natural presurgical position
and a tight osteowire may even further distort the position of the condylar head.
Ritzau et al. (1939) compared changes in condylar position after bilateral vertical
subsigmoid osteotomies with and without osteosynthesis and found no
correlation between postoperative condylar position whether or not
osteosynthesis had been used. He noted that the postoperative condylar
75
position was, however, significantly different when related to its original
position. Athanasiou et al. (7991,) reported that the placement of wire
osteosynthesis between the mandibular bony segments had no significant effect
on the postoperative stability in their study of 52 patients. Nordin et al. (1986)
compared the skeletal and dental relapse rates as well as mandibular function
between extraoral and intraoral approaches and concluded that there were no
significant differences between the two surgical techniques. On the contrary,
Isaacson et al. ('1,978), in a dedicated study, examined the movement of the
segments following surgery and generally found that there were examples of
condyles being displaced inferiorly and anteriorly in their fossa. They also noted
that if, the proximal segments were not tied in their displaced position by
intraosseous fixation, then they frequently returned to a stable position and no
postsurgical occlusal relapse occurred. Flowever, relapse of dental open bite was
evident in the first few days after release of maxillomandibular fixation if the
proximal segments were fixed securely. When Paulus and Steinhauser (7982)
compared patients having wire osteosynthesis to those treated with screw
fixation for vertical subsigmoid osteotomies to treat mandibular prognathism
there appeared to be less difference in stability between the groups. Sund et al.
(1983) have shown specificallf , in a study of temporomandibular joint changes,
that there were also no unfavourable effects on the joint with the use of
osteosynthesis wiring between the fragments.
76
4.6 MAXILLOMANDIBULAR FIXATION
4.6|1. Period of maxillomandibular fixation
It has been suggested that the period of maxillomandibular fixation is an
important factor in relapse of the mandible. Most authors recommend a
fixation period of six to seven weeks (Hinds, 1957; Bell and Creekmore 7973;
Hirose et al. 1,976; Werndah and Blomquist, 1981 cited in Rosenquist et at. 1986).
Other researchers recommend variable time periods of maxillomandibular
fixation. Alling (1967) initially suggested five to six weeks but in a later review,
a shorter period of fixation of two weeks was used (Alling, 1965). Astrand and
Ridell (1,973) recommended a longer period of seven to eight weeks and
Hogeman (1967) proposed an even longer period of ten weeks. These results are
summarised in Table 4.1.
Table 4.1 Period of maxillomandibular fixation
3-5
6
7
5-7
8
6
5-6
10
6
8-9
1954
1958
1958
7967
1961,
7967
1965
1967
1968
7991
Caldwell & Letterman
Hinds
Robinson
Shira
Thoma
Georgiade & Quirur
Alling
Hogeman
Nordenham & Waller
Hogevold
WEEKS OF FIXATIONYEARAUTHOR
A pre-requisite for displacement of the mandibular body without displacement
of the condyles (ie. relapse) is non union or a plasticity of the osteotomy site.
77
Early reports believed that excellent bone healing had occurred at the time of
removal of maxillomandibular fixation (Caldwell and Letterman, 7954; Hinds,
7957; Alling, 7967; Shira, 1961.; Proffit and White, 7970; Reitzik, '1.983; Rosenquist
et al. 7987). However, Ware and Taylor (7968), Astrand and Ridell (1973) and
Reitzik (1980) all became aware of the possibility that the bone scar at the time of
removal of maxillomandibular fixation may be unable to resist the muscle
forces when function was regained. It was not until this possibility was raised
that experimental work on monkeys was undertaken to determine the time
period at which full strength of osteotomy sites was re-established. It was found
that a minimum time periodof 20 weeks was necessary for remodelling to occur
in monkeys and a further 4-6 weeks was necessary for remodelling to occur in
humans. Hence 26 weeks is the minimum period required to minimise plastic
deformation of the mandible although clinically this time period is impractical.
Management problems may be encountered with the use of maxillomandibular
fixation. These can range from loss of weight to respiratory problems.
Maxillomandibular fixation causes partial obstruction of the oral airway and
possibly oxygen saturation levels may be affected (Barton and Harris,7970). Loss
of weight during fixation may occur unless careful consideration is given to diet.
Ritzau (1,973) highlighted this problem in patients placed into
maxillomandibular fixation as a method to treat mandibular fractures.
4.6.2 Maturitv of bone union
A pre-requisite for displacement of the mandibular body without displacement
of the condyles is non union or plasticity of the osteotomy site. Immaturity of
the bony callus at the osteotomy site has been implicated as a cause of relapse
(Martis, 1,984; Reitzik, 1980). Worms et al. (1980) stated that the union at the
osteotomy site may actually be fibrous rather than bony. Reitzik (1982) has
78
shown that, even under the most ideal conditions, it takes 20 weeks for full
strength to return to an osteotomy site in the monkey and the equivalent time
period when extrapolated to man is about 26 weeks. Johanson et al. (7979) in a
study reviewing 112 patients found bone healing to be uncomplicated in every
case and radiographic examination showed that the healing process was
complete within one and a half years. However, Rosenquist et al. (7987)
recorded, by means of X-ray stereometry, mobility between the proximal and
distal segments two years after surgery and stated that relapse after oblique
sliding osteotomy continues as long as the functional matrix can influence an
unstable osteotomy site.
Other issues raised in relation to bone repair include the effect of cortex to cortex
contact and its subsequent healing and the effect of interfragmentary mobility
during the fixation period as physiology principles dictate that mobility has a
detrimental effect on bone repair. Osteoprogenitor cells, required for bone
healing originate from the cambium layer of the periosteum and endosteum
(Hempenstall, 1980). Theoretically, íf cortex to cortex healing is attempted
following osteotomy without decortication, both the cells and the blood supply
necessary for healing may be reduced at the site and consequently the relapse
potential may be greater. Reitzik (1983) studied this issue and established that
firm bony union occurred at seven weeks, only where cortical surfaces were in
intimate contact and rigidly fixed. He also showed that external callus filled the
gaps between the cortical surfaces only if the gaps were less than 0.8 mm wide
whereas fibrous union occurred if the gaps were greater than 0.8 mm.
79
4.6.3 Wires
Ductility of wires, ie. stretching of wires between visits, affects osteotomy site
healing. It has been noticed that, during the period of maxillomandibular
fixation, loosening of the maxillomandibular wires occurs, to some extent,
allowing freedom of movement of the mandible. Although, in most cases,
minor movement is possible, relapse associated with this entity has never been
addressed. It is known that wires have plasticity and ductility to the point of
stretching under force. It is also known that immobilisation has a major
influence in bone repair. Hence wire distortion must account for some
component of relapse during maxillomandibular fixation.
4.6.4 Skeletal fixation
In '1.947, Goldstein alluded to the possibility of extrusion of teeth during the
period of fixation stating that "the load should be as well distributed over all the
teeth as possible to avoid any extrusion". Many authors advocated the use of
skeletal fixation in addition to maxillomandibular fixation to minimise skeletal
relapse as displacement of the mandible occurs during the fixation period and
also to avoid incisor extrusion (Astrand and Ridell, 1973; Rosenquist et al. 1982;
Jonsson et al. 1,983; Rosenquist, 1.985; Stella, 1.986; Epker and Wessberg, 1,982;
Nystrom et al. 7984). Komori et al. (1989) compared mandibular setbacks via
sagittal split osteotomies with and without skeletal fixation and found
statistically significant similar results with good control of the corrected chin
position and incisor extrusion. Further, Hall et aL. (7975) reassured that the
absence of intraosseous wiring of the fragments permitted the condyle to move
out of its fossa which in turn led to occlusal relapse. However, Isaccson et al.
(7978) and Astrand et al. (7973) found no evidence for greater stability with the
use of intraosseous wiring. Tornes and Wisth (1988) indicated that skeletal
80
fixation in combination with maxillomandibular fixation reduces the extrusion
of incisors but, except for a more stable anterior facial height, the influence on
skeletal changes is limited. This was further confirmed by Ahlen and
Rosenquist (1990) who concluded that the anterior skeletal fixation seemed to
prevent the previously observed increase in anterior facial height and a decrease
in the posterior shortening of the mandible but this effect was marginal.
Baumrind et al. (7974) noted in their study that the mandibular plane angle was
found to have increased between the presurgical and postsurgical films. It was
suggested that there was a tendency for the upper and lower incisors to extrude
slightly from the investing bone coupled with the findings that the point
gonion tended to move superiorly more than the inferior movement of
menton and this accounted for the increased mandibular plane angle.
4.6.5 Nutritional aspects of healing
The patient undergoing maxillofacial surgery presents unique nutritional
problems especially when the jaws are fixated for a period of time. Since the
oral cavity is the natural entry into the alimentary tract, surgery or trauma to
this area can easily lead to difficulties in alimentation. The major cause of
nutritional problems is the inability to ingest adequate amounts of nutrients
orally. This can be due to a mechanical problem of not being able to get food
into the mouth as well as the inability to meet the increased metabolic demands
(Buchanon and Levine, 1983). Maxillomandibular fixation is known to
compromise nutritional status which consequently leads to weight loss
(Worrall, 7994).
Basic wound healing dictates that an adequate source of vitamin C, calcium,
protein and minerals are required for an acceptable maturation of the surgical
wound. In addition, it is known that a negative nitrogen balance will occur in
81
these patients postoperatively resulting from both a decreased protein synthesis
and accelerated catabolism of muscle protein (Fallender et al. 7987). The
importance of proteins in healing is demonstrated in a number of areas; they
provide a source of heat and energy, and they provide amino acids for the
formation of antigens, hormones, antibodies and enzymes. Proteins are
necessary for the transport of lipids in the body and for maintenance of normal
blood volume, serum protein levels and total circulating blood cell mass.
Proteins are important regulators of osmotic pressures between various body
fluids. Proteins are also the substrates for the repair and replacement of injured
and destroyed tissue. Consequently, proteins play an important role in bone
healing. Adequate dietary proteins favour deposition of calcium in the bone
and the subsequent formation of callus following fractures. Research has shown
that little callus formation occurs in the hypoproteinemic animal following
fracture whereas good callus formation occurs in animals receiving protein
intake (Rhoads and Kasinskas, 1,942).
When the dietary intake in a healthy patient is reduced for as little as 10 - 12
days, vitamin and protein deficiencies may occur which consequently affects
physical fitness, lowers resistance to disease and interferes with healing (Zintet,
7964). Rodgers et al. 09n) found that a jaw wired for obese patients on an 800
cal/day diet had no biochemical evidence of protein catabolism. Goss (personal
communication, 1994) performed a sagittal split osteotomy on a morbidly obese
patient with prognathism. This patient required jaw wiring for obesity and
orthognathic surgery to correct her prognathic mandible. Satisfactory union
occurred despite being on a very low caloric fluid diet. At five years, however,
both the mandibular setback and obesity had significantly relapsed.
82
Therefore, by providing a nutritionally adequate diet in the preoperative and
postoperative periods and during convalescence, the duration of disability after
surgery can be significantly shortened, complications reduced and wound
healing improved (Jones, 7970).
The literature presents varying figures as to the appropriate requirements
necessary for healing to occur and has recommended that non protein calories
be provided in the diet so that proteins are used for repair and not as energy.
The recommendations have ranged from a non protein source of 2,800
calories/day (Calloway and Spector, 7954) to an increase in protein from 30Vo to
700Vo in order to fulfil the demands of these functions (Hayes, 7959). In
conclusion, protein, calories and all nutrients need to be supplied in liberal
amounts. As a guide, it is necessary to provide 150 grams of protein and 3,000
non protein calories daily for the patient in convalescence (Jones, 7970).
4.7 MUSCULAR INTERACTIONS
4.7.7 Tongue pressure after reduction of tongue space
Surgical procedures designed to correct dentoskeletal deformities inevitably
affect the size and position of the surrounding soft tissues by altering the pre-
existing soft tissue - hard tissue relationship. This alteration is well documented
with established ratios for soft and hard tissue changes for chin and lips (Lew,
1,990; Mommaerts and Marxer, 1,987; Dewan and Marjadi,7983; Obwegeser and
Marentette,'l.,986). Flowever, the effects on pharlmgeal tissues has not been
studied as extensively. Bear and Priest (1980) and Kuo (7979) noted that
mandibular advancement improved sleep apnoea and early investigations
showed that the tongue adapted to its new environment following mandibular
setback procedures (Wickwire et al. 1972; Proffit and White,7970). However, it is
83
possible that in the early postoperative period, the tongue may have an adverse
effect on the postsurgical position of the mandible. The changes in the position
of the tongue have been implicated in relapse by Hovell (7964). There is the
philosophy that eliminating the area of the floor of the mouth by mandibular
setback procedures will not allow the tongue to accommodate. This factor could
result in a forward movement of the mandible as labial pressure decreases and
lingual pressure increases correspondingly after the operation. It may also cause
some difficulties in speech, mastication, and swallowing (Malakouti,7970).
Contrary to these proposals, Greco et al. (1990) found that mandibular setback
procedures created a relative narrowing of the hypopharyngeal airway space due
to tongue positioning as seen on lateral head cephalograms. Hence the tongue
must either re-adapt in this new position by changing its size, shape or position
or try to enforce its preoperative position with subsequent relapse of the
mandible. The tongue is believed to play an important role in the pathogenesis,
continuation and relapse of dysgnathic disorders and reduction of the tongue
has been indicated for a number of reasons. Moss (1990) studied the position of
the tongue following surgery and reported that in stable mandibular setbacks,
the tongue position shifted upwards and backwards whereas in those that
relapsed, the tongue position shifted upwards only. This implied that the
anterior tongue forces remained constant in relapse cases. The premise for
reduction of tongue volume is that muscular pressure exerted on adjacent
structures following tongue reduction would reduce and this would decrease
relapse of mandibular setback procedures.
u
1
Tongue reduction has been suggested in the following situations:
To support orthodontic treatment of abnormalities in which the tongue
possibly plays a role in the pathogenesis (Becker, 1,966; Egyedi, 1964;
Rheinwald, 1,960).
2. Partial glossectomy has also been suggested preparatory to surgical
treatment of dysgnathic disorders especially mandibular prognathism,
open bite and bimaxillary protrusion (Becker,7966; Kole, 7963; Onland,
7972; Rheinwal d, 7960).
3. Reduction of tongue volume is also indicated in cases of macroglossia
due to a tumour of the tongue (Becker, 1,966; Rheinwald,7960).
Much of the controversy about tongue reduction exists because it is difficult to
establish objectively to what extent tongue volume, function and position are
important in the pathogenesis of dysgnathic disorders. Some authors support
the idea that the tongue plays a role almost exclusively in causing relapse of
mandibular setback procedures (Egyedi and Obwegeser, 7964; Reichenbach, 1955;
Korkhaus,1958; Hinds and Kent, 1969). On the contrary, Proffit (7970) postulated
that the tongue pressure does not seem to cause relapse following surgery and
explained that the period of maxillomandibular fixation retrains the function of
the tongue. Rosenquist et al. (1985) reported in a study using a stereometric
methodology that there was no correlation between the amount of surgical
setback and the amount of relapse along the sagittal plane. They reasoned that
the length of the suprahyoid muscles was reduced, hence the tension of these
muscles did not contribute to relapse. Two other findings were evident in this
research. Firstly, an almost significant correlation was found between anterior
rotation of the mandible and posterior relapse. Assumedly, the suprahyoid
85
muscles were stretched during this anterior rotation. Secondly, the relapse was
in the form of posterior translation rather than posterior rotation.
Smeets (7969), on the other hand, studied the position of the tongue before and
after correction of mandibular prognathism and concluded that the tongue
could not be held responsible for mandibular relapse. Studies by several
researchers have supported this concept and have stated that tongue pressure
against lower incisors following mandibular setback surgery did not change, nor
did flaring of incisor teeth or skeletal relapse occur which otherwise would
indicate increased tongue function (Joffe,1,964; Walker, 1,977).
A retrospective study by Onland (7972) concluded that the tongue plays a role in
relapse of mandibular setback procedures only when the dentoalveolar portion
is moved posteriorly, as in a Kole procedure, whereas no relapse occurs if a
stepped ostectomy is performed. On this basis, any surgery performed in the
ascending ramus simulates a stepped ostectomy and hence no relapse is
expected. He further explained that the tongue space is less reduced when the
whole anterior portion of the mandible is setback thereby reducing the space for
the floor of mouth musculature as well as the tongue. In contrast,
dentoalveolar setback impinges on tongue space because the musculature of the
floor of the mouth remains largely in the same position as does the tongue but
it occupies considerably less space after the Kole procedure. Significant changes
in tongue position can be assessed by analysing changes of hyoid position
(Athanasiou et al. 1991). Hyoid position and its orientation has been studied in
Class I and Class III malocclusions by Adamidis and Spyropolous (1992). The
conclusions showed that there were statistically significant differences in
position and inclination of the hyoid bone in the two groups. Class III patients
exhibited a more anterior position of the hyoid bone and also a reverse
inclination of the long axis of the hyoid bone to the mandibular plane.
86
Wickwire et al. (7972) elaborated on the effect of mandibular osteotomy on
tongue position and concluded that the tongue position changed after surgery,
which was indicated by the hyoid position. After this initial adjustment there
was a tendency for the hyoid bone to return to its original position and hence
the stability of the surgical result would hinge on the stability of the hyoid
position. The hyoid bone is suspended between the conjoint actions of the
supra and infra hyoid muscles, consequently it is influenced by a number of
variables which include head posture and respiratory function. Also noting that
linear measurements of hyoid position on cephalometric recordings (Stepovich,
1965) of less than 2.0 mm are considered to be within physiological variation.
Solow and Kreiborg (7977) developed a model and suggested that changes in
craniofacial morphology will lead to changes in head posture through changes
in respiratory resistance. Two cephalometric studies have investigated the
airway after surgical correction of mandibular prognathism (Wenzel et al. 7989a;
Wenzel et al. 1989b). It was found that there was a reduction of the
anteroposterior dimension of the nasopharynx. Consequently, two
compensatory effects may be seen. Firstly, a cervical hyperflexion occurs and
secondly, tongue posture may re-adapt with forward repositioning of the
tongue. In each of these compensatory mechanisms, the hyoid bone is
repositioned to maintain the airway dimensions. Athanasiou et al. (7991)
showed that there were no significant changes in the anteroposterior position of
the hyoid bone in relation to the anterior pharyngeal wall because the hyoid
bone was directed downward and not backward following mandibular setback.
Wenzel et al. (1989a) remarked that cervical hyperflexion may be influenced by a
patient's increase in self esteem which stimulates the patient to lift their head
rather than an alteration of airway function. Phitlips et al. (1991) has shown in a
study of orthognathic surgery on head posture that, following maxillary
intrusion and mandibular setback, there was a trend toward persistent head
flexion. Valk et al. (7992) showed that anterior repositioning of the head is a
87
natural reflex following any type of mandibular surgery, whether advancement
or setback.
4.7.2 Bite force and its vector components
Animal experiments by Picton and Moss (1978) have shown that the presence of
cusps retard tooth migration and that cuspal inclines either aid or hinder tooth
movement depending on the direction of the slope and the occlusal force
(Picton and Moss, 1980). Presumably, following surgery, poor interdigitation
would allow tooth migration and whether this is solely dental or in conjunction
with skeletal relapse is not known. Alternatively, good interdigitation of the
teeth would minimise relapse as the occlusal forces would oppose muscular
forces.
4.7.3 Masticatorymuscles
Electromyographic studies by Moss (7973) identified different patterns of muscle
activity in various types of malocclusion. Patients with Class III malocclusions
have a distinctive pattern of activity (Moss and Chalmers, 1,974). It has been
thought that, following surgical treatment of mandibular prognathism, this
muscle pattern would not have changed but evidence supports the idea that
there is altered activity. Therefore failure of the masticatory muscles to re-adapt
to the repositioned segments has been thought to contribute to relapse
(Pepersack and Chausse, 7978; Moss, 7984; Yellich, 1981). Moss (7984) suggested
that patients who do not show an increased activity in the anterior temporal
and posterior masseter muscles at the end of the retention period would tend to
relapse. A correlation was shown between increased muscle activity and
muscles which were less active in the untreated prognathic mandible and
therefore, if remained inactive, would tend to revert to their original position.
88
Operative rotation of the proximal segment in any type of mandibular setback
procedure puts the pterygomasseteric sling under tension only if the muscle
sling is iatrogenically or physiologically shortened, which then continues until
biological equilibrium is achieved (Reitzik, 1980). Additionally, susceptibility to
relapse after release of maxillomandibular fixation supports the idea that
mandibular excursion may contribute to relapse. Functional movement of the
mandible activates the musculature to relieve the tension caused by operative
repositioning of the proximal segment. Consequently, the forces due to the
sling cause anti clockwise rotation of the proximal segment (now healed with
the distal segment) thereby causing relapse (Michiwaki et al. 1,990).
Hirose et al. (1976) described a new technique of a curved oblique osteotomy for
mandibular setback in which the ascending ramus was cut obliquely on a curved
line from the anterior border of the ramus to the mandibular angle by the
submandibular approach. In this procedure, the masseter and medial pterygoid
muscles were detached from the bone but were repositioned to their original
sites with no change in the direction and position in relation to the condyle and
to each other. This was thought to minimise relapse as the muscle forces are
involved in relapse. Although no conclusive evidence was available in this
study to support this conjecture, Reitzik (1988) also reported that reducing
changes to the muscle length and direction also reduced relapse following
surgery.
89
4.8 VASCULAR CONSIDERATIONS OF OSSEOUS SEGMENTS
4.8.1 Healing of osseous segments
The vertical subsigmoid osteotomy is designed for comparatively large
retropositioning of the distal segment during surgery. Only then is the
adaptation of the segments optimal for healing. Small degrees of mandibular
setback lead to minor overlapping and poor adaptation of the segments. The
proximal segment would be angulated laterally and the contact with the distal
segment would be a line rather than an area. This inevitably does not lead to
optimal healing of the osteotomy sites and consequently relapse is further
enhanced (Astrand and Ericson, 1,974). It has also been suggested that medial
displacement of the proximal segment adversely affects healing in that firstly, a
haematoma develops in the space created as a result of medial displacement of
the proximal segment and secondly, the masseter muscle is not able to reattach
to the medially displaced proximal segment hindering the revascularization
Process.
Many advantages are achieved when the vertical subsigmoid osteotomy
technique is employed however there is considerable disagreement as to the
histopathologic and the chronological nature of the osseous healing in the
region of the bone section. The necessity of decortication of the distal segment
prior to mandibular setback has been emphasised to effect bony union (Caldwell
and Letterman, "1,954; Shira, 7967). Boyne (7966) reported that in monkey
experiments, the principle of decortication of the segments as a prerequisite to
effecting adequate osseous healing is in conflict with other widely held views.
He also found at autopsy of the monkeys that no mobility of the osteotomy sites
was discernible at 25 and 30 days.
90
4.8.2 Viabilitv of osseous sesments
For any tissue to heal, an essential requirement is the maintenance of the
vascular supply to that tissue. Bell (1973) pioneered the studies of vascular
supply for the Le Fort I maxillary osteotomy. He has determined the vascular
supply for the oblique osteotomy of the mandible and using rhesus monkeys
(Bell et al. 7974), determined that when the segments are pedicled, the
intraosseous circulation was maintained. When the muscle and capsular
ligaments were detached from the proximal segment a free osseous segment
resulted and ischaemia, avascular necrosis and delayed healing occurred.
Westesson et al. (7991,) investigated the osseous and muscular changes after
vertical subsigmoid osteotomies with the use of magnetic resonance imaging
and found no evidence of avascular necrosis but did report atrophic changes in
muscle tissue with decreased volume and fatty changes.
4.9 GROWTH
4.9J1, Normal growth
The timing of skeletal ossification has a significant influence on diagnosis and
treatment planning. The assessment of skeletal maturity influences clinical
decisions related to the commencement of orthopaedic forces, functional
appliances and orthognathic surgery. Considerable disagreement is found in the
literature on the timing of surgical procedures for correction of dentofacial
anomalies. Some authors contend that surgical correction of mandibular
prognathism can be carried out at a very early age (Biederman, 7967; Ware and
Taylor, 7968; Isaccson et al. 1978; Macintosh , 1981,; Lehman, 1981). Other authors
caution against such corrections prior to growth maturity since individuals with
Class III malocclusions tend to have a prolonged period of mandibular growth
97
(Goldstein, 7947; Proffit and White, '1,970; Hinds and Kent, 7972). In a study by
Bell and Creekmore (1973), four patients had postoperative relapse and this was
attributed to excessive mandibular growth associated with their young age at the
time of operation. Efforts have been made to establish ways to treat Class III
malocclusions surgically during the growth period but these efforts seem to
meet with a high degree of relapse. In these circumstances, having orthodontic
appliances on the teeth after surgery has offered some, if only minimal, help
(Proffit and White,1.970). Other postoperative growth studies of patients with
mandibular prognathism treated by early osteotomy (ages 9-72) have shown no
gross relapses (Knowles, 1,970).
Since the incidence of unfavourable results is definitely higher in young
patients than in adults, it must be assumed that growth plays an important role.
Vijayaraghavan et al. (7974) confirmed this concept and found that condylar
growth and mandibular posture were important factors producing relapse. The
ideas of delaying operating until the end of the growth period and detaching the
medial pterygoid muscle and the sphenomandibular ligament were offered to
minimise relapse" Freihofer (7982) has empirically stated that
maxillomandibular disharmonies of the Angle Class III type should not be
corrected before facial growth has been completed. The literature is replete in
supporting the clinical observation that surgery of the mandible in the growing
patient does not affect its subsequent growth potential (Cook and Hinrichsen,
7973; Egyedi et al. 1981). Clinically, this observation pre-empts that surgery in
patients presenting with mandibular prognathism before the completion of
growth would result in greater relapse than those who underwent surgery at the
completion of growth. On the contrary, there would be no relapse in the
growing patient presenting with a retrognathic mandible and the potential
growth would be welcome in these patients.
92
Rosenquist et al. (1986), in their study assumed that completed mandibular
growth could be confirmed by radiographic examination of the hand and wrist
but this cannot be substantiated as mandibular growth continues after cessation
of growth in general. It is impossible to define precisely the end of the growth
period of the facial skeleton. Although some authors found that mandibular
growth is usually completed by the age of 20, (Bambha, 796'I..; Hunter, 1,966;
Nanda, 1955), it has also been stated that residual growth can be found beyond 20
years of age (Bjork, 7963; Tanner et aL.1966). Sorokolit and Nanda (1990) verified
completion of growth by the use of superimposition of serial cephalometric
raCicgraph tracing:.
Differences in growth between males and females are well known. Females
tend to commence and complete growth before males, with females
experiencing minimal growth changes after 74 or 15 years of age. Downs (1956)
remarked that males developed up until the early twenties. Brown et al. (1,971,)
and Grave and Brown (7976) determined that the peak age of facial growth
ranged from 13 to 13.8 years in males and from 1,'J,.7 to 72.2 years in females
(Figure 4.1).
93
Figure 4.1 Average growth curves for males and females
(from Grave and Brown, 79761
BOYS8
4
&trl
¿,U
I
ÈUoJtu
FEItf¡E
6
10
2
10 11 12 13 t4 15 16 77 18
ACE - YEARS
GIRLS
94
The timing of facial growth has very important clinical implications as it affects
the amount of relapse which can occur and is directly dependent on the residual
growth potential. Wolford et al. (1.978) reported that a major proportion of
growth is complete by age 9 years and 98Vo of growth completed by age 15 years
in girls. Boys attained 85% of growth by 9 years,90Vo by 13 years and 98Vo by 19
years of age.
Baum (1966) reviewed the effects of growth on the facial profile and Farrer (7984)
summarised these findings:
(i) Males coûunenced and finished growth later in life and tended to grow in
all directions whereas females grew between 8-L3 years and ceased growth
by 15 years of age.
(ii¡ At the end of growth, males attained a longer face whereas females
displayed deeper faces. Facial convexity flattened with age for both sexes
but the effect was greater in males.
(iii) The faces of 1,2 year old males underwent marked changes while faces of
1.2 year old females did not change significantly at adulthood except in
dimension.
The chin, formed from accessory cartilages associated with the ventral ends of
Meckel's cartilage, is very poorly developed in the infant. It is said to develop
as an independent unit of the mandible, influenced by sexual as well as genetic
factors (Sperber, 1,976). Sex differences in the symphyseal region of the
mandible are not significant in childhood but become more prominent during
adolescence. Enlow and Harris (196a) believed that the chin was "associated
with a generalised process of cortical recession in the flattened regions
95
positioned between the canine teeth. The process involves a mechanism of
endosteal cortical growth". On the lingual surface behind the chin, heavy
periosteal growth occurs with dense bone merging and overlapping on the
labial side of the chin to produce its characteristic shape. Its prominence is
accentuated by bone resorption that occurs in the alveolar region above it,
creating the supramental concavity known as Point B. Particularly, in the
male, bony apposition at the symphysis seems to be the last change in shape of
the mandible and occurs some time between 16 and 23 years of age (Graber,
7972).
4.9.2 Hemimandibular elongation and hemimandibular hyperplasia
Pathological growth of the mandible can result in mandibular prognathism.
Several authors have made mention of the variety of pathological entities
which cause occlusal disturbances and dentofacial deformities as a result of
abnormal condylar growth (Norman and Painter, 1.980; Slootweg and Muller,
7986; Ianetti et al. 1989). Obwegeser and Makek (1986) stated that there are only
two basically distinct pathological malformations of the condyle,
hemimandibular hyperplasia and hemimandibular elongation. Pure and mixed
forms of both growth disturbances can occur and different pathophysiological
and histological patterns within the condyles are evident to account for these
growth disturbances. Hemimandibular hyperplasia is characterised by
enlargement of one side of the mandible with enlargement of the condyle,
condylar neck and the ascending and horizontal rami. A tilted occlusal plane
results from this type of abnormal growth. Hemimandibular elongation, in
contrast, is characterised by a horizontal displacement of the mandible plus chin
towards the unaffected side without tilting of the occlusal plane. Histologically,
hemimandibular hyperplasia displays a distinct proliferative fibrocartilaginous
layer distributed in a diffuse but regular manner all over the condylar head
96
whereas in hemimandibular elongation, the pathological hyperactive condylar
focus is located in the centre of the condyle.
4.10 SINGLE JAW oercus BIMAXILLARY PROCEDURES
Combinations of prognathic and retrognathic upper and lower jaws require
bimaxillary surgery to be undertaken to achieve a satisfactory functional and
cosmetic result. Moser and Freihofer (1980) found that combined maxillary and
mandibular surgery was preferable to single jaw surgery as it gave a more
aesthetic improvement than did mandibular surgery alone, especially in severe
Class III deformities. Many studies have reported that in long term evaluation,
the position of the maxilla in the horizontal direction is stable but a variable
amount of vertical relapse occurs (Luyk and Ward Booth, 7985; Carlotti and
Schendel, 1987; Louis et al. 1,993). Other studies have confirmed similar results
of vertical maxillary relapse of about 40-50Vo (Kufner, 7977; Willmar, '1,974; BeIl,
7975; Bell and Scheideman, 1981). In a study by Kahnberg and Ridell (1988) in
which bimaxillary surgery was performed to correct prognathism, it was found
that maxiilary relapse occurred, and skeletal relapse of the mandible in both
vertical and horizontal directions was also evident but no more than in
mandibular surgery cases alone. Kahnberg and Ridell (1988) suggested that the
amount of mandibular relapse tends to be less in bimaxillary cases than in
mandibular surgery alone probably because the setback in bimaxillary cases is
proportioned between the maxilla and mandible, implying that the greater the
amount of mandibular setback, the greater the relapse potential. Franco et al.
(1989), in their study of bimaxillary cases in which the mandible was setback via
sagittal split osteotomy and rigidty fixed, found that the position and amount of
rotation of the proximal segment solely accounted for relapse in these
bimaxillary cases. In comparing both single jaw cases and bimaxillary cases the
mandible relapsed forwards (43.7 7o and 53.47o respectively) suggesting that there
97
was minimal influence of the maxillary movement on the mandible. Even
though this is observation, it is important to recognise that the stability of the Le
Fort I procedure, in particular, in its vector components, influences mandibular
relapse. Examination of the total anterior facial height dictates that when
maxillary intrusion occurs in the postoperative period, a decrease in total facial
height occurs and consequently counter clockwise rotation of the mandible
occurs advancing Point B forward and hence "Íelapse" occurs. This was evident
in the bimaxillary cases of Franco's study (1989).
4.\1, CORONOIDECTOMY
Removal of the coronoid process has been advocated as an adjunct in the
surgical technique of mandibular setback. In patients with open bite, the
proximal and distal fragments, following oblique sliding osteotomy, are
approximated with a pronounced overlap at the superior ends of the cut for
which a coronoidectomy may assist in the posterior positioning of the distal
segment (Boyne 7966). Akin and Walters (1975) has also suggested that
coronoidectomy may be performed to gain better access and for better visibility
of the sigmoid notch although they maintain that they have never had to
undertake this exercise.
4.12 HIGH ANGLE MANDIBLES
An obtuse gonial is one of the characteristic features of mandibular prognathism
and it is desirable that the surgical treatment of the deformity also result in an
improved gonial angle. Different surgical procedures affect the gonial angle in
different ways. Jonsson (1981) studied the gonial angles in sagittal split
osteotomies and compared them to oblique sliding osteotomies. He found that
the gonial angle increased when treated by sagittal split osteotomy and decreased
98
when treated by oblique sliding osteotomies. Explanations for the changes are
detailed in this study and an increase in gonial angle following sagittal split
osteotomy is possibly due to the effect of forward rotation of the proximal
segment thereby increasing the angle as well as resorptive changes in the gonial
region secondary to ischaemic necrosis of the proximal segment. It has been
reported that a negative correlation exists between the mandibular plane angle
and relapse of points gnathion and gonion. The same correlation also is true of
the cranial base angle and the changes in the "t'' co-ordinate of points gnathion
and gonion (Astrand and Ridell, 7973).
Kelsey (1968) demonstrated that the gonial angle undergoes changes following
vertical osteotomy of the ramus. Initially following operation, the gonial angle
is indeed reduced but surprisingly returns to its original, presurgical value. He
speculated that the locking forces of the occlusion stabilised the body of the
mandible during the healing and remodelling period while the effects of muscle
tension causes the proximal segment to be pulled anteriorly until it resumes its
functional and stable position. Shepherd (1980) studied the resorptive changes
of the mandible following different surgical techniques and found that the
vertical subsigmoid osteotomy displayed the greatest amount of resorption in
the region of gonion and the posterior border of the mandible. This resorption
was variable along the length of the ramus and resulted in narrowing of the
ramus in the anteroposterior direction owing to the gonial angle being
constructed at a tangent to the posterior border of the mandible and lower
border of the mandible. A^y resorptive changes to these areas of the mandible
will ultimately affect the gonial angle measurement.
99
CHAPTER 5
CEPHALOMETRY
5.1. INTRODUCTION
Lateral skull cephalometric analysis is the standard method used in the
assessment of dentofacial deformity. Spatial changes of craniofacial structures
are usually evaluated by superimposition of radiographic cephalometric tracings
taken at different times and after identifying certain landmarks the changes
between cephalometric tracings are measured. This method of superimposition
allows for evaluation of cranial changes either in a cross sectional or
longitudinal (serial) manner and is an acceptable means of measuring the effects
of surgical manipulation of the facial skeleton (Brodie, 1955). In order to
evaluate facial changes, the structures on which the superimposition occurs
must remain stable and the landmarks be identifiable.
The accuracy of cephalograms is relative and not absolute. Various sources of
error are documented (Houston, 1,983; Buschang et al. 1,987) and various
methods have been employed to reduce possible errors (Bjork, 1947; Baumrind
and Frantz, 7971.a; Broch et al. 7987; Bondevik et al. ].987; Richardson, 7966;
Savara et al. 1966; Carlsson, 1967; Midtgard et aI.'1.974; and Bergin et aL. 7978).
The types of errors in experimentation are classified into systematic and random
errors. Systematic errors result from a permanent fault in the apparatus or from
its incorrect calibration. When a measurement is repeated several times, a
range of values that cluster about a particular value maybe obtained. Such
variations are due to random errors.
100
The conventional process of recording data from lateral cephalograms involves
a number of steps, namely:
(i)
( ii)
(iii)
(iv)
(v)
taking of the lateral head radiograph;
tracing the cephalogram;
identification of landmarks;
recording the observation; and
measuring the observation.
In cephalometry, there are numerous potential sources of error and
undoubtedly these pertain to the methods of obtaining and recording data listed
above. Gravely and Murray Benzies (1,974) classified errors into two categories
which included "projection errors" and "tracing errors". They identify
projection errors as occurring due to the conversion of a three dimensional
object into a two dimensional radiograph and identify the factors that contribute
to this which include the relative positions of the x-ray tube, the object and the
film. Tracing errors arise as a result of any factor which limits the clarity of
cephalometric landmarks and include blurring of the image, lack of film
contrast and emulsion grain. Measurement errors such as pencil thickness and
parallax also contribute to tracing errors. Several authors have found that the
main source of error is in the reproducible identification of landmarks (Savara
et aL. 1966; Carlsson,7967; Midtgard et aL. 1974).
Given the method of obtaining and recording cephalometric data, errors can be
classified according to Hing (1989) into:
101
(i)
(ii)
(iii)
(iv)
(v)
(vi)
errors of projection;
errors of superimposition;
errors of landmark identification;
errors of digitising;
errors of measuremenf and
errors attributable to operator variability.
s.2 ERRORS OF PROIECTTON
Errors due to projection of the three dimensional object onto a two dimensional
film have been recognised by numerous authors (van Aken, '1,963; Salzmann,
1,964; Moyers and Bookstein, 7979; Ahlqvist et al. 1983). Carlsson (1.967)
identified a number of components in the total error of the cephalometric
procedure and defined these as being geometric errors and non geometric errors.
Geometric errors "arise in the projection of the skull and include the
enlargement, departures from parallelism between the median and film planes,
especially when the patient is fitted in the cephalostat, deviations in the position
of the focus in relation to an imaginary line through the ear rods and geometric
unsharpness due to the area of focus". There are also non geometric errors
which are predominantly associated with radiographic film properties,
positioning of the patient in the cephalostat and operator errors.
Various studies have been undertaken with the object of investigating these
errors, calculating the precision "(a quality associated with a Class of
observations and referring to the closeness of replicated or repeated observations
around a mean - Hallert '1,964)" and accuracy "(closeness of observations,
computations or estimates to the true values or values assumed to be true -
Hallert 1.964)" of the method under varying conditions and analysing the
702
magnitude of the individual errors (Hatton and Grainger, 7958; Bjork and
Solow, 7962; van Aken, 1.963; Savara et al. 7966; Solow, 7966).
Enlargement and distortion in cephalometry is a result of the inherent property
of x-rays to proceed on straight lines diverging from the source or anode which
is a very small area or "point". Several techniques have been introduced to
compensate or eliminate enlargement (Pacini, 1922; Adams, 7940) and standard
tables are available to correct for these distortions. (Bergesen, 1980).
tarqet - obiect distance size of obiecttarget - film distance size of image
In addition to those factors elucidated by Carlsson(7967), head films are further
distorted by foreshortening of distances between points lying in different planes
and by radial displacement of all points and structures not on the principal axis.
Baumrind and Frantz, (7977a), Eliasson et al. (1982) and Ahlqvist et al. (1983) also
confirmed that major errors are associated with misalignment of the x-ray
source, the cephalostat, the film or the subject.
Although geometric errors of projection may be of significance, they are usually
considered to be of less importance than other errors (Bjork, 7974; Savara et al.
1,966; Carlsson, 1,967; Baumrind and Frantz, 7977; Houston et al, 1986). Ahlqvist
et al. (1986) studied the magnitude of projection errors on length measurements
in cephalometry and concluded that if the rotation of the object was less than 5o,
the error of the length measurements extrapolated to less than one percent.
Therefore, if lateral cephalograms were correctly and carefully taken, projection
errors could be minimised and be scientifically acceptable (Houston et al. 1,986;
Bjork, 7947; Solow, 1,966; Midtgard et at.1974; and Ahlqvist et al. 1986).
103
5.3 ERRORS IN SUPERIMPOSITION
When comparing lateral head films taken at two or more time points two
approaches can be employed. These may be characterised as the individual film
method and the superimposition method. In the individual method, head
films at different times are individually analysed using the same set of
measurements and the measured values for one tracing are subtracted from
those of another tracing. These differences in values are then used as the
measures between the different time periods. Alternatively, the
superimposition method can be used. This involves placing two head films one
on top of the other, registered on some anatomic plane and assessing the
relative displacement of structures between time periods. The planes most
commonly used are the anterior cranial base, the line sella-nasion (registered on
sella), the palatal plane and the mandibular border.
Baumrind et al. (1.976) detailed the effects of primary and secondary errors when
tracings of lateral head radiographs are superimposed. Primary errors of
superimposition are biologically induced judgement errors in an attempt to
achieve biological best fit, therefore errors in a line segment result from
rotation, translation or a combined effect. Secondary errors are systematically
related to the primary errors as they are mathematically calculated from the
same variables.
Houston and Lee (1985) investigated the accuracy of different methods of
superimposition on cranial base structures. These included registration of
radiographs directlyj the blink method; the subtraction method; registrations of
tracings of the cranial base structures and of tracings on the sella nasion line,
registered at sella. Their findings showed that there were appreciable errors
associated with each method of superimposition but the method of
704
superimposing on sella-nasion gave the lowest error. As a result of this
problem, they stressed the importance of clearly reporting the method error of
superimposition for all serial studies. Battagel (7993) also supported the idea of
performing and quantifying an error study for all cephalometric investigations.
To minimise registration errors, several authors have developed a number of
techniques. The use of fiducial landmarks, by punching holes in the radiograph,
is one of the acceptable methods of transferring registrations from one film to
another (Baumrind and Frantz, 1,971,a; Broch et al. 7987; McWilliarn, 1,982b;
Strabrun and Danielsen, 1,982; Vincent and West, 1,987). Vincent and West
(1987) used a specific registration method known as the Protocol Standard Film
Register Punch to minimise the registration error with superimposition but
concluded that each landmark investigated had envelopes of error characteristic
of each point. As this method required only one point to be digitised, the
potential error in superimposition was decreased.
Bjork and Solow (7962) investigated the effect of marking the reference points
on the radiograph prior to performing measurements and found that this
technique introduced another source of error. It could also be shown that if
measurements were performed accurately, the registration errors were of the
same order of magnitude, whether or not the reference points were marked in.
Sluiter et al. (1985) introduced a new method of superimpositioning,by using
computer technology aided by simple mathematical calculations. They
eliminated the use of punch holes serving as fiducial landmarks by employing
the physical dimensions of each radiograph or tracing itself and using computer
transformations to calculate the vector of displacement and rotation of the
second film compared to the first. The magnitude of error was reported to be
much lower than by other methods.
105
5.4 ERRORS OF LANDMARK IDENTIFICATION
Baumrind and Frantz (1977a) consider errors of identification to be the second
general class of errors in head film measurements. These are the errors
involved in the apparently straightforward process of identifying specific
anatomic landmarks on lateral head films. These authors, reportedly, were also
the first to undertake the task of directing studies toward quantitation of errors
in landmark identification. The fact that errors occur has generated an
enormous amount of discussion on the topic (Bjork, 1947; Hixon, 1,956; Hatton
and Grainger/ 1958; Miller et al. 1,966; Richardson, 7966; Savara, et al. 1,966;
Brown et al. 1,970; van der Linden, 7977; Midtgard et al. 7974; Broch et al. "1987;
Richardson, 7981.; Strabrun and Danielsen, 1982; Houston, 1.983; Phillips et al.
79M; Chate, 1987; Savage et al. 1.987; Vincent and West, 7987).
Numerous authors have exposed the greatest source of random error in head
film measurements to be the identification of landmarks and the inaccuracy of
landmark identification (Graber, 7958; Miller et al. 7966; Houston, 7983; Chate,
7987). Broch et al. (1981) have even been bold enough to suggest that if all
digitising equipment and instrumentation is in order, and the machinery is
correctly operated, then the only source of error is in landmark identification.
The reliability of landmark identification depends on five factors:
(i)
(ii)
(iii )
characteristics of the cranial structures;
the general quality of the headplate;
blurring of the anatomical structures caused by secondary radiation or
movement during exposure;
precision of the recording method; and
accuracy of the operator.
(iv)
(v)
706
The magnitude of error was noted to vary greatly from landmark to landmark
but fortunately, the distribution of errors for each landmark had its own
characteristic and usually elliptical envelope of error which varied from 0.25
mm to several millimetres (Richardson, 'l.,966; Baumrind and Frantz, 7977a;
Broch et al. 1981). It has been reported that the error due to the variability of
location of landmarks was about five times that due to measurement (Savara et
aL.1966).
In order to reduce the error associated with landmark identification,
xeroradiography, the process of recording a latent radiographic image on a
selenium coated aluminium plate, was trialed by Hurst et al. (1978) to assess its
feasibility. The conclusion drawn from this study favoured only four of
fourteen landmarks to be more easily identifiable on xeroradiography and the
remaining landmarks were more accurately identified on the conventional
cephalogram.
To reduce errors in identification of landmarks, Houston (1983) recommended
that duplicate tracings be made and in particular that the landmarks are
identified on each tracing and averaged rather than the measurements
replicated and averaged. Baumrind and Miller (1980) suggested that tracings be
repeated four times which would then halve the random error. Computer
based digitising would also be of help in reducing the tedium of multiple
tracings. Eriksen and Solow (1991.) have reiterated that the error in landmark
identification can be reduced somewhat by thorough definitions of the reference
points, by u good knowledge of radiographic anatomy, and by a high image
quality of the radiographic films.
It was common belief that a time interval between the first and second
determination of the same tracing initiated a high degree of error. A number of
707
authors have disproved this assumption as well as showing that no difference
has been apparent when measurements have been carried out on lateral head
films taken on different tracings on separate occasions (Richardson, '1.966;
Baumrind and Frantz, 197'l,a; Midtgard et al. 1,974). The importance of routine
double determinations was considered less important by Brown (1,973) provided
that the measuring techniques were carefully scrutinised and an intraobserver
replicability study had been performed to assess the variability of error.
5.5 ERRORS OFDIGMSING
The errors related to the recording procedure comprise two components. The
first is the precision with which a marked point on the radiograph or tracing can
be identified by the cross hair of the recording device, usually about * 0.1 mm,
and the second is related to the errors of the digitising system. It has been
shown that direct digitising of the anatomic reference points from the
radiographs is more reproducible than digitising of the anatomic points from
tracings of the radiographs (Richardson, 1987; Cohen, 79M; Flouston, 1.982;
Sandler, 1988).
A number of researchers have remarked that when a digitiser is used, the only
source of error is in landmark identification (Bergin et al. 1978; Broch et al. 1,981.;
Bondevik et al. 7981.; Richardson, 1981). However, Eriksen and Solow (1991,)
have brought attention to the precision and linearity of the digitising tablet.
Errors of linearity are caused by the distortion of the x and y co-ordinates of the
digitising tablet due to the electromagnetic fields over the entire surface not
being homogenous. If a digitising system is not linear, a given line segment will
be recorded as having different lengths depending on where it is placed on the
digitising surface.
108
In a study comparing traditional and computerised methods of cephalometric
analysis, Richardson (1981) found that overall, the traditional methods were
slightly inferior to those obtained by the digitiser but for some digitised
landmarks, the traditional method produced more accurate results. Two
advantages of the digitiser were noted. The digitiser was able to offer speed in
preparation of the computer analysis as well as being able to locate extremal
points better, e.g. "most anterior", "most posterior", "highest" or "lowest"
points.
Errors in digitisation of selected points have been shown to be of the order of
less than 0.1. mm whereas the process of manually measuring is associated with
an error of approximately 0.5 mm in each of the two planes of space (Bondevik
et al. 1981).
5.6 ERRORS OF MEASUREMENT
Since the major component of recording error is that of point identification,
some authors believe there is little to choose between direct digitising and the
use of an intervening tracing stage (Cohen, 1,9M; Sandler, 1988). Others are of
the opinion that digitising procedures offer the greater advantage in minimising
measurement errors (Broch et al. 1981.; Bondevik et al. 1931). Battagel (7993)
remarked that the results of a cephalometric study should be interpreted in
relation to its associated measurement error and in a study comparing different
methods of error assessment, Dahlberg's estimation proved to be the soundest
method, mathematically, to evaluate measurement error.
In a study by Carlsson (1,967), it was found that measurement error and the
various geometric and technical radiographic errors were small. In an analysis
of the measurement methods, it could be shown that the precision of
709
measurements was significantly greater in two areas, for callipers than for those
measured with a ruler, and if the measurements were estimated to one tenth
than to one half a degree or millimetre. Bjork (7947) found that errors in
measurements of lateral head films arose from other sources of error, namely
projection error, landmark identification errors, and mechanical errors in
drawing lines and in the use of rulers and protractors.
Midtgard et al. (1974) stated that the size of errors of distance measurements
through calculation of the accidental error between double determinations was
insufficient. There was a necessity to determine the variance of the error as a
percentage of the total variance and should not exceed 37o.
Enlargement and distortion of a radiograph is an inherent characteristic of
cephalometry. Consequently, variable enlargement of 4.6% to 7.2% in the lateral
film and from 0.37o to 9.2Vo in the frontal film affects cephalometric
measurements. Bergesen (1980) devised a method to compensate for
enlargement and distortion of radiographs and has constructed compensation
tables to allow accurate interpretation of tracings. From this study, it was found
that errors in all measu¡ed planes did not exceed 0.7Vo.
5.7 THE SELECTION OF A SUITABLE LINE OF REFERENCE
Cephalometry involves the comparison of either serial or longitudinal
radiographs. This is achieved by superimposition of either radiographs or
tracings derived from radiographs. In order to superimpose the details, an ideal
line of reference is necessary (Steiner,1953; Wei, 1,968) and should:
110
(i)
(ii)
(iii)
superimpose easily;
remain perfectly stable despite growth; and
be based on reference points which are easily identifiable and
consequently have a minimal envelope of error.
A number of reference lines have been investigated to determine the ideal
reference line (Figure 5.1) and include:
(i) Frankfort horizontal
This line passes through the centre of each auditory meatus and lower
margin of the respective orbits (Finlay, 1980).
(ii) Nasion - Sella line (Broadbent Line)
This line extends from nasion, the most anterior point on the nasofrontal
suture, to sella, the midpoint of the sella turcica (Krogman,7957).
(iii) SN7 line
This line is a surrogate line with origin based either on sella or nasion
and angulated 70 to the nasion-sella line but affords the advantages of
reorientating the head so that the influence of extremal landmarks is
minimised.
A comprehensive review of these lines has been recorded by Hing (1989). He
concluded that the nasion-sella line is favoured for its ease of location and its
low method error when it is used for superimposition.
111
Figure 5.1 Reference lines (Hing,1989)
S
Nasion-Sella Line
SN-7 Line
Frankfort HorizontalPo Or
112
III
MATERIALS AND METHODS
113
CHAPTER 6
EVALUATION OF POST SURGICAL RELAPSE
6.1, SELECTION OF PATIENT RECORDS
The names of all patients who had undergone a vertical subsigmoid osteotomy
for the treatment of mandibular prognathism were retrieved from the general
theatre operating records since the time this procedure was introduced into the
Oral and Maxillofacial Surgery Unit (1983). Fifty three patients with the
diagnosis of mandibular prognathism were treated at the Royal Adelaide
Hospital between April 1983 and July 1992 by six consultants and lL registrars
who all followed the same operative procedure. The patient sample was drawn
from a biased population in South Australia. Only patients holding a health
care card were eligible for treatment (school students, unemployed people with
sickness benefits and those without private hospital insurance). This meant
that socioeconomic factors influenced their selection of the patient population.
Cephalometric radiographs were retrieved from patient files held either in the
Records Department or in the Orthodontic Deparhnent.
Cephalometric records were accepted for study if the following criteria were met
(i) at least one year postoperative follow-up;
(ii) surgery was limited to vertical subsigmoid osteotomy alone or combined
with a maxillary osteotomy;
(iii) availability of lateral head cephalometric radiographs preoperatively and
at arbitrarily defined postsurgical intervals:
774
T1
T2
T3:
T4:
T5:
T6:
T7:
pre orthodontic treatment
at completion of orthodontic treatment
immediate postoperatively (within 7 days)
six weeks postoperatively
either three to six months postoperatively, whichever was
available
twelve months postoperatively
the most recent lateral head cephalogram taken at least 24 months
postoperatively.
Of the 53 patients who underwent surgical treatment, a total of 24 patients were
accepted into the study. The remainder of the patient records were excluded for
the following reasons:
(i)
(ii)
(iii)
(iv)
incomplete radiographic records necessary for detailed analysis (n:26);
syndromic patients with physical disabilities (n=1);
unilateral vertical subsigmoid osteotomy and unilateral sagittal split
osteotomy for treatment of mandibular asymmetry (n=1); and
craniofacial anomalies requiring extensive surgery (n=1).
155
Therefore, the number of lateral head cephalograms available for analysis was
Nineteen of the patients received presurgical and postsurgical orthodontic
treatment through the Department of Orthodontics at the Adelaide Dental
Hospital. The remaining five patients in the study received no orthodontic
treatment and therefore had arch bars (with cleats) ligated to the teeth at the
time of surgery. These were used for both the surgical procedure as well as
maxillomandibular fixation at the end of the surgical procedure. All patients
115
had a mandibular setback using the vertical subsigmoid procedure. Other
surgical procedures were performed on the 24 patients in conjunction with the
vertical subsigmoid procedure (Table 6.1).
Table 6.1 Procedures performed in conjunction with vertical
subsigmoid osteotomy (VSSO)
The records were assigned to the one of the following groups:
I.
il.
III.
IV.
Le Fort I ,/vertical subsigmoid osteotomy
Segmental Le Fort I /vertical subsigmoid osteotomy
Quadrangular Le Fort Il,/vertical subsigmoid osteotomy
Vertical subsigmoid osteotomy only
(N=14)
(N=6)
(N=2)
(N=2)
The age at which each patient underwent surgery was calculated from the date
of birth to the nearest month and expressed in years (Table 6.2).
13
6
1
2
2
24
VSSO + Le Fort I
VSSO + Le Fort I (segmental)
VSSO + Le Fort I + genioplasty
VSSO + Le Fort II + genioplasty
VSSO only
TOTAL
NUMBER OF PATIENTSPROCEDURE
11.6
Table 6.2 Age at operation
6.2 RADTOGRAPHTCTECHNTQUE
Radiographs were taken by the Radiology department at the Dental Hospital
using TMAT6, Ortho M or Cronex Lodose or Fuji double emulsion film. When
the patient presented for lateral head cephalogram it was customary to request a
barium soft tissue marker to outline the soft tissue profile. This barium
sulphate was painted on the patient's face in the midsagittal plane prior to
taking the radiograph. With new soft tissue collimators, the barium paint was
discarded as soft tissue outline was much more pronounced and required no
highlighting with the paint. The film, selected at the discretion of the
radiographer, was inserted into a Kodak Lanex regular cassette with a Kodak
Lanex regular screen. The cassettes were slotted into a Kodak Lanex film
holder. The distance between the film and mid sagittal plane was standardised
at'I..6 centimetres for all cases.
A standardised technique for lateral head cephalograms was followed (Farrer
1,984). The patients were gently positioned by a Lumex cephalostat
(Copenhagen) in the Frankfort horizontal plane whilst standing upright. An
aluminium wedge filter was aligned with the soft tissues of the face. Head
orientation was checked by using vertical and horizontal light beams projected
onto mirrors from the machine. Patients were instructed to bite gently on their
back teeth and asked to maintain a relaxed lip posture (Burstone, 1.967;
43.4
20.8
44.7
59.4
36.1,
59.4
76
15.3
15.3
11.9
7.7
9.8
22.9
23.2
23.0
72
72
24
Male
Female
TOTAL
RANGEMAXIMUMMINIMUMSTANDARD
DEVIATION
MEANAGE
(YEARS)
NUMBERSEX
177
Hiltesund et al. 1,978). Radiation was generated by a Philips super 50 CPl80 CP
microprocessor - controlled unit. A Kodak RP X-OMat film processor and
subsequently a Fuji FPM 21.00 x-ray processor was used to process the films
automatically. The enlargement factor (Figure 6.1) was calculated by Farrer
(79U) in a previous study using the same facilities.
118
Figure 6.L Calculation of the enlargement factor for points lying on the
mid-sagittal plane (Hing, 1989)
FM A
Xl* Y
Z
F: Film plane
M = Mid-sagittal plane
A = Focus
X=160mm
Y = 1818 mm
Z = 7978 mm
E = Enlargement Factor
E = 100 xV- 1)
Y
=100x 7978 -11818
= 8.8To
L79
6.3 TRACING AND DIGITISING PROCEDURE
Each of the 155 radiographs were placed over a fluorescent light box in a
darkened room with exclusion of extraneous light by placing a black cardboard
frame around the perimeter of the lateral head cephalogram. An acetate sheet
was secured to the radiograph with cellulose tape at the top and bottom margins
such that the hard tissue profile was encompassed. Hard tissue details were
then identified and recorded on the acetate sheet with a sharp HB pencil. A ten
centimetre line was constructed on the presurgical radiograph seven degrees to
the nasion-sella line with origin at sella turcica. The location of each
cephalometric point was determined with the film orientated to the SN-7 line
(Figure 6.2).
A mandibular template from the presurgical film was used to transfer points
condylion (Co), Menton (Me), pogonion (Po) and Down's Point B to maintain
the relative position of extremal points. Where an occlusal wafer was secured
during operation, postoperative radiographs were corrected by rotating a
mandibular template at hinge axis (HA) until the lower incisal tips contacted the
upper incisal tips. This eliminated the anticlockwise rotation of the mandible
following removal of the occlusal wafer.
The acetate tracings from each radiograph were secured by cellulose tape and
then digitised on a Haalett Packard 9874A digitiser configured to an Apple IIe
computer. Tracings were orientated to the SN-7 line on the digitiser tablet. The
software program, Cephs, developed for cephalometric research by Brown
(personal 7986, communication), was programmed to record individual patient
details, accept each digitised record and transform these digitised points into
cartesian co-ordinates relative to the SN-7 line with origin at sella turcica.
Alphanumeric data relating patient details and the magnification factor were
120
entered. Magnification of 8.8% was not corrected. Each nominated point was
centrally aligned in the large window cross hair cursor and registered by
depressing a perimeter button on the cursor. Data was transformed
automatically by the computer and saved to disk for editing. All tracing and
digitising procedures were carried out by the one person over a number of
sittings.
121
Figure 6.2 Hard and soft tissue points lísted in order of digitising sequence
(modified from Hing, 1989)
S SN-7
Co OrPo
0 . FIA
ANSPNS A
MSMI tr
AI B
IS^aGOt
Hy
1.
LJ.
45.
6.
7.
8.
9.
10.11.
72.
S SellaN NasionPo PorionOr OrbitaleCo CondylionHA Hinge axisAr ArticulareGo GonionMe MentonPg PogonionB Down's Point B or supramentaleAI Lower incisal apex
13.
74.15.
76.77.18.
79.20.2t.22.
23.24.
IIIS
ASAANSPNSMSMIHyAPPPG/2
Lower incisal edgeUpper incisal edgeUpper incisal apexDown's Point A or subspinaleAnterior nasal spine or acanthionPosterior nasal spineUpper molar crownLower molar crownHyoidAnterior pharyngeal wallPosterior pharyngeal wallCervical vertebrae 2
122
6.4 REFERENCE POINTS AND LINES
Reference points and reference lines (Figures 6.2 and 6.3; Figures 8 and 9)
throughout the text were selected from the thesis as formulated by Hing (1989)
which were derived from the Adelaide Oral and Maxillofacial Surgery Unit
handbook (1983) and from the Quick CephrM manual (1986). A number of
points and variables have been amended to suit the requirements of the study.
Cephalometric points which relied on bilateral radiographic structures (porion,
orbitale, pterygoid, condylion and gonion) were taken as the midpoint where
the two images did not coincide.
6.4.7 Hard and soft tissue points (figure 6.2)
Sella (S): The centre of the pituitary fossa of the sphenoid bone determined by
inspection (van der Linden, 7977; Vincent and West,1987).
Nasion (N): The most anterior point of the frontonasal suture (Brown, 1,973).
Porion (Po): The most superior point on the external auditory meatus (Koski
and Virolainen, 1,956; Ricketts, 1,979; Savara and Takeuchi, 1979; Pancherz and
Flansen, 1,984; Wolford, Hilliard and Dugan, 1985; Blaseio, 1986; Vincent and
West, 1,987). The external auditory meatus has three radiolucent areas which
distinguish it from the internal auditory meatus: the fenestrum vestibulae
superiorlli the fenestrum cochlea posteriorly; and the promontory anteriorly
(Yen, 1960).
Orbitale (Or): The lowest point on the average of the right and left borders of the
bony orbit (Riolo et aL.1,974).
Condylion (Co): The most superior point on the head of the condyle (Tracy and
Savara, 1,966; Sekiguchi and Savara, '1,972; Brown, 1,973; Lake et al. 7981';
McNamara, 1.984; Smith et al. 1985). Several authors, notably Björk and Palling
(1954') have defined condylion as the most supero-posterior point on the head of
723
the condyle. It is determined as the point of tangency to a perpendicular
construction line to the anterior and posterior borders of the condylar head.
Condylion, therefore, is located as the most superior axial point of the condylar
head rather than as the most superior point on the condyle (Riolo et al. 7974).
Hinge axis (HA) or condyle: Centre of the condylar head determined by
inspection (Blaseio, 7986). Kohn (1978) defined the point condyle as the centre of
the head of the condyloid process.
Articulare (Ar): The point at the junction of the contour of the external cranial
base and the dorsal contour of the condylar processes projected in the
midsagittal plane (Wei, 7965; Brown, 7973).
Gonion (Go): The point of intersection of the line tangent to the lower border
and a line through articulare and the posterior border of the ramus (Kelsey,
7968). This point is identified on the proximal fragment of the mandible
following surgery and is extensively variable from radiograph to radiograph as
the proximal fragment is free floating during the healing phase.
Menton (Me): The most inferior point on the symphyseal outline (Riolo et al.
7974).
Pogonion (Pg): The most anterior point on the contour of the bony chin relative
to a perpendicular to SN-7 plane (Riolo et aL.7974).
Down's Point B or supramentale (B): The deepest point in the midsagittal plane
between infradentale and pogonion, usually anterior to and slightly below the
apices of the mandibular incisors (Burstone, 1.978). According to Moyers (1987)
Point B cannot be determined if the chin profile is flat.
Lower incisal apex (AI): The root tip of the mandibular central incisor (Riolo et
aL.1974).
Lower incisal edge (II): The incisal tip of the mandibular central incisor (Riolo et
aL.1974).
Upper incisal edge (IS): The incisal tip of the maxillary central incisor (Riolo et
aL.7974).
124
Upper incisal apex (AS): The root tip of the maxillary central incisor (Riolo et al.
7974).
Down's Point A or subspinale (A): The deepest point in the midsagittal plane
between the anterior nasal spine and supradentale, usually around the level of
and anterior to the apex of the maxillary central incisors (Burstone,7978).
Anterior nasal spine or acanthion (ANS): The tip of the median sharp bony
process of the maxilla at the lower margin of the anterior nasal opening (Riolo
et aL.1974).
Posterior nasal spine (PNS): The most posterior point at the sagittal plan on the
bony hard palate (Riolo et aL.7974).
Upper molar crown (MS): The distal contact (height of contour) of the maxillary
first molar relative to the occlusal plane (Riolo at al. 7974).
Lower molar crown (MI): The distal contact (height of contour) of the
mandibular first molar relative to the occlusal plane (Riolo et al. 1.974).
Hyoid (Hy): The most superoanterior point on the body of the hyoid bone
(Athanisou et al. 7991).
Cervical vertebrae 2 (CvZlz The most anteroinferior point on the corpus of the
second cervical vertebrae (Athanisou et al. 1991).
Anterior pharyngeal wall (AP): The anterior pharyngeal wall along the line
intersecting the most anteroinferior point of the corpus on the second cervical
vertebrae and the point hyoid (Athanisou et al, 1997).
Posterior pharyngeal wall (PP): The posterior pharyngeal wall along the line
intersecting the most anteroinferior point of the corpus on the second cervical
vertebrae and the point hyoid (Athanisou et al. 7997).
125
6.4.2 Cephalometric lines (fisure 6.3)
Nasion-sella line (NSL): A line passing through nasion and sella (Solow, 7966).
Sella-nasion-7 (SN-7): A line constructed by drawing a line 7" to SN plane with
its origin at sella as described by Marcotte (1981). Burstone (7978) refers to SN-7
as a surrogate Frankfort plane with its origin at nasion.
Frankfort horizontal (FH): The line passing through porion and orbitale (Scott,
1,e67).
Mandibular line or plane (ML): A line drawn through menton and gonion.
This line has also been defined as the tangent to the lower border of the
mandible or a line joining gonion and gnathion (Salzmann, 1960).
Functional occlusal line (FOL): A line averaging the points of posterior occlusal
contact from the first permanent molars to the first premolars (Moyers, 1,987).
726
Figure 6.3 Cephalometric lines (Hing, L989)
S
Nasion-Sella Line
SN-7 Line
Frankfort Horizontal
Occlusal Line
Mandibular Line
Po
MS
MI
Or
Me
Ar
IS
Co
727
6.4.3 Calculation of linear and angular variables
The variables were selected from those reported by Kohn (1978), Lake et al. (1981)
and Athanasiou (1997). A second program by Brown (personal communication,
7986), Neu) Scorer, was used to compute all measurements. A menu within the
program allows a variety of combinations between any of the digitised points.
Fourteen linear and eight angular variables (Figure 6.4) were calculated from the
digitised points and stored as disk files. The files were transferred from an
Apple IIGS computer to an Apple Macintosh SE computer via Mac Transfer L.01
(Southeøstern Software, 1.984) for final editing and statistical evaluation.
Lineør oøriables
Anterior facial height (AFH): The distance between menton and nasion
perpendicular to the SN-7 line.
Posterior facial height (PFH): The distance between gonion and sella
perpendicular to the SN-7 line.
Condylar displacement horizontal (S-HAx): The horizontal distance between
sella turcica and hinge axis perpendicular to the SN-7 line.
Condylar displacement vertical (S-HAy): The vertical distance between sella
turcica and hinge axis perpendicular to the SN-7 line.
Point A horizontal (Ax): The distance between Down's Point A and a line
drawn perpendicular to nasion-sella 7line.
Point A vertical (Ay): The distance between Down's Point A and a line drawn
perpendicular to nasion-sella T line passing through Sella turcica.
Point B horizontal (Bx): The distance between Down's Point B and a line drawn
perpendicular to nasion-sella 7 line.
Point B vertical (By): The distance between Down's Point B and a line drawn
perpendicular to nasion-sella 7 line through Sella turcica.
128
Overjet (OJ): The distance between IS and II measured parallel to the occlusal
plane.
Overbite (OB): The distance between IS and II measured perpendicular to the
occlusal plane.
Hy point horizontal (Hyx): The distance between the most superoanterior point
of the hyoid bone and a line drawn perpendicular to nasion-sella line.
Hy point vertical (Hyy): The distance between the most superoanterior point of
the hyoid bone and a line drawn perpendicular to nasion-sella line through
sella turcicà.
Pharyngeal depth IAP-PP (x)]: The distance between the anterior pharyngeal
wall and the posterior pharyngeal wall measured in the horizontal direction
between the hyoid point and the cervical vertebrae 2 point.
Pharyngeal depth IAP-PP (y)l: The distance between the anterior pharyngeal
wall and the posterior pharyngeal wall measured in the vertical direction
between the hyoid point and the cervical vertebrae 2 point.
Angular aariables
Mandibular plane angle (SNGoMe): The angle formed between nasion-sella
line and the mandibular line.
SNB: The angle formed between nasion-sella line and a line drawn through
nasion and Down's Point B.
Gonial angle (ArGoMe): The angle formed by a line tangent to the mandibular
ramus and the mandibular plane.
Ramal angle (SNArGo): The angle formed between nasion-sella line and the
line Ar-Go.
Upper incisor angle (MxL-SN7): The angle between SN7 and a line drawn
through IS and AS.
Interincisal angle (IIA): The angle between the line IS-AS and the line II-AL.
729
Lower incisor angle (IMPA): the angle between the mandibular line and the
line II-AI.
Figure 6.4 Angular and linear variables used to evaluate dentoskeletal
changes following vertical subsigmoid osteotomy
SNA¡Go S SN-7
SNGoMe
A (",y)
B (^,y)
Hy(t,y)
0
IS
Linea¡ va¡iablesAnterior facial height (AFH)Posterior facial height (PFH)Condylar displacement horizontal (SHAx)Condylar displacement vertical (SHAy)Point A horizontal (Ax)Point A vertical (Ay)Point B horizontal (Bx)
Point B vertical (By)OverjetOverbiteHy point horizontal (Hyx)Hy point vertical (Hyy)Pharyngeal depth horizontal [AP-PP (x)]Pharyngeal depth vertical IAP-PP (y)ì
Angular variablesMandibular plane angle (SNGoMe)SNBSNAConial angle (ArGoMe)Ramal angle (SNArCo)Uppur incisor angleInterincisal angleI¡wer incisal angle
a
PFH
(*,y)
130
6.5 STATISTICAL ANALYSIS
Each variable within the four groups was assessed by the mean value, standard
error and minimum and maximum value using Stataiew SE 1.03 (Abacus
Concepts Inc., 1988). The differences between each period T1 to T5 for t}:.e 22
variables were calculated by Statview SE., The Student's ú-test for paired and
unpaired values was used to determine the significance of differences for each
variable (Table 6.3).
Table 6.3 Statistical analysis of mandibular relapse following vertical
subsigmoid osteotomy
ï Mean IxN
sse Standard error of the mean
r Correlation coefficient
t Student's unpaired t-test
/N
I (x-Ð (y-f)
> fr."l'(y-y)'
(x1-x2)
[r,.,,' +f'] . [t(*,)2 +,'1
.IH,*']
2 Nr+Nz-z
73't
where N
S
x,y
X1
x2
= number of determinations
= standard deviation
= observed scores
= mean of the group 1 observations
= mean of the group 2 observations
1,32
CHAPTER 7
ERRORS OF THE METHOD
7.1. MATERIALS AND METHODS
To establish the validity of results in this study, an assessment of the magnitude
of cephalometric errors was necessary. The magnitude of error associated with
tracing, superimposition and digitising was assessed by a series of double
determinations for ten cephalograms from three cases. These were randomly
selected from the radiographic files of the Oral and Maxillofacial Surgery Unit,
The University of Adelaide.
Repeat tracing, superimposition and digitising were separated by one week and
re-recorded by one observer. Tracings were orientated to the SN-7 line on the
digitiser tablet and secured with cellulose tape. Alphanumeric data relating tape
details and magnification compensation were entered. Magnification of 8.8%
(Farrer, 7984) was not corrected. Twenty four tissue points and two fiducial
points (x and x') were digitised on a Heu¡lett Packard 987A digitiser configured to
an Apple IIe computer (Figure 7.1). Each nominated point was centrally aligned
in the large window cross-hair cursor and registered by depressing a perimeter
button. Data was transformed automatically by the computer and saved to disk
for editing. The cephalometric software program developed by Professor
Tasman Brown, The University of Adelaide, computes transformations of the
cartesian coordinates relative to a nominated reference line. The line formed by
x-x' served as the line of reference. The computer was also programmed to
perform superimpositions using the first fiducial point (x) as the point of
registration. Error associated with the digitising equipment has been critically
133
assessed by Farrer (7984). The total error from the Hewlett Packard digitiser was
+ 0.01 mm under normal operating conditions.
Figure 7.1 Hard and soft tissue points listed in order of digitising sequence
(modified from Hing, 1989)
a.-4
x'x
aOLrO
fiducial point 1
fiducial point 2
SellaNasionPorionOrbitaleCondylionHinge axisArticul¡areGonionMentonPogonionDown's Point B or supramentale
SN-7
Or
IS
AI B
l.ower incisal apexLower incisal edgeUpper incisal edgeUpper incisal apexDown's Point A or subspinaleAnterior nasal spine or acanthionPosterior nasal spineUpper molar crownLower molar crownHyoidAnterior pharyngeal wallPosterior pharyngeal wallCerrrical vertebrae 2
S
CoPo
0 a
PNSANSA
MSMI
Hy
1.
LJ.
45.
6.
7.
8.
9.
10.11.
t213.
X
x'S
NPoOrCoFIAAIGoMePgB
74.15
76.77.18.
79.20.2r.22.
?3.
24.25.26.
AIIIISASAANSPNSMSMIHyAPPPC'12
Scattergrams were produced to illustrate the reproducibility of each point using
the method described by Broach et al. (1981). The first reading for each point was
arbitrarily assigned as origin. The individual points on the scattergram
represented the difference between the first and second cephalogram indicating
the dispersion of the location errors.
The differences between the first and second determination were expressed as
the mean difference (M diff), the standard error of the mean difference E (M
difÐ, the standard deviation of a single determination (S error) and the
percentage of the observed variance attributable to errors following the
procedure of Dahlberg (19a0). The Student's f-test for paired values was used to
assess whether the differences differed significantly from zero at the 5To (t=2.262)
and'L%o (t=3.250) levels for 9 degrees of freedom. Table 7.1 lists the respective
formulae.
TableTJl. Statistical analysis of the experimental error
M aff Mean difference between two determinations t ¿iff
E (M ¿i¡9 Standard error of the mean difference
N
s ¿in
S (error) Standard deviation of a singledeviation (Dahlbert, 1940)
> diÍf.'
734
2S (error) xL0
S2
M¿in
.^-
2N
VoEvar. Error variance per cent
t value Student's paired t-test
E (Mdifo
135
where diff =
N=
2N=e2J
difference between two determinations
number of double determinations
number of single determinations
observed variance of the measurement
736
IV
RESULTS
737
CHAPTER 8
RESULTS: EARLY,INTERMEDIATE AND LONG TERM DENTOSKELETAL
EFFECTS FOLLOWING VERTICAL SUBSIGMOID OSTEOTOMY
8.1. INTRODUCTION
Initial examination of the data involved analysis of the horizontal movement
of Point B for each group and its subsequent relapse.
The following groups were used:
I. Le Fort I osteotomy/vertical subsigmoid osteotomy.
II. Segmental Le Fort I osteotomy/vertical subsigmoid osteotomy.
m. Quadrangular Le Fort II osteotomy/vertical subsigmoid osteotomy.
IV. Vertical subsigmoid osteotomy only.
8.2 ANALYSIS OF VARIABLE BY GROUPS
Group I. Le Fort I/VSSO (N = 14)
The mean mandibular setback of point B (T2-T3) for this group was -5.29 mm t1.08 mm. The long term relapse following this movement was measured as a
further backward shift of -0.07 mm + 0.5 mm from time period T3 to TZ but this
shift was not statistically significant (Table 8.1).
138
Table 8.1 Comparison of relapse at point B(x) for Group I
* statistically significant (p < 0.01)
II.
The mean mandibular setback of point B (T2-T3) for this group was -2.85 mm *
0.94 mm. The long term shift following this movement was measured as a
further mandibular backward shift of -0.98 mm * 0.55 mm from time period T3
to T7 but this shift was not statistically significant (Table 8.2).
Table 8.2 Comparison of relapse at point B(x) for Group II
Group III. Ouadrangular Le Fort IIIVSSO (N=2)
The mean mandibular setback of point B (T2-T3) for this group was -8.67 mm *
7.8 mm. The long term relapse following this movement was measured as a
relapse of mandibular setback of +0.59 mm * 0.32 mm from time period T3 to T7
but this shift was not statistically significant (Table 8.3).
I
< 0.001*
0.63
0.89
4.90
0.50
0.14
-5.291 1.08
{.29r 0.58
{.07 + 0.5
T2-T3
T3-T6
T3 -W
PROBABILITYT-VALUESHIFT (mm)TIMEPERIOD
0.03
0.18
0.13
3.02
1,.67
7.79
-2.85+ 094
{.80r 0.50
{.9810.55
T2-T3
T3-T6
T3-W
PROBABILITYú-VALUESHIFT (mm)TIMEPERIOD
739
Table 8.3 Comparison of relapse at point B(x) for Group III
Grouo IV. VSSO onlv (N=2)
The mean mandibular setback of point B (T2-T3) for this group was -5.99 mm *
0.07 mm. The long term relapse following this movement was measured as a
relapse of +0.67 mm * 1.04 mm for time period T3 to T7 but this shift was not
statistically significant (Table 8.4).
Table 8.4 Comparison of relapse at point B(x) for Group IV
8.2.7 Horizontal mandibular movement at point B
The results for each group, all of which had vertical subsigmoid osteotomy,
were compared for relapse from immediate postoperative (T3) to long term
postoperative (T7) time period in both horizontal and vertical directions by
Student's f-test for unpaired values (Tables 8.5 and 8.6). No statistically
significant differences (P < 0.01) were found for the variable of point B in the
horizontal direction between groups indicating no differences between the
0.46
0.83
0.32
1.11
0.27
-1.86
-8.67! 7.8
4.nt 2.84
+0.59+ 0.32
T2 -T3
T3 -T6
T3 -W
PROBABILITYú-VALUESHIFT(mm)TIMEPERIOD
1.0
1.0
0.&
0
0
-0.64
-5.99+ 0.07
-1.1+ 0.01
+0.67!l.M
T2 -T3
T3 -T6
T3 -W
PROBABILITYú.VALUESHIFT (mm)TIMEPERIOD
740
mean relapse of each group, therefore the four groups were combined and
analysed as one group.
Table 8.5 Comparison of relapse at point B(x) between groups
Table 8.6 Comparison of relapse at point B(y) between groups
8.3 ANALYSIS OF VARIABLES
8.3.1 Mandibularmovement
8.3.1.1 Horizontal setback and relapse
A mean setback of -4.98 mm * 0.93 mm (T2-T3) was measured at point B for the
24 patients who underwent mandibular setback. In the interim period (T3-T6), a
further setback of the mandible was noted and measured at -0.56 mm * 0.41. mm.
0.37
0.43
0.63
0.10
0.95
0.34
-0.93
0.82
0.56
-2.03
0.08
7.28
I-III. IIII. IVII-mtr-IVm-Iv
PROBABILITYT-VALUEGROUP
0.27
0.99
0.65
0.27
0.65
0.89
-1.31
0.01
-0.59
-1,.67
-0.6
-0.77
I-III .IIII.IVII. UI
II-rvItr. IV
PROBABILITYf .VALUEGROUP
74't
In the long term, the total postoperative shift was measured as a further setback
of -0.18 mm * 0.35 mm at T7. Hence a slight, but statistically non significant,
relapse occurred from the interim period to long term (Table 8.7).
Table 8.7 Comparison of relapse at point B(x) - pooled data
* statistically significant (p < 0.01)
8.3.1.2 Vertical movement and relapse
An upward movement of -1.08 mm + 0.68 mm was measured at Point B. Afurther upward movement of Point B was evident by time T6 and measured -
0.39 mm t 0.47 mm. The total vertical shift recorded from immediately
following surgery to time T7 was -0.1l. mm + 0.25 mm, which meant that
evidence of relapse had occurred between the interim period and long term
follow-up, but this shift was not statisticatly significant (Table 8.8).
Table 8.8 Comparison of relapse at point B(y)-pooled data
<0.001*
0.20
0.61
5.37
1.35
0.52
-4.98+ 0.93
{.5610.41
-0.18+ 0.35
T2-T3
T3-T6
T3 -W
PROBABILITYú.VALUESHIFT (mm)TIMEPERIOD
0.72
0.42
0.65
1.59
0.82
0.46
-1.08r 0.68
439! 0.47
-0.11+ 0.25
T2-T3
T3 -T6
T3 -W
PROBABILITYú.VALUESHIFT (mm)TIMEPERIOD
742
8.3.1.3 Ansle SNB
Following mandibular setback, the angle SNB decreased by a mean of -2.72o *
0.45o (T2-T3). From time period T3 to T7 a further decrease of -0.1,7 * 0.19o was
measured but this shift was not statistically significant (Tabte 8.9).
Table 8.9 Comparison of relapse for angle SNB - pooled data
* statistically significant (p < 0.01)
8.3.2 Proximal and distal sesment alteration
8.3.2.1. Condylar displacement (S-HA)
(a) Vertical movement
Following vertical subsigmoid osteotomy, the proximal segment was observed
to sag and this was measured at +1.33 mm * 0.32 mm (T2-T3). The proximal
segment returned to within its preoperative position at time T7. This relapse
was statistically significant with moderate change from the interim period T6 to
T7 (Table 8.10).
<0.001+
0.03
0.37
6.M
2.42
0.91
-2.720+ 0.450
{.55'+ 0.230
4.17"+ 0.19"
T2 -T3
T3 -T6
T3 -W
PROBABILITYf .VALUESHIFT (des.)TIMEPERIOD
1,43
Table 8.10 Comparison of relapse for distance S - HA(y)-pooled data
< 0.01*
0.03
< 0.01*
-4.77
2.49
3.6
+1.33+ 0.32
-1.291 0.51
-1.14+ 0.32
T2 -T3
T3 -T6
T3 -W
PROBABILITYú-VALUESHIFT (mm)TIMEPERIOD
+ statistically significant (p < 0.01)
(b) Horizontal movement
In addition, to the vertical displacement of the proximal segment in an inferior
direction, the condylar segment also moved minimally posteriorly, and this was
measured at -0.33 mm * 0.35 mm. It retu¡ned to its preoperative position by T6
(Table 8.11).
Table 8.L1 Comparison of relapse for distance S - HA(x) - pooled data
* statistically significant (p < 0.01)
8.3.2.2 Posterior facial height (PFH)
A mean decrease of -1.06 mm * 1.06 mm was measured as the change in
posterior facial height for the total group of 24 patients undergoing mandibular
setback using the vertical subsigmoid osteotomy procedure. Over the long term,
the posterior facial height increased +7.62 mm * 0.99 mm but this relapse was
not statistically significant (Table 8.12).
0.35
< 0.01*
0.04
0.96
0.96
-2.22
{.3310.35
+0.49t 0.24
+0.4510.20
T2 -T3
T3 -T6
T3 -W
PROBABILITYú,VALUESHIFT (mm)TIMEPERIOD
7M
Table 8.L2 Comparison of relapse for distance PFH-pooled data
8.3.2.3 Anterior facial heieht (AFH)
Anterior facial height decreased a mean of -1,.46 mm * 0.62 mm for the 24
patients at surgery. This parameter shortened a further -0.48 mm * 0.45 mm at
time T6 but relapsed slightly at T7. This resulted in a total decrease in anterior
facial height of -'1..74 mm t 0.55 mm and this overall shift was statistically
significant (Table 8.13).
Table 8.L3 Comparison of relapse for distance AFH - pooled data
* statistically significant (p < 0.01)
8.3.2.4 Mandibular nlane anele (SN-Go-Me)
The mandibular plane angle immediately post surgery increased minimally,
measuring +0.52" + 0.86o. In the follow-up period, the mandibular plane angle
decreased from time period T3 to T7, an amount of -0.16o + 0.52o favouring a
return to its preoperative position although not completely and this shift was
not statistically significant (Table 8.14).
0.33
0.77
0.11
1.0
-1.43
-1,.65
-1.061 1.06
+1.44 + 1.01
+1,.6È.0.99
T2 -T3
T3 -T6
T3 -W
PROBABILITYú-VALUESHIFT (mm)TIMEPERIOD
0.03
0.30
< 0.01*
2.36
7.07
0.99
-7.46t 0.62
{.48+ 0.45
4.28! 0.26
T2-T3
T3 -T6
T3 -W
PROBABILITYú-VALUESHIFT (m¡n)TIMEPERIOD
745
Table 8.L4 Comparison of relapse for mandibular plane angle (SN-Go-Me) -
pooled data
0.55
0.92
0.76
-0.61
0.10
0.31
]{).52'+ 0.860
-0.060+0.550
{.160+ 0.520
T2 -T3
T3 -T6
T3 -W
PROBABILITYú.VALUESHIFT (deg.)TIMEPERIOD
8.3.3 Sesmental inter - relationships
8.3.3.1 Gonial ansle (Ar-Go-Me)
A mean decrease in gonial angle of -2.1,0" + 0.66" was noted immediately
following surgery (T2-T3). In the follow-up period to time T7,t}:.e gonial angle
relapsed +3.13 o + 0.42o and this shift was statistically significant. This relapse
was evident by time T6 with minimal change to T7 (Table 8.15).
Table 8.15 Comparison of relapse for gonial angle (Ar-Go-Me) - pooled data
< 0.01*
< 0.001*
< 0.01*
3.2
-5.2
-7.49
-2.100+ 0.60
+3.08'+ 0.59"
+3.13o+ 0.42"
T2-T3
T3 -T6
T3-W
PROBABILITYT.VALUESHIFT (deg.)TIMEPERIOD
* statistically significant (p < 0.01)
8.3.3.2 Ramal anele (SN-Ar-Go)
The ramal angle increased +3.55o t 0.83o (T2-T3). This was followed by complete
relapse of -3.2o t 0.32o over the period T3 to T7 and this shift was statistically
significant and also evident by time T6 (Table 8.16).
't46
Table 8.L6 Comparison of relapse for ramal angle ( SN-Ar-Go) - pooled data
< 0.001*
< 0.001'+
< 0.01',+
-4.26
4.28
8.22
+3.55"+ 0.83"
-3.01'+0.700
-3.20+ 0.32"
T2 -T3
T3 -T6
T3 -W
PROBABILITYú-VALUESHIFT (dee.)TIMEPERIOD
*statistically significant (p < 0.01)
8.3.4 Dentoskeletal chanees
8.3.4.1 Maxillarv incisal anele (Mx 1 SN)
-
Following maxillary incisal decompensations prior to surgery, the maxillary
incisal angle decreased by -3.88" + 7.72". Following surgery, the maxillary incisal
angle increased to an amount of +2.58o + 0.82o in the follow-up period at time
T7 and this was statistically significant (Table 8.17).
Table 8.L7 Comparison of relapse for angle Mx L SN - pooled data
* statistically significant (p < 0.01)
8.3.4.2 Interincisal anele
As a result of the maxillary incisal changes, the interincisal angle increased by
+2.85o t 2.35o. This was followed by u statistically significant decrease in
0.003*
0.02
0.005*
3.U
2.75
-3.15
-3.88"+ 1.12"
+2.23'+ 0.81"
+2.58"+ 0.82o
T2 -T3
T3 -T6
Ti-w
PROBABILITYf .VALUESHIFT (des.)TIMEPERIOD
747
interincisal angle of -4.02" + 7.17o from T3 to T6 with a further increase in
interincisal angle over the long term follow-up (Table 8.18).
Table 8.18 Comparison of relapse for interincisal angle - pooled data
*statisticalty significant (p < 0.01)
8.3.4.3 Lower incisal ansle (IMPA)
Dental decompensations in Class III malocclusions usually result in an increase
in lower incisal angle. This was not evident in this study which demonstrated a
mean decrease or retroclination of -1.6o + 0.77". However, this dental
movement was not stable resulting in a proclination of lower incisors of +1..78"
+ 0.87" which was seen at time T6 but this was not statistically significant.
Stability over the long term was relatively maintained following this relapse
(Table 8.19).
Table 8.L9 Comparison of relapse for ansle IMPA - pooled data
0.24
< 0.01*
0.42
-1,.22
3.44
0.82
+2.85o + 2.35o
4.02" + 7.77"
-2.06" + 2.520
T2 -T3
T3 -T6
T3 -W
PROBABILITYú-VALUESHIFT (dee.)TIMEPERIOD
0.05
0.06
0.1
2.07
-2.04
-7.74
-1..6" + 0.77"
+7.78" + 0.87o
+1.18" + 0.68o
T2-T3
T3-T6
T3 -W
PROBABILITYú-VALUESHIFT (deg.)TIMEPERIOD
748
8.3.4.4 Overiet
-The overjet in Class III malocclusions manifest as a negative relationship. The
mean overjet prior to surgery was measured at -4.0 mm + 0.96 mm. Following
surgery, the overjet in this group of patients was improved to a positive value
of +2.79 + 0.2L mm. At the one year review, the overjet remained stable
averaging +2.82 + 0.27 mm. The long term stability was maintained with
minimal change, measuring +2.78 mm f 0.26 mm. This change was statistically
not significant (Table 8.20).
Table 8.20 Comparison of relapse for overjet - pooled data
*statistically significant (p < 0.01)
8.3.4.5 Overbite
In this group of patients, a tendency to open bite was noted with the overbite
prior to surgery, measuring -0.34 mm t 0.58 mm. The average increase in
overbite recorded for these patients was +2.94 mm * 0.64 mm following surgery.
A minor relapse occurred in the follow-up period resulting in a decrease of -0.32
mm * 0.24 mm at time T7 but this shift was not statistically significant (Table
8.27).
< 0.01*
0.48
0.92
-7.15
-0.73
-0.11
+6.78 !0.95
+{.21 + 0.28
+{.03 t 0.30
T2 -T3
T3 -T6
T3 -W
PROBABILITYf .VALUESHIFT (mm)TIMEPERIOD
749
Table 8.21 Comparison of relapse for overbite - pooled data
*statistically significant (p < 0.01)
8.3.5 Sex of patients
The results of the relapse rates of the 24 patients in this study sample were
grouped by sex to determine if there were any differences in relapse between the
sexes. The study sample divided evenly into two groups resulting in 12 patients
in each group. No statistical significance as analysed by Student's f-test, could be
determined between the relapse of the two groups (Table 8.22 and Table 8.23).
Table 8.22 Comparison of differences in telapse at point B(x) for sexes
*statisticalty significant (p < 0.01)
Table 8.23 Comparison of differences in relapse at point B(y) for sexes
< 0.001*
0.72
0.20
-4.62
7.&
1.31
+2.94!0.64
4.46 +0.28
4.32!0.24
T2-T3
T3-T6
T3 -W
PROBABILTTYú.VALUESHIFT (mm)TIMEPERIOD
< 0.001*
0.20
6.04
1.35
T2-T3
T3-W
PROBABILITYT-VALUETIMEPERIOD
0.15
0.42
1.5
0.82
T2-T3
T3-W
PROBABILITYú.VALUETIMEPERIOD
150
8.3.6 Period of maxillomandibular fixation
The period of fixation for each patient was calculated from the day of operation
to the day of removal of maxillomandibular fixation inclusive. The minimum
and maximum periods of fixation was then determined for each sex and a mean
as well as the standard deviation and range was subsequently calculated (Table
8.24).
Table 8.24 Period of maxillomandibular fixation
26
79
29
65
55
65
40
36
36
7.7
5.9
6.7
47.3
47.9
47.6
72
12
24
IVÍALE
FEMALE
TOTAL
RANGEMAXIMI.]MMINIMUMSTANDARD
DEVIATION
MEAN
DAYS
NUMBERSEX
To assess whether there was a relationship between the period of
maxillomandibular fixation and relapse pattern, the study sample was divided
into two groups. Postsurgical relapse (T3-T7) was compared befween cases with
a period of maxillomandibular fixation greater than the mean of 47 days and
those with a period of maxillomandibular fixation less than the mean of 47 days.
Using the Student's ú-test, no statistical significance was ascertained between the
two groups (Table 8.25).
Table 8.25 Comparison of relapse with different periods of
maxillomandibular f ixation
0.90
0.22
-0.13
7.27
0.171 0.60
4.26+ 039
0.05 + 0.67
0.36+ 0.29
T3-T7B(x)
T3-TzB(v)
PROBABILITYú-VALUERELAPSE
> 47 DAYS
RELAPSE
< 47 DAYS
TIMEPERIOD
151
8.3.7 Age of patient at time of su¡gery
Growth of the mandible is an important factor in relapse of mandibular setback
procedures. Chronological age is used as an indicator to determine potential
growth, therefore, further comparisons were performed to assess age as a factor
in relapse of mandibular setback. The study sample was again divided into two
groups and comparisons were made between cases who were older than the
mean chronological age of 23 years and those who were younger than the mean
age of 23 years. A further sub-division of those younger than 23 years of age into
males and females was necessary due to sex differences influencing relapse.
Analysis by the Student's f-test, showed no statistical significance being evident
between the two groups as well as within the subgroup (Table 8.26).
Table 8.26 Comparison of relapse at point B(x) for age and sex
8.3.8 Orthodontics zersøs no orthodontics
Twenty patients of the 24 patients in the study group had presurgical
orthodontics to align and decompensate the dentition prior to surgery. The
remaining four patients had surgery utilising arch bars ligated to the dentition
to enable maxillomandibular fixation. Comparisons were made between these
two groups to determine if there were any differences in relapse. Analysis by the
Studen.t's ú-test, showed no statistical significance being evident between the two
groups (Table 8.27).
0.72
0.13
0.57
-1.65
-7.63
0.59
FEMALES > 23 VS
MALES > 23 VS
MALES <23 VS
<23
<23
<23 FEMALES
PROBABILITYú.VALUEAGE and SEX
752
Table8.27 Comparison of relapse between orthodontics versus
no orthodontics
8.3.9 Influence of maxillarv sureerv
-
Horizontal and vertical movements of the maxilla following surgery may
influence the relapse potential of mandibular movements. When maxillary
surgery is undertaken in conjunction with mandibular surgery, its influence on
skeletal changes is evident in that the amount of setback required is markedly
reduced as the maxilla is surgically advanced. Therefore, the influence of
mafllary changes was assessed to determine if it had any effect on the relapse
potential of mandibular setback procedures.
8.3.9.L Horizontal movement and relapse
A mean advancement of +2.39 mm * 0.78 mm (T2-T3) was measured at Point A
for the 22 patients who underwent maxillary surgery. In the long term, relapse
was measured to be -7.07 mm * 0.29 mm at T7 and this was statistically
significant. However this relapse was also evident by time T6 with minimal
change over the period T6 to T7 (Table 8.28).
0.78
0.88
-0.31
-0.15
0.49 + 1.36
0.07 + 0.27
0.05 + 0.45
0.01 + 0.30
T3-TZB(x)
T3-TZB(v)
PROBABILITYú-VALUEMEANRELAPSE
NO ORTHO.
MEAN RELAPSE
ORTHO.
TIMEPERIOD
153
Table 828 Comparison of relapse for point A(x) - pooled data
* statistically significant (p < 0.01)
8.3.9.2 Vertical movement and relapse
A downward movement of +7.52 mm * 0.61 mm was measured at point A. Arelapse movement at point A was evident by time T6 and the total relapse
measured at T7 was -1.4 mm * 0.36 mm and this was statistically significant
(Table 8.29).
Table 829 Comparison of relapse for point A(y) - pooled data
*statistically significant (p < 0.01)
8.3.9.3 Angle SNA
Following maxillary advancement surgery, the angle SNA increased by a mean
of +2.19 + 0.77" (T2-T3). From time period T3 to T7 a decrease of -7.1,6 + 0.36o was
measured (Table 8.30).
< 0.01*
0.08
0.001*
-3.06
1.86
3.75
+2.39 !0.78
{.96 + 0.51
-1,.07 + 0.29
T2-T3
T3 -T6
T3-T7
PROBABILITYú-VALUESHIFT (mm)TIMEPERIOD
0.02
0.02
< 0.001*
-2.49
2.67
4.18
+1.52 + 0.61
-1.5 r 0.59
-1.4+ 0.36
T2-T3
T3-T6
T3-T7
PROBABILITYú-VALUESHIFT (mm)TIMEPERIOD
1,54
Table 8.30 Comparison of relapse for angle SNA - pooled data
*statistically significant (p < 0.01)
8.3.L0 Influence of hvoid position
8.3.10.L Horizontal movement and relapse
The data showed that the hyoid bone shifted +1.35 mm * 1..47 mm horizontally
forwards following setback surgery but returned towards its preoperative
position over the follow-up period (Table 8.31). This relapse occurred within
the first six weeks following surgery with minor shifts until biological
equilibrium was established. The movement and relapse of the hyoid bone in
the horizontal direction was not statistically significant (Table 8.32).
Table 8.31 Horizontal movement of hyoid bone and subsequent relapse
+1.35
- 7.61
- 7.24
- 1.03
mm+ 1.47
mmt 1.61
mm+ 1.47
mm+ 1.14
T2-T3
T3-T4
T3-T6
T3-W
MOVEMENT(mn)TIMEPERIOD
< 0.01*
0.02
< 0.01*
-3.07
2.æ
3.23
+2.19o + 0.77o
-1.35'+ 0.51"
-1.16'+ 0.36"
T2-T3
T3 -T6
T3 -W
PROBABILITYú-VALUESHIFT (deg.)TIMEPERIOD
155
Table 8.32 Comparison of relapse for point H(x) - pooled data
8.3.L0.2 Vertical movement and relanse
In the vertical direction, the hyoid bone displaced inferiorly +4.1,9 mm + 1.09
mm but over the follow-up period, its repositioning upwards exceeded its initial
inferior movement. The measured superior repositioning amounted to -6.2
mm * 1.05 mm. This relapse was statistically significant at t}:re 1.Vo level (Table
8.33).
Table 8.33 Comparison of relapse for point H(y) - pooled data
0.001*
< 0.001*
< 0.001*
-3.86
5.04
5.91
+4.19!1.09
-5.531 1.09
-6.t 1.05
T2 -T3
T3 -T6
T3 -W
PROBABILITYf-VALUESHIFT (mm)TIMEPERIOD
*statistically significant (p < 0.01)
8.3.LL Pharyngeal depth (AP-PP)
A preliminary assessment of the pharyngeal depth was performed to assess if
there were any changes as a consequence of the mandibular setback.
0.37
0.41,
0.38
-0.92
0.84
0.90
T2-T3
T3-T6
T3-W
PROBABILITYt. VALUETIMEPERIOD
1,56
8.3.L1.1 Horizontal movement and relapse
Pharyngeal depth in the horizontal direction immediately following surgery
resulted in'an increase in depth of +1.11 mm t 1.06 mm and had relapsed -0.47
mm t 0.99 mm by T7 (Table 8.34).
Table 8.34 Comparison of relapse for pharyngeal depth tAP - PP(x)l
- pooled data
8.3.L1.2 Vertical movement and relapse
Following surgery, the pharyngeal depth in the vertical direction decreased in
dimensions -0.24 mm * 0.31 mm with a fu¡ther decrease of -0.47 mm * 0.33 mm
by time T7 (Table 8.35).
Table 8.35 Comparison of relapse for pharyngeal depth IAp - PP(y)l
- pooled data
0.31
0.74
0.&
-1.05
0.34
0.47
+1.111 1.06
{.3010.89
-0.47! 0.99
T2 -T3
T3 -T6
T3 -W
PROBABILITYú.VALUESHIFT (mm)TIMEPERIOD
0.43
0.32
0.1,6
0.80
1.03
1.45
4.24! 0.31.
{.31r 0.30
4.471 0.33
T2 -T3
T3 -T6
T3 -W
PROBABILITYú.VALUESHIFT (mm)TIMEPERIOD
'1.57
8.4 COMPLICATIONS FOLLOWING VERTICAL SUBSIGMOID
OSTEOTOMY
8.4.1 Intraoperative complications
8.4.1.L Haemorrhage
Experience of a brisk haemorrhage was noted during one operation whilst the
author was performing the vertical subsigmoid osteotomy in the region of the
sigmoid notch. The osteotomy cut was completed to enable access to the
bleeding vessel and this was subsequently cauterised with no further
consequences. It was assumed that the madllary artery was lacerated. This
assumption was made for two reasons; the rapidity of bleeding and the patient
experienced no neurosensory deficit of the inferior alveolar nerve on
postoperative testing.
8.4.2 Immediate postoperative complications
8.4.2.7 Condylar dislocation
Although an uncommon occurrence, condylar dislocation has been reported by
Quinn and Wedell (1988). In an unreported case in the South AusÍalian Unit, a
trainee of the Unit inadvertently dislocated the proximal segment anteriorly on
one side. This required a second operation to relocate the fragment and this was
performed by a preauricular approach. There were no further problems
associated with the postoperative recovery following this operation.
158
8.4.3 Delayed postoperative complications
8.4.3.L Postooerative infection
The South Australian Oral and Maxillofacial Surgery Unit has had experience of
two cases of infection out of 53 patients who underwent 104 vertical subsigmoid
osteotomies. There were no apparent reasons for these infections, as in both
cases/ the patients presented with facial swelling at least three weeks after
surgery. It is also the policy of the Oral and Maxillofacial Surgery Unit to
administer antibiotics prophylactically at the time of induction of general
anaesthesia.
8.4.3.2 Sequestration of proximal segment
An unreported case of sequestration of a portion of the proximal fragment in
the South Australian Oral and Maxillofacial Surgery Unit was associated with
infection. The patient presented with facial swelling during the period of
maxillomandibular fixation. It was necessary to explore and drain the facial
swelling and this was performed under general anaesthesia. Exploration of the
swelling identified a fragment of bone which appeared non vital and
necessitated its removal.
159
CHAPTER 9
RESULTS: ERRORS OF THE METHOD
9.1 ERRORS OF THE METHOD
The magnitude of errors in the horizontal and vertical axes for ten sets of
double determinations were calculated and summarised in Tables 9.7 and 9.2.
The maximum mean difference measured in both the vertical and horizontal
axes was 2.24 mm. The mean differences in the horizontal dimension had more
error when compared to the mean differences in the vertical dimension. The
errors for the mean differences varied widely ranging from 0.11 to 2.24 in the
horizontal axis and from 0.01 to 0.21 in the vertical axis. The standard errors of
the mean differences varied from 0.08 to 0.99 in the horizontal axis and from
0.05 to 0.19 in the vertical axis.
The most variable point in identification in the horizontal plane was the point
pogonion with a standard error of the mean being measured at 0.99 mm.
Discrepancies in the location of this point ranged from -0.75 to 0.34 mm in the
horizontal plane. In the vertical direction, the most variable point was gonion
with a standard error of the mean being measured at 0.19 mm. Discrepancies in
the location of this point ranged from -0.37 to 1..52 mm in the vertical plane.
The most reliable point in the horizontal plane was the apex of the upPer
incisor with a standard error of 0.08 mm. In the vertical plane, the most reliable
point was pogonion with a standard error of 0.05 mm.
't60
The two tail Student's ú-test for paired values showed that the posterior nasal
spine in the vertical plane was significant at the 'l,Vo level. In the horizontal
plane, a number of points showed significance at t}:.e 'l,Vo level. These were
points condylion, hinge axis, articulare, gonion, anterior nasal spine, upper
molar crown.
Scattergrams for each of the hard tissue points are illustrated showing errors in
the horizontal and vertical axes.
76't
Table 9.1 Error for hard tissue points (horizontal axis) by double
determination
0.12
0.11
0.14
0.11
0.09
0.12
0.23
0.74
0.10
0.11
0.1,4
0.08
0.15
0.08
0.08
0.13
0.11
0.'t2
0.1.6
0.72
0.11
0.14
0.11
0.09
0.12
0.23
0.14
0.99
0.11
0.74
0.08
0.15
0.08
0.08
0.13
0.11
0.72
0.16
0.34
0.&
0.78
0.61
0.54
0.47
2.72
0.&
0.34
0.41
0.47
0.57
0.36
0.36
0.16
0.65
0.56
0.92
0.81
-0.95
-0.52
-0.95
-0.51
-0.37
-0.65
-0.55
-7.02
-0.75
-0.74
-0.92
-0.27
-1.31
-0.39
-0.53
-0.73
-0.44
-0.45
-0.95
0.72
0.11
0.14
0.11
0.æ
0.10
0.23
0.14
0.10
0.11
0.74
0.08
0.14
0.08
0.08
0.13
0.11
0.12
0.16
-0.18
-1.60
-0.55
0.64
0.53
0.45
7.43
-0.55
0.08
-0.24
-0.46
2.24
-0.91
0.91
-7.27
-0.86
0.11
2.10
0.43
NxPox
Orx
C-ox
FIA x
Arx
C¡x
Mex
Pgt
Bx
Ax
ANS x
PNS x
ISx
ASx
IIxAIxMSx
MIx
EVo var.S (enor)Max.MturE (M difoM diffVariable
762
Table 9.2 Enor for hard tissue points (vertical axis) by double determination
0.08
0.08
0.13
0.11
0.1,23
0.10
0.19
0.09
0.0s
0.08
0.16
0.11
0.11
0.72
0.16
0.11
0.07
0.10
0.08
0.08
0.08
0.13
0.11
0.72
0.10
0.19
0.09
0.05
0.08
0.16
0.10
0.11
0.72
0.76
0.11
0.07
0.10
0.08
0.31
0.35
0.60
0.48
0.90
0.52
1.52
0.47
0.26
0.44
0.90.72
0.61
0.50
r.06
0.63
0.30
0.48
0.ø
-0.53
-0.35
-0.59
-0.56
-0.49
-0.44
-0.37
-0.65
-0.23
-0.28
-1.08
-0.42
-0.39
-0.80
-0.57
-0.59
-0.26
-0.53
-0.10
0.08
0.08
0.13
0.11
0.12
0.10
0.11
0.08
0.05
0.08
0.15
0.10
0.10
0.72
0.16
0.10
0.06
0.09
0.07
-0.08
0.07
0.07
0.06
0.16
-0.08
0.18
-0.07
0.02
0.06
-0.72
0.02
0.19
0.03
0.21
-0.03
0.01
0.06
0.18
NyPoy
oryCoy
HAyA.yGoy
Mey
Pgy
ByAy
ANS y
PNS y
ISy
ASy
IIyAIyMSy
MIv
E%o var.S (eror)Max.MirLE (M difoM di-ffVariable
1.63
Figure 9.1 Differences between digitised double determinations for
nasion (N)
3
z o
2
3
,{
3 2 oNx
2 3 1
Figure 9.2 Differences between digitised double detenninations for
porion (Po)
3
2
0où
I 0Poy
2 3 4
't64
Figure 9.3 Differences befween digitised double determinations for
orbitale (Or)
1
3
2
o 0
0Or
2 3 ¡l
I
Figure 9.4 Differences between digitised double determinations for
condylion (Co)
3
2
oo()
2
3
i ^à^lt
l a/¡
oCox
2 3 1
165
Figure 9.5 Differences between digitised double detenrrinations for
hinge axis (HA)
1
3
2
I o
I
3 2 oHAx
? 3 4
Figure 9.6 Differences between digitised double detenninations for
articulare (Ar)
1
3
2
1
o
2
2 oAr x
aA-'^ l:^ r
2 3 1
766
Figure 9.7 Differences between digitised double deter:ninations for
gonion (Go)
1
3
2
oo o
oGox
Figure 9.8 Differences between digitised double detenninations for
menton (Me)
¡l 2 3 a
o
1
3
?.
1
o
3^
2 2oIr¡þ x
3 1
767
Figure 9.9 Differences between digitised double detenninations for
pogonion (Pg)
oC
4
3
1
o
2 o 2 3Pgx
Figure 9.10 Differences between digitised double determinations for point B
o
,l
3
2
1
o
2
3 oBx
2 3
168
Figure 9.11 Differences between digitised double detenninations for point A
1
3
2
t
o
3 2 2 3oAx
Figure 9.12 Diffetences between digitised double detenninations for ANS
aoz
1
3
2
I
o
I
2 oANS x
2 3
1.69
Figure 9.L3 Differences between digitised double determinations for PNS
at,
À
,t
3
2
1
o
-13 2 o
PNS x
olSx
2 3 a
Figure 9.L4 Differences between digitised double determinations for upper
incisat tip (IS)
at)
1
3
2
1
o
-¡l3 2 2 3 1
770
Figure 9.L5 Differences between digitised double detenninations for upper
incisal apex (AS)
I
3
2
ato
4 3 2 0ASx
2 3 Á
Figure 9.16 Differences between digitised double detenninations for lower
incisal tip (AI)
4
3
2
a 0
3 2
¡fâ
2 0Al r
3
777
Figure 9.17 Differences between digitised double determinations for lower
incisal apex (II)
3
2
0
1 oll x
2 3
Figure 9.L8 Differences between digitised double detenninations for upper
molar crown (MS)
3
2
s)0
2
A^^
oMSx
2 3 1
772
Figure 9.L9 Differences between digitised double determinations for lower
molar crown (MI)
3
2
=
-{2 o
MI2 3 4
773
V
DISCUSSION
174
CHAPTER 1,0
DISCUSSION
1.0.1 PATIENTSELECTION
Fifty three case records were retrieved from the surgical files of the Oral and
Maxillofacial Surgery Unit, The University of Adelaide. Of the 53 patients who
underwent surgical treatrnent, a total of 24 patients were accepted into the study.
The remainder of the patient records were excluded for reasons of:
(i)
(ii )
(iii)
incomplete radiographic records necessary for detailed analysis (n=26);
syndromic patients with physical disabilities (n=1);
unilateral vertical subsigmoid osteotomy and unilateral sagittal split
osteotomy for treatment of mandibular asFnmetry (n=1); and
craniofacial anomalies requiring extensive surgery (n=1).(iv)
The problem of incomplete records is not uncommon, even in the most
dictatorial of surgical units internationally. Sailer, (personal communication,
1,993) emphasises that there still exists room for improving the methods of
record-keeping to enable accurate and concise research. Sailer's Oral and
Maxillofacial Surgery Unit experienced a radiograph retrieval rate of only about
60%. For example, Johanson et aL. (1,979) had a retrieval rate of only 20 cases at
the end of five years with the initial sample comprising 87 patients.
Even though an established protocol for taking radiographs existed in the
department, numerous cases were found to have incomplete radiographic data.
This was due to records frequently being misplaced, not requested postsurgically
775
by the surgeon or orthodontist, requested but not taken or the patient was lost to
follow-up.
The reason for lack of radiographic collection stemmed from the underlying
socioeconomic factors influencing patient commitment as many of the school
students and unemployed patients in this study moved interstate from Adelaide
to pursue further studies and work opportunities. Only one patient was
pregnant at the time of recall and did not wish to be exposed to radiation.
The selected sample ranged in age from 15.3 years to 59.4 years with a mean age
of 23 years. Bone age in this study could not be confirmed in this retrospective
study as hand - wrist films were not taken at the time of surgery. Although
some hand and wrist radiographs were taken at the initial presentation and
consultation with the orthodontist to assess the degree of deformity and the
timing of treatment, the decision to undertake surgery was based primarily on
the post pubertal changes as well as chronological age. Hand and wrist
radiographs would have provided a more reliable guide to developmental
status than clinical assessment but on a number of occasions the technique of
superimposition of serial radiographs was performed for those deemed to be
still active in growth.
A comparison with untreated patients matched for skeletal maturation, sex and
dentoskeletal pattern may have provided a clearer indication of the effects of
growth. Flowever, this issue could be addressed by closer co-operation between
the Orthodontic Department and the Oral and Maxillofacial Surgery Unit and
also by the establishment of a more efficient filing system to store records. The
rate limiting step in this exercise is the referral of all dentoskeletal Class III
patients by the orthodontists to the Oral and Maxillofacial Surgery Unit. These
776
dentoskeletal Class III patients would be deemed, by the orthodontists, to be
treatable by orthodontics alone with no surgical assistance required at all.
The number of female patients matched the number of male patients in this
study sample only because of exclusion of patients with incomplete records
although most orthognathic studies show a higher proportion of females
undergoing surgery (Pepersack and Chausse, 1978; Franco et al. 1,989). Further
analysis of the statistics for orthognathic surgery from the Oral and Maxillofacial
Surgery Unit showed that the number of female patients undergoing
orthognathic surgery exceeded the number of male patients with an
approximate ratio of two to one. The initial records (n=53) enlisted for the
study, prior to culling, also showed a ratio of two to one with females
undergoing orthognathic surgery more often than males. A problem was
identified during the follow-up period in that there was a higher number of
females who failed to attend for postoperative radiographs and review. This
resulted in a number of records being excluded from the study.
Comparison studies with non surgically, orthodontic treated patients are usually
difficult in the management of Class III malocclusions, as the greater the degree
of deformity, the greater the need to utilise surgical procedures to achieve
functional and aesthetic balance. Camouflage orthodontic techniques are
acceptable only when the skeleton does not exhibit gross disproportions as well.
10.2 MATERIALS AND METHODS
The technique of the vertical subsigmoid osteotomy surgically renders the
mandible into three separate fragments which move independent of each other
until healing has completed. Gonion is usually the point at the angle of the
mandible constructed by bisection of the angle of the tangents to the lower
177
border of the mandible and posterior border of the ascending ramus. As a result
of the mandibular surgery, point gonion becomes difficult to construct as the
proximal fragment contains this point and is "free floating" until the fragments
unite. In this study, point gonion was selected as being the intersection of the
tangents to the lower border of the mandible and posterior border of the
ascending ramus (Kelsey, 1968).
178
CHAPTER 11
DISCUSSION: FACTORS IN RELAPSE OF VERTICAL SUBSIGMOID
OSTEOTOMY
The results of this study showed that there were no statistically significant
differences between sexes and between age for any of the variables studied.
There was also no evidence of differences in relapse between the four
subgroups, consequently the four subgroups were combined and the variables
analysed as a pooled group.
77..]. DEFINITION OF RELAPSE
In this study, point B was primarily used as the indicator of assessing relapse as
this landmark was the only point not surgically repositioned. Its identification
is cephalometrically easier than other mandibular landmarks. Even with the
one case of genioplasty performed as part of the vertical subsigmoid osteotomy,
the osteotomy for this procedure is placed well below the Point B used in the
analysis to determine relapse.
17.2 ORTHODONTICS AND OCCLUSION
Presurgical orthodontics to align and decompensate the dentition has been
mentioned as a factor in skeletal stability. Greater stability of mandibular setback
procedures is thought to be associated with a better postoperative occlusion. In
this study, a positive overbite and overjet were achieved long term in all but
one patient and this supports the thinking of Phillips et aI, (t986); Wisth, (1981)
and Becker, (7966). Minimal and statistically non significant relapse of overbite
779
and overjet were recorded in the postoperative period. A comparison between
orthodontic treated (n=20) and non orthodontic (n=4) treated mandibular
setbacks was performed and no statistically significant differences in relapse was
found between the two groups. This is contrary to the findings of Poulton,
Taylor and Ware (7963) who advocated surgery be performed prior to
orthodontics as this was believed to be more stable. This study also confirms
that of Johanson et al. (1,979) who compared surgery with orthodontics and
without orthodontics and found the relapse to be of the same magnitude.
Stability of dental decompensations was found to be variable in this study with
the mean proclination of the lower incisors relapsing. Vasir et al. (1997)
highlighted that dental decompensations in their study of surgically corrected
Class III malocclusions were stable whereas Artun et al. (7990) acknowledged
that relapse of decompensated dentition was inevitable in the long term.
Difficulties are also encountered when measuring relapse of dental
decompensations in conjunction with surgical movement of the maxilla and/ or
mandible. The difficulty is in determining whether the relapse is due solely to
dental movements or due to reangulation of the maxilla and/or mandible. The
surgical movements would consequently alter the angles used to measure
incisor position in the same direction as if dental relapse had occurred.
Simpson (1,974) eluded to the role of the tongue in causing relapse of the lower
incisors following surgery and postulated that this postsurgical proclination of
the lower teeth was due to active tongue pressure but this correlation was not
observed in this study. Hyoid position was analysed to reflect tongue position
and the changes in this study would suggest that no active tongue pressure was
present after surgery as the tongue occupied a higher position relative to its
preoperative position This instability of dental decompensations would also
explain the further shift of Point B in the same direction as the setback. As
relapse of a decompensated maxillary arch occurs the buccal segments would
180
rotate palatally and inferiorly causing displacement of the mandible in a
clockwise direction. This would rotate Point B posteroinferiorly simulating a
further shift of the mandible in the direction of the setback. Hirose et al. (7976)
trialed the use of elastics as well as the wearing of chin caps for as long as six
months after surgery in an attempt to prevent relapse and found this to be of
great benefit in their study population. This concept was also adopted in this
study whereby every patient used guiding elastics in the postoperative phase.
This may account for a reduction in relapse potential as the elastics were placed
such that there was a vector force directed in the same direction as the surgical
setback.
1.1.3 MAGNITUDE OF MANDIBULAR SETBACK
The amount of correction at the time of surgery has been cited as one of the
possible causes of relapse (Abe et al. 1980; Reitzik, 7980; Astrand et al. 1,973). It
was also shown that a significant relapsing potential may exist when the
amount of correction exceeded 10 mm (Kobayashi et aI. 7986). In this study,
there was minimal relapse evident following the vertical subsigmoid osteotomy
and this finding supports those of Pepersack and Chausse (1,978) and Sorokolit
and Nanda (1990) who found no correlation between magnitude of mandibular
setback and relapse. No anterior open bite deformities resulted following
surgery in this study whereas this problem was encountered by Astrand (1973b)
and Reitzik (1980). Moss (1990) in identifying the tongue as a cause of relapse,
reasoned that the degree of relapse would be related to the amount of
mandibular setback but this would only occur if tongue space had been reduced
with counter pressure imposed on the mandible and dentition. The tongue
position altered in this study but favourably enough not to cause mandibular
relapse.
181
17.4 CONDYLAR POSITION
Orthognathic surgical procedures have been associated with minor
displacements of the condyle in relation to the mandibular fossa. In this study,
there was evidence of condylar sag of the proximal segment immediately
following surgery and the direction of this movement was inconsistent with
other reports (Sund et al. 1983; Wisth and Tornes,1975). The condylar fragment
showed a posteroinferior displacement in this study but returned to itspreoperative position. This condylar movement represents a hybrid of those
reported in the literature where the most commonly reported displacement
occurred in an anteroinferior direction although studies have reported
displacements in all directions. Normalisation of the condyle to the
preoperative position is found during the period of maxillomandibular fixation
and later at progress examination. Initially, this normalisation of the condyle is
associated with reverse displacement of the condyle and thereafter is dependent
on a combination of displacement and skeletal remodelling (Ritzau et al. 1,989).
Elaborating on this event, it is interesting to note that the return of the condyle
during the period of maxillomandibular fixation is not total and that a
significant anterior and inferior displacement of the condyle is evident at three
years postoperatively (Petersson and Willmar-Hogeman, 1989). Therefore/ a
correlation should be evident between mandibular relapse in the posterior
direction and this residual non return of the condyle to its preoperative
position. But this is not the case. A number of interesting reasons account for
this. Firstly, condylar remodelling (new bone formation) in the posterosuperior
direction was identified in the study of Petersson and Willmar-Hogeman, (7989)
and this correlated to the degree of postoperative inferior displacement of the
condyle. The average width of new bone formation in the posterosuperior
portion of the condylar head amounted to 7-2 mm which is largely equivalent to
the amount of residual displacement of the condyle in an inferoanterior
782
direction which does not return to the preoperative condyle position. Eckerdal
et al. (1986) also showed similar results with skeletal remodelling of the TMJ
taking place in 80Vo of cases after oblique sliding osteotomies. The mean
amount of bone apposition in the condyle was 1.4 mm. Hollender and Ridell
(7974) found changes in joint relations in 727o and Kundert and Hadjianghelou
(1980) in 88%. Legrell and Nystrom (1990), comparing condylar changes in
intraoral and extraoral oblique sliding osteotomies, found, most commonly,
signs of sclerosis and bone remodelling in 85Vo and 73Vo of cases respectively but
these differences were not statistically significant. Eckerdal et al. (1986) also
showed that there were no differences in skeletal remodelling whether wiring
or non wiring of the fragments had been used. Interesting to note also in an
experiment by Boyne ("1,966), was the distinct new bone formation at the
attachment of the lateral pterygoid muscle at the neck of the condylar head.
This form of remodelling was only seen as part of the later healing process and
suggests the existence of altered condylar relationships due to the operation.
Edlund et al. (1979) also reports adverse remodelling changes in the condylar
head following operation in the form of erosions located in the superior part of
the condyle which healed within three years and osteophytes which were
located in the anterior part of the condyle and remained. The clinicopathologic
significance of these were undetermined. No analysis was performed on our
group of patients to identify condylar remodelling as tomograms, which are best
suited for this exercise, were not taken for any of the patients in this group. As
this was a retrospective study it was not possible to include this type of analysis
but prospective studies can be formulated with this change in condylar
morphology. It would have been interesting to determine whether bone
apposition had occurred and where it would have occurred in this study as the
displacement of the condyles was in the opposite direction to that of other
studies, ie. in the posteroinferior direction.
183
1-1.5 ROTATIONAL EFFECTS BETWEEN FRAGMENTS
In this study there were rotational effects between the proximal and distal
fragments. The gonial angle was measured as having decreased from the
preoperative to the postoperative period and this was due to a clockwise
rotation of the proximal segment as the distal segment was positioned
posteriorly. The proximal segment returned to its preoperative position over
the follow-up period and had occurred within a year following surgery. Franco
et al. (1989) and Komori et al. (7987) held the opinion that detachment of the
medial pterygoid muscle was necessary to minimise relapse and reasoned that
clockwise rotation of the proximal segment placed the medial muscle
attachments under tension with consequent relapse when muscle function
returned to equilibrium. This investigation provided no evidence to support
this idea as the proximal segments did rotate in a clockwise direction and also
returned to its original position with no significant relapse. Astrand and
Ericson (1974) postulated that a greater angulation with a large space between the
proximal fragment and the lateral surface of the ramus should be associated
with a longer healing period and, consequently, undesirable positional changes
of the mandible. However, the conclusion drawn from this study showed that
there was no significant correlation between the angulation of the condylar
fragment and the positional changes of the mandible at six months. AIso this
study showed that small overlapping areas between the fragments was almost
significantly correlated with a superior shift of gonion implying that greater
bone contact reduces postoperative relapse of the mandible. The lateral
angulation of the proximal segment was not investigated in this study. There
would be a need to cephalometrically standardise the radiographic technique
before this could area could be reviewed although there were no cases where the
proximal segment was adversely positioned when reviewing the
posteroanterior mandibular radiographs. The current protocol which exists in
7U
the Oral and Maxillofacial Surgery Department is to take posteroanterior
mandibular radiographs without cephalometric head orientation to identify that
the proximal segments are laterally positioned.
There were no cases of medial displacement of the proximal segment in this
study and this was confirmed by radiographs in the immediate postoperative
phase. Rosenquist (1990) has shown that medial displacement of the proximal
segment is of no consequence and even defends the concept that medial
displacement of the proximal segment could in fact lead to greater stability. He
explains that less angulation of the proximal segment results in less relapse
because the contact area with the distal segment increases and consequently
healing is improved.
However, there was one case in this series in which the condylar head was
dislocated from the mandibular fossa. Relocation of the condylar head was
required and a preauricular open surgical approach was undertaken to achieve
this. The remainder of the convalescent period for this patient was unevenúul.
77.6 WIRE OSTEOSYNTHESIS BETWEEN THE PROXIMAL AND DISTAL
SEGMENTS
Wire osteosynthesis of the proximal and distal segments following osteotomy
can only be achieved when the operation is performed via an extraoral
technique. In this study, every osteotomy was performed via an intraoral
approach, therefore the effects of interfragment wiring could not be assessed.
Some studies have shown no differences in relapse whether or not the
fragments are wired together (Nordin et al. 1,986; Athanasiou et al. 1991) and
others have shown results to the contrary (Isaacson et al. 1978).
185
17.7 MAXILLOMANDIBULARFIXATION
Controversy exists as to the time period in which a patient should be in
maxillomandibular fixation. Variable time periods have been reported ranging
from two to ten weeks. In this study the time period ranged from 5.6 to 9.3
weeks. The mean time period of fixation was 6.8 weeks. When comparing the
relapse between those below and above the mean fixation period, no statistical
significance in relapse was noted. The literature adequately supports the
variation in time periods of maxillomandibular fixation in which minimal or
no relapse has been measured. However, no agreement has been reached as to
the optimal period of maxillomandibular fixation. Studies have been
performed to determine the minimum time required for complete bone healing
to occur and results have estimated that up to 20 weeks in monkeys is necessary
and a further six weeks is necessary in humans (Reitzik, 1982). Others have
estimated up to one and a half to two years before total maturation of the bony
union (Johanson et al. 7979; Rosenquist et al. 1987).
It is thought that relapse may occur as long as the functional matrix can
influence an unstable osteotomy site. Flence, another issue raised in the review
of literature was that of decortication of the fragments to enable cortex to cortex
healing which some believe improves the strength of the bony union
(Reitzik,1983). No support for this concept was found in this study as no
decortication was performed on any of the osteotomies and no subsequent
relapse was evident.
186
The stretching of wires during the maxillomandibular fixation period would
allow minor movement of the fragments before completion of bone healing but
this did not result in any problem. Suffice to say that the wires were tightened at
each review appointment. Skeletal fixation has been trialed (Astrand and
Ridell, 1,973; Rosenquist et al. 7982; Jonsson et al. 7983; Rosenquist et al. 7985;
Stella, 7986; Epker and Wessberg, 7982; Nystrom et al. 1984) as it was thought to
reduce relapse by preventing extrusion of incisors and increase in anterior facial
height, but in this study no skeletal fixation was used and therefore did not
support the philosophy of skeletal fixation in the prevention of relapse. In fact,
a decrease in anterior facial height was measured in this series in the immediate
postoperative phase but returned to its preoperative position in the long term
follow-up.
Management problems have been reported with the use of maxillomandibular
fixation and in this series of. 24 patients no increased morbidity was
encountered. All patients were instructed in the removal of maxillomandibular
fixation in the event of respiratory embarrassment and all patients were
counselled by a dietitian prior to discharge from hospital. A number of patients
experienced loss in weight during the period of maxillomandibular fixation.
More importantly, this weight loss was appreciated by most of the patients who
were endeavouring to improve their self esteem by having corrective jaw
surgery with no consideration being given to an obesity problem.
Unfortunately, this weight loss was not long lasting and was subsequently
regained very rapidly following removal of the maxillomandibular fixation as it
enabled them to return to their normal presurgery eating habits.
787
1.1.8 MUSCULARINTERACTIONS
Tongue pressure has been singled out as an important cause of relapse and
consequently tongue reduction surgery was performed to reduce the size of the
tongue. The only method of assessing tongue size and posture in this study was
to measure the position of the hyoid bone as it reflected tongue movements and
could be radiographically determined. Therefore, an analysis of the data was
undertaken to determine if a relationship between tongue position and relapse
of the mandible following setback surgery was evident. The most
superoanterior point of the body of the hyoid bone was identified as the
landmark to assess its position relative to the line S-SN7. Greco et al. (1990)
found that mandibular setback resulted in reduction of the hypopharyngeal air
space due to tongue repositioning. In this study, it was found that the hyoid
bone shifted anteriorly and inferiorly in the immediate postoperative period.
Within six weeks following operation, the horizontal shift of the hyoid had
relapsed to its original position but more importantly, the hyoid bone occupied a
more superior position relative to its preoperative position. This would
indicate that the tongue had re-adapted to a new position to maintain the
hypopharyngeal airway space by shifting vertically to occupy more of the space
of the mouth. It may also suggest that tongue function has altered to
acconunodate for the mandibular setback (Proffit and White,7970). Also noted
to compensate for narro*irg of the airway was the change in the pharyngeal
depth. The depth of the pharynx had increased in dimensions over the time
period studied. Moss (1990) reported that where relapse of the mandible
occurred following mandibular surgery, the tongue shifted upwards only. In
those that did not relapse the tongue position shifted upwards and backwards.
This study did not support Moss's findings, in that relapse should have occurred
as only an upward shift of the tongue was found.
188
Tongue reduction has been practised in the past in an effort to minimise relapse
(Becker, 1966; Kole, 7963; Onland and Merkx, "1.972). It was shown in this study
that the tongue was not a contributing factor in relapse of mandibular setback
surgery and the conclusions drawn would strongly advise against such
procedures. The risk of life threatening complications is a potential for any
surgery which may contribute to obstruction of the airway. One of the
consultants of the Oral and Maxillofacial Surgery Unit, The University of
Adelaide, experienced such a complication following tongue reduction,
performed in preparation for orthognathic surgery. The patient in this case
required re-intubation and admission to the intensive care unit for further
monitoring and management. This involved a transfer from one of the
peripheral private hospitals to the Royal Adelaide Hospital, a major teaching
hospital in South Australia. Once the airway was secured no further
complicating events ensued and the patient recovered fully.
Changes in masticatory function have been reported following mandibular
setback procedures. Moss (1973) using electromyographic techniques showed a
distinctive pattern of muscle activity, pre and postoperatively. Further studies
by Moss (1984) demonstrated that an increase in activity of anterior temporal
and posterior masseter muscles was recorded following mandibular setback and
if these were not evident then a tendency towards relapse would be expected.
This increased muscle activity was correlated to the fact that these muscles were
less active in the untreated prognathic mandible and therefore if remained
inactive would tend to reposition itself back to its original position. A recent
publication (Raustia and Oikarinen, 7994) also confirmed similar findings of
increased activity of the masseter and temporal muscles following mandibular
setback surgery.
789
11..9 GROWTH
The timing of orthognathic surgery is an important factor in minimising relapse
secondary to growth. Freihofer (7982) remarked upon postoperative instability
after correction of the prognathism in patients operated on before 17 years of age.
Although, in this study, no evidence of relapse was found when the results
were reviewed, there was only one case of relapse (Figure 11.1) identified on
clinical review, and this was clearly associated with mandibular growth as the
patient had reported substantial increase in height postoperatively. This patient
underwent orthognathic surgery at age 76 at a time when his skeletal maturity
was thought to have neared completion. He presented for review again five
years postoperatively. He had stated that he had grown in height and analysis of
serial lateral cephalograms showed that further mandibular growth had
contributed to relapse following the initial orthognathic surgery. An offer of
further orthognathic surgery was made and this was accepted. The work-up to
follow includes a bone scan to assess whether there was any evidence of
pathological or continued activity of the condyles. This scan was reported as
showing no further growth activity and therefore further orthognathic surgery
is being planned for this patient to correct the dentofacial deformity. Some
authors contend that surgical correction of mandibular prognathism can be
carried out at a very early age (Biederman, 7967; Ware and Taylor,7968; Isaccson
et al. 1978; Macintosh, 7987; Lehman, 1981). Other authors caution against such
corrections prior to growth maturity since individuals with Class III
malocclusions tend to have a prolonged period of mandibular growth
(Goldstein, 7947; Proffit and White , 7970; Hinds and Kent, 7972). It is the view of
this Oral and Maxillofacial Surgery Unit, University of Adetaide, that treatment
of mandibular prognathism should not be undertaken until the completion of
growth and although its assessment is difficult many methods are available to
790
provide some scientific basis to this problem (Rosenquist et aI. 1.986; Sorokolit
and Nanda,'1.990).
197
Figure 1L.1 Mandibular relapse identified on clinical review
L
792
L1.L0 SINGLE JAW aersus BIMAXILLARY PROCEDURES
The literature suggests that bimaxillary procedures are more stable than single
jaw procedures (Kahnberg and Ridell, 198s). Franco et al. (1,989), however,
showed no significant differences between the one or two jaw groups for any
predictor of relapse at different time intervals. In this study, there was no
evidence of any differences in relapse found when comparing bimaxillary
procedures to single jaw procedures although the sample size did not warrant
statistical comparison as only two single jaw procedures were performed in this
study. Bimaxillary surgery was the common surgical procedure performed due
to the magnitude of the discrepancy between maxilla and mandible. Kahnberg
and Ridell (1988) suggested that the amount of mandibular relapse tends to be
less in bimaxillary cases than in mandibular surgery alone probably because the
setback in bimaxillary cases is proportioned between the maxilla and mandible,
implying that the greater the amount of setback, the greater the relapse
potential.
11.17 CORONOIDECTOMY
Removal of the coronoid process has been advocated to allow setback of the
distal segment of the mandible following osteotomy. No coronoidectomies
were performed in this study as no difficulties were experienced in the
mandibular setback.
1']..12 HIGH ANGLE MANDIBLES
The obtuse gonial angle is a characteristic feature of the prognathic mandible.
The construction of the gonial angle is difficult when the procedure of vertical
subsigmoid osteotomy is undertaken to set the mandible back. Usually this
793
procedure leaves the distal tip of the proximal fragment 'overhanging' the lower
border of the mandible and the point gonion is arbitrarily identified by the
intersection of the tangents to the lower border of the mandible and the
posterior border of the mandible. Due to changes that occur following surgery
the 'overhanging' distal tip of the proximal fragment is completely remodelled
and consequently the point gonion moves as resorption occurs. This ultimately
affects the linear and angular measurements associated with this point. In this
study the gonial angle was found to decrease following surgery and relapsed
further than the initial shift. This change did not affect the stability of the
vertical subsigmoid osteotomy procedure. One explanation is that resorptive
changes in the gonial region can alter the gonial angle unfavourably (Shepherd,
1980) without causing a forward shift of the mandible.
794
VII
CONCTUSIONS
195
1
CHAPTER 12
CONCLUSIONS
The results of this study showed that no statistically significant relapse
occurred in the short, intermediate nor long term. Therefore, the
technique of vertical subsigmoid osteotomy is a stable procedure.
2. No significant differences in relapse could be assigned to age nor to the
differences in sexes in any period of study.
3. The period of maxillomandibular fixation had no influence on relapse of
mandibular setback.
4. The procedure of vertical subsigmoid osteotomy was stable whether
orthodontics was undertaken prior to surgery or whether no orthodontics
was used at all.
Displacement of the condyle occurred during the period of fixation but
returned to its preoperative position in the intermediate and long term.
The anterior facial height decreased during the period of fixation but
relapsed to its preoperative height.
Both the gonial and ramal angles were displaced in a clockwise direction
by the setback of the mandible but returned to the preoperative position
with no relapse of the mandibular setback.
5
6
7
796
8.
9
The type of surgery, whether single jaw or bimaxillary, did not influence
relapse. Similarly segmentalization of the maxilla had no influence.
Relapse of the maxilla following advancement was statistically
significant. This is contrary to the literature which generally states that
maxillary advancement is stable.
The orthodontic decompensation of the upper and lower incisors proved
to be unstable with relapse of both the upper and lower dentition. This
did not influence the stability of the surgical changes.
Positive overjet and overbite were achieved with minimal relapse and no
tendency towards open bite following long term follow-up.
The hyoid position altered significantly following mandibular setback.
Initially, following surgery, the hyoid bone returned to its preoperative
position horizontally but moved superiorly. In the long term the hyoid
bone was positioned more superiorly than its preoperative position.
Consequently, the tongue position (indicated by hyoid position) had no
influence on relapse following vertical subsigmoid osteotomy.
The airway depth increased following mandibular setback.
10.
11.
12.
13.
197
VII
APPENDIX
198
APPENDIX
INTRAORAL VERTICAL SUBSIGMOID OSTEOTOMY
1. INDICATIONS
(a) Mandibular anteroposterior excess assessed on cephalometric and clinical
analysis
þ) For minor setback of mandible (less than 10 mm), minor mandibular
asymmetry and corrections of vertical discrepancies in the mandibular
ramus
2.
(a)
(b)
CONTRAINDICATIONS
Airway compromise
Intermaxillary fixation not advisable
PREOPERATIVE WORK UP
Before ailmission
Orthognathic Surgery work up as per major surgery protocol, Oral and
Maxillofacial Surgery Unit, University of Adelaide. This involves the
following:
(i) Clinical and medical assessment;
(ii) Anaesthetic assessment;
(iii) Autologous blood donations;
(iv) Radiographs - lateral head cephalogram, orthopantomogram,
posteroanterior cephalogram;
(v) Photographs of face and dentition;
(vi) Quick Cephru analysis;
3.
3.7
(a)
199
(b)
(c)
3.2
(a)
þ)(c)
(d)
(vii) Study models;
(viii) Body image and Illness behaviour questionnaire; and
(ix) Oral and Mafllofacial Surgery Unit clinical work up sheets
Model surgery to indicate movements and construction of occlusal wafer
Confirm means of maxillomandibular fixation:
(i) arch bars; and
(ii) orthodontic bands on 1st molars, premolars and canines and high
hat pins
On øilmission:
Full presurgical work up;
Check accuracy of occlusal wafer;
Notify theatre - osteotomy instrument requirements; and
Notify higher dependency ward
4. OPERATIVE PROCEDURE
4.7 Anøesthesia
(a) Advise anaesthetist of the use of maxillomandibular fixation during and
at the completion of operation;
þ) Nasoendotracheal intubation;
(c) Standard anaesthetic medications; and
(d) Standard anaesthetic monitoring which routinely involved:
(i) pulse oximetry
(ii) cù(iii) blood pressure
(iv) pulse rate
(v) tidal volume
(vi) ECG
200
4.2
(a)
4.3
(a)
(b)
(c)
Instruments
Obwegeser osteotomy tray:
(i) 2 stripping periosteal elevators (small and large) needed;
(ii) Sagittal saw and 120 degree right angle saw blade needed;
(iii) Sigmoid retractors needed; and
(iv) Le Vasseur Merrill retractors needed
Preparation
Intravenous dexamethasone 8 milligrams and cephalothin L gram;
1.Vo Corlrcf ointment to lips; and
Clean and prepare in conventional way for intraoral operation
Access:
Cheek and tongue retractors are positioned (assistant number 2);
Arch bars are ligated to teeth if necessary; and
Haemostasis: infiltrate along ramal border with Xylocaine 2Vo and
adrenalin 1/80000. 4 mls each side
Mu cop erio ste al Refle ctio n :
Lateral aspect of the anterior angle of mandible to subsigmoid notch;
Do not strip off the fibres of masseter that are attached to the notch at the
mandibular angle;
Use two periosteal elevators to reflect (small and medium);
4,4
(a)
(b)
(c)
4.6
(a)
þ)
4.5 Incision:
(a) Along external oblique ridge similar to incision for sagittal split
osteotomy; and
(b) From approfmately a quarter way up ascending ramus to the 2nd molar
Ensure the incision is not made too high
(c)
201
(d)
(e)
(f)
Place a forked Langenbeck at the anterior ramal border;
Establish the position of the sigmoid notch at the superior aspect of
reflection;
After stripping posteriorly and inferiorly, place a fibre optic retractor distal
to the posterior ramal border;
Locate the condyle; and
Locate the angle
Bone cuts
After locating the antilingula (if present) commence bony cut with 120
degree right angle sagittal saw blade positioned in middle of ramus
between sigmoid notch and mandibular angle;
Angle the saw so that its action gives maximum mechanical advantage;
After the bone cut has been made through both plates in the centre
continue superiorly in the see-sawing manner;
Stop short of the sigmoid notch by 2-3 mm and check cut with a No. 6
Ash plastic;
If free continue superiorly, if there are spurs remaining deepen them
with the saw cut;
Once the upper 1,/2 is sectioned, the lower 7/2 is cut by using the saw in
the manner described in (c); and
Check with No. 6 Ash plastic to make sure bone cut is completely through
The angle of the saw will ensure that the saw cut is oblique to minimise
damage to the inferior dental nerve
4.8 Separøtion
(a) If not mobile complete split wittr curved Obwegeser osteotome;
(e)
(h)
4.7
(a)
(b)
(c)
(d)
(e)
(f)
(g)
NB
202
(b) Insert two periosteal elevators, superior and inferior and check mobitity
of fragments;
(c) To remove Le Vausser Merrill retractor, insert an elevator medial to the
proximal fragment so that this fragment is not displaced medially on
removal of the retractor; and
(d) Repeat procedure for other side after placing moist tampon at surgical site
4.9
(a)
(b)
(c)
(d)
(e)
Fixøtion
Check occlusion with wafer;
Check that proúmal fragments of ramus are lateral to distal fragments;
Remove throat pack and suction out pharynx;
Apply maxillomandibular fixation with 26 gauge wire; and
Soft tissue closure with 3/0 chromic cat gut sutu¡e
5.1
(a)
o)
5. POSTOPERATIVE MANAGEMENT
Immediate
High dependency recovery for first 24 hours;
Intravenous dexamethasone 8 milligrams L2 hourly and cephalothin 1
gram 6 hourly for 48 hours postoperatively;
Narcotic analgesia intravenously or intramuscularly 4 hourly prn is
gradually replaced with paracetamol-codeine preparations; and
Clear fluids are given in the first 24 hours
(c)
(d)
203
5.2
(a)
þ)
Postoperøtioe recooery
Oral intake and ambulation are encouraged; and
Postoperative lateral head cephalogram, PA mandible and OPG are taken
as early as possible to confirm the accuracy of surgery, in particular the
proximal fragments of the mandible are laterally positioned and the
condylar heads are enlocated.
204
VIII
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20s
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