Treatment effects of headgear biteplane and bionator appliances

ORIGINAL ARTICLE

Treatment effects of headgear biteplane andbionator appliancesRenata Rodrigues de Almeida-Pedrin,a Marcio Rodrigues de Almeida,b Renato Rodrigues de Almeida,c

Arnaldo Pinzan,d and Fernando Pedrin Carvalho Ferreirae

Bauru, and Lins, SP, Brazil

Introduction: The purpose of this investigation was to evaluate the dentoalveolar and skeletal cephalometricchanges produced by headgear (HG) biteplane and bionator appliances in subjects with Class II Division 1malocclusion. Methods: The sample comprised 60 patients with Class II Division 1 malocclusion; 30 (15boys, 15 girls; mean age, 10.02 years) were treated with the HG biteplane for a mean period of 1.78 years,and 30 (15 boys, 15 girls; mean age, 10.35 years) were treated with a bionator for a mean period of 1.52years. For comparison, a control group of 30 untreated Class II children (15 boys, 15 girls) with an initial meanage of 10.02 years, followed for 1.48 years, was established. Lateral cephalometric headfilms were obtainedat the beginning and at the end of the treatment or observation period. Results: The results showed thatforward growth of the maxilla was restricted in the HG biteplane group. Bionator treatment, however,produced a statistically significant increase in mandibular protrusion. Both appliances provided increases intotal mandibular and ramus lengths. There were no statistically significant differences in craniofacial growthdirection. The mandibular incisors were tipped labially with bionator treatment and lingually in the HGbiteplane group. The maxillary incisors were retruded with both appliances; there also were a significantincrease in mandibular posterior dentoalveolar height and a restriction in the vertical development of themaxillary molars. Conclusions: Class II treatment with HG biteplane and bionator appliances is efficient overthe short term, with pronounced dentoalveolar movements and smaller but still significant skeletal effects.The stability of these results should be examined in a long-term study. (Am J Orthod Dentofacial Orthop
2007;132:191-8)
In Class II malocclusion patients, discrepanciesappear in many combinations of dental, skeletal,and profile problems, and they should be treated

differently. Several types of orthopedic and functionalappliances currently used for Class II treatment attemptto improve dental and skeletal imbalances and soft-tissue harmony. Treatment approaches for growth mod-ification in Class II correction is controversial, and

aAssociate professor, Lins Dental School, Methodist University of Piracicaba,SP, Brazil.bPostdoctoral fellow, Department of Orthodontics, Bauru Dental School,University of São Paulo, Bauru, SP, Brazil; associate professor, Lins DentalSchool, Methodist University of Piracicaba, SP, Brazil.cAssociate professor, Lins Dental School, Methodist University of Piracicaba,SP, Brazil.dAssistant professor, Department of Orthodontics, Bauru Dental School,University of São Paulo, SP, Brazil.ePhD student, Bauru Dental School, University of São Paulo, SP, Brazil.Supported by CAPES (Brazilian National Research Foundation).Based on research by Renata Rodrigues de Almeida-Pedrin in partial fulfill-ment of the requirements for the PhD degree in orthodontics, Bauru DentalSchool, University of São Paulo, Bauru, SP, Brazil.Reprint requests to: Renata Rodrigues de Almeida-Pedrin, Department ofOrthodontics, Bauru Dental School, University of São Paulo, R. OctávioPinheiro Brizolla, 9-75 Bauru, São Paulo, CEP: 17012-901 Brazil; e-mail,[email protected], April 2005; revised and accepted, July 2005.0889-5406/$32.00Copyright © 2007 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2005.07.030
some mechanisms involved in these appliances are notwell understood.1,2 However, there is consensus thatorthopedic functional appliances such as headgear(HG) and bionators can correct Class II malocclusionby allowing changes in the growth pattern and com-pensating dentoalveolar mechanism.1-11

Previous studies demonstrated that HG biteplane1,2

and bionator3,5,11-14 treatments enhance mandibulargrowth, improve anteroposterior apical base relation-ships, and promote favorable dental changes and soft-tissue modifications. It is well known that HG therapyrestricts maxillary forward growth, but this effect is lessclear with bionator treatment.

The purpose of this study was to investigate theshort-term effects of HG biteplane and bionator thera-pies in patients with Class II Division 1 malocclusioncompared with a matched untreated Class II controlsample.

MATERIAL AND METHODS

This prospective clinical study was designed toevaluate cephalometrically the short-term skeletal anddentoalveolar effects of Class II correction obtainedwith HG biteplane and bionator appliances. The exper-
imental group included 60 treated subjects with skeletal
191

American Journal of Orthodontics and Dentofacial OrthopedicsAugust 2007

192 Almeida-Pedrin et al

and dental Class II malocclusion; they were comparedwith a matched, untreated control group of 30. Theexperimental sample was collected by random evalua-tion by 1 operator.

The control sample was obtained from the files ofthe Orthodontic Department at Bauru Dental School,University of São Paulo, Brazil; subjects selected forthe control group (n � 30; 15 boys, 15 girls) hadbilateral distal molar relationships greater than one-halfcusp, ANB angles �4.5°, an initial mean age of 10.02years (range, 8.0-10.9 years), and a final mean age of11.51 years (range, 9.0-11.6 years) (Table I). Thesesubjects had no previous orthodontic treatment andwere observed for 1.49 years.

The patients in the HG biteplane group (n � 30; 15boys, 15 girls) were treated at the Department ofOrthodontics, Bauru Dentistry School, University ofSão Paulo, Brazil, for a mean period of 1.78 years.These subjects had Class II Division 1 malocclusioncharacterized by bilateral distal molar relationshipgreater than one-half cusp and ANB angle �4.5°. Theirinitial mean age was 10.02 years (range, 8.2-11.0years); final mean age was 11.80 years (range, 9.2-12.0years) (Table I).

The patients in the bionator group (n � 30; 15 boys15 girls) were treated at the same faculty for a meanperiod of 1.52 years. They had Class II Division 1malocclusion characterized by bilateral distal molarrelationship greater than one-half cusp and ANB angle�4.5°. Their initial mean age was 10.35 years (range,8.2-11.0 years); final mean age was 11.87 years (range,9.2-12.0 years) (Table I).

Initial (T1) cephalometric films of the treatedgroups were obtained within 2 weeks of applianceplacement; posttreatment (T2) films were taken 4weeks after appliance removal to eliminate forwardposturing of the mandible caused by the appliance.

Lateral cephalograms for each patient at T1 and T2in all groups were standardized as to magnificationfactor (9%) and digitized with Dentofacial Plannersoftware (version 7.0, Dentofacial Planner, Toronto,Ontario, Canada). The reference points and measure-

Table I. Sample description

Group n Girls Boys

Mean

T1

Control 30 15 15 10.02HG biteplane 30 15 15 10.02Bionator 30 15 15 10.35

NS, Not significant.

ments are shown in Figures 1 to 4.

The treated groups and the control group werehomogeneous at T1 as to the maturation of the cervicalvertebrae. The mean stage for all groups at T1 wasbetween cervical vertebrae maturation (CVM) stages 1and 2 according to the classification of Franchi et al.15

These stages represent the time before the peak ofskeletal maturity. Therefore, both groups were ade-quately matched in chronological age and skeletalmaturation for direct comparison.

Statistical analysis

All statistical analyses were performed with acommercial statistical package (Statistica for Windows,version 6.0, SPSS, Chicago, Ill).

To assess the error of localizing the referencepoints and the digitizing procedure, 20 randomlyselected tracings were retraced and remeasured about1 month later by the same examiner. The randomerrors were assessed with Dahlberg’s16 formula, andsystematic errors were ascertained with paired t tests.The random error of the method did not exceed 0.90°or 1.00 mm. Paired t tests showed only 1 statisticallysignificant systematic error (for L6-GoMe measure-ments).

To evaluate the data distribution, the data wereanalyzed with the Kolmogorov-Smirnov test. In con-sidering a normal distribution of the data, the T1cephalometric measurements of the groups and thechanges over the treatment/observation period werecompared by using ANOVA and Tukey tests.

RESULTS

The treated and control samples were comparedbefore treatment to determine their similarities and toassist in the interpretation of the results (Table II). Theoverall comparison of the starting forms of the 3 groupsshowed a high level of similarity. Of the 22 variables,only 3 had statistical differences. Maxillary and man-dibular sagittal positions compared favorably in the 3groups, as did ANB angle. However, the effective

)Average treatment/

observation (y)ANOVAP value Significance2

.51 1.49 .345 NS

.80 1.78 .372 NS

.87 1.52 .116 NS

ages (y

T

111111

lengths of the maxilla (Co-A) and the mandible (Co-

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 132, Number 2

Almeida-Pedrin et al 193

Gn) and posterior facial height (S-Go) were greater inthe bionator group.

The analysis of treatment effects (T2-T1) wasderived from analysis of the tracings of the pretreat-ment and posttreatment cephalometric headfilms. Thesedata were compared with corresponding data from thecontrol sample (Table III).

In all 3 maxillary skeletal measurements (SNA,Nperp-A, Co-A), there were statistically significantdifferences among the groups (Table III). The max-illae of the HG biteplane patients showed a signifi-cant restriction in forward growth (SNA, Nperp-A).

A statistically significant increase in mandibular

Fig 1. Cephalometric landmarks: sella (S), midpoint ofsella turcica; nasion (N), most anterior point of fronto-nasal suture; porion (Po), uppermost point of externalear meatus; orbitale (Or), lowermost point of orbit;subspinale (A), deepest concavity of anterior maxilla;supramental (B), deepest concavity of anterior mandib-ular symphysis; anterior nasal spine (ANS); posteriornasal spine (PNS); menton (Me), most inferior point onmandibular symphysis; gonion (Go), most posteriorinferior point of angle of mandible; gnathion (Gn), mostanterior inferior point on mandibular symphysis; pogo-nion (P), most anterior point of bony chin; condylion(Co), most posterior superior point of condyle; upperincisor edge (UIE); lower incisor edge (LIE); upper inci-sor apex (UIA); lower incisor apex (LIA); first upper molarmesial point (FUMMP); first lower molar mesial point(FLMMP).

protrusion (SNB, Nperp-P) was observed in patients

treated with the bionator (1.23° and 1.23 mm).Effective mandibular length (Co-Gn) increased 3.23mm in the control group, 5.29 mm in the HGbiteplane group, and 4.15 mm in the bionator group,but these differences were not statistically significant(Table III).

The ANB angles in the HG biteplane and bionatorgroups were reduced (�1.95° and �1.55°, respec-tively); this variable remained essentially unchanged(�0.45°) in the control group, a difference that wasstatistically significant (P �.01).

The mandibular plane (SN.GoGn) and the palatalplane (SN.PP) were unaffected by treatment. No dif-ferences in lower anterior face height (ANS-Me) andposterior facial height (S-Go) were noted between thegroups.

The maxillary dentoalveolar component had statis-tically significant changes (P �.01), with incisor retrac-tion of 9.26° (HG biteplane) and 4.48° (bionator) forU1.NA, and 1.77 mm (HG biteplane) and 0.69 mm(bionator) for U1-NA in treated groups (Table III). Themaxillary molars did not differ significantly whenextrusion to the palatal plane (U6-PP) was evaluated.

Fig 2. Angular measurements: 1, SN.PP (palatalplane-SN line); 2, SN.GoGn (mandibular plane-SN line);3, SNA (sella-nasion-A); 4, SNB (sella-nasion-B); 5, ANB(maxillomandibular relationship); 6, IMPA (mandibularincisor long axis-mandibular plane angle); 7, 1.NA (an-gle between maxillary incisor long axis-NA line; 8, 1.NB(angle between mandibular incisor long axis-NB line).

Horizontally, the first molars showed distal movement



(U6-FHp) with HG biteplane treatment (�1.27 mm); inthe control (0.92 mm) and bionator (0.10 mm) groups,these teeth were mesially moved.

The mandibular dentoalveolar component alsoshowed significant changes (P �.01), with incisorproclination of 4.25° for L1.NB and approximately1.12 mm for L1-NB in the bionator group; in the HGbiteplane group, the incisors retroinclinated 2.22° and0.2 mm. The mandibular molars extruded significantly(P �.01) more in the treated groups (HG biteplane,1.78 mm; bionator, 1.55 mm) than in the controls (0.79mm). The first molars moved mesially more (P �.01)in the treatment groups (HG biteplane, 2.69 mm;bionator, 3.27 mm) than in the controls (1.05 mm).

DISCUSSION

To our knowledge, only 1 study in the Englishliterature1 compared the treatment effects of the HGbiteplane and bionator appliances. An interesting studyaddressing the long-term effect of the bionator appliancewas conducted by Faltin et al.12 Our findings, although

Fig 3. Skeletal linear measurements: 1, Go-Gn (dis-tance between points Go and Gn); 2, Co-A (distancebetween points Co and A); 3, Co-Gn (distance betweenpoints Co and Gn); 4, LAFH (lower anterior face height);5, S-Go (distance between points S and Go); 6,Nperp-A (perpendicular distance between point A toFrankfort perpendicular plane [N]); 7, Nperp-P (perpen-dicular distance between point P to Frankfort perpen-dicular plane [N]).

limited to a specific skeletal maturation stage at T1 (CVM

1 to 2) and evaluating only a short term, agree withprevious studies1,3,4-6,8-10,14,17-19 that suggested that cor-rection of Class II Division 1 malocclusion with bothappliances is achieved by a combination of significantdentoalveolar changes and maxillomandibular skeletaleffects.

There was a significant restriction of maxillaryforward growth only in the HG biteplane group, withdecreases in SNA angle (�1.48°) and Nperp-A (�1.38mm) compared with the control (�0.49°, �0.77 mm)and bionator (�0.34°, �0.35 mm) groups. This resultagrees with others who also found significant changesin maxillary growth in patients treated with the maxil-lary splint or the HG biteplane appliance.2,4,8,10,17,20 Onthe other hand, few studies18,21,22 have noted a restric-tive effect in maxillary displacement with bionator

Fig 4. Dental linear measurements: 1, 1-NA (distancebetween most anterior point of maxillary central incisorand NA line; positive value assigned when structure wasposterior to line); 2, 1-NB (distance between mostanterior point of mandibular central incisor and NB line;positive value assigned when structure was posterior toline); 3, 6-PP (perpendicular distance from maxillary firstmolar mesial point to palatal plane); 4, 6-GoMe (perpen-dicular distance from mandibular first molar mesialpoint to palatal plane); 5, 6-FHp (perpendicular distancefrom maxillary first molar mesial point to Frankfortperpendicular line [S]); 6, 6-FHp (perpendicular distancefrom mandibular first molar mesial point to Frankfortperpendicular line [S]).

therapy.



A statistically significant increase in mandibularprotrusion with increases in SNB angle (1.23°) andNperp-P (1.23 mm) was observed in the bionator group.This finding of increased mandibular growth afterfunctional appliance treatment agrees with the results ofother investigations involving bionator/activator appli-ances,1,3,9,18,19,21,23-28 although Harvold and Varger-vik22 did not find such an increase.

In the HG biteplane group, an increase in mandib-ular protrusion (SNB angle, 0.46°; Nperp-P, 0.44 mm)was also observed compared with the controls (SNBangle, �0.18°; Nperp-P, �0.83 mm), but these differ-ences were not statistically significant; this agrees withothers studies.1,8,10,20

Numerically larger changes, but lacking statisticalsignificance, occurred in the measurements of mandib-ular length with increases in Co-Gn and Go-Gn in bothtreated groups. In the HG biteplane group, mandibularlength (Co-Gn) increased an additional 2.06 mm andGo-Gn an additional 0.78 mm compared with the

Table II. Comparison of T1 cephalometric measuremen

Cephalometric measurement

Group 1, control(n � 30)

G

X SD X

Maxillary skeletalSNA (°) 80.44 2.92 81Nperp-A (mm) �2.21 2.62 �1Co-A (mm) 81.02 3.96 78

Mandibular skeletalSNB (°) 75.36 3.14 75Nperp-P (mm) �10.68 4.72 �11Go-Gn (mm) 65.56 3.52 64Co-Gn (mm) 99.25 4.41 96

MaxillomandibularANB (°) 5.07 1.87 6

VerticalSN.GoGn (°) 32.36 3.79 34SN.PP (°) 7.67 2.75 7LAFH (mm) 58.76 3.97 58S-Go (mm) 64.19 3.79 61

Maxillary dentalU1.NA (°) 24.89 6.89 27U1-NA (mm) 4.73 1.42 5U6-FHp (mm) 32.86 3.94 32U6-PP (mm) 18.26 1.73 18

Mandibular dentalL1.NB (°) 24.82 5.80 27L1-NB (mm) 4.42 1.32 4L6-FHp (mm) 32.90 4.07 31L6-GoMe (mm) 26.05 1.73 25IMPA (°) 94.72 5.94 94

NS, not significant; X, mean.*P �.01.

control group. In the bionator group, mandibular length

also increased, with Co-Gn increasing 0.92 mm morethan in the control group.

According to the CVM analysis15 used in this study,all patients started orthopedic treatment before the puber-tal growth spurt (CVM 1 to 2). At the end of the treatment,these patients were still before the pubertal growth spurt(CVM 2). Mandibular length increased slightly more inthe treated groups than in the controls. Based on samplesize (90 subjects), however, the standard deviations of theT1 to T2 change in mandibular length (Co-Gn) were about5.2 and 4.1 mm for HG biteplane and bionator groups,respectively. Considering the power of this study (a valuethat indicates the probability to assess false-positive find-ings), the level for clinical significance for the supplemen-tary increase in mandibular length should be about 2 mm.The actual difference between the HG biteplane subjectsand the controls of 2.06 mm, shown in Table III for themeasurement Co-Gn, even if statistically insignificant, canbe considered clinically relevant.

This finding of increased mandibular length after

HGne0)

Group 3, bionator(n � 30) Significance

SD X SD 1-2 1-3 2-3

3.46 81.45 3.55 NS NS NS3.04 �1.43 3.27 NS NS NS2.97 82.28 3.94 NS NS *

3.23 75.48 3.17 NS NS NS6.11 �11.05 6.21 NS NS NS2.80 66.73 5.19 NS NS NS3.55 100.31 4.80 NS NS *

1.79 5.96 1.78 NS NS NS

4.86 33.25 5.85 NS NS NS2.88 7.61 2.88 NS NS NS3.73 59.88 4.59 NS NS NS3.42 64.73 4.47 * NS *

4.98 26.22 6.71 NS NS NS1.15 5.54 2.02 NS NS NS2.99 34.07 3.98 NS NS NS1.40 19.19 1.94 NS NS NS

4.97 26.42 6.05 NS NS NS1.54 5.20 1.82 NS NS NS3.28 33.91 4.33 NS NS NS1.95 26.24 1.75 NS NS NS4.80 95.38 6.64 NS NS NS

ts

roup 2,bitepla(n � 3

.37

.47

.83

.19

.23

.49

.96

.18

.48

.62

.77

.15

.89

.57

.06

.27

.09

.88

.76

.33

.84

orthopedic appliance treatment agrees with the results



other investigations involving HG biteplane and biona-tor appliances.1,3,11,12,19,21,22,27 However, other studiesshowed no influence of orthopedic appliances in themandibular length increase.6,7,29

As reported by Keeling et al,1 the contribution ofthe HG biteplane to enhanced mandibular growth isunclear, but their findings included mandibular in-crease. Our data do not provide the answer either, but itis clearly demonstrated that mandibular length in-creased more in this treatment group. According to Youet al,30 disarticulation of the occlusion to minimize theeffects of the adaptive changes of the dentoalveolarcomplexes should greatly facilitate Class II treatment ingrowing patients. Perhaps this is the key to understand-ing the mandibular length increase with the biteplaneappliance that disarticulates the occlusion.

The maxillomandibular relationship showed im-provement in both the HG biteplane and bionatorgroups compared with the control group (Table III),with no statistically significant difference between the

Table III. Difference in mean changes (T1 to T2)

Cephalometric measurement

Group 1, control(n � 30)

G

X SD X

Maxillary skeletalSNA (°) �0.49 1.32 �1.4Nperp-A (mm) �0.77 1.39 �1.3Co-A (mm) 2.33 2.88 1.7

Mandibular skeletalSNB (°) �0.18 1.37 0.4Nperp-P (mm) �0.83 2.99 0.4Go-Gn (mm) 2.57 1.82 3.3Co-Gn (mm) 3.23 3.43 5.2

MaxillomandibularANB (°) �0.45 0.93 �1.9

VerticalSN.GoGn (°) �0.36 1.57 �0.1SN.PP (°) 0.77 1.39 0.8LAFH (mm) 1.45 1.77 2.3S-Go (mm) 2.76 2.20 3.6

Maxillary dentalU1.NA (°) 0.68 3.80 �9.2U1-NA (mm) 0.48 1.23 �1.7U6-FHp (mm) 0.92 2.13 �1.2U6-PP (mm) 1.19 1.13 0.6

Mandibular dentalL1.NB (°) 0.33 3.60 �2.2L1-NB (mm) 0.24 0.80 �0.2L6-FHp (mm) 1.05 1.69 2.6L6-GoMe (mm) 0.79 1.21 1.7IMPA (°) 1.00 2.98 �2.4

NS, Not significant; X, mean.*P �.05; †P �.01.

treated groups. Improvement in basal bone relationship

resulted from changes in maxillary anterior growth andby the anterior positioning of the mandible in thesegroups. Similar results were found with bionator ther-apy by some authors3,9,11,18,19,21,23,28,31 and also for theHG biteplane.1,4,8,10,20,21,29 Changes in ANB angle inthe treated groups were a result of several small butcumulative effects on dentofacial structures associatedwith normal craniofacial growth; these were not suffi-cient to correct or improve the skeletal Class II rela-tionship in the untreated group.

As a result of the observed interplay of both anteriorand posterior facial heights, the mandibular plane wasnot significantly affected. There was a greater tendencyfor clockwise rotation of the maxillary plane (SN.PP)during HG biteplane and bionator therapy comparedwith the control group that did not adversely affectLAFH. Although increases in LAFH were observed inall 3 groups, there were no statistically significantdifferences between the control (1.45 mm), HG bite-plane (2.38 mm), and bionator (2.59 mm) groups. This

HGe

0)Group 3, bionator

(n � 30) Significance

SD X SD 1-2 1-3 2-3

1.30 �0.34 1.04 † NS †

1.23 �0.35 1.00 NS NS †

2.47 0.81 2.10 NS * NS

1.23 1.23 1.29 NS † *2.50 1.23 2.46 NS † NS2.25 2.33 1.88 NS NS NS3.70 4.15 2.66 NS NS NS

1.40 �1.55 1.29 † † NS

1.58 0.22 1.83 NS NS NS1.38 0.44 1.34 NS NS NS1.90. 2.59 2.40 NS NS NS2.39 3.70 1.89 NS NS NS

7.05 �4.48 5.24 † † †

2.04 �0.69 1.31 † * *2.74 0.10 1.66 † NS NS1.49 0.88 1.30 NS NS NS

3.93 4.25 4.31 * † †

0.88 1.12 1.15 NS † †

2.03 3.27 2.14 † † NS1.28 1.55 1.09 † * NS3.93 2.79 4.03 † NS †

roup 2,biteplan(n � 3

882

6459

5

9986

6779

22988

result is probably related to the posterior bite opening



when the mandible was brought forward in the exper-imental groups and the molars are encouraged to erupt.Posterior facial heights also increased in all 3 groups,with no difference among them.

As it has been shown in many other investigationsof almost all orthopedic appliances, both the HGbiteplane and the bionator produced lingual tipping andretrusion of the maxillary incisors.3,4,6,11,20,22,23,29 Thiseffect was expected because both appliances have intheir construction a labial wire that contacts the incisors(HG biteplane) or might come in contact with themduring sleep (bionator), causing them to retract.14,25

In the control group, the maxillary first molarsextruded 1.19 mm, which was not statistically differentfrom the HG biteplane (0.69 mm) and bionator (0.88mm) groups.

HG treatment results in maxillary molar distaliza-tion,4,6,8-10,17,21,29 so the maxillary molars moved dis-tally in the HG biteplane (�1.27 mm) group, whereas,in the bionator group (0.10 mm) and the controls (0.92mm), the molars showed mesial movement.

In the control group, the mandibular incisors re-mained stable (0.33°) relative to the nasion-Point Bline. As other studies3,19,26,28 mentioned, significantproclination of the mandibular incisors was found in thebionator group (4.25°), and IMPA increased by 2.79°.This effect is probably consequent to the resultantmesial force on the mandibular incisors induced by theprotrusion of the mandible. However, in the HG bite-plane group, the mandibular incisors tipped lingually(IMPA, �2.22° and �2.48°) and retracted (�0.2 mm)due to significant retraction (�9.26° and �1.77 mm) ofthe maxillary incisors and probably greater lower lippressure on this area.4

The vertical eruption of the mandibular first molars(6-GoMe), however, was greater in the HG biteplane(1.78 mm) and bionator (1.55 mm) groups compared withthe control group (0.79 mm). This effect was also reportedby others with bionator/activator appliances.3,19,22 How-ever, when evaluating this measurement, one can arguethat there was a systematic error. Thus, care should betaken when interpreting results of the vertical eruptionof the mandibular first molars.

The acrylic in the bionator group must be trimmedaway in the posterior inferior region to provide nocontact with the posterior mandibular teeth. This pro-cedure allows greater vertical increase of the mandib-ular posterior teeth and helps correct the overbite, theClass II molar relationship, and the deep curve of Spee.

The first molars moved mesially more in the HGbiteplane (�2.69 mm) and the bionator (�3.27 mm)groups than in the controls (1.05 mm).

Overall, we suggest that correction of Class II

Division 1 malocclusion with the HG biteplane andbionator appliances is achieved by a combination ofmaxillomandibular skeletal effects and significant den-toalveolar changes.

CONCLUSIONS

Our results indicate that the skeletal and dentaleffects produced by HG biteplane and bionator appli-ances are as follows.

1. There was significant improvement of the antero-posterior relationship between the maxilla and themandible with both therapies.

2. There were changes in forward growth of themaxilla only in the HG biteplane treatment group.

3. A statistically significant increase in mandibularprotrusion was observed in patients treated with thebionator.

4. An increase in mandibular length was observed inthe treated groups (an additional 0.92 mm [biona-tor] and 2.06 mm [HG biteplane] of mandibularlength compared with control values) even thoughit was not statistically significant.

5. There were no statistically significant differences incraniofacial growth pattern or lower anterior andposterior facial heights among the groups.

6. The bionator produced labial tipping and linear pro-trusion of the mandibular incisors, whereas the inci-sors were retroinclinated in the HG biteplane group.Both appliances produced lingual inclination andretrusion of the maxillary incisors compared with thecontrols. Horizontally, the first molars showed distalmovement with HG biteplane treatment. In addition,there was significant extrusion of the mandibularmolars and mesial movement in the treated groups.

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Treatment effects of headgear biteplane and bionator appliances

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