Craniofacial growth in untreated skeletal class i subjects with low, average, and high mp sn angles-...

ORIGINAL ARTICLE

Craniofacial growth in untreated skeletal ClassI subjects with low, average, and high MP-SNangles: A longitudinal studyChun-Hsi Chung, DMD, MS,a and Vincent D. Mongiovi, DMDb

Philadelphia, Pa, and Washington Township, NJ

Sixty-eight (36 male and 32 female) untreated skeletal Class I subjects with low (� 27°), average (�27°-�37°),and high (� 37°) mandibular plane (MP-SN) angles were selected from the Bolton-Brush and BurlingtonGrowth Studies. Cephalograms of each subject at ages 9 and 18 were traced, and 28 parameters weremeasured. The difference in each parameter from ages 9 to 18 was calculated, and comparisons were madebetween the groups with low, average, and high angles. Results showed that, for boys and girls at age 9, thelow-angle groups exhibited significantly larger SNA angle, SNB angle, facial taper, PFH, PFH:AFH, andramus height, and the high-angle groups showed significantly larger ANS-Me and gonial angle. From ages9 to 18, all the male and female low-, average-, and high-angle groups showed an increase in SNA and SNBangles, and PFH:AFH, and a decrease in ANB angle, convexity (more flattened face), MP-SN angle, andgonial angle (mandibular forward rotation). The dental measurements showed few changes with growth in allgroups. In terms of skeletal measurements from ages 9 to 18, similar growth changes were found betweenthe sexes in most angular measurements, but males had larger values in linear measurements than females.(Am J Orthod Dentofacial Orthop 2003;124:670-8)

It is well known that sagittal facial growth iscomposed of vertical (downward) and horizontal(forward) growth.1-4 As Schudy1,2 and Isaacson et

al4 indicated, if vertical growth at the facial sutures andthe alveolar processes of the molars is greater thanvertical growth at the condyles, the mandible wouldrotate backward (bite opening), resulting in greateranterior facial height. Conversely, if vertical growth atthe condyles is greater than the sum of the verticalgrowth components at the facial sutures and the molarareas, the mandible would rotate forward (bite closing).Thus, the final vector of growth at the chin is a result ofthe competition between vertical and horizontalgrowth.

In predicting facial growth of a young patient, theclinician often considers the inclination of the mandib-ular plane (MP). According to Schudy1,2 and Isaacsonet al,4 the degree of inclination of the MP to the cranialbase (SN) has an effect on the degree of mandibular

rotation with growth. The larger the MP-SN angle, themore the mandible tends to become steeper, and themore the chin moves backward. The smaller the angle,the greater the tendency of the mandible to becomeflatter and the chin to grow forward. Bjork andSkieller,5 in their implant study, demonstrated theforward and backward rotation of the mandible and alsothe remodeling of the MP; this masks some mandibularrotation during growth. Interestingly, they found thatonly 2 of 21 subjects had backward mandibular rota-tion. Most subjects (19 of 21) showed forward rotation,including some with a high MP-SN angle.

In his longitudinal studies, Karlsen6,7 examined thecraniofacial growth changes in low (�26°) and high(�35°) MP-SN angle subjects from ages 6 to 15. Hefound that forward mandibular rotation took place in allsubjects. No cases of backward total rotation werenoted, although 7 children had MP-SN values of 40° ormore. He reported that the MP-SN angle decreased inboth the high- and low-angle groups, and concludedthat true posterior rotation occurred more rarely thanhad been previously assumed. Also, a steep MP isprobably an inherent characteristic in most subjects, notthe result of backward rotation. However, he did notseparate his subjects according to the sagittal skeletalpatterns (Class I, II, or III). This information is impor-tant because it is obvious that the facial growth patternsof skeletal Class II and III subjects are different.

From the Department of Orthodontics, School of Dental Medicine, Universityof Pennsylvania, Philadelphia.aAssociate professor.bFormer resident; private practice, Chadds Ford, Pa, and Washington Town-ship, NJ.Reprint requests to: Dr Chun-Hsi Chung, Department of Orthodontics, Schoolof Dental Medicine, University of Pennsylvania, 4001 Spruce St, Philadelphia,PA 19104-6003; e-mail, [email protected], September 2002; revised and accepted, February 2003.Copyright © 2003 by the American Association of Orthodontists.0889-5406/2003/$30.00 � 0doi:10.1016/j.ajodo.2003.02.004

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It has been shown that 60% to 70% of children haveClass I malocclusions.8,9 The dentofacial growth ofchildren with Class I malocclusions has always beenintriguing for many investigators. Many studies havebeen made, but very few took into account the effect ofa high, average, or low MP-SN angle on facial growth.Moreover, most reported studies have focused on thefacial growth of dental Class I subjects instead ofskeletal Class I. For example, Kerr10 examined thelongitudinal dentofacial growth of children from 5 to 15years from the Belfast Growth Study. He divided thesubjects into different groups by sex and dental rela-tionship (Angle classifications). He found that thegonial and MP-SN angles decreased in all groups(Classes I, II, and III) between 5 and 15 years. Also, theSNA angle did not change significantly, and the SNBangle increased slightly except for the Class II Division2 female group. He did not divide the subjects accord-ing to their MP-SN angles (high, average, or low).Sinclair and Little11 studied longitudinal craniofacialgrowth of untreated Class I male and female subjectswith good occlusions. They reported that from mixeddentition (6.18 to 10.30 years) to adult dentition (17.98to 21.83 years), both the SNA and SNB angles in-creased and the ANB angle decreased and a forward(bite closing) rotation of the mandible occurred. How-ever, the mean MP-SN angles were 36.68° � 0.77° intheir male mixed dentition group and 34.93° � 0.86° infemale group; no higher or lower MP-SN angle subjectswere included in their study. Bishara and Jakobsen12

examined longitudinal growth of 20 male and 15female untreated subjects with dental Class I relation-ship from ages 5 to 25. The subjects of each sex werecategorized according to 3 facial types: relative long,average, and relative short faces. They divided thesubjects into different groups using the ratio of poste-rior to anterior face heights (S-Go/N-Me) and theFrankfort horizontal-MP angle (FH-MP) of the adultcephalograms. They reported that most subjects (77%)had the same facial type at 5 years and 25.5 years ofage; there was a strong tendency to maintain theoriginal facial type with age. Also, the subjects in eachfacial type had relatively large variations in the size andrelationships of the various dentofacial structures. Theysuggested that longitudinal analysis of the data gavemore consistent and meaningful results than cross-sectional comparisons when facial growth trends areevaluated.

More recently, Chung and Wong13 incorporatedboth the sagittal skeletal relationship and the degree ofMP-SN in their growth study. They examined thecraniofacial growth of skeletal Class II (ANB�4°)untreated male and female subjects with low (�27°),

average (27°-36°), and high (�36°) MP-SN anglesfrom ages 9 to 18. They found that the SNA and SNBangles increased, and the ANB angle decreased in allgroups with age. Also, all groups showed a mandibularforward rotation with decreased gonial and MP-SNangles. They also reported that the skeletal growthchanges in angular measurements were similar betweenthe male and female groups. Yet linear measurementsshowed significant sex differences, especially in thehigh-angle group. Craniofacial growth studies of skel-etal Class I and Class III subjects with high, average, orlow MP-SN angles are not available in the literature.

The purpose of this study was to investigate thelongitudinal craniofacial growth changes in untreatedskeletal Class I subjects with low, average, and highMP-SN angles.

MATERIAL AND METHODS

The sample consisted of 68 subjects—32 (14 malesand 18 females) from the Bolton-Brush Growth Studyat Case Western Reserve University in Cleveland,Ohio, and 36 (22 males and 14 females) from theBurlington Growth Center at the University of Torontoin Canada. The subjects were selected according to thefollowing criteria: (1) lateral cephalograms available atabout ages 9 and 18, (2) skeletal Class I (0° �ANB�4° as determined from lateral cephalogram at age 9),(3) skeletal age determined by hand-wrist radiographscompared with standards by Greulich and Pyle14 (thosewhose skeletal ages were greater than their chronolog-ical ages by � 1 year were excluded), and (4) goodhealth with no orthodontic treatment.

The sample was divided into male (n � 36) andfemale (n � 32) groups. For each subject, 2 lateralcephalograms were traced by hand on acetate paper byan examiner (V.D.M.). For the male group, the meanages were 8.64 years for the first tracing (T1) and 17.36years for the second tracing (T2) (Table I). For thefemale group, the mean ages were 8.66 years at T1 and17.53 years at T2.

The sample was further divided into groups basedon the MP-SN angle at T1: (1) low angle (MP-SN �27°), (2) average angle (MP-SN greater than 27° and

Table I. Age of subjects

n Mean age (y) Range (y)

MaleFirst tracing (T1) 36 8.64 8-10Second tracing (T2) 36 17.36 16-18

FemaleFirst tracing (T1) 32 8.66 8-9Second tracing (T2) 32 17.53 16-18

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less than 37°), and (3) high angle (MP-SN � 37°). TheMP was drawn from menton (Me) to the inferior borderof the angular area of the mandible.1,2 These MP-SNvalues represented about 1 SD from the mean MP-SNangle of children ages 8 to 11 reported by Riedel.15 Forboys, the mean MP-SN angles at age 9 were 25.27° forthe low-angle group, 32.71° for the average-anglegroup, and 40.68° for the high-angle group (Table II).For girls, the mean MP-SN angles at age 9 were 26.08°for the low-angle group, 33.13° for the average-anglegroup, and 40.75° for the high-angle group.

The definitions of the landmarks used in this studycorrespond to those of Riolo et al.16 All lateral cepha-lometric tracings were digitized on a digitizer (Numon-ics Corp, Montgomeryville, Pa) by an examiner(V.D.M.) on a computer with Quick Ceph OrthodonticProcessing software, Version 2.6 (Quick Ceph Sys-tems, San Diego, Calif). The computer software wastested and confirmed for accuracy and reliability bycomparing values to the examiner’s hand measure-ments.

Because subjects from 2 growth studies were ex-amined, all linear measurements had to be convertedbecause of different enlargement factors for eachcephalostat. At the Burlington Growth Center, alllateral cephalograms, regardless of the patient’s age,were magnified by 9.84%.17 However, in the Bolton-Brush Growth Study, magnification was regulated ac-cording to the age of the patient (age 8, 5.5%; age 9-10,5.6%; age 6-18, 5.9%).18 All linear measurements fromboth studies were converted by eliminating the magni-fication factor to allow the data to be analyzed.

Cross-sectional and longitudinal data were col-lected and analyzed for each group. Statistical analysisof the cephalometric measurements included descrip-tive statistics at a 95% confidence interval and singlefactor analysis of variance (AVOVA) calculated foreach group. Paired t tests were conducted, and statisti-cal significance of compared measurements was de-fined at P � .05.

The following measurements were made and ana-

lyzed for each of the 136 lateral cephalograms (Fig).Sagittal: SNA angle (in degrees), SNB angle (in de-grees), ANB angle (in degrees), convexity (N-A-Pog,in degrees), Pog-NB (effective chin, in millimeters),ACB (anterior cranial base, N-S, in millimeters), man-dibular body (Go intersection-Me, in millimeters);vertical: MP-SN angle (in degrees), PP-SN (palatalplane ANS-PNS to SN, in degrees), facial taper (N-Gn-Go, in degrees), AFH (anterior facial height, N-Me, inmillimeters), PFH (posterior facial height, S-Go inter-section, in millimeters), PFH:AFH, ANS-Me (lowerfacial height, in millimeters), ANS-Me/N-Me (LFH:AFH), saddle angle (N-S-Ar, in degrees), articularangle (S-Ar-Go intersection, in degrees), gonial angle(Ar-Go intersection to MP, in degrees), ramus height(Ar-Go, in millimeters), PCB (posterior cranial base,

Table II. Group description at T1

Groups n Mean ANB Range Mean MP-SN Range

MaleLow-angle 13 1.94° 0-3.9° 25.27° 22-27°Average-angle 12 2.93° 0.4-3.7° 32.71° 28-35.5°High-angle 11 3.02° 1.1-4° 40.68° 37.5-45°

FemaleLow-angle 6 2.62° 1.3-3.5° 26.08° 24-27°Average-angle 12 2.94° 2.3-4° 33.13° 29-36°High-angle 14 2.99° 1.6-4° 40.75° 37.5-51°

Fig. Cephalometric landmarks and planes.

American Journal of Orthodontics and Dentofacial OrthopedicsDecember 2003

672 Chung and Mongiovi

S-Ar, in millimeters), Y axis (FH to S-Gn, in degrees);dental: 1/ to NA (maxillary incisor to NA, in millime-ters), /1 to NB (mandibular incisor to NB, in millime-ters), interincisal angle (in degrees), overbite (in milli-meters), overjet (in millimeters), 1/ to NA (maxillaryincisor to NA, in degrees), /1 to NB (mandibular incisorto NB, in degrees).

In addition, 15 randomly chosen lateral cephalo-grams were traced twice by the same examiner(V.D.M.) and measured separately on the Quick Cephcomputer software to determine whether an intraexam-iner error resulted from landmark selection, tracing, andmeasurement error. The same measurements weremade as in the subjects to be studied. Repeated mea-sures ANOVA and paired Student t tests were carriedout for all linear and angular measurements to deter-mine whether they were within acceptable limits. Thesignificance of differences was predetermined at P �.05.

The mean and SD were calculated for each cepha-lometic variable (measurement), and the differences ofeach variable between the groups were tested with theStudent 2-tailed t test. The significance of differenceswas predetermined at P � .05.

RESULTS

The assessment of intraexaminer error showed nostatistically significant difference between angular orlinear measurements (P � 0.84). In addition, the meandifferences in replicate measures of the same cephalo-grams showed a mean change of 0.3° between repeatedangular measurements and a 0.3 mm mean changebetween linear measurements.

For the boys, the mean and SD of each measure-ment at age 9 of the low-, average-, and high-anglegroups (cross-sectional data), and the statistical signif-icance (P value) between the groups are given in TableIII. The growth changes (longitudinal data) of the

Table III. Cross-sectional data of boys at age 9 (T1)

Group I (low)n � 13

Group II (average)n � 12

Group III (high)n � 11 Significance (P value)

Mean SD Mean SD Mean SD I vs II II vs III I vs III

SagittalSNA (°) 80.90 2.75 80.67 2.39 78.46 2.68 .82 .05 .04SNB (°) 78.96 2.29 77.74 2.54 75.44 2.45 .22 .04 .00ANB (°) 1.94 1.19 2.93 0.96 3.03 0.98 .03 .80 .02Convexity (°) 0.53 1.67 1.83 1.15 2.20 1.43 .03 .50 .02Pog-NB (mm) 2.01 1.02 1.64 1.16 1.36 1.24 .42 .58 .18ACB (mm) 63.43 2.00 64.42 2.43 64.22 3.24 .28 .87 .49Mand. body (mm) 60.95 4.37 61.14 3.63 60.64 2.03 .90 .68 .82

VerticalMP-SN (°) 25.27 1.75 32.71 2.68 40.68 2.40 .00 .00 .00PP-SN (°) 7.08 1.62 7.11 1.77 8.16 1.88 .96 .18 .15Facial taper (°) 72.95 2.88 68.60 2.57 63.47 1.48 .00 .00 .00AFH (mm) 97.65 5.80 101.99 5.36 103.13 3.21 .06 .54 .01PFH (mm) 68.98 5.81 66.97 4.43 60.72 2.86 .34 .00 .00PFH:AFH (%) 70.58 3.07 65.70 2.99 58.88 2.19 .00 .00 .00ANS-Me (mm) 54.06 3.64 57.77 3.02 58.54 2.90 .01 .54 .00ANS-Me/N-Me (%) 55.37 1.89 56.67 1.54 56.76 1.84 .07 .89 .08Saddle angle (°) 121.74 3.66 121.68 3.32 124.25 3.77 .96 .10 .11Articular angle (°) 143.86 6.52 143.54 4.34 139.83 7.06 .89 .15 .16Gonial angle (°) 121.16 5.38 127.43 3.35 136.16 4.95 .00 .00 .00Ramus height (mm) 40.65 3.14 39.62 4.17 35.74 3.49 .50 .02 .00PCB (mm) 31.94 3.48 30.86 2.72 28.97 1.95 .39 .07 .02Y-axis (°) 57.48 4.55 58.66 3.49 61.54 2.23 .47 .03 .01

Dental1/ to NA (mm) 4.53 2.37 4.44 2.04 4.72 1.58 .92 .72 .82/1 to NB (mm) 3.50 1.50 4.81 1.36 4.91 1.65 .03 .87 .04Interincisal angle (°) 127.67 11.28 127.94 8.57 125.98 8.17 .95 .58 .68Overbite (mm) 1.77 2.04 1.70 1.38 1.99 1.36 .92 .62 .76Overjet (mm) 3.36 1.09 3.36 0.90 3.87 0.91 1.00 .19 .221/ to NA (°) 25.65 9.02 24.66 5.95 25.60 4.53 .75 .67 .99/1 to NB (°) 22.67 6.79 25.33 3.99 25.37 4.65 .24 .98 .26



measurements in the low-, average- and high-anglegroups from ages 9 to 18 are shown in Table IV.

For the girls, Table V shows the mean and SD ofeach measurement at age 9 of the low-, average-, andhigh-angle groups (cross-sectional data), and the statis-tical significance (P value) between the groups. TableVI gives the longitudinal growth changes of the mea-surements in the low-, average-, and high-angle groupsfrom ages 9 to 18.

The statistical significance data (P value) of eachmeasurement between the low-angle male and femalegroups, the average-angle male and female groups, andthe high-angle male and female groups are listed inTable VII. Similar patterns of skeletal growth werefound in most angular measurements of boys and girls,but a significant sex difference was shown in somelinear measurements. Between male and female groups,no significant differences in dental angular and linearchanges were found from ages 9 to 18.

DISCUSSION

The cross-sectional data of this study showed that,at age 9, high-angle male and female groups hadsmaller SNA and SNB values than did the low- andaverage-angle groups (P � .05). Previous cross-sec-tional studies by Isaacson et al4 and Bishara andAugspurger19 had similar results (they did not dividetheir subjects into skeletal Class I, II, or III). A recentreport by Chung and Wong,13 who studied the cranio-facial growth in untreated skeletal Class II subjects withlow, average, and high MP-SN angles, also showedsimilar findings. Bishara and Augspurger,19 in theirstudy of men, found that the ACB of high-anglesubjects was significantly smaller than the average- andthe low-angle subjects. In the present study, there wasno difference between male groups with regard to thelength of ACB at age 9. However, in the girls, thehigh-angle group had a significantly smaller ACB than

Table IV. Male longitudinal growth changes from age 9 (T1) to age 18 (T2)




Mean change SD Mean change SD Mean change SD I vs II II vs III I vs III

SagittalSNA (°) 2.32 1.38 2.73 3.71 0.98 3.56 .73 .26 .26SNB (°) 2.79 1.17 4.16 3.27 2.89 2.98 .19 .34 .92ANB (°) �0.47 1.05 �1.43 1.37 �1.91 1.38 .06 .42 .01Convexity (°) �1.29 1.21 �2.08 1.66 �2.51 1.69 .19 .55 .06Pog-NB (mm) 2.07 0.78 1.69 1.09 1.37 1.22 .34 .52 .13ACB (mm) 6.30 1.34 5.85 2.51 6.38 2.91 .59 .65 .93Mand. body (mm) 14.17 1.93 12.32 2.14 13.36 2.37 .03 .28 .38

VerticalMP-SN (°) �2.42 2.36 �3.92 2.93 �3.18 2.19 .18 .50 .42PP-SN (°) �0.18 2.44 �1.38 2.66 �1.07 3.21 .25 .80 .46Facial taper (°) 0.17 3.06 �0.27 3.57 �0.24 2.26 .75 .98 .71AFH (mm) 17.58 4.21 15.90 3.40 16.84 4.24 .28 .57 .67PFH (mm) 17.53 3.51 16.09 3.63 13.41 3.07 .33 .07 .01PFH:AFH (%) 4.52 3.24 5.02 3.93 2.93 1.68 .73 .11 .14ANS-Me (mm) 9.23 2.83 9.46 1.63 9.84 2.18 .81 .64 .56ANS-Me/N-Me (%) �0.46 1.20 0.39 0.95 0.18 1.56 .06 .71 .28Saddle angle (°) 0.91 2.59 �1.58 3.20 0.08 4.11 .05 .30 .57Articular angle (°) 0.47 5.39 0.95 3.61 2.23 6.01 .79 .55 .46Gonial angle (°) �5.25 4.20 �4.05 5.11 �5.55 4.00 .53 .44 .86Ramus height (mm) 11.74 3.40 10.41 4.04 8.57 3.20 .39 .24 .03PCB (mm) 6.45 2.71 6.29 1.64 5.20 1.86 .86 .15 .19Y-axis (°) �0.22 3.68 0.55 2.53 �1.95 2.30 .54 .02 .18

Dental1/ to NA (mm) 0.62 1.37 2.10 1.73 2.73 3.00 .03 .55 .05/1 to NB (mm) 0.25 0.96 0.67 2.12 1.26 1.62 .54 .46 .09Interincisal angle (°) 1.62 6.96 �1.20 7.86 �3.35 10.31 .36 .58 .19Overbite (mm) 1.01 2.62 0.69 1.33 0.03 0.50 .70 .13 .21Overjet (mm) 0.19 1.62 �0.07 0.98 �0.85 1.09 .62 .09 .071/ to NA (°) 1.18 8.58 1.52 3.44 3.55 7.36 .90 .42 .47/1 to NB (°) �0.23 5.36 0.35 6.56 1.72 4.63 .81 .57 .35



the low-angle group at age 9. In terms of PCB, the malehigh-angle group showed a significantly smaller valuethan the male low-angle group at age 9.

Our cross-sectional data also showed that, at age 9,for both boys and girls, the facial taper, PFH:AFH, andramus height were significantly greater in the low-anglegroup than the high-angle group (P � .05), and theAFH, LFH, and the gonial angle were significantlygreater in the high-angle group than the low-anglegroup (P � .05). Isaacson et al4 and Bishara andAugspurger19 also reported greater AFH and LFH inthe high MP-SN angle subjects than in the low MP-SNangle subjects. We also found that there was nosignificant difference in mandibular body length be-tween groups of the same sex. Thus, we suggest that, inthe mandible, it is not the body that indicates diver-gency, but the ramus height.

From ages 9 to 18, the mean SNA and SNB anglesof all groups were not constant, but instead theyincreased. Similar findings were reported by Sinclair

and Little.11 Differently, Bishara and Jakobsen12 foundthat from ages 5 to 25, the mean SNA angle of thefemale subjects with average facial height decreasedslightly (�0.8°). Our data showed that as the SNA andSNB angles increased, so did the ACB (SN). Therefore,nasion (N) must have grown anteriorly less than PointA or Point B. The commonly used Steiner20 normalvalues, which do not change according to age, might, inessence, not apply to younger subjects. Riolo et al16

reported the mean of each cephalometric measurementon 47 boys and 36 girls yearly from ages 6 to 16. Theyalso found that the mean was not constant; it changedwith age. However, they did not separate their sampleaccording to skeletal Class I, II, or III. Thus, normalcephalometric values for skeletal Class I subjects atdifferent ages are needed; this notion deserves furtherattention and future research. Interestingly, our datashowed that the amount of SNB increase was greaterthan the SNA increase with age in all groups. As aresult, the ANB angle became smaller. Of the 68

Table V. Cross-sectional data of girls at age 9 (T1)




Mean SD Mean SD Mean SD I vs II II vs III I vs III

SagittalSNA (°) 81.70 1.85 81.09 2.13 78.52 2.76 .54 .01 .01SNB (°) 79.08 1.77 78.14 1.89 75.53 2.80 .32 .01 .00ANB (°) 2.62 0.86 2.94 0.50 2.99 0.92 .42 .86 .40Convexity (°) 1.63 0.94 2.31 1.21 1.94 1.23 .22 .45 .55Pog-NB (mm) 1.49 0.62 0.83 1.19 1.45 1.15 .14 .19 .91ACB (mm) 64.69 3.14 61.87 2.32 60.94 2.32 .09 .32 .03Mand. body (mm) 58.91 2.95 59.15 4.74 60.23 4.30 .90 .55 .44

VerticalMP-SN (°) 26.08 1.11 33.13 2.59 40.75 4.27 .00 .00 .00PP-SN (°) 9.00 1.94 8.82 2.56 10.53 3.79 .87 .18 .25Facial taper (°) 72.83 2.29 69.02 2.67 63.78 2.89 .01 .00 .00AFH (mm) 96.23 5.62 97.99 4.52 101.26 5.50 .52 .11 .10PFH (mm) 67.58 4.78 64.37 3.48 60.70 4.67 .18 .03 .02PFH:AFH (%) 70.20 1.56 65.72 3.36 60.00 3.98 .00 .00 .00ANS-Me (mm) 52.20 4.40 54.94 4.21 56.84 3.28 .24 .22 .05ANS-Me/N-Me (%) 54.22 2.36 53.50 8.17 56.14 1.64 .78 .29 .11Saddle angle (°) 119.57 2.62 120.18 3.78 123.12 4.50 .69 .08 .04Articular angle (°) 143.20 3.26 148.90 5.33 144.71 5.19 .01 .05 .44Gonial angle (°) 124.28 3.11 123.39 5.57 131.91 4.02 .67 .00 .00Ramus height (mm) 40.85 3.86 37.47 3.37 35.43 3.06 .10 .12 .02PCB (mm) 30.28 1.81 29.39 1.57 28.32 3.01 .33 .26 .09Y-axis (°) 56.53 3.02 58.15 4.50 59.19 3.84 .38 .54 .12

Dental1/ to NA (mm) 3.66 2.33 4.38 1.63 4.67 1.73 .52 .66 .37/1 to NB (mm) 3.87 2.38 5.27 1.65 4.83 1.50 .24 .49 .39Interincisal angle (°) 128.82 10.90 122.47 7.63 128.38 6.95 .24 .05 .93Overbite (mm) 1.92 1.16 1.56 1.43 0.93 1.76 .58 .32 .16Overjet (mm) 3.49 0.69 2.89 1.03 3.59 1.40 .17 .16 .831/ to NA (°) 23.98 4.91 24.60 5.30 24.14 4.87 .81 .82 .95/1 to NB (°) 24.30 7.98 29.83 5.32 24.46 3.39 .17 .01 .96



subjects in our study, only 8 (11.7%) had an increase inANB angle from ages 9 to 18. Of the 8 subjects, therewere 5 with low angles, 2 with average angles, and 1with a high angle with mean increases of 1.0°, 1.3°, and1.1°, respectively, with no gender preference. Lande,21

Riolo et al,16 Sinclair and Little,11 Bishara and Jakob-sen,12 and Chung and Wong13 also reported a decreasein ANB angle with age in their subjects. Consequently,new norms at different ages need to be developed forthe ANB angle as well, because it can be expected to besomewhat larger for a 9-year-old than for an adultwhose norm is 2 � 2° according to Steiner.20

Another interesting finding of the present study wasthat the mean MP-SN angle decreased from ages 9 to18 in all groups. Of the 68 subjects, we observed only7 (10.3%) who had an increase in MP-SN angle duringthe growth period. Of the 7 subjects, there were 1 witha low angle, 2 with average angles, and 4 with highangles, with mean increases of 1.0°, 1.0°, and 2.0°,

respectively, with no sex preference. Our findingsagreed with those of Karlsen,6 who found that all 15high-angle untreated males in his study had forwardrotation, and Riolo et al,16 who reported an MP-SNangle decrease from ages 6 to 16 in their male andfemale subjects. In Bjork and Skieller’s5 growth study,19 of 21 (90.5%) subjects had decreased MP-SN anglesand only 2 (9.5%) had increased MP-SN angles from 3years prepuberty to 3 years postpuberty. Chung andWong13 reported that, in their skeletal Class II subjects,79 of 85 (93%) had decreased MP-SN angles, and only6 (7%) had increased MP-SN angles from ages 9 to 18.Therefore, our data suggest that, in the treatment ofskeletal Class I growing patients, the MP-SN angletends to decrease with age as long as orthodonticmechanics do not extrude the posterior teeth.

Using the PHF:AFH ratio as an indicator of man-dibular rotation as suggested by Bjork,22 we found thatPFH:AFH increased in all groups; this demonstrated a

Table VI. Female longitudinal growth changes from age 9 (T1) to age 18 (T2)




Mean change SD Mean change SD Mean change SD I vs II II vs III I vs III

SagittalSNA (°) 1.73 2.31 1.48 1.54 0.91 2.04 .81 .43 .47SNB (°) 1.77 1.14 2.19 1.64 2.02 2.04 .53 .82 .73ANB (°) �0.05 1.58 �0.71 1.06 �1.11 1.27 .39 .39 .19Convexity (°) �0.67 1.85 �1.24 1.32 �1.16 1.41 .52 .89 .57Pog-NB (mm) 1.52 0.85 1.27 1.32 0.55 0.82 .64 .12 .04ACB (mm) 4.71 1.40 4.02 0.71 3.66 1.33 .30 .39 .15Mand. body (mm) 8.51 2.63 9.78 2.85 7.65 4.34 .37 .15 .60

VerticalMP-SN (°) �0.83 1.29 �2.75 2.85 �1.39 2.75 .07 .23 .54PP-SN (°) �0.53 2.32 �0.75 2.95 �0.60 1.73 .87 .88 .95Facial taper (°) �0.43 1.09 0.36 1.57 �0.92 1.61 .23 .05 .44AFH (mm) 12.62 3.04 11.89 1.53 11.99 3.43 .60 .92 .69PFH (mm) 11.81 2.87 11.72 2.73 9.20 2.40 .95 .02 .08PFH:AFH (%) 2.68 1.09 3.57 2.50 1.76 1.73 .31 .05 .17ANS-Me (mm) 6.92 2.73 6.78 1.65 7.32 2.53 .91 .52 .77ANS-Me/N-Me (%) �0.33 1.54 2.59 8.66 0.49 1.11 .28 .42 .27Saddle angle (°) 2.17 3.90 2.64 3.56 �0.38 3.82 .81 .05 .21Articular angle (°) �0.85 4.91 �3.48 4.37 0.75 3.79 .29 .02 .50Gonial angle (°) �3.37 3.18 �2.55 3.59 �1.55 2.30 .63 .42 .24Ramus height (mm) 9.41 2.90 8.68 2.86 6.08 2.78 .62 .03 .04PCB (mm) 3.17 1.83 3.93 2.00 3.43 2.26 .44 .56 .79Y-axis (°) 2.02 1.98 0.69 3.18 1.52 3.42 .30 .53 .69

Dental1/ to NA (mm) 0.58 1.87 1.52 1.67 2.00 1.84 .32 .50 .15/1 to NB (mm) 0.61 1.46 0.47 1.42 1.09 1.12 .85 .23 .49Interincisal angle (°) �0.50 9.24 1.16 5.78 �4.90 6.98 .70 .02 .33Overbite (mm) 0.20 0.84 0.59 1.54 0.35 1.77 .49 .71 .80Overjet (mm) �0.09 0.88 0.45 0.89 �0.23 1.33 .25 .14 .791/ to NA (°) �0.67 4.95 1.52 5.06 3.31 3.76 .40 .32 .12/1 to NB (°) 1.48 6.95 �1.83 2.55 2.73 4.25 .30 .00 .70



forward mandibular rotation. Other indicators sug-gested by Sinclair and Little11 were the MP-SN andgonial angles. As stated above, in our study, the meanMP-SN angle and gonial angle decreased in all groups;this suggested a forward mandibular rotation. Sinclairand Little11 also reported a forward (bite closing)rotation of the mandible with growth in their Class Inormal occlusion subjects. However, they did notseparate their subjects with respect to skeletal verticalpattern (high or low mandibular plane angle).

In agreement with Lande,21 Riolo et al,16 Bjork,23

Bishara and Jakobsen,12 and Chung and Wong,13 wealso recognized a decrease in convexity with growth inall groups. Interestingly, the Pog-NB (effective chin)increased in all groups with age; this might have beendue to the mandibular forward rotation or forwardgrowth of the chin. This might help to explain why theface flattens with age. There was no difference ob-

served between groups in ACB (SN) for either sex froma longitudinal outlook. However, between sexes, therewas a difference in magnitude. From ages 9 to 18,males on average had an incremental growth change ofabout 0.68 mm per year in ACB, and the females had anincrease of 0.45 mm per year. These values werecalculated without considering the magnification factorand the growth spurt.

The dental measurements in this study showed fewchanges from ages 9 to 18 in all groups. For overbite,there was a net increase in all groups, but the value wasvery small (� 1 mm). Overjet was also observed not toworsen with age. Thus, it is suggested that overbite andoverjet remain relatively stable with growth regardlessof the person’s vertical pattern. Sinclair and Little11

showed similar results and reported that incisor angu-lation appeared to be relatively stable.

Our results showed that there were some significantgrowth differences between the low-, average-, andhigh-angle groups from ages 9 to 18. For males, thisdifference resulted in a significantly greater similaritybetween the groups in ANB angle (low and average,low and high), convexity (low and average, low andhigh), AFH (low and high), and Y-axis (average andhigh, low and high), and a significantly greater differ-ence in Pog-NB (low and high), ANS-Me/N-Me (lowand average, low and high), saddle angle (average andhigh), PCB (average and high), 1/ to NA in mm (lowand high), and /1 to NB in degrees (low and high). Forfemales, a significantly greater similarity between thegroups was seen in facial taper (low and average),saddle angle (low and high), articular angle (low andaverage, average and high), interincisal angle (averageand high), and /1 to NB in degrees (average and high),but a significantly greater difference was noted inPog-NB (low and high), ANS-Me/N-Me (low andhigh), ramus height (average and high), 1/ to NA in mm(low and average, low and high), and 1/ to NA indegrees (average and high). In general, the facial typeof each group was maintained with age; this agreedwith the previous report by Bishara and Jakobsen.12

In this study, similar growth changes were foundbetween male and female groups in most skeletalangular measurements. However, marked sex differ-ences were found in most skeletal linear measurements.Males showed larger dimensions than females. Similarfindings were reported by Sinclair and Little11 andChung and Wong.13

CONCLUSIONS

The longitudinal growth changes from ages 9 to 18of 68 skeletal Class I subjects with low, average, and

Table VII. Comparison of longitudinal changes fromage 9 to age 18 between groups

Significance (P value)

Low male vslow female

Average malevs average

femaleHigh male vshigh female

SagittalSNA (°) .58 .30 .96SNB (°) .10 .08 .42ANB (°) .57 .16 .15Convexity (°) .47 .18 .05Pog-NB (mm) .21 .41 .07ACB (mm) .04 .03 .01Mand. body (mm) .00 .02 .00

VerticalMP-SN (°) .08 .33 .08PP-SN (°) .77 .59 .67Facial taper (°) .54 .59 .41AFH (mm) .01 .00 .01PFH (mm) .00 .00 .00PFH:AFH (%) .09 .29 .10ANS-Me (mm) .12 .00 .01ANS-Me/N-Me (%) .86 .40 .58Saddle angle (°) .49 .01 .78Articular angle (°) .61 .01 .49Gonial angle (°) .30 .42 .01Ramus height (mm) .15 .24 .05PCB (mm) .01 .00 .04Y-axis (°) .10 .91 .01

Dental1/ to NA (mm) .96 .41 .49/1 to NB (mm) .60 .79 .78Interincisal angle (°) .63 .41 .68Overbite (mm) .33 .87 .53Overjet (mm) .62 .19 .211/ to NA (°) .56 1.00 .92/1 to NB (°) .61 .30 .58



high MP-SN angles were examined. Our conclusionsare as follows:

1. At age 9, for boys, significant differences werefound between the low- and the high-angle groups inSNA, SNB, ANB angles, convexity, facial taper,AFH, PFH, PFH:AFH, ANS-Me, gonial angle, ra-mus height, PCB, Y-axis, and mandibular incisor toNB (mm).

2. At age 9, for girls, significant differences werefound between the low- and the high-angle groups inSNA and SNB angles, ACB, facial taper, PFH,PFH:AFH, ANS-Me, saddle angle, gonial angle, andramus height.

3. From ages 9 to 18, the SNA and SNB anglesincreased in all groups, and the ANB angle de-creased in all groups. The male high-angle groupshowed a greater decrease in ANB angle than didthe male low-angle group (P � .05). Among thefemales, there was no difference between groups.

4. From ages 9 to 18, a mandibular forward rotation(bite closing) was noted in all groups with a de-crease in MP-SN and gonial angles and an increaseof PFH:AFH ratio.

5. From ages 9 to 18, few changes in the dentalmeasurements were found in all groups.

6. Similar growth changes were found between maleand female groups in most angular measurements,but marked sex differences were found in mostlinear measurements. Males had larger overall val-ues in these linear measurements than females.

We thank Mrs Elizabeth Mongiovi and Drs WallaceWong, Solomon Katz, Jamie Ahl, and Stephen Tjoa fortheir help.

REFERENCES

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