Individual growth in Class III malocclusions and its relationship to the chin cap effects

CONTINUING EDUCATION ARTICLE

Individual growth in Class III malocclusions and itsrelationship to the chin cap effects

Hiroyuki Ishikawa, DDS, PhD,a Shinji Nakamura, DDS, PhD,b Choongjae Kim, DDS, PhD,c

Hiroshi Iwasaki, DDS, PhD,d Yoshiaki Satoh, DDS, PhD,d and Shigemitsu Yoshida, DDS, PhDe

Sapporo, Japan

Individual growth characteristics of the maxilla and the mandible in Class III malocclusions wereinvestigated in terms of growth amount, growth direction, and timing of growth; chin cap effectswere considered in the context of growth characteristics of the jaws. Longitudinal cephalograms ofsix untreated Japanese Class III subjects were used for the analysis of jaw growth from 8 to 14years of age. The facial patterns were classified into the five groups with different effects of therapyby discriminant functions derived from our previous chin cap study. The results obtained were asfollows: (1) Among the six subjects, inhibition of maxillary forward growth was found in foursubjects at ages before the maximum pubertal growth in body height occurred, resulting fromocclusal interference of anterior cross bite. The growth potential of the jaws appeared geneticallynormal, and the facial patterns were classified into groups in which chin caps have been found tobe effective to some extent. (2) A subject with growth characteristics of strong mandibulardownward growth was classified in a group showing backward growth of the mandible by chincaps. (3) One of the remaining sample showing the strongest mandibular forward growth wasclassified in a group where chin caps are not effective. (4) It was concluded that effects of chin captherapy are closely related to growth characteristics of the mandible in Class III treatment. (Am JOrthod Dentofacial Orthop 1998;114:337-46.)

Improvement of the horizontal jaw rela-tionship is of great importance in the treatment ofskeletal Class III malocclusions during growth.Early orthopedic treatment has been recommendedfor the last 20 years,1-5 but the results vary muchamong patients. In a recent article Thompson6

reported that uniquely individual timing, direction,rate, and increments of growth cause much of thevariability in treatment responses.

In a previous investigation on the effects of chincap therapy,7 growth changes of the jaws in patientstreated with chin caps were divided into five groups,and in two groups chin caps were not consideredeffective despite long-term treatment. It also be-came evident that the growth changes influenced bychin caps were closely related to facial morphologiccharacteristics at the start of treatment, and conse-quently discriminant functions were introduced to

predict chin cap effects based on pretreatment facialpatterns. These results suggest that the effects oforthopedic approaches essentially depend ongrowth characteristics of the jaws of the individualpatient in addition to the force magnitude, treat-ment timing, and the length of time that the appli-ances are worn. However, we have less informationon the variety of growth characteristics of jaws inClass III malocclusions, although much knowledgehas been obtained with regard to variations in facialmorphologic characteristics.8-13

The purpose of the present study was to investigateindividual growth characteristics of the maxilla and themandible in Class III malocclusions, in terms ofgrowth amount, growth direction, and timing ofgrowth. Longitudinal cephalograms of untreated ClassIII subjects were used in an analysis of the growth from8 to 14 years of age. In addition, the effects of chin captherapy were considered in the context of growthcharacteristics of the jaws by applying the discriminantfunctions derived from the previous study to facialpatterns of the untreated subjects.

EFFECTS OF CHIN CAP THERAPY RELATED TOFACIAL MORPHOLOGY

Before describing the present study, our previ-ous investigation7 on the relationship between facial

From the School of Dentistry, Hokkaido University.aAssistant Professor, Department of Orthodontics.bProfessor and Chairman, Department of Orthodontics.cFormer Resident, Department of Orthodontics.dInstructor, Department of Orthodontics.eProfessor and Chairman, Department of Oral Anatomy I.Reprint requests to: Hiroyuki Ishikawa, DDS, PhD, Department ofOrthodontics, School of Dentistry, Hokkaido University, Kita 13, Nishi 7,Kita-ku, Sapporo, 060 Japan.Copyright © 1998 by the American Association of Orthodontists.0889-5406/98/$5.00 1 0 8/1/86272

337

morphology and the effects of chin cap therapy willbe summarized briefly.

Forty-six Japanese Class III patients (25 males,21 females) treated with retractive chin caps wereselected from orthodontic patients at the HokkaidoUniversity Dental Hospital. The mean age at thestart of treatment was 8 years 11 months 6 6months. The mean duration of wearing chin capswas 4 years 6 months 6 11 months. A series ofcephalograms at three stages, start of treatment,normal overjet obtained, and 6 years after start oftreatment, was used for the analysis of facial pat-terns and growth changes of the jaws.

The investigation proceeded in two phases. First,cluster analysis (group average method) was appliedto the 46 patients on the basis of three variablesregarding growth direction of the jaws, in order toidentify different growth changes influenced by thechin caps. Details of the measurements will bedescribed later. The variables were the growth di-rection of the mandible for the entire 6 years, andthe balance of growth direction between the maxilla

and the mandible and the growth direction of themandible after normal overjet was obtained. As aresult, five groups were identified (G1, G2, G3, G4,and G5). A summary for each group is representedin Table I. Fig. 1 shows the mean positional changesof Point B in each of the five groups during the 6year observation period. From a comparison withJapanese children with normal occlusions,14 inhibi-tion of mandibular forward growth was clearly foundin G1 and G2 in which the horizontal jaw relation-ship had improved substantially. The mandibulargrowth direction was changed backward in G1 anddownward in G2 by chin cap therapy. G3 revealedsome improvement of the ANB angle, and thebalance of growth direction between both jaws wasalmost the same as in normal occlusions. Chin captherapy was considered effective for these threegroups, although there were some differences in thetreatment results. Groups G4 and G5 showed animbalance in the growth direction between themaxilla and the mandible, which caused the horizon-tal jaw relationship to worsen. The growth direction

Fig. 1. Mean positional changes of Point B in each of the five groups. Inhibitory effects ofchin caps on mandibular forward growth become more reduced in order from G1 to G5.(From Kim C, Ishikawa H.7 Reproduced with permission.)

Table I. Effects of chin cap therapy classified into five groups (From Kim C and Ishikawa H.7 Reproduced by permission.)

Group(number) b2 2 a (°) b1 (°) b2 (°)

ANB (°)

Start of treatment6 Years after

start of treatment

G1 (4) 36.60 6 7.48 126.60 6 6.51 120.55 6 7.77 20.06 6 3.03 3.84 6 1.70G2 (14) 17.94 6 5.78 94.83 6 10.25 88.83 6 11.76 20.02 6 1.73 2.20 6 1.36G3 (16) 5.11 6 3.99 78.61 6 10.30 72.03 6 10.08 20.72 6 1.74 0.65 6 1.74G4 (8) 23.01 6 2.55 75.08 6 9.67 68.13 6 8.94 1.30 6 1.34 20.25 6 1.17G5 (3) 24.50 6 4.90 48.70 6 10.06 43.16 6 14.88 21.33 6 3.04 21.48 6 2.59Normal (40) 6.20 6 5.20 72.10 6 11.10 —

b2 2 a, Balance of growth direction between the maxilla and the mandible after normal overjet was obtained.b1, Mandibular growth direction for 6 years of entire observation period.b2, Mandibular growth direction after normal overjet was obtained.

American Journal of Orthodontics and Dentofacial OrthopedicsSeptember 1998

338 Ishikawa et al.

of the mandible was dominantly forward in the G5group. No clinically satisfactory results were ob-tained with chin cap therapy in these two groups.This study showed that there is a wide variation oftreatment effects of chin caps among Class IIIpatients.

Second, the relationship between facial patternsand the chin cap effects was investigated by discrimi-nant analysis. Fig. 2 shows the mean pretreatmentprofilograms of each of the five groups. Theseprofilograms suggested that there were some differ-ences in facial morphology among the five groups,especially in mandibular form and size. Accordingly,17 conventional cephalometric variables, mainlyconcerning mandibular morphologic characteristics,were measured on pretreatment cephalograms. Dis-crimination of skeletal patterns of each of the fivegroups was performed by a stepwise variable selec-tion procedure. As a result of the analysis, 8 explan-atory variables were selected from 17 variables:SNB, ANB, SNP, GZN, chin-angle, Ar-Go, Ar-Me/AFH, and Go-Pog/AFH. The equations derived forclassification of skeletal patterns in the 5 groupswere as follows:

● G1: 7140.03X1 1 17.7488X2 1 37.7034X3 237.1532X4 2 55.6939X5 1 102.412X6 26185.05X7 1 18.5865X8 2 4596.37

● G2: 7030.69X1 1 17.6069X2 1 37.0365X3 236.0862X4 2 53.8827X5 1 99.9132X6 26084.8X7 1 18.781X8 2 4486.07

● G3: 7068.79X1 1 17.9767X2 1 37.2838X3 236.8165X4 2 57.7151X5 1 103.99X626180.01X7 1 17.7497X8 2 4494.94

● G4: 6947.04X1 1 17.2453X2 1 36.9573X3 235.5862X4 2 52.9018X5 1 98.3561X6 26010.49X7 1 18.8456X8 2 4401.35

● G5: 7059.87X1 1 18.0746X2 1 37.3942X3 235.2405X4 2 51.6043X5 1 97.339X6 26000.96X7 1 19.4414X8 2 4647.7

● X1, Ar-Me/AFH; X2, chin-angle; X3, GZN;X4, Ar-Go; X5, SNB; X6, SNP; X7, Go-Pog/AFH; X8, ANB.

Rates of correct discrimination in each group bythese equations were 100% for G1, 57.1% for G2,68.8% for G3, 87.5% for G4, and 100% for G5. G1,G4, and G5 showed high rates of correct discrimi-nation, and G2 and G3 showed low rates because ofsimilarities in pretreatment facial morphologyamong the groups where chin cap treatment wasconsidered effective. However, the discriminantfunctions derived were clinically significant becausefacial patterns of the noneffective groups were ap-

parently discernible from those of the effectivegroups.

MATERIAL AND METHODS

For this investigation dealing with chin cap effects, sixsubjects who showed a deteriorating horizontal jaw rela-tionship with growth were selected from nine untreatedJapanese Class III subjects with anterior cross bite en-rolled in the files of the Craniofacial Growth Study atHokkaido University Dental School.15 The three remain-ing subjects who showed improvement of a jaw relation-ship with growth were not used because the jaw growthcharacteristics were considered unsuitable for this studyconcerning chin cap effects.

Six years of longitudinal cephalograms from 8 to 14years of age were used to analyze the facial morphologicand growth characteristics of the jaws (Table II). Duringthe observation period in this study, the maximum puber-tal growth in body height took place in all subjects, andnone showed spontaneous correction of the anterior crossbite.

Fig. 2. Mean profilograms of each of the five groupswith different effects of chin cap therapy. (From Kim C,Ishikawa H.7 Reproduced with permission.)

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 114, No. 3

Ishikawa et al. 339

Fig. 3 shows cephalometric measurements used todescribe skeletal patterns. The eight variables related tothe discriminant functions7 were included. Fig. 4 repre-sents the method used to evaluate growth characteristicsof the maxilla and the mandible in terms of amount anddirection.14 Cephalometric tracings at different timepoints were superimposed on SN plane, registered onSella. The growth direction and growth amount weremeasured at Point A and Point B (Angle a, Angle b,Distance a, Distance b), drawing a line to connect twolandmarks at different time points and extending tointersect SN plane. The balance in growth direction andgrowth amount between both jaws was evaluated fromb 2 a and a/b respectively.

The present study proceeded in two phases. First,individual growth of the jaws in the six untreated Class IIIsubjects was analyzed in terms of growth amount, growthdirection, and timing of growth. Second, facial patterns atthe age of 8 in the six subjects were classified into the fivegroups with different effects of chin cap therapy by thediscriminant functions,7 with a view to considering therelationship between chin cap effects and growth charac-teristics of the jaws.

RESULTS

Fig. 5 shows longitudinal changes in the ANBangle of the six untreated individuals. Table IIIshows the ANB angle at the ages of 8 and 14 years.Among the six subjects, the timing of ANB changesvaried considerably. Four subjects, nos. 1, 2, 3, and4, showed sharp decreases in ANB before theyreached the age of maximum pubertal growth inbody height. Thereafter the ANB was slightly de-creasing or almost constant. Subject 5 showed aremarkably decreasing ANB angle from 8 to 10years of age, and a continued gradual decrease afterthe age of maximum pubertal growth. Subject 6showed a sharp decrease in ANB throughout theobservation period. The ANB angle continued todecrease substantially even after the completion ofthe maximum pubertal growth. The greater changesin the ANB angle from 8 to 14 years of age werefound in subjects 5 and 6, showing decreases ofabout 3.0°. Four of the others showed less than2.0° changes.

Longitudinal changes in SNA and SNB anglesare shown in Fig. 6. In the four subjects where theANB changes were greater before the maximumpubertal growth, the changes in SNA and SNBangles were clearly different, whereas the ANBdecreased sharply. The SNA angle was constant insubject 3, slightly increasing in subject 1 and de-creasing in subjects 2 and 4; the SNB angle wasgradually increasing in all four persons. However, ata later time, the rates of increment in both angleswere very similar. In the two subjects who showedremarkable decrease in ANB angles, the changes inSNA of subject 5 and in SNB of subject 6 weredifferent from the other subjects. Throughout theobservation period, the SNA of subject 5 continuedto decrease gradually, and the SNB of subject 6showed a strong increase.

The amount and direction of jaw growth charac-

Fig. 3. Cephalometric measurements.

Table II. Summary of the materials used in this study

Subject(sex)

Age

8Years

9Years

10Years

11Years

12Years

13Years

14Years

No. 1 (M) V V V V V V& V

No. 2 (M) V V V V& V V V

No. 3 (M) V V V V V & V

No. 4 (M) V V V V V V& V

No. 5 (F) V V V& V V

No. 6 (F) V V & V V V V

V Cephalograms were available.& Maximum pubertal growth in body height.


340 Ishikawa et al.

teristics in the six untreated subjects are illustratedin Fig. 7. Each measurement was performed withcephalograms at 8 and 14 years of age. The meanand one standard deviation of normal occlusions atthe same age14 are indicated for comparison. For thebalance of the growth amount between the upperand lower jaws, four of the six subjects showed thea/b values smaller than –1 standard deviation (SD)of the normal group. The smallest value was foundin subject 6 with the maximum ANB change. For thebalance of growth direction, the b – a values werebelow –1 SD of the normal in all subjects. Thesmallest b – a value was found in subject 6, due to anextreme value of b showing strong forward growthof the mandible. Subject 5 showed the secondsmallest value of b – a, due to the highest value ofa representing retarded maxillary forward growth;however, a value b was the highest in the subjects.

To consider treatment effects of chin caps in thecontext of growth characteristics of the jaws, the sixsubjects were classified into five groups with differ-ent effects of the chin cap.7 Eight variables related tothe discriminant analysis were measured on thecephalograms at the age of 8 (Table IV). As ananalysis of the discrimination of the facial patterns,five of the six were determined to be members ofgroups, G1, G2, and G3, where chin caps have beenfound to be effective. Particularly, subject 5 with thehighest b value was classified into G1 showingbackward growth of the mandible by chin caps.Subject 6 with strong mandibular forward growthwas classified into G5 where chin caps are noteffective (Table V).

DISCUSSION

The growth analysis of the present study wasbased on data selected from the serial records of

Japanese subjects included in the files of the Longi-tudinal Craniofacial Growth Study at HokkaidoUniversity Dental School.15 The records, includingdental casts, cephalograms, and body measurementswere obtained from children living in Nanporo townnear Sapporo between 1970 and 1982. The growthdata of the six untreated Class III subjects wereobtained from children who refused to receive or-thodontic treatment in spite of advice from dentists.Compared to longitudinal growth data of Class IIImalocclusions in other reports,16-18 the data have theadvantage of a longer observation period and coverages before and after the maximum pubertal growth.Details of the facial morphology have been reportedby Takeuchi et al.,19 and the growth changes havealso been evaluated by cephalometric templatesobtained from normal occlusions. In the presentstudy, the growth characteristics of the maxilla andthe mandible in Class III subjects were investigatedintensively for timing, amount, and direction ofgrowth.

The method of evaluating the growth directionand amount of the maxilla and the mandible hasbeen used in previous studies.7,14,20 It measures sixparameters including the growth direction andgrowth amount of each jaw and the balance betweenthe upper and lower jaws. In this study, however,four parameters were used in the evaluation, be-cause there were great differences in absolutegrowth increments, measured at Point A and PointB between male and female subjects, as seen in thelongitudinal growth study reported by Nanda andGhosh.21

Fig. 8 shows cephalometric tracings and super-impositions at the ages of 8 and 14 years in the sixsubjects. From the results of this investigation, thelongitudinal changes of the jaw growth varied con-

Fig. 4. Measurements of growth direction and amount of the jaws.


Ishikawa et al. 341

siderably among the subjects. In four subjects, 1 to 4,the anteroposterior relationship between both jawsworsened substantially a few years before the max-

imum pubertal growth, and the subsequent changeswere relatively slight. From the changes in SNA andSNB angles, the maxillary forward growth was re-tarded until the jaw relationship had worsenedsomewhat. For the balance of growth amount andgrowth direction between both jaws, the four sub-jects showed less disharmony than subjects 5 and 6who had greater changes in ANB angle. Althoughthe b – a values of the four subjects were below thenormal range, this was mainly due to the maxillarygrowth inhibition occurring in a relatively shortperiod. The abnormal occlusal relationship in theanterior part of the teeth may have changed the

Fig. 5. Longitudinal changes in ANB in the six untreated Class III subjects. The age ofmaximum pubertal growth is indicated by the vertical line. The dotted line shows the periodwithout cephalograms.

Table III. Changes in ANB (in degrees) of the six untreatedClass III individuals from 8 to 14 years of age

Subject 8 Years 14 Years Net changes

No. 1 1.76 0.19 21.57No. 2 21.56 23.38 21.82No. 3 3.46 1.65 21.81No. 4 0.05 21.72 21.77No. 5 20.87 23.75 22.88No. 6 0.86 22.44 23.30


342 Ishikawa et al.

maxillary growth direction more vertically in thefour individuals.22,23 The inhibition of maxillary for-ward growth seemed to continue until the inhibitoryeffects of anterior cross bite were reduced, with theincrease in anteroposterior gap between the upperand lower apical bases. After the interference ingrowth was released, the sagittal growth of themaxilla and mandible became balanced. From thisobservation, the growth potential of the jaws ap-pears genetically normal in the four subjects. Con-sidering treatment of this type of Class III maloc-clusions, early correction of anterior cross bite is ofgreat significance for preventing the deterioration of

the horizontal jaw relationship and will lead tonormal jaw growth. The horizontal jaw relationshipin subjects 5 and 6 progressively deterioratedthroughout the observation period, caused by con-tinuous downward growth of the maxilla in subject 5and sustained forward growth of the mandible insubject 6. Particularly, the manner of mandibulargrowth in subject 6, with strong forward growth evenafter the maximum pubertal growth, has also beenreported in other longitudinal growth studies.21,24 Asevere imbalance was found in both the growthamount and the growth direction between the jaws.These results suggest that the abnormal growth

Fig. 6. Longitudinal changes in SNA (thick line) and SNB (thin line) in the six untreatedClass III subjects. The age of maximum pubertal growth is indicated by the vertical line. Thedotted line shows the period without cephalograms.


Ishikawa et al. 343

tendencies of the maxilla in subject 5 and themandible in subject 6 were genetically determined,resulting in extremely deviated facial morphologiccharacteristics. Considering treatment of the twosubjects, careful consideration must be given to theacceleration of maxillary forward growth in subject 5and the inhibition of mandibular forward growth insubject 6. However, orthopedic forces, an environ-mental factor of facial growth, are not always effec-tive in changing genetically determined jaw growth,particularly when morphologic abnormality is pro-gressively amplified during growth. From a differentpoint of view, the growth control of the mandible insubject 5 and the maxilla in subject 6 may be the key

to improvement of the growth amount and growthdirection between both jaws, in spite of a possibilityof a longer lower face or anterior open bite occur-ring.

Based on the above results, differences in theeffects of chin cap therapy shown by the previousstudy7 were reconsidered. A classification of the sixuntreated individuals into the five groups was pos-sible, considering the growth characteristics of themandible. Subject 5 is considered to have less for-ward growth tendency of the mandible because of anunchanged SNB angle and the greatest b value. Thissubject was classified as G1 in which the mandibulargrowth direction was apparently changed backwardby chin cap therapy. Subject 6 with the strongestmandibular forward growth among the six subjectswas classified as G5, revealing difficulty of mandib-ular growth control. The other subjects in which thegrowth potential of the jaws was considered genet-ically normal were classified into groups where thechin cap modified the mandibular growth directionto some extent. These results strongly suggest that

Fig. 7. Amount and direction of growth characteristics of the jaws in the six subjects.Subject matter is shown in the boxes. Solid and dotted lines represent the mean 6 onestandard deviation of normal occlusions derived from a previous study.14

Table IV. Cephalometric measurements relating to the discriminant functions in the six individuals

Subject Ar-Me/AFHChin-

angle (°)GZN

(°)Ar-Go(mm)

SNB(°)

SNP(°) Go-Pog/AFH

ANB(°)

No. 1 0.87 73.24 73.93 42.60 79.45 78.49 0.57 1.76No. 2 0.90 71.98 81.47 38.32 79.97 79.70 0.65 21.56No. 3 0.90 69.35 81.94 41.32 82.00 81.82 0.64 3.46No. 4 0.91 75.52 80.87 39.34 80.82 80.51 0.66 0.05No. 5 0.94 73.91 79.58 40.36 84.60 83.85 0.68 20.87No. 6 0.93 80.49 79.42 46.14 81.35 80.41 0.63 0.86

Table V. Classification of the six untreated Class III subjectsinto five groups with different effects of chin cap therapy

G1 G2 G3 G4 G5

No. 5 No. 1 No. 2 — No. 6No. 3 No. 4


344 Ishikawa et al.

the effects of the chin cap therapy depend on theindividual growth characteristics of the mandible.There has been much discussion of treatment effectsof chin caps, and many studies1,2,17,25-30 have re-ported that chin caps could facilitate changes inmandibular growth, downward or backward. How-ever, some studies27,29 have also showed individualdifferences in the treatment effects among patients.It is evident that these differences mainly relate toindividual growth characteristics of the mandible.

Considerations of chin cap effects in this studywere based on the hypothesis that there is a closerelationship between facial patterns and growthcharacteristics of the face. The discrimination of thesix untreated Class III subjects was primarily basedon facial patterns. However, the results obtainedhere and in a previous study lead us to conclude thatfacial morphology, growth characteristics, and treat-ment results are interrelated in Class III treatment.Further investigation should be conducted to deter-mine the relationship between facial patterns andgrowth characteristics of jaws to enable appropriatetreatment plans for individual Class III patients.This kind of research has been scarcely studied since

Schulhof et al.31 showed a significant relationshipbetween abnormal growth in Class III patients andthe sum of the standard deviations from normal ofthe four cephalometric “predictor measurements,”mainly due to the difficulties in data collection. Toovercome this, adequate longitudinal growth data ofuntreated Class III subjects should be collected andanalyzed with joint research by several institutesholding such records.

CONCLUSION

Individual growth characteristics of the maxilla andthe mandible varied much among the six untreated ClassIII malocclusions, and the appropriate treatment has beendiscussed. From a classification of the facial patterns ofthe six subjects into the five groups with different effects ofchin cap therapy,7 it was possible to consider that theeffects of chin cap therapy depend on the individual growthcharacteristics of the mandible. Considerations of individualgrowth characteristics of the jaws are of great importanceto make treatment plans for individual Class III patients.

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Fig. 8. Cephalometric tracings and superimposition at the ages of 8 and 14 in the sixsubjects.


Ishikawa et al. 345

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Individual growth in Class III malocclusions and its relationship to the chin cap effects