Longitudinal comparisons of dental arch changes in normal and untreated Class II, Division 1 subjects and their clinical implications

The purpose of this study was to determine on a longitudinal basis whether the growth trends in maxillary and mandibular dental arch widths and lengths in persons with Class II, Division 1 malocclusions were different from those of normal subjects. Dental casts were available on a total of 37 subjects with Class II, Division 1 malocclusions (15 males and 22 females) and 55 normal subjects (28 males and 27 females). For each subject, three sets of casts were evaluated at the following developmental stages: (1) deciduous dentition ((X) over bar age = 5.0 years); (2) mixed dentition ((X) over bar age = 8.0 years); and (3) permanent dentition ((X) over bar age = 12.5 years). Eighteen dental arch lengths and widths parameters were measured on both the maxillary and the mandibular arches. Interexaminer and intraexaminer reliability were predetermined at 0.5 mm. The Analysis of Variance general linear models procedure was used to compare the various dental arch parameters on both a cross-sectional and a longitudinal basis. Curve parallelism and magnitude were evaluated. The results of the analysis of variance comparing the growth curves of the various dental arch parameters in the normal subjects and untreated subjects with Class II, Division 1 malocclusions indicated the absence of significant differences between the groups, i.e., the curves were parallel (p < 0.01). This finding indicates that the growth trends in the various dental arch parameters evaluated were similar in the normal and Class II, Division 1 malocclusion groups in both male and female subjects. In addition, the differences between the measurements of maxillary and mandibular intermolar arch widths were greater in the normal male subjects than in the male subjects with Class II, Division 1 malocclusions. Female subjects had similar trends but the differences were not statistically significant. In conclusion, the present findings indicate that the clinician should assume that the changes in arch lengths and widths in both the subjects with Class II, Division 1 malocclusions and the normal subjects follow the same general patterns. On the other hand, the relative constriction of the maxillary arch as related to the mandibular arch, in Class II malocclusions is expressed from the earlier stages of dental arch development. These trends continue in the mixed and early permanent dentitions and do not self correct without treatment. Therefore when such trends are diagnosed, early correction of the transverse discrepancy should be attempted together with that of the anteroposterior discrepancy.