The results from the present analysis suggest that a reduction in facial convexity tends to occur with age irrespective of the start overjet, although this improvement may be marginally more marked in those with larger overjet in pre-adolescence. Specifically, inter-maxillary relationships appeared to change slightly in both groups with minor increases in SNA (0.59 to 1.36°) being dwarfed by more substantial increases in SNB (2.26 to 2.5°) leading to an overall reduction in facial convexity reflected in a decrease in ANB by 1.12 to 1.91°. This finding is in keeping with previous research [15, 17]. This improvement appears, however, to have marginal effect in terms of occlusal relationships with the overjet decreasing slightly more in the group experiencing more favourable growth.
The straightening of the profile observed over a mean observation of 7.7 years from 8.1 to 15.8 years reflects changes arising in juvenile, pre-pubertal and adolescent years. This finding mirrors a longitudinal study based on the Belfast Growth Study, in which the SNA angle did not change significantly between 5 and 15 years in all groups (classes I, II and III) while the SNB angle increased slightly in all groups except for the class II division 2 females . Similarly, Chung and Wong  in an analysis of untreated skeletal class II males and females from ages 9 to 18 from the Bolton-Brush and Burlington Growth studies found that the SNA and SNB angles increased and the ANB angle decreased in all groups with age. The authors concluded that the skeletal class II relationship tended to improve with age, although no gender-related effect was observed in relation to angular measurements in keeping with the findings from the present study .
A demonstrable increase in SNB value (up to 2.5°) arose in both groups over the observation period. Subjects included in the present study were based on the initial overjet scores with growth in any direction therefore being conceivable. However, Riesmeijer (2004) in an analysis of 7- to 14- year-olds encompassing Fels, Michigan and Nijmegan databases, observed a greater increase in SNB in the class I group. Similarly, the ANB angle reduced less with age in both genders in the class II compared with the class I group . The latter was confirmed by Lundström and Woodside who concluded that mandibular retrognathia can be determined at age 9 becoming more marked with age . Conversely, in a longitudinal study involving 30 participants between 12 and 17 years of age, a 1° reduction in ANB angle was found in class II males while a more backwards and downward mandibular growth pattern was apparent in females . No gender-related trends were observed in the present larger sample suggesting that antero-posterior skeletal and occlusal changes are likely to be similar among both males and females during juvenile and adolescent growth.
Mean overjet was observed to reduce slightly in group 1. This may well reflect improvement in the inter-maxillary relationships; however, the difference was limited (1.05 mm). Conversely, a marginal increase in overjet (0.3 mm) was identified in group 2. Importantly, however, the overjet at the later time-period remained normal (3.28 mm, SD 1.33) in the latter cohort, while continuing to be excessive in group 1 (5.16 mm, SD 1.58). Similarly, in an analysis of untreated skeletal class I subjects from the Bolton-Brush and Burlington Growth Studies, Chung and Mongiovi observed that overjet did not worsen with age . The clinical relevance of this is clear with intervention required to address class II malocclusion, while early achievement of a class I incisor relationship is likely to be relatively stable over a period of growth. The latter has variously been confirmed with antero-posterior correction among the more stable orthodontic changes [22, 23].
In terms of dental change, marginal improvement was observed in the present study in the group with larger initial overjet. This contrasts with a previous analysis of 25 untreated subjects with class II malocclusion observed for a 2.5-year period from the deciduous into the mixed dentition, in which the clinical signs of class II malocclusions in the deciduous dentition persisted or become exaggerated. However, the cephalometric changes of the class II sample over this growth period showed significantly greater growth increments in the maxilla and smaller growth increments in the mandible . Conversely, Bishara et al. , in a comparison of untreated class II division I subjects with normal subjects in the mixed early permanent dentition, found that class II subjects with increased ANB angle had similar growth profiles to those of normal subjects. However, the analysis in this study did not extend beyond an average age of 12.2 years, when active growth is still ongoing. The authors concluded that class II malocclusion is not ‘self-correcting’ in growing patients . It is noteworthy that the assessment undertaken in the present analysis was more sustained incorporating both the period of maximal pre-pubertal growth and adolescent growth.
In terms of limitations, the present study was retrospective being based on historical data made available as part of the AAOF Craniofacial Growth Legacy Collections Project. As such, there are constraints in relation to the generalizability of the findings with the majority of subjects being white Caucasian. Moreover, the historical nature of the data is potentially problematic in view of the possibility of secular trends relating to changing facial appearance. The latter is a particular problem in comparative studies using historical controls in conjunction with contemporary groups . Notwithstanding this, while subtle changes in craniofacial form have been attributed to a ‘year of birth’ effect , there is no evidence to suggest that growth patterns over the adolescent period have changed over the past 90 years. Analysis was limited to cephalometric data; as such, there are associated constraints in terms of reliability and validity ; notwithstanding this, in view of the historical nature of the data, clinical correlation was not possible. Notwithstanding this, serial cephalometric analysis continues to form the mainstay for assessing the pattern and magnitude of craniofacial growth.