Thin-plate spline analysis of mandibular morphological changes induced by early class III treatment: a long-term evaluation

Objective: To evaluate the long-term mandibular morphological changes induced by early treatment of class III malocclusion with rapid maxillary expansion (RME) and facial mask (FM). Materials and Methods: Twenty-five subjects [10 boys, 15 girls; mean age at T1 (start of treatment) 9.3 ± 1.6 years] with class III disharmony were treated with RME and FM therapy followed by fixed appliances. The patients were re-evaluated at the end of growth (T2), about 8.5 years after the end of the treatment (mean age, 18.6 ± 2.0 years). Sixteen subjects with untreated class III malocclusion comprised the control group. Mandibular shape changes were analysed on the lateral cephalograms of the subjects of both groups by means of thin-plate spline (TPS) analysis. Procrustes average mandibular configurations were subjected to TPS analysis by means of both cross-sectional between-group comparisons at T1 and at T2 and longitudinal within-group comparisons. Statistical analysis of shape differences was performed using a generalized Goodall F test. Results : In the long term, the treated group exhibited a significant upward and forward direction of condylar growth. On the contrary, untreated class III subjects showed an upward and backward direction of condylar growth associated with a downward and forward deformation of the mandibular symphysis. Limitatio ns: Limitations are related to the small sample size of both treated and control groups and to the retrospective nature of the study. Conclusions: Early treatment of class III malocclusion with RME and FM is able to produce significant and favourable long-term mandibular shape changes characterized by an anterior morphogenetic rotation.