Soft tissue changes in patients with Class II Division 1 malocclusions treated using Twin Block appliances: finite-element scaling analysis.

To determine changes in soft tissue profile in patients with Class II division 1 malocclusions treated with Twin Block appliances (TBA), 99 pairs of lateral cephalographs were traced and 25 soft tissue landmarks digitized. Procrustes superimposition was used to generate average soft tissue profiles scaled to an equivalent size. Statistical differences between prepubertal, pre- and post-treatment profiles were found using ANOVA (P < 0.001). Similarly, significant differences were found between adolescent, pre- and post-treatment profiles (P < 0.001). Using a colour-coded finite element scaling analysis (FESA) programme to localize size change, male prepubertal post-treatment configurations revealed local increases in size at the labiomental groove (approximately 25%) with negative allometry (size-related form change approximately 5%) in the labial and symphyseal regions. For the female prepubertal post-treatment configuration, local increases in size were conspicuous also at the labiomental groove (approximately 6%). Male adolescent post-treatment configurations revealed increases in size in the nasal, mental, and labiomental groove regions (approximately 18%) with negative allometries associated with the upper and lower lips (approximately 20%). For the female adolescent post-treatment configuration, the labial fissure showed an increase in size (approximately 17%), whereas the upper and lower lips and symphyseal region exhibited negative allometries (approximately 5-15%). For shape change, all soft tissue post-treatment configurations were highly isotropic (uniform shape change) over the entire facial nodal mesh except in the areas of the labiomental region and the labial fissure. Thus, in children and adolescents treated for Class II malocclusions a less pronounced labiomental groove is associated with using TBAs, which may provide a more effective anterior lip seal.