Profile Characteristics Related to the Anatomy of the Chin in a Class II Treatment Population

Objectives: To evaluate facial esthetics as related to the anatomy of the chin in children treated for Class II, division 1 malocclusion. Methods: The material included lateral cephalographs of 63 children (7yrs2mos-13yrs4mos) treated with a headgear or a Frankel function regulator(FR) for 2years. Changes in facial morphology were measured in a coordinate system oriented on natural head position. The mean displacement of mandibular landmarks was evaluated upon anterior cranial base superposition, and after adjusting for the intercurrent forward growth of nasion (measuring changes relative to perpendicular through nasion). The cant (to the vertical) of the posterior and anterior symphyseal slopes was evaluated in relation to the position of the chin (pogonion, gnathion, menton). Soft tissue thickness was measured at the levels of bony landmarks, and analyzed relative to underlying hard structures. Results: Although the displacement of hard (p=0.08) and soft tissue (p=0.03) pogonion was more anterior in the FR than the headgear group, the cephalographs (and corresponding profile photographs) revealed, in both groups, patients with deficient and non-deficient projection of the chin within the face, despite achieving neutroclusion. Pearson correlation coefficients disclosed a tendency for: a backward inclination of the anterior symphyseal slope with the more anterior position of pogonion (r=-0.60); a forward tilt of the posterior slope when pogonion is more posterior (r=-0.45). Higher correlations were observed between thicknesses of: upper and lower lips (r=0.89); upper lip and soft tissue at various chin landmarks (r=0.71-0.79). Conclusions: 1- Profile differences between treatment groups were marginally statistically significant and apparently of less clinical significance. 2- Projection of the chin within the face seems to be associated with, among other factors, the anatomy and cant of the symphysis, and soft tissue thickness. The findings suggest that the nature of the dysmorphology is self-limiting from therapeutic and esthetic perspectives. NIH support: Grant R01-DE08722.