Methods: Pre and post-treatment lateral cephalograms (LC) of 31 subjects with Class II Division 1 malocclusions were digitized. Anterior, functional occlusal planes (AOP, FOP respectively) and upper incisors inclination (U1) angles relative to sella-nasion (SN) line were measured. Inter-canine (IC) width changes were measured utilizing 3D measuring software (Rapidform 2006). Utilizing proprietary software, 3DM®(National University of Singapore), virtual pre and post-treatment 3D laser scanned maxillary models were aligned 3-dimensionally along the mid-palatal suture to respective pre and post-treatment LC, subsequent two-dimensional superimposition of LCs facilitated the 3D superimposition of aligned pre and post-treatment models to evaluate 3D curvature changes. Principal Components Analysis (PCA) was utilized to identify patterns of changes from a 3D perspective, highlighting as a component the differential simultaneous effect in contribution of the variables that could possibly modify the 3D curvature. Multivariate linear regression analysis was utilized to determine the statistical significance of the differential effect of each variable within the components yielded from the PCA.(P<0.05)
Results: Of the 4 components derived, the 3D pattern demonstrating larger positive change in SN-AOP angle and simultaneous negative change in U1-SN angle resulted in positive curvature change of 1.94 degrees (95% C.I 0.44-3.45), p=0.01. The component demonstrating larger positive change in U1-SN angle and simultaneous negative change in SN-AOP angle resulted in negative curvature change of 1.55 degrees (95% C.I 3.06-0.46), p=0.04. The remaining components were not statistically significant (p=0.34, p=0.97).
Conclusions: The magnitude of the 3D maxillary arch curvature assessed frontally is not statistically related to changes in FOP inclination and IC width. It is related significantly to AOP orientation and inversely to U1-SN.