Constitutional differences of chin anatomy among growing and non growing patients with various facial divergence patterns -

Abstract

Association between bony chin, mandibular incisors, and symphyseal anatomy in different facial types has not been investigated. Aims: 1. evaluate components defining chin anatomy and determine constitutional differences in chin morphology, mandibular tooth size and position between hypodivergent and hyperdivergent patterns and across different types of malocclusions; 2. compare 2D and 3D imaging in determining specific morphological features of chin and teeth. Methods: Growing and non-growing patients were stratified into four groups based on mandibular plane inclination to cranial base angle (MP-SN). Measurements on pre-treatment lateral 2D (n=550) and 3D (n=296) cephalometric radiographs included: mandibular incisor crown (ICL) and total (IL) lengths; the following distances: between point D (center of symphysis) and both incisor apex (AD) and menton (DMe), chin width at the level of the incisor apex (CW1) and point D (CW2), between CEJ and menton (CEJ-Me), between the true vertical and points B and B1 (at intersection of the line through B parallel to MP, and posterior contour of the symphysis); and angles of anterior and posterior slopes, inter-slopes, mandibular plane and true vertical through nasion. Volume of the mandibular symphysis was measured using a special 3D imaging software. Group differences and associations between parameters were gauged using Kruskal Wallis test and non-parametric post hoc tests. Results: ICL, IL, AD, DMe and CEJ-Me were greaterin the hyperdivergent group (p0.001). CW1 and CW2 were wider in the hypodivergent group (p=0.003). Analogous results were found between 2D and 3D imaging. Volume of the chin and inter-slope angles were similar in all groups (p0.05), while anterior slope angle decreased with hyperdivegence (p0.005) in opposite pattern to the posterior slope angle (p0.005). Conclusion: Similarity in mandibular symphysis volume between opposite divergence patterns, along with shape differences among dental and symphyseal relations, underline the role of adaptive environ