Analysis of the osseous support of mandibular incisors in various facial growth and incisor inclination patterns: A CBCT study

INTRODUCTION: This study evaluated the osseous support of the mandibular incisors in patients with various Frankfort to mandibular plane angles (FMA) and lower incisor to mandibular plane angle (IMPA) inclinations.;METHODS: A total of 90 subjects with lateral cephalogram and cone-beam computed tomography (CBCT) records that met inclusion criteria were selected. Subjects were categorized into three groups (low-, normal- and high-angle) by FMA. The subjects were then subcategorized utilizing the IMPA (upright, normal, and proclined). Using CBCT scans, each mandibular incisor was analyzed for osseous support through eleven measurements. Two-way analysis of variance (ANOVA) was utilized for comparing the measurements with the two main effects: growth pattern and incisor inclination. Multiple comparisons were made using the Bonferroni post-hoc tests.;RESULTS: A decrease in mean value was observed as the backward jaw rotation increased for most of the variables, mostly between low- and high-angle followed by low- and normal-angle individuals (p<0.05). L medullary width-A and alveolar width-M measurements were mostly not different between the groups (p>0.05). Additionally, medullary and symphysis height measurements showed increases accordingly with the degree of mandibular divergence (p<0.05). Differences between low- and high-angle and low- and normal-angle individuals were significant for both of these measurements (p<0.05). Incisor inclination, as a main effect, was not significant for L medullary width-A, alveolar width-M, medullary and symphysis height, and W/H ratio-S and W/H ratio-A measurements (p>0.05). Other variables showed increases in mean values as the divergence of the jaws increased. Most of these changes were significant in the comparison of low- and high-angle and low- and normal-angle individuals (p<0.05).;CONCLUSIONS: Osseous support of the symphysis in high-angle subjects was tall and narrow, while it was short and wide in low-angle subjects. Additionally, medullary support at the level of the apices with upright lower incisors is narrow. The differences in the medullary bone support at the level of the apices occur predominantly in the facial aspect. Both facial growth pattern and incisor inclination have deterministic effects in the amount of bone and morphology of the mandibular symphysis.