Factors associated with the morphology of the mandibular symphysis and soft tissue chin

ABSTRACT Objectives: This study aimed to (I) assess the morphology of the symphysis and soft tissue chin associated with sex, age and sagittal/vertical skeletal patterns, and (II) identify the individual and combined contributions of these variables to different portions of the symphysis. Methods: This cross-sectional study included 195 lateral cephalometric radiographs from untreated adults. Alveolar, basal, and soft tissue of the symphysis were measured by an X/Y cranial base coordinate system, and divided in accordance to four predictor variables: sex, age, and sagittal/vertical skeletal patterns. Parametric tests were conducted for comparison and correlation purposes, while multiple regression analysis was performed to explore combined interactions. Results: Alveolar inclination is related to sagittal and vertical patterns, and both explained 71.4% of the variations. Alveolar thickness is weakly predicted and poorly influenced by age. Symphysis height was 10% higher in males, and associated with a vertical skeletal pattern and sex, and both explained 43.6% of variations. Basal symphyseal shows an individual thickness, is larger in males, and vertically short-positioned with age. Soft tissue chin is not necessarily related to the size of the underling skeletal pattern, and enlarges with age, even in adulthood. Conclusions: The symphysis and surrounding tissues are influenced by sex, age, and sagittal and vertical patterns, acting differently on the alveolar, basal and soft tissue portions. Sagittal and vertical skeletal patterns are the strongest association on alveolar symphysis inclination, whereas sex and age acts on the vertical symphysis position and soft tissues thickness.

摘要

研究目的：本研究旨在（I）评估与性别、年龄及矢状向/垂直向骨骼分型相关的颏联合（symphysis）及软组织颏部的形态特征；（II）明确上述变量对颏联合不同区域的单独及联合贡献。

研究方法：本项横断面研究纳入了195张未经治疗的成人头颅侧位X线片（lateral cephalometric radiographs。研究采用X/Y颅底坐标系（cranial base coordinate system）测量颏联合的牙槽、基骨及软组织特征，并按照性别、年龄、矢状向/垂直向骨骼分型四个预测变量进行分组。采用参数检验开展比较与相关性分析，同时实施多元回归分析以探究联合交互效应。

研究结果：牙槽倾斜度与矢状向及垂直向骨骼分型相关，二者可解释71.4%的变异量。牙槽厚度受年龄的预测性较弱且影响程度较低。男性的颏联合高度较女性高10%，该指标与垂直向骨骼分型及性别相关，二者可解释43.6%的变异量。基骨颏联合具有独立的厚度特征，男性基骨颏联合体积更大，且随年龄增长其垂直向位置偏短。软组织颏部并不一定与下方骨骼结构的大小相关，且随年龄增长而增厚，即便在成年阶段亦是如此。

研究结论：颏联合及其周围组织受性别、年龄及矢状向、垂直向骨骼分型的影响，且对牙槽、基骨及软组织区域的作用存在差异。矢状向与垂直向骨骼分型是影响牙槽颏联合倾斜度的最强关联因素，而性别与年龄则作用于颏联合的垂直向位置及软组织厚度。