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/垂直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。 方法：本横断面研究纳入195张未经治疗的成人头颅侧位头影测量片。采用X/Y颅底坐标系对颏联合的牙槽部、基底部及软组织进行测量，并依据性别、年龄、矢状/垂直骨骼分型四类预测变量进行分组。研究采用参数检验开展比较与相关性分析，同时通过多元回归分析探究变量间的联合交互作用。 结果：牙槽倾斜度与矢状及垂直骨骼分型相关，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。男性颏联合高度较女性高10%，且与垂直骨骼分型及性别相关，上述因素可解释43.6%的变异量。颏联合基底部具有独特的厚度特征，男性基底部厚度更大，且随年龄增长出现垂直向位置缩短。软组织颏部未必与下方骨骼结构的大小相关，且即便在成年阶段仍随年龄增长而增大。 结论：颏联合及其周围软组织受性别、年龄、矢状及垂直骨骼分型的影响，且对牙槽部、基底部及软组织区域的作用存在差异。矢状与垂直骨骼分型是影响颏联合牙槽部倾斜度的最强关联因素，而性别与年龄则对颏联合垂直位置及软组织厚度发挥作用。