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）分析不同性别、年龄及矢状/垂直骨型人群的颏联合（symphysis）与颏部软组织形态特征；（II）明确上述变量对颏联合不同区域的单独及联合影响效应。
研究方法：本横断面研究纳入195份未经治疗的成人头颅侧位X线片。采用X/Y颅底坐标系对颏联合的牙槽骨区、基骨区及软组织进行测量，并以性别、年龄、矢状/垂直骨型作为4个预测变量。研究采用参数检验开展组间比较与相关性分析，同时通过多元回归分析探究变量间的联合交互作用。
研究结果：牙槽骨倾斜度与矢状骨型及垂直骨型均相关，二者可解释71.4%的变异量。牙槽骨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%，且与垂直骨型及性别相关，上述因素可解释43.6%的变异量。基骨颏联合具有独立的厚度特征，男性基骨厚度更大，且随年龄增长呈现垂直向位置偏短的表现。颏部软组织与下方骨组织的大小并无必然关联，且随年龄增长（即使在成年阶段）仍会出现增厚。
研究结论：颏联合及其周围软组织受性别、年龄、矢状骨型与垂直骨型的共同影响，且对牙槽骨区、基骨区及软组织区域的作用模式存在差异。矢状与垂直骨型是影响颏联合牙槽骨倾斜度的最强关联因素，而性别与年龄则主要作用于颏联合的垂直位置及软组织厚度。