Department of Orthodontics, Institute of Stomatology, Riga Stradins University, 20 Dzirciema Street, Riga, LV 1007, Latvia.
Stomatologija. 2020;22(4):99-106.
The aim of this study was to analyse the volumetric and crossectional parameters of masseter and medial pterygoid muscles in the relation with mandibular skeletal morphology in individuals with different underlying growth patterns in the vertical dimension.
The study originally involved 76 individuals with definite clinical and radiological criteria: 31 skeletal Class III and 26 skeletal Class II patients before the orthognathic surgery and 20 skeletal class I (normal) individuals with complaints of wisdom teeth and associated medical problems. On the basis of cephalometric measurement of the mandibular plane and sella-nasion (MP-SN), the study sample was categorised according to the vertical facial dimension in 3 different growth pattern subgroups: 19 subjects with horizontal growth pattern, 25 subjects with vertical growth pattern and 33 subjects with neutral growth pattern. MRI was performed for the masseter and medial pterygoid muscles, and volume and cross-sectional area measurements were performed. Cone beam computed tomography (CBCT) investigation was performed for the assessment of craniofacial structures and the following measurements of the mandibular parameters were obtained: height of ramus, length of mandibular corpus, overall mandibular length, inter-angular width and intercondylar width.
There were statistically significant differences among all study groups regarding masseter volume (p<0.006) and CSA (p<0.006), with the highest values in the horizontal growth pattern group and the lowest values in vertical growth pattern group. After Bonferroni correction, statistically significant difference (p<0.004 and p<0.008) was noted between the horizontal and vertical growth pattern groups, respectively. A similar tendency was observed for the medial pterygoid, but with no statistical significance. A statistically significant negative correlation was observed between MP-SN and the volume of masseter and medial pterygoid in the overall sample. Of the seven muscular and mandibular variables included in the regression analysis, the final model included only four variables that were significantly associated with MP-SN and explained 37% of its variance (masseter volume (p=0.017), mandibular overall length (p<0.001), height of mandibular ramus (p=0.003), and length of mandibular corpus (p<0.001)).
The masseter muscle seems to be more sensitive to the variation in mandibular morphology than the medial pterygoid muscle, and volume as the biomechanical characteristic seems to be a more significant parameter of the size of the interaction with vertical skeletal growth patterns.
本研究旨在分析不同垂直向骨骼生长模式个体的咬肌和翼内肌的体积和横截面积参数与下颌骨骼形态的关系。
本研究最初涉及 76 名符合明确临床和影像学标准的个体：31 名骨骼 III 类和 26 名骨骼 II 类患者在正颌手术前，以及 20 名骨骼 I 类（正常）个体因智齿和相关医疗问题而就诊。根据下颌平面和蝶鞍-鼻根（MP-SN）的头影测量，研究样本根据垂直面型分为 3 个不同生长模式亚组：19 名水平生长模式者、25 名垂直生长模式者和 33 名中性生长模式者。对咬肌和翼内肌进行 MRI 检查，并进行体积和横截面积测量。进行锥形束 CT（CBCT）检查以评估颅面结构，并获得下颌参数的以下测量值：下颌升支高度、下颌体长度、下颌总长度、下颌角宽度和髁突间宽度。
所有研究组的咬肌体积（p<0.006）和 CSA（p<0.006）均存在统计学差异，其中水平生长模式组的数值最高，垂直生长模式组的数值最低。经 Bonferroni 校正后，水平生长模式组和垂直生长模式组之间存在统计学显著差异（p<0.004 和 p<0.008）。翼内肌也呈现出类似的趋势，但无统计学意义。在总样本中，MP-SN 与咬肌和翼内肌的体积之间存在统计学显著的负相关。在回归分析中纳入的 7 个肌肉和下颌变量中，最终模型仅包括 4 个与 MP-SN 显著相关且解释其 37%变异的变量（咬肌体积（p=0.017）、下颌总长度（p<0.001）、下颌升支高度（p=0.003）和下颌体长度（p<0.001））。
与翼内肌相比，咬肌似乎对下颌形态的变化更为敏感，而作为生物力学特征的体积似乎是与垂直向骨骼生长模式相互作用大小的更重要参数。
