Objectives: The aim of the present study is to evaluate the early and long-term postoperative dimensional changes of the muscles of the mandible in patients with orthognathic surgery for class II and class III malocclusions by using ultrasonography (US).
Material and methods: Twenty-six patients who underwent bimaxillary orthognathic surgery for class II or class III malocclusions (14 and 12 patients, respectively) were ultrasonographically examined. The length, width, and cross-sectional area of the masseter and suprahyoid muscles were measured at three different time points: T0 (preoperatively), T1 (early postoperatively at 1 month after the surgery), and T2 (late postoperatively at 9 months). A repeated measures ANOVA was used to calculate statistically significant dimensional changes of the mandibular muscles.
Results: Statistically significant dimensional changes were found postoperatively in class II malocclusion patients only. The digastric muscle showed higher values for the length and lower values for the width (p < .05) at T1. The geniohyoid muscles were higher in length at T1 and lower in cross-sectional area (CSA) (p < .05) at T2. A decreased measured length and an increased measured width were found in case of the mylohyoid muscle (p < .05) at T2. The early and long-term postoperative dimensional changes of the masseter muscle were not statistically significant.
Conclusions: The mandibular muscles showed a variable adaptive response to the orthognathic surgery. US should be considered for the long-term follow-up of muscular dimensional changes in class II malocclusion patients.
Clinical relevance: From a clinical perspective, US is a reliable, non-invasive, and widely available method, which allows monitoring the postoperative muscular changes occurring in class II malocclusion patients.
Keywords: Masseter muscle; Orthognathic surgery; Suprahyoid muscles; Ultrasonography.