Early and long-term changes in the muscles of the mandible following orthognathic surgery

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).

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.

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.

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.

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.