Ultrasound dimensional changes of the anterior belly of the digastric muscle induced by orthognathic surgery and botulinum toxin A injection in Class II malocclusion.

OBJECTIVES: The aim of the study is to evaluate the ultrasonographic dimensional changes of the anterior belly of the digastric muscle (ABDM), occurring after intramuscular botulinum toxin A (BTX-A) injection during orthognathic surgery, in a series of five Class II malocclusion patients. METHODS: All the patients received 20 units of BTX-A, into both ABDM, intraoperatively. The length, width and cross-sectional area (CSA) of the ABDM were ultrasonographically measured at three different time points: T(0) (preoperatively), T(1) (postoperatively at 2 weeks after the surgical intervention), and T(2) (postoperatively at 6-9 months). RESULTS: A statistically significant higher length of the ABDM was noted postoperatively, at T(1) and T(2) compared to T(0). The patients showed an increased length by 12.2% at 2 weeks postoperatively and continued to increase, reaching 24.6% at 6 months. A decreased width of ABDM by 6.5% at T(1) compared with T(0) was also found. CONCLUSIONS: Postoperative ultrasound (US) follow-up measurements in patients with Class II malocclusion, orthognathic surgery and intraoperative BTX-A injection in the ABDM, showed dimensional changes of the muscle, with elongation and thinning. The muscular modifications were more pronounced at 6 months postoperatively, indicating consistency and potential benefit of using BTX-A in reducing the risk of surgical relapse. Further data on longer-term follow-up and larger number of cases are necessary.