Changes in Masseter Muscle Following Curved Ostectomy of the Prominent Mandibular Angle: An Initial Study With Real-Time 3D Ultrasonograpy

Abstract

To investigate changes in the masseter muscle following osteotomy of the prominent mandibular angle using real-time 3-dimensional (3D) ultrasonography, and to supply guidance for resection of the mandibular angle. Real-time 3D ultrasonography was applied pre- and postoperatively (over a 6-month follow-up period) to 10 patients (20 hemimandibles) who underwent curved osteotomy with the following objectives: 1) to reconstruct morphological changes of the masseter under intercuspal position, maximal opening, maximal clenching, and maximal protruding conditions; 2) to assess masseter muscle volume changes, and 3) to obtain the dynamic morphological changes of masseter during mouth opening and closing. The reconstructed 3D images showed no significant differences in the appearances of masseter muscle in variant postures 6 months postoperatively; however, longitudinal diameters decreased and angle regions changed to be arc-shaped with significant thinning. The mean volume of masseter muscle was 18.222 +/- 3.028 cm(3) 6 months postoperatively, compared with the preoperation mass of 25.480 +/- 7.113 cm(3); the static difference was significant (P < .01). The pre- and postoperative dynamic images showed almost no differences in morphological changes of masseter muscle during mouth opening and closing motions. Transverse and longitudinal changes of the thickest masseter muscle section 6 months postoperatively were of no statistic difference (P > .01) compared with preoperation status. A certain extent of atrophy occurs in the masseter muscle after mandibular angle ostectomy, and simultaneously occurs primarily in the angle region; however, these changes do not significantly impair masseter muscle function. Therefore, we suggest a simple mandibular angle ostectomy without partial resection of the masseter muscle in cases of mild to moderate mandibular angle hypertrophy. By doing so, the cosmetic effect will be achieved with reduced complications. Real-time 3D ultrasonography offers a novel, safe, and convenient technique for masseter muscle reconstruction and observation of masseter muscle movement. Because of its safety and the convenience it offers for repeated patient examinations, real-time 3D ultrasonography represents a novel technique for the reconstruction and observation of masseter muscle movement.