Volumetric change of the muscles of mastication following resection of mandibular angles: a long-term follow-up.

Abstract

Mandibular angle resection is an accepted procedure for the correction of square face appearance due to mandibular angle prominence. Long-term follow-up of the changes in volume that occurs in the muscles of mastication and osseous structures has been inadequate in the literature. In this study, 3-dimensional computed tomography data were used to extract the mandible, masseter, medial pterygoid, and lateral pterygoid muscles for assessment of the volumetric changes that took place after angle reduction in 7 patients (14 hemimandibles) with an average age of 24.9 years and a mean follow-up time of 4.5 years. All measurements were performed twice to assure accuracy, with a difference of 1.2 +/- 1.1% noted. The hemimandible volume was reduced by 12.6% immediately after the reduction procedure and 8.2% at final follow-up. Osseous regeneration was observed as thickening of the bone and partial regrowth of the angles. None of the 14 hemimandibles had a complete return of the preoperative angular shape. The volumetric changes that occurred in the muscles of mastication were inconsistent among the patients. The masseter muscle was reduced by 5.2%, the medial pterygoid muscle was reduced by 14.4%, and the lateral pterygoid muscle was increased by 5.7% at final follow-up. The medial pterygoid muscle change was more significant than that of the masseter muscle (P = 0.00361). The objective findings of this study were not in agreement with the conventional thought and clinical impression that the masseter muscle becomes atrophic after mandibular angle resection. Only a slight reduction occurred in some patients in the volume of the muscles, with some actually displaying a slight increase. The end result was a satisfactory esthetic outcome for the patients in the long term despite the minor changes in muscle volume and slight bony regeneration that occurred.