EMG masticatory function in hemimandibulectomy patients

Aim: Treatment of oral cancer often requires radical surgical approaches to completely eliminate the pathology and to prevent possible relapses. Usually, vital masticatory structures are removed, altered or displaced by surgery. Large and aggressive tumors need a wide mandibular segmental resection with muscle displacement. Unfortunately, limited range of motion of the mandible, impaired mastication, speech and swallowing could result with a detrimental psychological impact on the patients. To date, some studies demonstrated that oncologic patients with mandibular reconstruction after surgery have better masticatory performances than non-reconstructed patients. Also, fixed implant-supported prosthetic rehabilitation in the reconstructed mandible seems to provide better functional outcomes and general well-being. Surface electromyography (EMG) of the masticatory muscles during chewing could represent a method to quantify functional recovery in these patients (1). Materials and Methods: Twelve oral cancer patients after hemimandibulectomy and reconstruction with autogenous bone grafts or free revascularized flaps participated in the study. All patients underwent a successful rehabilitation with a fixed implant-supported Toronto bridge prosthesis. At least one year later, surface EMG of the masseter and temporal muscles was performed during a 15-s unilateral gum chewing. EMG potentials were standardized as percentage of a maximum voluntary clench on cotton rolls. For each patient the masticatory frequency, the muscle activities (integrated areas of the EMG potentials over time) and the confidence ellipse of simultaneous differential left-right masseter and temporal activity were computed (2, 3). EMG values from hemimandibulectomy patients were then compared to normal reference data (2). Results: In both sides of mastication, chewing frequency was 15% higher in cancer patients than in the reference group. Muscle activities were larger in patients, particularly in the non-operated side with a great variability. The centers of the ellipses describing the unilateral chewing in the operated side of the patients were located in the correct quadrants, thus indicating a prevalent activity of the working side muscles. In contrast, the centers of ellipses of the non-operated side were located in the correct quadrants only in 25% of the patients. In cancer patients, the confidence ellipses of the resected side muscles were comparable to those computed in normal subjects, but larger in the opposite side of mastication. Conclusions: Globally, the neuromuscular coordination during chewing in hemimandibulectomy patients was satisfying, although some alterations were observed in the non-operated side of mastication. Indeed, mandible resection seems to affect muscle activities in the non-working side.