4-D Model for the patients with masticatory muscle tendon-aponeurosis hyperplasia

OBJECTIVES: Masticatory muscle tendon-aponeurosis hyperplasia is characterized by painless and severe limitation of mouth opening due to contracture of the masticatory muscles with hyperplasia of tendons and aponeuroses. The treatment modality of this pathology has been only surgical approach to masseter muscle or temporal muscle. However, we have not been able to surely diagnose which muscle was affected. Therefore, we clinically applied the “4-D Muscle Model” to explore the real target muscle. In this presentation, we will introduce our system and clinical experiences. METHODS: “4-D Muscle Model” was constructed from the digital data of 3D-CT and 4-D mandibular movements of the patients. It made us to able to visually observe the expansion rate of masticatory muscles at maximum mouth opening to their length at closed mouth position. Five patients were applied the “4-D Muscle Model” before the surgical treatment and 2 healthy volunteers (control group) were enrolled in this study. The expansion rate of masseter muscle and temporal muscle were compared between the patient and control groups. RESULTS: The expansion rate of temporal muscle at the maximum mouth opening in the patient group was significantly less than that in the control group (P<0.05). On the other hand, the masseter muscles of all patients were expanded enough, same as the control group. The main cause of limitation of mouth-opening was suggested to be a contracture of the temporal muscle. Consequently, we performed successful bilateral coronoidectomy with no surgical intervention to the masseter muscles in all patients. CONCLUSION: The present “4-D muscle model” would be valuable tool to decide the target muscle of surgical treatment for patients with masticatory muscle tendon and aponeurosis hyperplasia. In this pathology, contracture of the temporal muscle seems to be main cause of limited mouth opening.