Biomechanical effects of free-end missing dentition on temporomandibular joint loading in a rabbit model.

OBJECTIVE: This study investigated how free-end missing dentition affects temporomandibular joint (TMJ) loading in a rabbit model. Condylar displacement during masticatory-like movements was analyzed to infer the direction and relative magnitude of TMJ loading. DESIGN: Fifteen Japanese White rabbits were assigned to two series. In Experiment 1 (n = 5), free-end missing dentition was simulated by placing a metal occlusal plate on the premolars, followed by resection of the articular eminence (Ar-Em). In Experiment 2 (n = 10), normal molar occlusion was examined with and without Ar-Em resection. Grinding-type mandibular movements were elicited by cortical masticatory area stimulation. Condylar and incisal trajectories and masseter electromyographic (EMG) activity were recorded. Condylar displacement after Ar-Em resection was used as an indicator of TMJ load. RESULT: Ar-Em resection caused a clear anterosuperior shift in working-side condylar movement. Forward displacement was significantly larger with free-end missing dentition (1.96 ± 0.20 mm) than with normal occlusion (0.94 ± 0.23 mm, p < 0.01). No significant correlation was found between condylar displacement and masseter EMG amplitude. CONCLUSIONS: Condylar displacement analysis after Ar-Em resection may serve as a biomechanical indicator of TMJ loading and aid in understanding TMJ disorders linked to posterior tooth loss.