REFLEX RESPONSES OF THE MASSETER MUSCLE IN PATIENTS WITH CHRONIC ARTHRITIS OR INTERNAL DERANGEMENT OF THE TEMPOROMANDIBULAR-JOINT - A COMPARISON WITH SYMPTOM-FREE SUBJECTS

Averaged reflex responses in the masseter muscle to transverse taps de livered to the upper central incisor were studied in 13 patients with chronic arthritic temporomandibular joint (TMJ) disease (arthritis gro up) and 28 patients having internal TMJ derangement (derangement group ). The diagnostic assessment of TMJ disease was based on a combination of imaging methods. Fourteen symptomfree subjects served as a control for the electromyographic observations. The tapping force was increas ed in steps from 0.25 to 6 N. The pattern of the reflex response consi sted of various inhibitory and excitatory waves, which were found to c hange with increasing tapping force. The first inhibitory wave (I-1) i ncreased in duration with increasing tapping force in all subjects. At certain tapping forces, I-1 was of significantly lower amplitude and longer duration in the arthritis group than in the control group, but latency and threshold did not differ. The excitatory wave seemed to ha ve longer latency and higher amplitude in the arthritis group than in the control subjects at some tapping forces. In summary we conclude th at the pattern of the reflex response seemed to be similar in patients with different TMJ disorders and in symptomfree subjects. Only the le vel of inhibition, duration of I-1 and higher excitatory response, mig ht separate the patients with arthritic TMJ disease and internal TMJ d erangement from symptomfree subjects, but no specific differences betw een the groups could be found.