Reduction of Clinical Temporomandibular Joint Pain Is Associated with a Reduction of the Jaw-Stretch Reflex

Aims: To examine the jaw-stretch reflex after injection of local anesthetic (LA) into painful temporomandibular joints (TMJs), since the functional role of jaw-stretch reflexes in patients with painful temporomandibular disorders is still not well understood. Methods: Thirteen female patients with a clinical diagnosis of disc displacement without reduction and TMJ pain participated in this open study. Reflex responses were evoked by fast stretches at 15%of the maximal voluntary contraction level before and after injec-tion of 1 mL carbocaine into the painful TMJ. Electromyographic (EMG) activity was recorded from the left and right masseter and temporalis muscles, and the mean level of prestimulus EMG activ-ity and peak-to-peak amplitude of the stretch reflex were mea-sured. Visual analog scale ratings of TMJ pain and TMJ pressure pain thresholds (PPTs) were also obtained. Eleven healthy women were examined with the same protocol (except for PPT determina-tions) before and after injection of LA into the TMJ. Results: In patients, injection of LA reduced the TMJ pain during jaw move-ments and maximum clenching (P ＜ .021) and increased the PPTs in the painful TMJ (P ＜ .01). The prestimulus EMG activity in the masseter on the painful side (feedback muscle) was unaffected by the injection of LA (P ＞ .262). There were no significant side-to-side asymmetries of latency or amplitude measures of the stretch reflex in the patient group. Both the peak-to-peak amplitude and the normalized peak-to-peak amplitude of the stretch reflex were reduced in the masseter and temporalis muscles on the painful side and in the masseter on the nonpainful side after LA injections (P ＜ .048). There were no effects of LA injections into the TMJ in the healthy group on any EMG or stretch parameters. Conclusion: These results do not support the notion of asymmetries in the jaw-stretch reflex in patients with TMJ pain, but they do suggest that the reflex sensitivity can be influenced by nociceptive activity from the TMJ area.

local anesthesia; pain; pain thresholds; stretch reflex; temporomandibular joint; trigeminal nerve

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