Objectives: A series of studies has suggested that experimental clenching increases pain and can lead to a diagnosis of temporomandibular disorder (TMD) in otherwise normal, pain-free individuals. This study tested the hypothesis that inflammatory processes play a role in the development of pain induced by parafunctions. Methods: A double-blind, randomized trial design was employed, utilizing 400 mg ibuprofen or 400 mg lactose prepared into identical opaque capsules. Capsules were taken with water at the start of each training session. Six individuals participated in five consecutive days of 20-minute-long EMG biofeedback training sessions on the left and right temporalis and masseter muscles. Subjects were instructed to maintain EMG activity above 10 ìV in all four muscles; this level of effort could be attained by posterior tooth contact or light clenching. No subjects had TMD, as assessed by a blinded examiner, facial pain, or other chronic pain prior to training. Subjects reported no use of interocclusal appliances or chronic use of analgesics prior to training. Results: Self-report measures of worst pain immediately following training were significantly lower for the group receiving ibuprofen, F(1,4)=8.08, p < .05, adjusted R²=0.59, and non-significantly lower for all other self-reported measures of pain. As expected, groups performed similarly on EMG activity during training. Conclusions: Parafunctional clenching produces pain, and ibuprofen can block parafunction-induced pain. Inflammatory processes may play a role in the development of parafunction-induced pain.

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