This project is attempting to better characterize the pathophysiology of chronic facial pain through a series of clinical investigations. A recently completed study evaluated the use of iontophoretic drug administration as a method for achieving high therapeutic levels of drugs in the temporomandibular joint (TMJ) without systemic administration. A standard drug and dose normally administered by iontophoresis, 0.4% dexamethasone in a 4% lidocaine vehicle, was compared to saline placebo for pain referrable to the TMJ. Subjects completed a battery of analgesic questionnaires and measures of mandibular range of motion (vertical, lateral, and protrusive movements) prior to three applications by iontophoresis of either drug of placebo separated by 48 hours. Both dexamethasone and placebo produced a significant reduction in pain scores from baseline following the first two treatments. No difference, however, was seen between groups for pain report or mandibular range of motion. These data indicate that iontophoretically applied dexamethasone may be no more effective than saline placebo in providing pain relief for patients with temporomandibular joint pain. This observation suggests that iontophoretic drug administration to the TMJ may not be an effective method for administering investigational agents or prototypic drugs to investigate the pathophysiology of chronic facial pain originating from the TMJ and associated structures. A second study is evaluating the use of pain pressure thresholds (PPT) measured by a pressure algometer to quantify pain in the masseter and temporalis muscles in patients with chronic myogenic facial pain. Pain pressure threshold in the masseter and anterior temporalis muscles in patients with well defined myogenous orofacial pain were compared to asymptomatic controls. No significant PPT differences were found between the side indicated by the patient as most painful and the less painful side, supporting theories of centrally-mediated pain. Mean PPTs in patients differed over the four sessions which is consistent with reports of fluctuating levels of pain in patients with TMD. Within and between session reliability were high for patients and controls. These data provide evidence for the utility of pressure algometry as a tool for quantifying subjective pain symptoms of TMD patients in future studies.
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