The Effect of Topical Anesthesia on Jaw Pain Thresholds in Patients with Generalized Pain

Chronic widespread pain and fibromyalgia often coexist with temporomandibular disorders (TMD) and affects mostly women. Studies have shown lower pressure pain thresholds (PPT) in these patients indicating that hyperalgesia is involved. The aim for this study was to investigate the effect of topical anesthesia on PPT for jaw muscles in patients with widespread pain. The hypothesis was that the PPT in these patients would increase after applying topical anesthetic cream. Ten women (aged 25-64 years, median: 50 years) diagnosed with TMD associated with widespread pain, reported from at least three different anatomical sites apart from the jaw region and pain to palpation according to the American College of Rheumatology criteria 1990, were included in the study. The double blind randomized trial was based on measurements of PPT with an Algometer before and after the application of anesthetic cream (EMLA) or placebo cream. The chosen measurement sites were the anterior part of the temporal muscle bilaterally, the belly of the masseter muscle bilaterally and the pollicis transversa muscle of the dominant hand. In the statistical analysis Wilcoxon’s rank sum test was used and a P-value <0.05 was considered statistically significant. There was a large inter-individual variation of PPT. No statistically significant differences in PPT-values before and after application of the EMLA or placebo creams were observed. In conclusion, the study showed that application of topical anesthesia had no significant effect on PPT in patients with widespread pain. Mechanisms related to central sensitization may have contributed to this result.