Safety, efficacy, and mechanism of action of the temporo-masseteric nerve block.

The objective of the study was to assess the utility and safety of Temporo-masseteric Nerve Block (TMNB), and to explore the mechanism for its apparent sustained pain relief. This manuscript describes, (1) a retrospective study evaluating pain reduction in patients who received the TMNB injection for the management of masticatory myogeneous pain (myalgia, per Diagnostic Criteria for Temporomandibular Disorders (DC/TMD criteria)), and (2) a motor nerve conduction study (NCS) of the temporalis and masseter, performed in the absence of signs or symptoms of TMD, before and after the TMNB injection. The results were as follows. (1) Retrospective study: (n = 186). 52 instances had available baseline and post-TMNB Numerical Pain Rating Scores (NRS) scores, the TMNB injection reduced baseline NRS scores by 70%; pain difference was qualitatively documented in 90 instances (pain relief or improvement in 86/90 instances). 4 instances yielded no pain relief. Mild adverse events recorded included a vasovagal episode (n = 1), transient weakening of blink (n = 2) or burning sensation (n = 1). (2) The Motor NCS demonstrated impairment of the compound-motor-action-potential (CMAP) as recorded from temporalis and masseter muscles following the TMNB injection. In conclusion, the TMNB injection is efficacious and safe. Further studies are warranted to warrant its effectiveness.