[Jaw muscle pain--its neurobiological basis]

The masticatory muscles show morphologic, histochemical, electrophysical, and functional features that differ from the other muscles of the body. At least two kinds of masticatory muscle pain should be distinguished: A local pain associated with peripheral mechanical overuse, and a pain associated with changes in the central nociceptive system. Biomechanical factors appear to be important for the first type of muscle pain. Since the typical reaction of a painful muscle consists of inhibition of its activity, traditional concepts that postulate the maintenance of the pain by chronic overuse of the whole muscle are not supported by the current literature. Instead, differential overuse of discrete intramuscular regions appear to provide a more plausible explanation. On the other hand, the possible relationships between functional and structural neuroplastic changes and the second form of chronic muscle pain (e.g., fibromyalgia) still remain speculative.