Masticatory muscle pain: Causes, consequences, and diagnosis

Masticatory muscle pain is known as myogenous temporomandibular disorder (TMD) pain. It has a prevalence of approximately 10% in the general population and affects women more than men. It is usually characterized by a dull, aching pain, which aggravates on function. The etiology of TMD pain is still not clear, and multiple factors are considered to play role. Oral parafunctions, like the habit of chewing gum or bruxism (i.e., clenching and/or grinding of the teeth), are thought to play a pivotal role in the initiation and perpetuation of TMD pain, even though this has not yet been verified unequivocally by epidemiological and experimental studies. At the same time, the effects of TMD pain on the masticatory sensory-motor function are not fully understood either. Two models, the vicious cycle model and the pain adaptation model, have been proposed to explain these effects the best, although neither of them is able to fully explain the effects that are present in TMD-pain patients. In everyday clinical practice, for the establishment of a TMD-pain diagnosis, palpation and dynamic/static tests are commonly used, however without having full insight into the factors that influence the responses of these tests. To further clarify the above-outlined gaps in the current knowledge, this thesis includes five studies. Chapters 2, 4, and 5 describe studies on the role of experimental parafunctions in the provocation of TMD pain and on the effects of this pain on masticatory muscle function. Chapter 3 is a methodological paper about the recording of the jaw-stretch reflex (i.e., the short-latency response of the jaw-closing muscles after a sudden stretch), which is an important descriptor of motor function. Chapter 6 deals with the factors influencing the outcome of clinical diagnostic tests for TMD pain.