A multitude of terms have been used to describe patients presenting with pain and dysfunction of the temporomandibular joint (TMJ) and related masticatory muscles: Costen’s syndrome (Costen 1934), dysfunctional temporomandibular joint and muscle pain (Ramfjord 1961), myofascial pain dysfunction (MPD) (Laskin 1969), temporomandibular joint syndrome (Carraro et al. 1969), mandibular dysfunction (Thompson 1971) and craniomandibular disorders (McNeill 1990). These terms include several entities that have different etiology, but present with similar signs and symptoms (Westesson 1993).
Temporomandibular disorders (TMD) are one subgroup of any of these terms, and they embrace a number of clinical problems that involve the masticatory muscles and/or the temporomandibular joint (Laskin 1969, Agerberg & Carlsson 1975, McNeill et al. 1990, Westesson 1993). This term is most frequently used in clinical practice (Raustia et al. 1994, Eberhard et al. 2000, Steed & Wexler 2001).
The studies of internal derangement of TMJ (TMJID) focus on displacement of the disc in temporomandibular joint (Farrar 1978, Wilkes 1978a,b). Wilkes defined the criteria of TMJID in 1978. The criteria were based on clinical symptoms, surgical findings, radiological findings, and they were later combined with MRI findings of TMJ (Wilkes 1989, Schellhas 1989a). In past decades, a number of reports have been presented indicating that the disc displacement is associated with the pain and dysfunctional symptoms of TMJ (Farrar & McCarty 1979, Schellhas 1989a, Katzberg et al. 1996, Emshoff et al. 2001). The studies also showed that the disc displacement correlated with disc deformity (Yoshida et al. 2000, Taskaya-Yilmaz & Ogutcen-Toller 2001) and osteoarthritic changes of the hard tissues in TMJ (Westesson 1985, Kurita et al. 2000, Bertram et al. 2001). The pathological evidence in TMJs with disc displacement have been confirmed by histological (Larheim et al. 1999, Leonardi 2001) and anatomical studies in autopsy specimens (Westesson & Rohlin 1984a, Widmalm et al. 1992, Kondoh et al. 1998).
However, some questions have arisen based on the clinical studies. In Wilkes’s criteria, the internal derangement of TMJ was described as a progressing procedure in radiological stages; oppositely, clinical symptoms show as a chronically released procedure (Wilkes 1989). The symptoms of some patients might be relieved after conservative or surgical treatment, but the severe disc displacement and degenerative changes of TMJ might still exist (Montgomery et al. 1992, Sato et al. 1999, Nishimura 2001). Other reports found that the symptoms of the patients with severe disc displacement of TMJ might be resolved even without any treatment (Lundh et al. 1992, Kurita at al. 1998, Sato et al. 1998). On the other hand, pain and dysfunction symptoms have also been found in TMJs without disc displacement (Benito et al. 1998). The results of these studies indicate that the disc displacements of TMJ cannot always explain the alterations of the clinical symptoms. If the views only encompass disc displacement, it may not be enough for the diagnosis and treatment of TMJ problems. The function and dysfunction of the masticatory muscles in TMD should also be taken into account (Helkimo 1974a,b, Solberg 1986a, Katzberg et al. 1996, De Laat 1998, Greene 2001). Identification of pathological changes of masticatory muscles is still lacking in diagnostic criteria of TMD, and more evidence of pathological changes of the masticatory muscles in TMD is needed.