It has been estimated that the prevalence of temporomandibular disorders is in 20-30% of population, but the need of treatment is in less than 5%. However, early treatment is needed for individuals with limitation of opening mouth or pain during the mandibular function.
Various contributing factors for temporomandibular disorders have been enumerated; occlusal factors, trauma, habits (bruxism, lip-, tongue-, and nail-biting) and psychological factors. However, prominent factors have not been found.
The relation between retruded contact position (RCP), oblique slide from RCP to intercuspal position (ICP), and temporomandibular disorders (TMDs) has not been demonstrated. Recently, occlusal discrepancy between habitual occlusal position (HOP) and bite plate-induced occlusal position (BPOP) has been reported to be related with sign (TMJ clicking) of TMD in a cross-sectional study. And elimination of the occlusal discrepancy is inferred to cure TMDs.
The value of retruded contact position (RCP) as a reference position for an occlusal analysis has not been demonstrated. On the other hand, muscular contact position (MCP) has been found to be important for a reference position in occlusal analysis and occlusal equilibration.
The reproduction of a habitual (natural) closing movement is considered to be important because this closing movement ends at the muscular contact position (MCP), otherwise known as the intercuspal position (ICP). This closing movement was originally regarded as a hinge-like movement. However, it has since been demonstrated to be a bodily movement, that is, a vertical movement. This vertical movement can be reproduced on an articulator.
There have been various therapies to relieve the symptoms of temporomandibular disorders. These therapies are required to relax the masticatory muscles and to precisely analyze, and equilibrate an occlusion in the muscular contact position (MCP).
Occlusal equilibration in the muscular contact position (MCP) is required to obtain bilateral occlusal contact in the MCP. It is essential to equilibrate an occlusion on dental casts mounted on an articulator with bite plate-induced occlusal position record (BPOP record).
Regarding the mechanism of temporomandibular disorders (TMDs), TMD pain including muscle tenderness to palpation is considered to be caused by masticatory muscle fatigue induced with occlusal discrepancy. Temporomandibualr joint (TMJ) derangement is considered to be occurred due to mandibular displacement from muscular position to habitual position.
Tension type headache is considered to be occurred due to hypertension of masticatory muscles induced with occlusal discrepancy. Aural symptoms are also considered to be occurred due to hypertension of masticatory muscles or fatigue of them. Burning mouth syndrome and glossodynia are considered to be caused by chorda tympani squeezed between malleus and incus.
Conservative treatments for temporomandibular disorders (TMDs) are symptomatic treatments, and therefore, they cannot completely cure TMDs. The signs and symptoms of TMDs completely disappear by using occlusal equilibration in the muscular contact position (MCP). This is a causal treatment for TMDs. The evaluation of outcome of treatment should be performed to strictly confirm whether or not signs and symptoms have disappeared.