The tempromandibular complex is affected by two distinct disorders, articular and muscular. The articular disorders include disc condyle complex incoordination namely disc displacement with reduction and disc displacement without reduction. This group is often classified as internal derangements. The muscle disorders include myofascial pain, myositis, spasm and contracture, with myofascial pain being the most common form of TMD. Inflammatory mechanisms account for TMD pain. Some of the other suggested etiological factors are bruxism, occlusal interferences, emotional and behavioral stressors, trauma, and low estradiol serum level; however, neither one of these factors have been validated.
The association of occlusal issues and TMD or headache is very controversial. To date, the role of occlusion as a headache etiology is not supported by a literature meta-analysis.
The TMJ is one of the most complex joints in the body since it allows a hinging movement in one plane and at the same time provides for gliding movements, making it a ginglymoathrodial synovial joint. It has two compartments an upper and lower joint space. The mandibualr condyle and the temporal fossa are separated by an articular disc.
The condylar stability during mandibular movement is maintained by the articular disc which is mostly devoid of vasculature and nerve tissue. In contrast, the retrodiscal tissue on the posterior aspect of the disc is highly vascularized and well innervated and plays a major role in the pathophysiology of TMJ pain. Additionally, inflammation or injury of the joint capsule and the synovial tissues can cause pain within the joint but this inflammatory process usually resolves without any complications.
Asides from capsulitis and synovitis, polyarthritides are the other primary inflammatory conditions of TMJ. Polyarthritides are primarily associated with rheumatologic diseases and are uncommon. Chronic TMD is most often associated with painful derangement of the joint.
The articulating surfaces, including the disc, are composed of dense fibrous connective tissue which make them more resistant to degenerative changes and give them a greater capacity to repair. However, alteration in the disc morphology and elongation of the retrodiscal ligament may lead to disc displacement and tissue breakdown. Different factors like age, gender, stress, previous trauma and systemic illness can contribute to this process. Most often acute and chronic disc displacements are not painful.
Disc derangement disorders are categorized as either disc displacement with reduction or disk displacement without reduction. In a disc displacement with reduction during mouth opening, the temporarily misplaced disc improves or reduces its structural relationship with the condyle and a clicking or popping accompanies this movement.
If the noise is also heard during the mouth closing, the clicking is called reciprocal which is produced by the redisplacement of the disc. Clicking noise in the reducing disc displacement is very common and is not pathogenic or a sign of degeneration. In an asymptomatic sample of individuals with TMD, over 33% can have moderate to severe derangement and as many as 25% of clicking joints display normal or slightly displaced disc positions. Therefore, treatment is not warranted in asymptomatic clicking joints.
Disc displacement with reduction may persist for years to decades without any complication or progression to disc displacement without reduction. The condition where the dislocated disc is nonreducing and or unable to return to its normal position on the condyle is called disc replacement without reduction or closed lock. In the acute stage, there is a sudden onset of a persistent marked limited opening and pain due to a jamming or trapping of the disc.
Clinically the acute phase is manifested with a lack of joint noise in the affected joint, deflection of mandible to the ipsilateral side as well as marked limited laterotrusive movement to the contralateral side. With the transition into a chronic stage, there is a significant pain reduction or complete pain relief and gradual increase of opening range to normal.
