8.5. Disorders of the TMJ

Disc displacement is the most common disorder of the TMJ. This occurs when the articular disc is dislocated anteriorly with the mouth closed. The retrodiscal tissue is found in between the mandibular condyle and the mandibular fossa. Biting in this condition can be very painful as compression of the retrodiscal tissue will damage it and stimulate its pain receptors.

If the mouth opens fully, the condyle slides anteriorly, over the articular disc. The posterior end of the articular disc might form a salience, however, representing an obstacle to the movement. This will cause clicking sounds when the mouth is opened or closed and the mandibular condyle passes over the salience back and forth between retrodiscal tissue and articular disc. This condition is called disc displacement with reduction.

If the salience formed by the posterior end of the articular disc becomes too prominent, it may prevent the mandibular condyle from sliding over the articular disc. There is no click, but the mandible is locked, unable to produce translation. Mouth opening is limited to the 20 mm allowed by mandibular rotation. This condition is called disc displacement without reduction.

Dislocation of the TMJ may occur when opening the mouth too wide (such as when taking a large bite) or following a blow to the jaw, resulting in the mandibular condyle moving beyond (anterior to) the articular tubercle. In this case, the individual would not be able to close his or her mouth. Temporomandibular joint disorders may also arise due to arthritis, wearing of the articular cartilage, muscle fatigue from overuse or grinding of the teeth, damage to the articular disc within the joint, or jaw injury. Temporomandibular joint disorders can cause headache and impaired chewing. Pharmacologic agents for pain or other therapies, including bite guards, are used as treatments.

Bruxism

Bruxism is excessive teeth grinding or jaw clenching. It occurs at times other than eating or talking. It is a common problem affecting 8–31% of the general population. Bruxism causes hypersensitive teeth, aching jaw muscles, headaches, tooth wear, damage to dental restorations (e.g. crowns and fillings) and damage to teeth.

The tooth grinding can occur during sleep or during wakefulness. Dental damage may be similar in both cases. The symptoms of sleep bruxism tend to be worse on waking and improve during the course of the day, whereas the symptoms of awake bruxism may not be present at all on waking, and then worsen over the day.

The causes of bruxism are not well understood and various factors seem to influence it, but social stress seems to be commonly involved. Several treatments are in use, including medications, psychological intervention, stress relief therapies, dental guards (to reduce further damage) and dental treatment.

Summary

Disc displacement and bruxism are the most common clinical issues observed in the TMJ. They can have various causes but both can be treated and resolved in most cases.

Key terms

Mandibular eminence, retrodiscal tissue, disc displacement with reduction, disc displacement without reduction, bruxism, dental guard

Figure credits

Figure 1 by en:user:DRosenbach - en:Image:Deviated midline.JPG, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3302677

Figure 2 by Mik81 - Photography of author, original description page was here., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2478383