TMJ Diseases and Disorders
Diseases of the TMJs are mainly intra-articular disorders (Fig 11-3), with distinctions drawn between reversible microtrauma and irreversible macrotrauma and between congenital and acquired developmental disorders. Inflammatory microtraumas are joint noises (eg, clicking) occurring occasionally or constantly that result from rough joint surfaces caused by compression. If the compression is removed by means of a muscle relaxation splint (centric relation splint), the microtrauma is also eliminated.
Irreversible macrotraumas are partial or total, usually anterior displacements of the articular disc, with damage to the disc and to other joint structures, as well as massive joint changes (TMJ osteoarthritis; see Fig 11-6). In the case of partial or total anterior disc displacement (or disc derangement), the disc can be pushed back into its original position on opening (disc displacement with reduction), which is associated with a typical clicking or popping sound. Disc derangements and the associated displacement of the condyles are often caused by tooth loss, or the absence of individual support areas, and by occlusal disorders.
In this condition, the articular disc is displaced forward; ie, the disc lies anterior to the condyle when the mouth is closed (Fig 11-4). When the mouth is opened, the disc slides onto the condyle (reduction of the disc), which is associated with a distinct clicking or popping of the joint. On maximum mouth opening, the condyle, disc, and fossa lie in the correct positions in relation to each other; once the mouth is closed, the disc slides forward again (disc prolapse) with distinct clicking (Fig 11-5). This opening and closing movement can be painful, but this functional disorder usually follows a pain-free course.
In anterior disc displacement without reduction, the disc remains anterior to the condyle throughout the entire opening and closing movement. In this case, the disc has sustained degenerative changes. Distinct pain occurs in the joint area during mandibular movement, and the mouth-opening movement is restricted.
Anterior disc displacement is treated with splints for repositioning the mandible. As a result, the disc is brought into a normal or improved position.
Degenerative changes (TMJ osteoarthritis) are apparent as extensive damage to articular soft tissues, such as massive wear of the joint cartilage, fibrillation of the bone at the condyles, and fibrillation of the disc, which may be perforated or completely abraded (Fig 11-6). As a result of these remodeling processes, mandibular movements are severely restricted, and stabbing pains occur in the joint area as well as rubbing joint noises. This is accompanied by functionally induced damage to the dental hard tissue, such as wear facets and wedge-shaped defects.
The therapeutic measures for functional disorders of the masticatory system are performed with occlusal guards, which change the occlusal conditions so that the TMJ symptoms are eliminated as well as the occlusal anomalies. Reorientation involving interaction of the occlusal pattern, muscles, joints, and nerves then ensues.
Splints produce physiologic, psychologic, and biomechanical effects as they:
- Stabilize the relationship between condyle and disc
- Remove occlusal interferences
- Relieve periodontal tissues (or implants)
- Diminish activities of the masticatory muscles
- Unload the TMJs
- Reduce tooth abrasion
They alter the vertical and anterior position of the mandible and the relationship of the condyle to the disc by repatterning the neuromuscular habit. Muscle pains, headaches, and subjective hearing problems can be eliminated in the process. Incorporating canine guidance into the splints keeps the posterior teeth apart during mandibular excursions. Movements out of centric occlusion lead to antagonist canine contact and disoc-clusion of the posterior teeth.The canine guidance produced by splints actually reduces contractile muscle activity considerably, which applies to chewing movements, teeth grinding, and eccentric clenching.
As muscle activity diminishes, the TMJ clicking during laterotrusive and protrusive excursions is reduced because the joints are relieved with less muscle contraction.