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is essential in implantology, corrective measures, if possible, should be instituted before an implant is considered.

Class III. In Class III malocclusion all mandibular teeth are anterior to their maxillary opponents. This type of malocclusion may be improved by orthodontic treatment or combined orthodontic treatment and surgical procedures. However, a severe Class III malocclusion usually contraindicates the use of implants because both arches of teeth may never be properly occluded. Many false Class III malocclusions can be corrected by reconstructing one or both arches and bringing the new upper anterior restorations over the lower ones and locking them into this position.

Temporomandibular joint dysfunctions

Because disturbances in temporomandibular joint articulation generally result in occlusal disharmony, the health and functioning of this site are of special importance to the implantologist. Poor habits, such as subluxation or partial dislocation, may contraindicate implants unless the patient can be retrained. Diseases affecting the temporomandibular joint, unless cured or controlled, contraindicate implants.

Ankylosis. When the articular disk is damaged, fibrous tissue may link the condyle directly with the glenoid fossa, causing partial ankylosis. If it is unilateral, occurring in only one temporomandibular joint, there is a deviation from the midline in mouth opening and a loss of gliding action (Fig. 6-34). Facial asymmetry may also be noticeable. If partial ankylosis occurs bilaterally there is no midline deviation, but a loss of gliding movement or a restriction of mouth opening results. In some cases—complete ankylosis   there is a bone-to-bone fusion, with a marked or.full limitation of jaw movement.

Partial ankylosis may result from developmental anomalies, traumatic injuries, inflammation, various collagen diseases, occlusal disharmonies, and neoplasms. Complete ankylosis may follow pyogenic or nonsuppurative arthritis, condylar osteomyelitis, fractures, or traumatic insults to the joint. If the asymmetry resulting from the ankylosis has a direct effect on the occlusion, then implants may be contraindicated. If, however, the ankylosis does not have a detrimental effect on the occlusion, implants can be used.

Temporomandibular joint arthritis. Rheumatoid, degenerative, or traumatic arthritis may involve the temporomandibular joint. Marked limitation of movement and severe pain are common complaints.

Fig. 6-34. A disturbance in one temporomandibular joint may result in a deviation from the midline while opening the mouth.

Unilateral limitation of mandibular movement is frequent, whereas bilateral involvement is usually rare. Faulty occlusion is usually a contributory factor. The patient's history often reveals emotional stress accompanied by grinding and clenching of the teeth.

The temporomandibular joint has an upper and lower chamber, and inflammation in the lower chamber may limit movement of the mandible in lateral excursion. Reduced vertical opening of the jaws, in addition to interfering with chewing, may prevent inserting implants because the patient is unable to open his mouth widely enough.

The symptoms of acute temporomandibular joint arthritis often subside after 3 to 5 days of voluntary or induced immobilization of the mandible. A soft diet and limited vertical opening is recommended for a 2-week period. Improvement generally follows intraarticular injection of 0.5 to 1.0 ml. hydro-cortisone. The injection is made with the mouth opened widely. If any premature contacts of the teeth exist, they should be ground away to produce balanced occlusion. In more severe cases of rheumatoid arthritis or osteoarthritis, hydrocortisone injections may have to be repeated at intervals varying from several weeks to several months.

Miscellaneous conditions. Some of the other conditions causing temporomandibular joint disturbances are arthropathogenic anatomic variants, traumatic habits, rheumatoid disease, muscular disorders, occlusal disharmony, tension, and acute arthropathogenic conditions. All of these situations