Malocclusion of teeth

Alternative names:

crossbite; crowded teeth; misaligned teeth; overbite

Definition:

A dental condition involving misalignment of teeth.

Causes, incidence, and risk factors:

Malocclusion is the most common reason for referral to an orthodontist. Occlusion involves the alignment of teeth and the way that the upper and lower teeth fit together (bite). Ideal occlusion occurs when all upper (maxillary) teeth fit slightly over the lower (mandibular) teeth. The points of the molars fit the grooves of the opposing molar. All teeth are aligned, straight, and spaced proportionally. The upper teeth keep the cheeks and lips from being bitten and the lower teeth protect the tongue.

Very few people have perfect occlusion. However, most occlusion abnormalities are so minor that they do not require treatment. Benefits of treatment of moderate or severe malocclusion include improved oral health and the cosmetic and psychologic benefits of improved appearance. The teeth are easier to clean, reducing the risk of tooth decay and periodontal diseases (gingivitis or periodontitis). Treatment eliminates strain on the teeth and jaws, which lessens the risk of breaking a tooth and reduces symptoms of temporomandibular joint disorders.

Malocclusion is most often hereditary. There may be a disproportion between the size of the upper and lower jaws or between jaw and tooth size resulting in overcrowding of teeth or in abnormal bite patterns. Extra teeth, malformed teeth, impacted or lost teeth, and teeth that erupt in an abnormal direction may contribute to malocclusion. Ankylosis (deformation) of the mandible may affect its shape, as can birth defects such as cleft lip and palate.

Less frequent causes include habits such as thumb sucking or tongue thrusting. The improper fit of dental restorations (fillings, crowns and so on) or appliances, retainers or braces, misalignment of jaw fractures, and tumors of the mouth or jaw may cause malocclusion.

Type 1 malocclusion is the most common. It occurs when the bite is normal but there are crowded or malpositioned teeth.

Type 2 malocclusion, called retrognathism or overbite, occurs when the upper jaw and teeth severely overlap the bottom jaw and teeth.

Type 3 malocclusion, called prognathism or underbite, is the least common. It occurs when the lower jaw protrudes forward and the lower teeth extend over the upper teeth.