Alternate Names: Crowded teeth; Misaligned teeth; Crossbite; Overbite

Causes and Risks: 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.

Prevention: Many types of malocclusion are not preventable. Control of habits (such as thumb sucking) may be necessary in some cases.

Symptoms:

• abnormal alignment of teeth
• abnormal appearance of the face
• difficulty or discomfort when biting or chewing
• speech difficulties (rare)

Signs and Tests: Most malocclusion is discovered by the dentist on routine examination. Occlusion is checked by pulling the cheek outward and having the person bite down normally. The dentist usually refers the person to an orthodontist for diagnosis and treatment.

Dental X-rays, head/skull X-rays, or facial X-rays may be required. Impressions (plaster or plastic molds of the teeth) are often needed.

Treatment: The goal of treatment is to correct the positioning of the teeth.

Braces or other appliances may be used to change the positioning or alignment of teeth. Metal bands are placed around each tooth or metal, ceramic, or plastic bonds are attached to the surface of the teeth. Wires or springs apply force to the teeth. The alveolar bone (tooth sockets) responds to pressure by remodeling--dissolving bone in front of the tooth and replacing bone behind the tooth. Other appliances may be recommended instead of, or in addition to, braces.

Extraction (removal) of one or more teeth may be required if overcrowding contributes to malocclusion. Rough or irregular teeth may be adjusted down, reshaped, and bonded or capped. Misshapen restorations (fillings or crowns) and dental appliances should be repaired. Surgery may be required on rare occasions. This may include surgical reshaping to lengthen or shorten the jaw (orthognathic surgery). Wires may be used to stabilize the jaw bone (similar to surgical stabilization of jaw fracture).

Meticulous oral hygiene is vital during orthodontic treatment. Plaque accumulates on orthodontic appliances and may permanently mark teeth or cause tooth decay.

Retainers (appliances used to stabilize the teeth) may be required for an indefinite time to maintain the new position of the teeth.

Prognosis: Malocclusion is easier, quicker, and less expensive to treat when it is corrected early. Treatment is most successful in children and adolescents because their teeth and bones are still developing. Treatment usually lasts 6 months to 2 or more years.

Treatment of orthodontic disorders in adults is often successful but may require prolonged treatment.

Complications:

• tooth decay
• discomfort during treatment
• appliances may irritate the mouth and gums (causing gingivitis)
• chewing and speaking may be difficult during treatment

Call your orthodontist if toothache, mouth pain, or other new symptoms develop during orthodontic treatment.