Occlusion refers to the alignment of teeth and the way that the upper and lower teeth fit together (bite). Ideally, all upper teeth fit slightly over the lower 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.

Malocclusion is the most common reason for referral to an orthodontist. Very few people have perfect occlusion. However, most occlusion abnormalities are so minor that they do not require treatment. By treating moderate or severe malocclusion, the teeth are easier to clean and there is less risk of tooth decay and periodontal diseases (gingivitis or periodontitis). Treatment eliminates strain on the teeth, jaws and muscles, 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. Variations in size or malformation of either jaw may affect its shape, as can birth defects such as cleft lip and palate.

During infancy, personal habits like thumb sucking, tongue thrusting, pacifier use beyond the age of three, and prolonged use of a bottle can greatly affect the shape of the jaws as well. The improper fit of dental fillings, crowns, appliances, retainers or braces may contribute to malocclusion. Misalignment of jaw fractures after a severe injury, and tumors of the mouth or jaw may cause malocclusion as well.

• Type 1 malocclusion is the most common. It occurs when the bite is normal but teeth are crowded or malpositioned.
• Type 2 malocclusion, called retrognathism or overbite, occurs when the upper jaw and teeth overlaps the bottom jaw and teeth.
• Type 3 malocclusion, called prognathism or underbite, occurs when the lower jaw protrudes forward and the lower teeth extend over the upper teeth.

• Abnormal alignment of teeth
• Abnormal appearance of the face
• Difficulty or discomfort when biting or chewing
• Speech difficulties (rare) including lisp
• Mouth breathing (breathing through the mouth without closing the lips)

Most malocclusion is discovered by the dentist during a routine examination. Occlusion is checked by pulling the cheek outward and having the person bite down normally, which tests the alignment of the back teeth. The dentist usually refers the person to an orthodontist for diagnosis and treatment.

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

The goal is to correct the positioning of the teeth. Braces or other appliances may be used. Metal bands are placed around some teeth or metal, ceramic, or plastic bonds are attached to the surface of the teeth. Wires or springs apply force to the teeth.

Extraction (removal) of one or more teeth may be required if overcrowding is part of the problem. Rough or irregular teeth may be adjusted down, reshaped, and bonded or capped. Misshapen restorations 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, in a similar manner to the surgical stabilization of jaw fracture.

Meticulous oral hygiene and regular visits to the general dentist are vital. Plaque accumulates on orthodontic appliances and may permanently mark teeth or cause tooth decay if not properly cared for.

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

• Tooth decay
• Discomfort during treatment
• Irritation of mouth and gums (gingivitis) caused by appliances
• Chewing or speaking difficulty during treatment