Malocclusion is abnormal alignment of the teeth and the way in which the upper and lower teeth fit together. Normally, the upper teeth overlap slightly outside the lower teeth. This overlap allows the projections (cusps) on each tooth to fit in the corresponding depressions of the opposite tooth. Proper alignment makes for the most effective chewing and also distributes chewing forces equally. Normal chewing produces over 150 pounds (1,000 kilopascals) of force on the molars and 250 pounds (1,700 kilopascals) when clenching during sleep. If this force is unequally distributed, teeth can wear abnormally, portions of the crown may fracture, and teeth may eventually loosen.
There are several causes of misaligned teeth:
The most common cause of misaligned teeth is when the jaw is too small compared to the size of the teeth. A slight size mismatch causes teeth to be too crowded and thus misaligned.
People who habitually suck their thumb or push their tongue up against their front teeth may cause the upper teeth to protrude.
A lost permanent tooth creates a gap that nearby teeth may shift into, causing misalignment unless a dentist places a bridge, implant, or partial denture in the gap. Normally, lost baby teeth are quickly replaced by permanent teeth. However, if children lose a baby tooth too soon (such as due to an injury), nearby teeth can similarly shift, causing misalignment.
Birth defects of the jaw and fractures of the jaw often cause misalignment.
Most often, the main reason to correct misalignment is to improve appearance. However, treatment of severe misalignment may be needed to prevent tooth damage and improve speaking and chewing.
Correction of the misalignment requires braces, or for some people, dentist-prescribed tooth aligners.
For braces, dentists attach (bond) brackets to the teeth. The brackets are connected to each other by wires and elastic bands that apply force to slowly and gradually pull teeth into proper alignment. By pulling slowly, the underlying bone of the tooth socket actually reshapes, resulting in a permanent shift of the teeth. Sometimes teeth must first be removed to allow room for realignment. Sometimes one or more teeth need to be slightly ground down or built up so they meet better. After the teeth are properly aligned, braces are removed and people wear a plastic and wire retainer to keep teeth from shifting back. First the retainer is worn 24 hours per day, then it is worn only at night for 2 or 3 years.
Tooth aligners are sometimes referred to as clear braces or invisible braces. Tooth aligners are a set of clear plastic appliances (similar to retainers) that are used in a specific order to gradually move teeth (up to 0.3 mm per aligner). Each aligner is worn for about 2 weeks and then changed for a new one until the misalignment is corrected. As with traditional braces, a retainer is used to keep the teeth from shifting back.
Sometimes birth defects of the jaw and improperly healed jaw fractures must be corrected with surgery.