Overbite, underbite and crossbite: causes and treatment options

The way your upper and lower teeth meet when you close your mouth is called your bite. When the teeth or jaws do not line up as expected, the result is a bite problem, known to dentists as a malocclusion. Overbite, underbite and crossbite are three of the most common types. Some are mild and cause no trouble; others affect chewing, wear the teeth unevenly or change the balance of the face. This guide explains what each term means, why bite problems develop and how they are treated.

What a typical bite looks like

MedlinePlus describes malocclusion as a misalignment of the teeth in which the upper and lower teeth do not fit together properly when you bite. In the most common arrangement, sometimes called a Class 1 bite, the upper teeth slightly overlap the lower teeth. Some overlap is normal; problems arise when the overlap is too great, reversed or uneven.

The American Association of Orthodontists (AAO) explains that the aim of orthodontic treatment is a healthy bite, in which the forces of chewing, biting and speaking are spread evenly. A bad bite happens when teeth meet incorrectly or do not meet at all. Possible signs listed by MedlinePlus include crooked teeth, a change in the appearance of the face, difficulty biting or chewing, breathing through the mouth and, rarely, speech difficulties such as a lisp.

Overbite and deep bite

MedlinePlus describes a Class 2 malocclusion, often called an overbite, as one in which the upper jaw and teeth overlap the lower ones markedly. The AAO describes a related problem, the deep bite, in which the upper front teeth cover the lower teeth vertically more than usual. In some people the upper teeth bite into the lower gums, or the lower teeth bite into the roof of the mouth.

According to the AAO, a deep bite can be linked to childhood habits, early loss of baby teeth, overdevelopment of the supporting bone and differences in the growth of the jaws. If untreated, it can contribute to tooth wear, damage and sensitivity, gum problems and jaw pain. The AAO also describes protrusion, often called buck teeth, where the upper front teeth sit too far forward; prominent front teeth are more likely to be injured and can make it hard to close the lips comfortably.

Underbite

An underbite, described by MedlinePlus as a Class 3 malocclusion, is when the lower jaw juts forward past the upper jaw, so that the lower front teeth sit in front of the upper front teeth. The AAO explains that an underbite may be inherited or may develop as the front teeth come through in childhood, and that it is usually caused by the upper and lower jaws growing at different rates.

Beyond its effect on appearance, an underbite can make biting and chewing more difficult, contribute to speech problems and excessive tooth wear, and place extra stress on the jaw joints, which may cause jaw pain.

Crossbite

The AAO defines a crossbite as one in which some upper teeth fit inside the lower teeth. It can involve a single tooth or a group of teeth. A posterior crossbite affects the back teeth and is the more common type; an anterior crossbite affects the front teeth. Crossbites can be caused by misaligned teeth, including baby teeth, or by the position of the jaws.

The AAO notes that an untreated crossbite can shift the jaw to one side, which can result in lopsided jaw growth, and can wear down tooth enamel and contribute to gum disease and jaw problems.

What causes bite problems

MedlinePlus states that heredity is the most common cause. Other factors it lists include:

• a mismatch between the size of the jaws and the size of the teeth, or differences in jaw shape;
• birth differences such as cleft lip and palate;
• childhood habits, including thumb sucking, tongue thrusting and prolonged use of a dummy or bottle;
• extra, lost or impacted teeth;
• poorly fitting dental work or appliances;
• jaw fractures after an injury, and, rarely, tumours of the mouth or jaw.

The AAO adds that habits such as thumb sucking or mouth breathing in early childhood can also lead to an open bite, where the upper and lower teeth do not touch when the mouth is closed. MedlinePlus notes that many bite problems cannot be prevented, but that managing habits such as thumb sucking and finding problems early can help.

How bite problems are assessed and treated

A dentist often notices a bite problem during a routine check-up and may refer you or your child to an orthodontist. MedlinePlus explains that X-rays of the teeth, head or face and models of the teeth may be used to understand the problem. In the UK, the NHS describes the orthodontist examining the teeth and jaws and taking X-rays, photographs or scans.

Many bites never need correcting; MedlinePlus says the majority of alignment problems are small and can be left alone. When treatment is advised, options described by MedlinePlus include braces or clear aligners, removing teeth to relieve crowding, and reshaping or repairing irregular teeth. The NHS lists upper and lower jaws not meeting properly, such as an overbite or underbite, among the reasons braces are used.

For growing children with prominent upper teeth, the British Orthodontic Society (BOS) describes functional appliances, such as the Twin Block, which are used mainly to correct Class II problems, in which the upper teeth bite in front of the lower teeth. The BOS says these are believed to be most effective before or during the growth spurt of adolescence, and they are often followed by fixed braces to straighten the teeth. The AAO notes that bite problems in children will likely not fix themselves and are ideally treated while the child is still growing. After any treatment, a retainer is needed to keep the teeth stable.

MedlinePlus explains that the length of treatment depends on how much correction is needed, ranging from around half a year to beyond two years, and that adults may need longer. Your orthodontist will advise on the likely timeline.

When jaw surgery is considered

Sometimes the teeth are only part of the problem and the jaws themselves are out of balance, for example with a prominent lower jaw or a small, set-back lower jaw. MedlinePlus notes that jaw surgery is rarely needed, but in these cases braces alone may not be enough. Cambridge University Hospitals explains that jaw surgery, called orthognathic surgery, is recommended when the bones of the face and jaws are out of balance and it has not been possible to correct the bite with orthodontics alone. The BOS describes it as surgery used to correct the bite and change the facial profile; in some cases the change in appearance is minimal, while in others it is more noticeable.

This treatment combines orthodontics and surgery and is planned by an orthodontist and a surgeon together. A leaflet from University Hospitals Plymouth explains that braces are usually worn for a period before surgery to line the teeth up so they will meet correctly afterwards, and for some months after the operation, with elastic bands helping to guide the bite. The same leaflet notes that the jaws generally finish growing by around 18, so surgery is normally considered from the late teens, and that patients should expect to wear fixed braces for at least two years in total, sometimes longer. Your orthodontist and surgeon will advise on timing, recovery and the risks that apply to you.

Next steps

If you or your child have a bite that feels uneven, makes chewing difficult or causes jaw discomfort, an orthodontic assessment can show whether the problem lies in the teeth, the jaws or both, and whether treatment is needed. Visit our orthodontist specialty overview for background on bite care, or go to Find my physician to be matched with an orthodontist for an examination.