Types of Malocclusion: Overbite, Underbite, Crossbite and Crowding

Malocclusion is the clinical term for teeth that do not fit together the way they ideally should when the jaws close. The word literally means "bad bite." It covers everything from teeth that are slightly crowded or twisted to jaws that meet in a markedly off relationship, and it is one of the most common reasons adults and children are referred for orthodontic assessment.

A useful way to picture it is in two layers. The first is how the individual teeth are positioned — whether they are crooked, rotated, crowded together or spaced apart. The second is how the upper and lower arches relate to each other as a whole. Most real bites are a mix of both, which is why two people described as having "an overbite" can need quite different plans.

Malocclusion is genuinely common rather than rare. A worldwide meta-analysis put the overall prevalence at roughly 56%, and the World Health Organization lists malocclusion among the most significant oral health conditions after tooth decay and gum disease. In other words, a less-than-perfect bite is the norm, not a defect — and only a share of cases need treatment at all.

Orthodontists most often describe bites using the Angle classification — Class I, II and III — which sorts cases by how the first molars and front teeth meet. The plain-language labels most people search for, such as overbite, underbite, crossbite, open bite, crowding and diastema, sit on top of that framework and are the ones this page focuses on.

Most bite problems fall into a handful of recognisable patterns, and many people have more than one at the same time. The table below summarises the main types, what each one means and the everyday effects it can have. None of these descriptions is a diagnosis — only an in-person assessment, usually with X-rays or a 3D scan, can establish what is actually going on.

Type

What it means

Typical effect

Overbite

The upper front teeth overlap the lower front teeth vertically more than they should (a "deep bite")

Lower teeth can bite into the palate over time; increased wear on front teeth; sometimes jaw-joint strain

Underbite

The lower front teeth sit in front of the upper front teeth when the jaws close; often driven by jaw growth

Harder, less efficient chewing; uneven tooth wear; can affect facial profile and speech

Crossbite

One or more upper teeth bite inside the lower teeth, at the front or the back, instead of slightly outside them

Uneven wear, a jaw that may shift to one side to close, and strain on specific teeth

Open bite

The upper and lower front (or back) teeth do not meet at all when the jaws close, leaving a visible gap

Difficulty biting through food, altered speech, and a habit history (such as prolonged thumb-sucking) in some cases

Crowding

There is not enough room in the jaw for the teeth, so they overlap, rotate or sit out of line

Harder to clean between teeth, which can raise the risk of decay and gum problems; often the most-noticed cosmetic concern

Diastema

A visible gap or spacing between teeth, most familiar as a gap between the upper front teeth

Usually a cosmetic concern; can occasionally relate to tooth size, missing teeth or a prominent gum attachment

These categories overlap in real life. Crowding frequently travels with a crossbite; an open bite can sit alongside an overjet, where the upper teeth point forward; and an underbite is often as much about jaw position as tooth position. The labels are a starting point for a conversation, not a substitute for examination.

Many people assume orthodontics is purely cosmetic. Straighter teeth are certainly part of the appeal, but the case for treating malocclusion is as much about function and long-term health as appearance.

Functionally, the bite is what lets you cut and grind food efficiently and speak clearly. When teeth meet unevenly — as in an underbite or open bite — chewing can become less effective and certain teeth take more load than they were designed for. Over years, that uneven loading can contribute to accelerated wear, chipping and, in some people, strain on the jaw joints and chewing muscles.

On the health side, crowded or overlapping teeth are simply harder to keep clean. Plaque collects in spots a toothbrush and floss struggle to reach, which can raise the local risk of tooth decay and of periodontal disease.

Where teeth are eventually lost, a poor bite can also complicate later restorative work — for example the planning of a dental bridge, a single tooth implant or dental implants more broadly, since these depend on a stable, well-distributed bite.

None of this means every malocclusion must be treated. Plenty of mild cases are perfectly healthy and best left alone. The aim of an assessment is to separate the cases where alignment protects function and tissue from the cases where treatment would be elective and cosmetic — and to be clear with the patient about which is which.

Treatment for malocclusion is matched to the cause and severity of the problem, and to whether it is mainly a tooth-position issue or a jaw-position one. There is no single "best" method; the right answer depends on the case, the patient's age and the underlying anatomy.

For mild-to-moderate crowding, spacing and many bite problems, clear aligners — such as Invisalign — use a series of removable trays to move teeth gradually.

Fixed braces remain the workhorse for more complex movements; the different types of braces suit different cases, and our braces vs clear aligners guide compares the two routes. The choice between them is clinical, not just cosmetic.

Where the problem is genuinely skeletal — the jaws themselves sit in the wrong relationship, as in many true underbites — tooth movement alone may not be enough. In those cases jaw surgery (orthognathic surgery) may be discussed to reposition the upper or lower jaw, almost always combined with a phase of orthodontics.

After any orthodontic treatment, a retainer is needed to hold the corrected position and prevent relapse.

Smaller, mainly cosmetic concerns sit at the other end of the scale.

A single diastema or a couple of minor irregularities on otherwise well-aligned teeth can sometimes be addressed with dental bonding, veneers or, where teeth are also worn or discoloured, dental crowns or a wider Hollywood smile design — but these restore the look of teeth rather than correcting an underlying bite.

A trustworthy plan starts from a proper diagnosis and offers the least invasive option that genuinely solves the problem.