Overbite, Underbite, Crossbite: What's the Difference and Can Orthodontics Fix It?

If you've been told you have an overbite, underbite, or crossbite — or if you've noticed that your teeth don't quite meet the way they should — you're not alone. Bite problems are among the most common reasons people seek orthodontic treatment in the UK, affecting millions of adults and children. But the terms can be confusing: what exactly is the difference between an overbite and an underbite? Is a crossbite serious? And can orthodontics actually fix them, or do you need surgery?

This guide covers all three bite problems in plain English — what causes them, what they look and feel like, when they need treatment, and what your options are. Whether you're exploring treatment for yourself or a child, understanding your bite is the first step to knowing what to do about it.

What Is a Malocclusion? The Common Thread

Before examining each bite problem individually, it helps to understand the umbrella term: malocclusion. Malocclusion simply means that the upper and lower teeth do not fit together correctly when the jaws are closed. The British Orthodontic Society classifies malocclusions into three broad categories based on how the upper and lower jaws relate to each other — Class I (good jaw relationship but crowded or misaligned teeth), Class II (upper jaw or teeth protrude forward relative to the lower), and Class III (lower jaw or teeth sit in front of the upper). Overbites typically fall into Class II; underbites into Class III; crossbites can occur within any class.

Malocclusions range from minor aesthetic issues to significant functional problems affecting how you chew, speak, and breathe. The severity, cause, and recommended treatment all vary — which is why a proper assessment by a qualified orthodontist is essential before any treatment decisions are made.

What Is an Overbite?

An overbite occurs when the upper front teeth overlap the lower front teeth vertically by an excessive amount. Some vertical overlap is normal — a healthy overbite is typically around 2 to 4 millimetres, where the upper teeth slightly cover the lower teeth when you bite down. Problems arise when this overlap is too deep (a deep bite) or, in some cases, when the upper front teeth protrude significantly forward (often called an overjet).

Overbite vs overjet — what's the difference?

These two terms are frequently confused, including by patients who have been told they have one or the other. An overbite is a vertical measurement — how much the upper teeth overlap the lower teeth when the mouth is closed. An overjet is a horizontal measurement — how far the upper teeth protrude forward in front of the lower teeth. Many people have both. Colloquially, both are sometimes called an overbite, but they describe different dimensions of the same problem and may require different treatment approaches.

What causes an overbite?

Overbites can be caused by skeletal factors (the position of the jaw bones relative to each other, inherited genetically) or dental factors (the position of the teeth within the jaws, often influenced by habits). Common causes include:

Dental overbites (caused by tooth position rather than jaw structure) are generally more straightforward to treat with orthodontics alone. Skeletal overbites involving the jaw bones may require functional appliances in childhood or jaw surgery in adulthood.

Symptoms and problems caused by an overbite

A mild overbite may cause no symptoms at all. A significant overbite can lead to:

Can orthodontics fix an overbite?

Yes — most overbites can be corrected with orthodontic treatment. In children and teenagers, fixed braces often combined with functional appliances (such as the Twin Block or Herbst appliance) can guide jaw growth and move teeth simultaneously. In adults whose jaw growth is complete, dental overbites respond well to fixed braces or clear aligners. Skeletal overbites in adults — where the jaw positions themselves are significantly misaligned — may require orthognathic (corrective jaw) surgery combined with orthodontics for a full correction, though many patients choose orthodontics alone to improve their bite functionally and aesthetically without surgery.

What Is an Underbite?

An underbite is the opposite arrangement to an overbite: the lower front teeth sit in front of the upper front teeth when the jaw is closed, rather than behind them. This creates a characteristic appearance where the lower jaw protrudes forward. In the UK, underbites are less common than overbites — they affect approximately 5 to 10% of the population — but they are often more visible and can have significant functional consequences.

Dental vs skeletal underbite

Like overbites, underbites can be primarily dental (the lower front teeth are angled too far forward or the upper front teeth too far back) or skeletal (the lower jaw bone itself is positioned further forward than the upper jaw). A dental underbite may be correctable with orthodontics alone. A skeletal underbite, particularly a severe one where the jaw position itself is the primary cause, is more likely to require jaw surgery to fully correct in adulthood — though orthodontics can still improve function and aesthetics significantly even without surgery.

What causes an underbite?

Symptoms and problems caused by an underbite

An underbite that goes untreated can cause:

Can orthodontics fix an underbite?

In children, underbites are often treated early — ideally between the ages of 7 and 10 — using growth modification appliances such as a facemask (reverse-pull headgear) that encourages the upper jaw to grow forward to meet the lower. This approach works only while the face is still growing. In teenagers with an active growth phase, functional appliances combined with braces can produce significant improvement.

In adults, mild to moderate dental underbites can be corrected with braces or clear aligners. Severe skeletal underbites in adults may be treated with orthodontics alone to improve function and appearance, or with orthognathic surgery for a more complete skeletal correction. The decision depends on the severity, the patient's priorities, and their suitability for surgery.

What Is a Crossbite?

A crossbite occurs when some of the upper teeth sit inside (behind) the lower teeth rather than outside (in front of) them when you bite down. Unlike overbites and underbites — which describe the overall relationship between the upper and lower jaws in the front-to-back direction — a crossbite can affect just one or two teeth or a whole section of the bite, and it can occur at the front or the back of the mouth.

Anterior crossbite vs posterior crossbite

An anterior crossbite involves the front teeth — one or more upper front teeth sit behind the lower front teeth, creating what looks like a localised underbite. An posterior crossbite involves the back teeth — the upper back teeth (premolars or molars) sit inside the lower back teeth on one or both sides. Posterior crossbites often cause the jaw to shift to one side when closing, which can lead to facial asymmetry over time and is a significant functional concern in growing children.

What causes a crossbite?

Why crossbites should be treated early

Of the three bite problems covered in this guide, crossbites are the one where early treatment is most strongly recommended by the British Orthodontic Society. A posterior crossbite that causes the jaw to shift when closing can contribute to facial asymmetry that becomes progressively harder to correct as growth continues. Treating a crossbite in a growing child — typically between ages 7 and 12 — is significantly more straightforward than treating the same crossbite in an adult.

Can orthodontics fix a crossbite?

Yes — and for most crossbites, orthodontic treatment alone is sufficient. In children, a narrow upper arch causing a posterior crossbite is commonly treated with a palatal expander (a fixed appliance that gradually widens the upper arch). This is most effective before the midpalatal suture fuses in the mid-teens. Fixed braces can then align the teeth into the corrected arch. In adults, a posterior crossbite may require surgically-assisted rapid palatal expansion (SARPE) to widen the arch, since the midpalatal suture is fused. Anterior crossbites can often be corrected with braces or aligners alone, depending on their cause.

Comparing the Three Bite Problems Side by Side

How Bite Problems Are Diagnosed

A proper bite assessment involves more than just looking at your teeth. An orthodontist will evaluate your dental and facial photographs, take dental X-rays to assess tooth and root positions, check the jaw joint for any signs of dysfunction, and measure the relationship between your upper and lower jaws in three dimensions. In complex cases, a CBCT (cone beam computed tomography) scan may be used to produce a three-dimensional image of the jaw bones.

For many patients, the first step is completing an online orthodontic assessment — submitting photographs of your teeth and bite from home and receiving a clinician response that outlines what they can see and what options may be appropriate. This doesn't replace a clinical examination but gives you a useful starting point before committing to an in-person consultation fee.

If you're concerned about NHS eligibility for your bite problem, the IOTN score checker provides an estimate of whether your case might qualify based on the Index of Orthodontic Treatment Need — the scale used by the NHS to prioritise treatment for children under 18.

NHS Treatment for Bite Problems — Who Qualifies?

NHS orthodontic treatment in England, Wales, and Northern Ireland is available for children under 18 whose bite problem meets a minimum threshold on the Index of Orthodontic Treatment Need (IOTN). The IOTN assigns scores from 1 (no need) to 5 (very great need). Generally, children with overbites greater than 6mm, underbites, significant crossbites, and certain severe bite problems will score IOTN 4 or 5 and qualify for NHS treatment at no cost.

Adults are not eligible for NHS orthodontic treatment through the standard pathway. Adult NHS treatment is available only in exceptional circumstances — typically as part of combined orthodontic and surgical treatment for severe skeletal malocclusions — and requires a specialist referral. Most adult patients seeking bite correction will do so privately.

The NHS orthodontic eligibility checker on Virtual Consultant Online provides guidance on whether your bite problem is likely to meet NHS treatment criteria, which can help you understand your options before seeking a formal referral from your NHS dentist.

Treatment Options: What Can Fix Each Bite Problem?

Fixed braces

Fixed metal or ceramic braces remain the most versatile treatment for bite correction. They can apply precise forces to move individual teeth, adjust the angulation of roots, and work in conjunction with additional appliances such as elastics, headgear, or functional appliances to address the jaw relationship as well as the tooth positions. For complex bite problems involving multiple types of misalignment simultaneously, fixed braces are often the treatment of choice.

Clear aligners (Invisalign and alternatives)

Clear aligners have become increasingly capable at treating bite problems, including moderate overbites, anterior crossbites, and some underbites. They work by moving teeth in small increments through a series of custom-made transparent trays. Their limitations lie primarily in skeletal bite problems — where the jaw position itself needs to change — and in cases requiring precise root torque movements that aligners struggle with. Your orthodontist will advise whether aligners are appropriate for your specific bite problem or whether fixed braces would give a more reliable outcome.

Functional appliances (children)

For growing children with overbites or underbites, functional appliances use the forces of the growing jaw to redirect development. The Twin Block appliance is commonly used for Class II (overbite) cases; the reverse-pull facemask for Class III (underbite) cases. These appliances are effective only during active facial growth and are not used for adults. They are typically followed by a phase of fixed braces to refine tooth positions once the jaw relationship has been corrected.

Palatal expanders (crossbite)

A rapid palatal expander (RPE) is a fixed appliance cemented to the upper back teeth that applies gentle outward pressure to gradually widen the upper arch. A small screw in the centre of the appliance is turned by the patient or parent daily using a key. Over six to twelve weeks, the upper arch is expanded enough to correct the crossbite and create space for the teeth. This is significantly easier to achieve in children under 14, before the midpalatal suture fuses.

Orthognathic surgery (severe cases)

When a bite problem is primarily caused by the position of the jaw bones rather than the teeth — and when the severity is significant — orthognathic (corrective jaw) surgery may be recommended. This typically involves pre-surgical orthodontics (braces worn before the operation to position the teeth correctly within each arch), followed by surgery to reposition the upper jaw, lower jaw, or both, followed by post-surgical orthodontics to finalise the bite. The process takes 18 to 36 months in total. Orthognathic surgery is available on the NHS for qualifying cases and is performed by oral and maxillofacial surgeons, usually in a hospital setting.

Does Having a Bite Problem Mean You Need Braces?

Not always. Whether treatment is recommended depends on the severity of the bite problem and whether it is causing or is likely to cause functional problems. A small overbite within the normal range (2 to 4mm) needs no treatment. A very mild anterior crossbite on a single tooth may be monitored rather than treated immediately. However, if your bite is causing wear on your teeth, jaw pain, difficulty chewing, speech problems, or significant self-consciousness, treatment is worth discussing seriously.

The common mistake is assuming that bite problems are purely aesthetic — that treatment is optional in the way that whitening or veneers might be. Some bite problems, left untreated, cause progressive damage to tooth enamel and the jaw joint that becomes increasingly expensive and complex to address with age. Crossbites in children that cause the jaw to shift are in this category: the younger the child when it's corrected, the simpler the treatment and the better the long-term outcome.

If you're trying to understand what orthodontic problems your teeth have, the problems guide on Virtual Consultant Online covers the full range of conditions that orthodontics addresses, from spacing and crowding to jaw relationships and bite correction. The treatments section explains the specific treatment types used for each condition and what to expect during the process.

What Happens If You Don't Treat a Bite Problem?

The consequences of leaving a bite problem untreated depend on its type and severity. For mild issues, the answer is often that nothing serious happens — the bite remains as it is without causing significant additional problems. For more significant bite problems, the risks of non-treatment include:

How to Get a Bite Assessment

If you think you or your child may have an overbite, underbite, or crossbite, the first step is getting a proper assessment. Your options in the UK are:

To find an orthodontist near you, the Virtual Consultant Online location tool can help you identify practices in your area that offer digital assessment and bite consultations.