Overbite, Underbite & Crossbite: Types of Malocclusion Explained

Editorially reviewed by the Dental.me Editorial Team · Updated July 2026

If a dentist or orthodontist has ever told you that your teeth “don’t line up right,” they were describing malocclusion. It is one of the most common reasons people seek orthodontic care, yet the terminology can be confusing. Overbite, underbite, crossbite, overjet, Class II, open bite, crowding: these words get used loosely and sometimes interchangeably, even though they describe genuinely different problems. This guide breaks down the main types of malocclusion in plain language, explains how orthodontists classify them, what causes them, and how each one is treated.

What Does Malocclusion Mean?

“Malocclusion” simply means a bad bite. “Occlusion” is the way your upper and lower teeth meet when you close your mouth, and the prefix “mal-” means the fit is off in some way. In an ideal bite, the upper teeth rest slightly in front of the lower teeth, the points of the molars fit neatly into the grooves of the opposing molars, and the teeth are evenly spaced without crowding or gaps.

Very few people have a textbook-perfect bite. Mild malocclusion is extremely common and often needs no treatment at all. It becomes clinically important when it causes uneven tooth wear, jaw strain, difficulty chewing or speaking, or teeth that are hard to keep clean. Malocclusion can be dental (the teeth are tilted or out of position but the jaws are aligned) or skeletal (the jaws themselves are positioned or sized differently). That distinction matters, because it often decides whether braces alone can fix the problem or whether more involved treatment is needed.

The Common Types of Malocclusion

Most bite problems fall into a handful of recognizable categories. Many people have more than one at the same time.

• Overbite (deep bite). This is vertical overlap: the upper front teeth cover too much of the lower front teeth when you bite down. A deep overbite can wear the lower teeth and, in severe cases, the lower teeth bite into the gum behind the upper front teeth.
• Underbite. The lower front teeth sit in front of the upper front teeth. It is usually skeletal, driven by a lower jaw that grows longer than the upper jaw, and is the hallmark of a Class III bite.
• Crossbite. One or more teeth bite on the wrong side of the opposing teeth. An anterior crossbite affects the front teeth (a small underbite of one or two teeth), while a posterior crossbite affects the back teeth, often because the upper jaw is too narrow. Crossbites can push the lower jaw to shift sideways when closing.
• Open bite. The front teeth (or sometimes the back teeth) don’t touch at all when the back teeth are closed, leaving a visible gap. It is frequently linked to prolonged thumb-sucking or tongue thrust.
• Crowding. There isn’t enough room in the jaw for all the teeth, so they overlap, rotate, or push out of line. Crowding is the most common reason people get braces and makes cleaning harder.
• Spacing. The opposite problem: gaps between teeth, either because teeth are small relative to the jaw or because a tooth is missing.

Overbite vs. Overjet: Clearing Up the Confusion

These two terms are the most commonly mixed up, and the difference is worth understanding because they call for different fixes. Both are normal in small amounts.

• Overbite is vertical overlap: how far the upper front teeth come down over the lower front teeth. Picture the top teeth hiding the bottom teeth from view. A “deep bite” is an excessive overbite.
• Overjet is horizontal protrusion: how far the upper front teeth stick out ahead of the lower ones, measured front to back. This is what most people mean casually by “buck teeth.” A large overjet often comes with a Class II bite and can be skeletal, from a lower jaw set back relative to the upper.

You can have one without the other. A patient might have a deep overbite with normal overjet, or teeth that protrude forward (large overjet) with very little vertical overlap. Orthodontists measure both in millimeters, because the numbers guide whether the goal is to intrude and reposition the front teeth, hold back the upper jaw’s growth in a child, or address the jaw relationship directly.

Angle’s Classification: Class I, II, and III

Orthodontists organize bites using a system developed by Edward Angle, based on how the upper and lower first molars meet. Translated into plain language:

• Class I. The molars meet in the normal, ideal relationship, but there may still be crowding, spacing, or a mild overbite. The jaws are essentially aligned; the issue is with individual teeth.
• Class II. The lower molar sits too far back relative to the upper, so the upper teeth are ahead of the lower. This is the pattern behind many cases of increased overjet and a retruded lower jaw.
• Class III. The lower molar sits too far forward, so the lower teeth are ahead of the upper. This is the classic underbite pattern and is often skeletal.

The class describes the underlying jaw relationship, while terms like overbite, crossbite, and crowding describe specific features on top of it. A single patient might be “Class II with a deep overbite and mild crowding,” which tells the clinician exactly what needs correcting.

What Causes Malocclusion?

Most malocclusion comes from a mix of inherited traits and habits, not from any single cause. The main contributors are:

• Genetics. Jaw size and shape, tooth size, and the number of teeth are largely inherited. You can inherit a small jaw from one parent and large teeth from another, a recipe for crowding.
• Prolonged thumb-sucking or pacifier use. Sustained pressure on the growing front teeth and palate can push teeth forward and create an open bite or increased overjet, especially past about age three or four.
• Tongue thrust. A habit of pushing the tongue against or between the front teeth when swallowing or at rest can hold an open bite open and resist closure.
• Early or late loss of baby teeth. Baby teeth hold space for the adult teeth. Losing one too early lets neighboring teeth drift into the gap, so the permanent tooth erupts crooked or is blocked out.
• Mouth breathing and airway issues, injury, or large fillings and poorly fitted dental work can also nudge teeth out of alignment over time.

Why Correcting Malocclusion Matters

Straightening a bite is not only cosmetic. Left unaddressed, significant malocclusion can lead to real functional problems:

• Uneven wear. When teeth don’t meet evenly, some carry more force than they should, chipping, flattening, or wearing down enamel prematurely.
• Jaw pain and TMJ strain. A bite that forces the jaw to shift or overwork can contribute to muscle fatigue and jaw-joint discomfort. If you grind or clench and wake with a sore jaw, it is worth learning more about TMJ disorders and what triggers them.
• Chewing and speech. Open bites and severe underbites can make it harder to bite through food cleanly or to form certain sounds.
• Cleaning difficulty. Crowded and overlapping teeth trap plaque in spots a brush can’t reach, raising the risk of decay and gum disease.

Not every mild case needs braces, and a good orthodontist will tell you when watchful waiting is the smarter choice. But correcting a bite that is actively causing wear or strain protects the teeth you have for decades.

Treatment Options and Timelines

The right treatment depends on the type of malocclusion, its severity, and whether the problem is in the teeth or the jaws. Common approaches include:

• Braces. Fixed braces remain the workhorse for moving teeth precisely and are especially effective for crowding, rotations, deep overbites, and complex cases. If you’re curious about the mechanics, our guide to how braces actually move teeth walks through it.
• Clear aligners. Removable, nearly invisible trays can correct many mild to moderate cases of crowding, spacing, and some bite issues. They aren’t right for every problem, so it helps to compare Invisalign against traditional braces and to read a broader look at clear aligners versus braces before deciding.
• Palatal expanders. In children and some teens whose upper jaw is too narrow, an expander widens the palate to fix posterior crossbites and create room, taking advantage of a still-growing skeleton.
• Jaw surgery (orthognathic surgery). For severe skeletal underbites, large skeletal overjets, and pronounced open bites in adults who have stopped growing, braces or aligners are combined with surgery to reposition the jaws. This is reserved for cases that tooth movement alone cannot correct.

Timelines vary widely. Simple spacing or minor crowding might resolve in six to twelve months, while a comprehensive case with braces commonly runs about eighteen to thirty months. Skeletal cases with surgery take longer and are staged around the procedure. Adults can absolutely be treated; movement can be a little slower once growth is complete, but the biology still works, as our overview of braces for adults explains. Whatever the method, treatment isn’t finished when the braces come off. Teeth naturally drift back, so wearing a retainer as directed is what makes the result last; if you’re unsure what that involves, here’s what a retainer does and why it matters. The best first step is an orthodontic evaluation, where a specialist measures your bite and tells you exactly which type of malocclusion you have and what, if anything, is worth correcting.

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