An overbite is a vertical overlap where your upper front teeth cover too much of your lower front teeth when you close your mouth. An underbite is the opposite: your lower jaw and teeth sit in front of your upper teeth. Both are types of malocclusion, meaning the teeth don’t line up the way they should, and both can range from barely noticeable to severe enough to affect chewing, speech, and long-term dental health.
How Overbite and Underbite Work
When your jaw is closed, a small amount of vertical overlap between your upper and lower front teeth is completely normal. Dentists consider 1 to 3 millimeters of overlap a healthy overbite. Once that overlap exceeds about 4 millimeters, it’s classified as a deep overbite (sometimes called a deep bite). At that point, your upper teeth may cover a third or more of your lower front teeth, and in extreme cases, the lower teeth can bite into the roof of the mouth.
An underbite goes in the other direction. Instead of the upper teeth sitting slightly in front, the lower jaw extends forward so that the bottom teeth overlap or protrude past the upper teeth. This creates a concave facial profile, where the chin appears more prominent and the midface looks flatter. Underbites fall under what orthodontists call Class III malocclusion, and they’re far less common than overbites. Globally, only about 6% of people have a Class III bite, compared to roughly 22% who have a deep overbite.
Overbite vs. Overjet
People often confuse overbite with overjet, but they describe two different problems. An overbite is vertical: the upper teeth come down too far over the lower teeth. An overjet is horizontal: the upper teeth angle outward and protrude forward past the lower teeth, sometimes called “buck teeth.” A gap of more than 2 millimeters between the front surface of the lower teeth and the back of the upper teeth is considered a significant overjet. You can have one without the other, or both at the same time.
What Causes These Bite Problems
Genetics is the primary driver of both conditions. If one of your parents had an overbite or underbite, you’re more likely to develop one yourself. In overbites, the upper jaw may be overdeveloped or the lower jaw underdeveloped. In underbites, the mandible (lower jaw) grows excessively long while the upper jaw stays short or sits too far back. These skeletal proportions are largely inherited.
Childhood habits play a supporting role. Prolonged thumb sucking, pacifier use past toddler years, and tongue thrusting (pushing the tongue against the front teeth when swallowing) can all shift tooth position over time and worsen an existing tendency toward a bad bite. Losing baby teeth too early, whether from decay or injury, can also allow neighboring teeth to drift and change how the adult teeth come in.
How a Bad Bite Affects Your Health
A mild overbite or underbite may never cause noticeable problems. But as the severity increases, so do the consequences.
Uneven tooth wear is one of the most common issues. When teeth don’t meet properly, certain surfaces grind against each other more than they should, wearing down enamel unevenly over years. This makes those teeth more vulnerable to chips, cracks, and decay. People with significant bite misalignment are also more prone to jaw joint problems, collectively known as temporomandibular disorders (TMD). These can show up as pain or tenderness in the jaw, clicking or popping sounds when opening the mouth, headaches, neck discomfort, and restricted jaw movement. Over time, TMD can lead to chronic pain, poor sleep, difficulty eating, and reduced quality of life.
Speech can also be affected. Both deep overbites and underbites can interfere with how the tongue and lips interact during speech, sometimes producing a lisp or difficulty with certain sounds. Breathing patterns may change too, particularly with underbites that alter the airway space behind the jaw.
Treatment Options for Overbites
Most overbites are corrected with braces or clear aligners. Traditional metal braces remain the most versatile option, especially for moderate to severe cases. They’re effective at controlling vertical tooth movement, closing spaces, and aligning the bite in all three dimensions. Treatment typically takes anywhere from 12 to 24 months depending on severity, though complex cases can run longer.
Clear aligners work well for mild to moderate overbites. They’re effective at straightening crowded teeth, closing small gaps, and making minor bite adjustments. However, they have limitations. Movements like significant extrusion (pulling teeth downward into position) and correcting large front-to-back discrepancies are harder to achieve with aligners alone. A comparative study found that while aligners and traditional braces performed equally well for space closure and aligning tooth margins, braces were better at correcting bite depth and achieving proper contact between upper and lower teeth.
For children and teens, early treatment can take advantage of jaw growth. Devices like palate expanders widen a narrow upper jaw, and functional appliances can guide lower jaw growth forward. The American Association of Orthodontists recommends children have their first orthodontic evaluation by age 7, when there’s still enough growth remaining to influence jaw development and potentially avoid more invasive treatment later.
Treatment Options for Underbites
Underbites are generally harder to treat than overbites because they more often involve a skeletal mismatch between the jaws rather than just tooth positioning. In children, early intervention with devices that encourage forward growth of the upper jaw (like a reverse-pull headgear or facemask) can be effective while the bones are still developing.
In adults, mild underbites caused mainly by tooth position can sometimes be managed with braces or aligners that tip the upper teeth forward and the lower teeth back. But when the underlying problem is skeletal, meaning the lower jaw is physically too long or the upper jaw too short, orthodontics alone often can’t fully correct the bite.
That’s where orthognathic (jaw) surgery comes in. Surgery is typically considered when the skeletal discrepancy is severe enough to cause functional problems with chewing. Specific thresholds that point toward surgical correction include an overjet of 0 millimeters or a negative value (meaning the lower teeth sit ahead of the upper teeth), or a molar relationship that’s off by 4 millimeters or more. Jaw asymmetries greater than 3 millimeters with a corresponding bite mismatch also fall into surgical territory. These values represent deformities at least two standard deviations from normal. Surgery repositions the jawbones themselves, followed by a period of orthodontic fine-tuning.
What to Expect During Correction
Whether you’re dealing with an overbite or underbite, the treatment process follows a general pattern. You’ll start with imaging (X-rays, sometimes a 3D scan) so your orthodontist can see how the teeth and bones relate to each other. From there, a treatment plan maps out the sequence of movements needed.
With braces, expect adjustment appointments every 4 to 8 weeks. Soreness after adjustments is normal and usually fades within a few days. One thing to know: braces make cleaning your teeth harder, and plaque buildup around brackets can irritate gums. Good brushing and flossing habits matter more during treatment than at any other time. Clear aligners sidestep this issue since you remove them to eat and brush, but they require discipline. Most need to be worn 20 to 22 hours a day to stay on schedule.
If surgery is part of the plan, orthodontic treatment typically comes first to align the teeth within each jaw, then surgery repositions the jaws, and a final phase of orthodontics settles everything into its final position. The full process from start to finish can take two to three years. Recovery from jaw surgery itself usually involves a few weeks of a soft diet and limited jaw movement, with most people returning to normal activity within four to six weeks.