An overjet is when your upper front teeth protrude horizontally past your lower front teeth by more than 2 millimeters. Most people have some degree of overlap between their upper and lower teeth, and about 2 millimeters of horizontal protrusion is considered normal. Beyond that threshold, it’s classified as an overjet, sometimes called “buck teeth.”
Overjet vs. Overbite
These two terms get mixed up constantly, but the difference is simple: direction. An overjet is a horizontal problem where the upper teeth stick out forward, away from the lower teeth. An overbite is a vertical problem where the upper teeth overlap the lower teeth too deeply when you bite down (more than 3 millimeters of vertical coverage). Think of overjet as a gap between front and back, and overbite as upper teeth covering lower teeth top to bottom.
You can have both at the same time. In fact, the most common pattern in orthodontic classification pairs the two together: upper teeth that are both pushed forward and overlapping deeply. This combination is what orthodontists call a Class II Division 1 malocclusion, and it often comes with a narrow, V-shaped upper arch and difficulty closing the lips comfortably at rest.
How Overjet Is Measured
Your dentist or orthodontist measures overjet by checking the horizontal distance from the back surface of your upper front teeth to the front surface of your lower front teeth. Normal is 1 to 2 millimeters. Anything above 2 millimeters is considered an overjet, and cases of 8 to 10 millimeters or more are classified as severe. That severity threshold matters because it determines whether orthodontic treatment alone can fix the problem or whether jaw surgery becomes part of the conversation.
What Causes an Overjet
Overjet develops from a combination of genetics, jaw growth patterns, and childhood habits. The two broad categories are skeletal and dental. A skeletal overjet means the jaw bones themselves are mismatched, typically because the lower jaw didn’t grow forward enough relative to the upper jaw. A dental overjet means the jaw bones are reasonably well-aligned but the teeth themselves are angled or positioned too far forward. In practice, most overjets involve some degree of both.
Childhood habits play a significant role. Pacifier sucking at 12, 18, and 30 months of age is associated with overjet development. The same goes for thumb or finger sucking during those ages. If either habit persists beyond 48 months (about four years old), the potential for causing a lasting bite problem increases considerably. Tongue thrusting, where the tongue pushes against the front teeth during swallowing, contributes as well. Children who weren’t breastfed or were breastfed only briefly show higher rates of these oral habits and the jaw development issues that follow.
Health Risks of Untreated Overjet
The most well-documented risk is dental trauma. Children with an overjet of 6 millimeters or more are roughly 3 to 4 times more likely to suffer injury to their front teeth compared to children with normal overjet. A prospective study tracking children over time found that those with large overjets had a relative risk of 3.37 for dental trauma. The reason is straightforward: teeth that protrude are less protected by the lips and more exposed during falls, sports, and everyday collisions.
Beyond trauma, a significant overjet can affect speech. Certain sounds, particularly “s,” “z,” and “th,” require the tongue to interact with the front teeth in specific ways, and a large horizontal gap between upper and lower teeth makes that harder. Some people develop a lisp or whistling quality to their speech. Difficulty biting into food with the front teeth is also common, since the upper and lower incisors don’t meet properly. Over time, the uneven bite distribution can lead to excessive wear on the back teeth that compensate for the front.
Treatment Options
How an overjet gets corrected depends on whether the problem is mainly dental, mainly skeletal, or a mix of both, and on the patient’s age.
For dental overjets where the jaw structure is fine but the teeth are angled forward, braces or clear aligners can gradually reposition the teeth. Mild cases typically take 6 to 12 months, moderate cases 12 to 18 months, and severe cases 18 months to two years or longer. Teenagers generally respond faster than adults because their jaws are still growing and more adaptable to movement.
For younger children with skeletal components, orthodontists sometimes use functional appliances that guide jaw growth while the child is still developing. These devices encourage the lower jaw to grow forward or restrain upper jaw growth, depending on the specific pattern. Palate expanders can also be part of early treatment when the upper arch is too narrow. The American Association of Orthodontists recommends children have their first orthodontic evaluation by age 7, which gives enough time to catch skeletal problems before growth is complete.
For adults with severe skeletal overjets, orthodontics alone often can’t solve the problem. Research shows strong consensus among orthodontists that a positive overjet greater than 8 millimeters typically can’t be corrected with braces or aligners by themselves. In these cases, orthognathic (jaw) surgery repositions the upper or lower jaw to correct the underlying bone discrepancy, with braces used before and after surgery to fine-tune the tooth alignment. This is a more involved process, but it addresses the root cause in a way that braces alone cannot when the jaw bones are significantly mismatched.
Dental vs. Skeletal: Why the Distinction Matters
If your overjet is purely dental, meaning your teeth are tilted forward but your jaws line up well, treatment is more straightforward and less invasive. Braces or aligners can tip the teeth back into proper position, and the results tend to be stable. If the overjet is skeletal, the teeth may already be compensating for the jaw mismatch by tilting in ways that partially mask the problem. Simply moving the teeth without addressing the jaw discrepancy can create an unstable result or compromise facial aesthetics.
Your orthodontist determines which type you have through X-rays that measure the relationship between your upper and lower jaw bones, not just the teeth. This is why a thorough evaluation matters before starting treatment. Two people with the same millimeter measurement of overjet can need very different treatment plans based on what’s happening underneath.