A crossbite is when one or more upper teeth bite inside the lower teeth instead of outside them. Normally, your upper teeth sit slightly wider than your lower teeth, like a lid on a box. When that relationship is reversed, even on just one side or for a single tooth, that’s a crossbite. It affects roughly 6 to 9% of children and adolescents, making it one of the more common bite problems orthodontists see.
What a Posterior Crossbite Looks Like
A posterior crossbite involves the back teeth, your molars and premolars. When you bite down, one or more upper back teeth sit inside the lower back teeth rather than outside them. If you ran your tongue along the biting surfaces, you’d feel that the upper teeth are closer to your tongue than the lower ones on the affected side.
This can happen on one side (unilateral) or both sides (bilateral). Unilateral posterior crossbites are more common, showing up in about 8% of children, while bilateral crossbites occur in roughly 2.5%. When only one side is affected, the bite often looks noticeably lopsided. You might see the jaw shift to one side as the mouth closes, because the person is unconsciously repositioning their lower jaw to get more teeth to touch comfortably. That sideways shift is called a functional shift, and it’s one of the most visible clues that something is off.
What an Anterior Crossbite Looks Like
An anterior crossbite involves the front teeth. Instead of the upper front teeth sitting in front of the lower ones when you bite down, one or more upper teeth tuck behind the lower teeth. This is different from a full underbite, where the entire lower jaw juts forward. With an anterior crossbite, the problem may be limited to just one or two teeth, while the rest of the bite looks normal.
From the outside, an anterior crossbite can make the smile look uneven or slightly reversed in one spot. You might notice that one upper tooth appears pushed back, sitting behind the tooth below it. In a full underbite, the entire lower jaw is visibly ahead of the upper jaw, giving the chin a prominent, forward appearance. A single-tooth anterior crossbite is subtler and easier to miss unless you look closely at how the teeth overlap.
How a Crossbite Changes Your Face
A crossbite doesn’t just affect the teeth. Over time, especially when it starts in childhood, it can reshape the face itself. When the lower jaw consistently shifts to one side to compensate for a posterior crossbite, the muscles and bones adapt to that position. Research on adults with unilateral posterior crossbites shows measurable asymmetry: the lower jawbone grows longer on one side, and the chin point drifts toward the shorter side. The result is a face that looks slightly uneven, with one side of the jaw appearing fuller or more angular than the other.
Children are especially vulnerable to these changes because their bones are still growing. A jaw that shifts to one side year after year can develop permanent skeletal differences that become harder to correct later. In some adults, correcting the facial asymmetry caused by a long-standing crossbite requires surgery in addition to orthodontic treatment.
Signs to Watch for in Children
Crossbites can develop in baby teeth, and spotting them early makes a real difference. Here are the visual cues parents typically notice first:
- Jaw shifting: Your child moves their jaw to one side when biting down or chewing.
- A narrow upper jaw: The upper arch looks visibly narrower than the lower one.
- An off-center smile: The midline of the upper teeth doesn’t line up with the midline of the lower teeth.
- Uneven contact: One side of the bite touches before the other when the mouth closes.
- Reversed overlap: The front teeth overlap in the wrong direction, with upper teeth sitting behind lower ones.
These signs can appear as early as the toddler years. Even if your child isn’t complaining of discomfort, a visible jaw shift or narrow upper arch is worth having evaluated.
What Happens If a Crossbite Goes Untreated
A crossbite forces teeth to grind against each other in ways they weren’t designed for. Over months and years, this wears down enamel unevenly, particularly on the side where the crossbite is. Thinner enamel means teeth become more sensitive to heat and cold, and they’re more vulnerable to cavities.
The strain goes beyond the teeth. A jaw that consistently shifts to accommodate a crossbite puts extra stress on the jaw joints and muscles. This can lead to jaw pain, clicking, or headaches. The longer the crossbite persists, the more the surrounding bone and muscle adapt to the misaligned position, making the problem progressively harder to fix with simple orthodontic adjustments alone.
How Crossbites Are Corrected
The approach depends on whether the crossbite is caused by the teeth being in the wrong position, the jaw being too narrow, or both. For children, the most effective window for treatment opens around age 7 or 8, when the jawbones are still developing and the suture running down the center of the palate hasn’t fully fused. A palatal expander, a device anchored to the upper back teeth, gradually widens the upper jaw over several weeks by gently separating that suture. This creates enough room for the upper teeth to sit outside the lower teeth where they belong.
For mild to moderate crossbites in older teens and adults, braces or clear aligners can shift individual teeth into the correct position. Clear aligners work well when the issue is mainly dental, meaning the jaw width is fine but certain teeth are simply tilted or positioned incorrectly. For more complex cases involving skeletal narrowness, traditional braces give the orthodontist more precise control over individual tooth movement.
Adults whose palatal suture has fully hardened sometimes need a surgically assisted expander. An oral surgeon places the device directly into the mid-palatal suture, allowing the bone to be gradually widened in a way that wouldn’t be possible with a standard expander on mature bone. Recovery is straightforward, but the process takes longer than it does for a child whose bones are naturally more flexible.
Dental vs. Skeletal Crossbite
Not all crossbites look the same on the inside. A dental crossbite means the teeth themselves are tilted or positioned incorrectly, but the underlying jawbones are a normal width. The teeth on the crossbite side lean inward on top and outward on the bottom, creating the reversed overlap. This type is generally easier to fix because it’s a tooth-position problem, not a bone-structure problem.
A skeletal crossbite means the upper jaw is genuinely narrower than the lower jaw. Research comparing the two types in adults found that skeletal crossbites produce more pronounced asymmetry: the lower jawbone grows to different lengths on each side, and the chin deviates measurably toward the affected side. From the outside, a skeletal crossbite tends to be more visible in the overall shape of the face, while a dental crossbite may only be noticeable when you look at the teeth themselves.