Crossbite: why it matters, and how it is treated

What a crossbite is

In a normal bite the upper teeth sit slightly outside the lower ones all the way round, like a lid on a box. In a crossbite that relationship is reversed somewhere: an upper tooth, or a run of them, closes inside the lower teeth.

• Anterior crossbite affects the front teeth: one or more upper incisors bite behind the lower ones. A single upper tooth stuck behind the lower teeth is common and often noticed in the early teens.
• Posterior crossbite affects the back teeth, on one side or both. The upper molars and premolars close inside the lowers, usually because the upper arch is narrower than the lower.
• A scissor bite is the rarer opposite, where the upper back teeth close completely outside the lowers and the cusps do not meet at all.

A crossbite can be dental, caused by individual teeth tipping the wrong way, or skeletal, caused by an upper jaw that is narrow or set back. Most adult crossbites are dental, or a mild skeletal narrowing that tooth movement can compensate for.

How to recognise one

Bite together and look at where the upper teeth meet the lower ones. Any upper tooth sitting behind a lower tooth is a crossbite. People with a posterior crossbite often notice that their jaw slides to one side as they close, or that their chin looks slightly off-centre. Other clues are biting your cheek or tongue on one side, teeth wearing faster on one side than the other, gum recession on a single tooth that takes the force, and a front tooth that looks shorter or more worn than its neighbour.

What causes it

A narrow upper jaw is the usual reason for a posterior crossbite, and that is inherited or the result of long-term mouth breathing or thumb sucking in childhood. An anterior crossbite often starts when a baby tooth is lost late and the adult tooth comes through behind the line of the others. Crowding plays a part in both: a tooth with nowhere to go erupts inside the arch.

Why it is worth treating

A crossbite concentrates the chewing force on the wrong parts of the wrong teeth. Over the years that means uneven wear, chipped edges, and recession of the gum on the teeth taking the load. A jaw that has to slide sideways to close puts strain on one joint more than the other. In a child it can change how the jaw grows, so a one-sided crossbite in a child is one of the few orthodontic problems worth treating early rather than waiting.

How Invisalign corrects it

For a dental crossbite the plan moves the crossed upper teeth outwards and, where needed, the opposing lower teeth inwards, until the uppers sit outside again. Because a crossed tooth is held in place by the tooth it bites against, the aligners usually hold the bite slightly apart for a stage so the tooth can jump across; small attachments and sometimes elastics give the extra control. A mild posterior crossbite can be corrected by expanding the upper arch a few millimetres, tipping the back teeth outwards, which aligners do well in adults. The animation on this page shows a front crossbite being unlocked and the arches settling into a normal overlap.

Children and teenagers

In a child whose upper jaw is still growing, a narrow arch is best widened with an expander while the bones are still soft enough to move; the result is more stable than tooth tipping alone. Invisalign Teen can treat many crossbites in younger patients, and Louise will say when an expander or a referral to a specialist orthodontist is the better first step.

What treatment looks like here

A single front tooth in crossbite with otherwise straight teeth can be an Express or Lite case, three to seven months. A crossbite combined with crowding is usually Moderate or Comprehensive, nine to eighteen months. Every plan is shown to you in 3D at your consultation before you commit.

At Clear Braces Solihull every Invisalign package includes your consultation, iTero scan, X-ray, Dental Monitoring, Vivera retainers, professional whitening and twelve months of aftercare, in one written price. Interest-free monthly payments are available.

Questions people ask

Can Invisalign fix a crossbite?

Most dental crossbites, and mild posterior crossbites in adults, yes. A narrow upper jaw in a child is usually better widened with an expander first.

How long does crossbite treatment take?

A single crossed front tooth can be corrected in a few months. Crossbites with crowding usually take nine to eighteen months.

Can a crossbite cause jaw pain?

It can contribute, particularly when the jaw slides sideways to close. Correcting the bite often helps, but jaw pain has several causes and we would not promise it.

Will my child grow out of a crossbite?

No. A crossbite does not self-correct, and in a child it can affect how the jaw grows, which is why early assessment is sensible.

Do I need elastics or attachments?

Often a few attachments, and sometimes elastics for a stage. Both are discreet and Louise will show you how they work.