Posterior Crossbite
What Is a Posterior Crossbite?
A posterior crossbite occurs when one or more upper back teeth bite inside the lower back teeth instead of outside them.
In a healthy bite, the upper teeth should fit slightly outside the lower teeth, much like a lid fitting over a container. When the upper back teeth fit inside the lower teeth, a posterior crossbite is present.
Posterior crossbites can affect one side of the mouth (unilateral crossbite) or both sides (bilateral crossbite). Some children also develop a functional shift, where the lower jaw moves to one side when they bite together in order to find a comfortable position.
Posterior crossbites are one of the most common orthodontic problems seen in growing children and are frequently associated with a narrow upper jaw.
Why Does a Posterior Crossbite Happen?
Posterior crossbites can develop for several reasons, including:
Genetics
A narrow upper jaw
Differences in jaw growth
Prolonged thumb or finger sucking
Mouth breathing
Enlarged tonsils or adenoids
Airway-related growth patterns
Delayed or abnormal tooth eruption
In many cases, the underlying problem is not the position of the teeth themselves. Instead, the upper jaw is simply too narrow relative to the lower jaw.
A narrow upper jaw often results in:
Narrow dental arches
Dental crowding
Limited space for permanent teeth
Bite discrepancies
Posterior crossbites
Some children with narrow upper jaws are chronic mouth breathers or have a history of allergies, enlarged tonsils, enlarged adenoids, or other conditions that affect normal nasal breathing.
Because the upper jaw forms the floor of the nasal cavity, orthodontists and physicians have become increasingly interested in the relationship between jaw development and airway health. Research suggests that some children with narrow upper jaws may also have reduced nasal airway dimensions and an increased likelihood of sleep-disordered breathing.
It is important to understand that a posterior crossbite does not automatically mean a child has a sleep disorder, and orthodontic treatment should never be viewed as a substitute for medical care. If snoring, restless sleep, daytime fatigue, behavioral concerns, pauses in breathing, or other symptoms of sleep-disordered breathing are present, we always recommend evaluation by your child's physician or an appropriate medical specialist.
Understanding why a crossbite developed helps us determine the most effective treatment and the best time to intervene.
How Does a Posterior Crossbite Change Over Time?
Posterior Crossbite in Baby Teeth
Posterior crossbites are often first noticed during the primary dentition years.
Parents may observe that the upper and lower teeth do not fit together properly or that their child's jaw appears to shift to one side when biting.
While crossbites can certainly be diagnosed at this age, there is minimal evidence showing permanent negative consequences from delaying treatment during the primary dentition years alone.
For many young children, careful observation and monitoring is often appropriate until they reach the mixed dentition stage.
Posterior Crossbite During the Transition to Adult Teeth
This is often the ideal time for treatment.
As permanent teeth begin erupting, the upper and lower jaws are still growing and responding to orthopedic treatment. Children at this age are also generally better able to:
Brush around orthodontic appliances
Follow instructions
Attend regular appointments
Avoid damaging foods
If a jaw shift is present, it often becomes more noticeable during this stage.
Because growth remains active, correcting a posterior crossbite during the mixed dentition years is often efficient, predictable, and well tolerated by patients.
Posterior Crossbite in Permanent Teeth
Once all permanent teeth have erupted, the crossbite becomes more established.
Patients may experience:
Uneven tooth wear
Bite imbalances
Gum recession
Increased stress on individual teeth
Continued jaw asymmetry
Treatment remains highly effective, but some orthopedic treatment options become less effective as growth slows and eventually stops.
Posterior Crossbite in Adults
Adults often adapt remarkably well to a crossbite and may not realize a problem exists.
However, the effects can accumulate over time and may include:
Excessive tooth wear
Chipped teeth
Gum recession
Bite instability
Jaw discomfort
Functional limitations
Because growth is complete, correction can become more complex than it would have been during childhood.
Will My Child Outgrow a Posterior Crossbite?
In most cases, no.
Posterior crossbites rarely correct themselves as children grow.
While the bite may appear stable for years, the underlying discrepancy between the upper and lower jaws often remains unchanged.
The good news is that identifying a posterior crossbite early allows us to monitor growth carefully and determine the ideal timing for treatment.
Does a Posterior Crossbite Need to Be Fixed?
In many cases, yes.
Posterior crossbites are often associated with:
Narrow upper jaws
Functional jaw shifts
Bite imbalances
Uneven tooth wear
Asymmetrical jaw development
The decision to treat depends on:
The severity of the crossbite
Whether a functional shift is present
The patient's age
Growth potential
Overall oral health
Not every posterior crossbite requires immediate treatment, but most should be evaluated by an orthodontist.
When Is the Best Time to Fix a Posterior Crossbite?
Posterior crossbites should be evaluated as soon as they are noticed, but evaluation and treatment are not always the same thing.
While crossbites can be identified in very young children, the best time to correct most posterior crossbites is often during the mixed dentition stage, when both baby teeth and permanent teeth are present.
At this age:
Growth can still be guided
Orthopedic correction is often more predictable
Children are typically better able to cooperate with treatment
Oral hygiene around appliances is easier to maintain
Treatment is often better tolerated
Importantly, there is minimal evidence showing permanent negative consequences from delaying treatment during the primary dentition years alone. For many children, careful observation until the mixed dentition stage provides an excellent balance between timely intervention and treatment efficiency.
The goal is not to treat as early as possible.
The goal is to treat at the right time.
How Is a Posterior Crossbite Fixed?
Treatment depends on the patient's age, growth pattern, and the cause of the crossbite.
Observation
Some young children benefit from periodic monitoring until treatment can be performed more effectively during the mixed dentition stage.
Palatal Expansion
The most common treatment for a posterior crossbite caused by a narrow upper jaw is palatal expansion.
An expander gently widens the upper jaw, allowing the upper teeth to fit properly over the lower teeth.
Expansion can:
Correct the crossbite
Improve arch development
Create space for erupting teeth
Reduce dental crowding
Improve upper jaw width
Because the upper jaw forms part of the nasal airway, some studies have demonstrated improvements in nasal airflow following expansion in certain patients. However, orthodontic expansion is not considered a treatment for sleep apnea.
Any concerns regarding snoring, sleep-disordered breathing, or obstructive sleep apnea should always be evaluated by a physician.
MARPE (Miniscrew-Assisted Rapid Palatal Expansion)
As patients mature, the bones of the upper jaw become more resistant to traditional expansion. For some older teenagers and adults, a specialized appliance called a Miniscrew-Assisted Rapid Palatal Expander (MARPE) may be recommended.
Unlike traditional expanders that rely primarily on the teeth for support, MARPE uses temporary orthodontic miniscrews to apply expansion forces directly to the upper jaw.
This approach may allow some older adolescents and adults to achieve skeletal expansion that would otherwise require more invasive treatment.
Not every patient is a candidate for MARPE, and the decision depends on factors such as age, skeletal maturity, and the severity of the discrepancy.
Braces
Braces may be used to align teeth and fine-tune the bite after expansion or as part of comprehensive treatment.
Clear Aligners
Some adolescents and adults may be candidates for aligner treatment depending on the severity of the crossbite.
Surgical Treatment
In rare adult cases involving significant skeletal discrepancies, orthodontic treatment may be combined with jaw surgery.
Signs Parents Should Watch For
You may want to schedule an orthodontic evaluation if you notice:
Upper back teeth biting inside lower back teeth
A jaw that shifts when your child bites down
A chin that appears off-center
One side of the bite fitting differently than the other
A noticeably narrow upper arch
Crowded upper teeth
Chronic mouth breathing
Frequent snoring
Restless sleep
Difficulty fitting the upper and lower teeth together
Why Early Diagnosis Matters
Early diagnosis does not necessarily mean early treatment.
In many cases, the greatest benefit of an early orthodontic evaluation is determining the ideal time to intervene.
Some children benefit from treatment shortly after diagnosis, while others can be monitored safely until the mixed dentition stage when treatment may be more efficient and easier to tolerate.
The goal is not to treat as early as possible.
The goal is to treat at the right time.
By evaluating growth early, we can monitor jaw development, identify functional shifts, assess arch width, and develop a personalized treatment plan that supports long-term health and stability.
Why Families Trust Smile Squad
Posterior crossbites may seem straightforward, but determining whether they are caused by a narrow upper jaw, a functional shift, or a more complex growth discrepancy requires experience and careful diagnosis.
Dr. Martinez has spent more than a decade treating thousands of orthodontic patients and has extensive experience managing posterior crossbites, narrow arches, and developing bite problems in growing children.
In addition to private practice, Dr. Martinez serves as faculty at UNLV, where he teaches orthodontic biomechanics, ABO literature review, esthetics in orthodontics, and Phase I diagnosis and treatment planning. He also developed the Phase I curriculum used within the UNLV orthodontic residency program.
At Smile Squad, our orthodontic and pediatric dental specialists work together to identify concerns early, monitor growth carefully, and recommend treatment only when it provides a meaningful benefit to the patient.
This collaborative approach allows us to provide comprehensive care under one roof while helping children achieve healthy, functional, and confident smiles.
Frequently Asked Questions About Posterior Crossbites
What is a posterior crossbite?
A posterior crossbite occurs when the upper back teeth bite inside the lower back teeth instead of outside them.
Is a posterior crossbite serious?
It can be. Some posterior crossbites are associated with narrow upper jaws, jaw shifts, bite imbalances, and uneven tooth wear.
Will my child outgrow a posterior crossbite?
Most posterior crossbites do not correct themselves naturally.
What causes a posterior crossbite?
Common causes include a narrow upper jaw, genetics, thumb sucking, mouth breathing, and differences in jaw growth.
What is a palatal expander?
A palatal expander is an orthodontic appliance used to widen the upper jaw and correct crossbites caused by a narrow upper arch.
Can a palatal expander help my child breathe better?
Some studies have shown improvements in nasal airflow after expansion in certain patients. However, expansion is performed to correct orthodontic and skeletal problems, not to treat sleep apnea.
Can an expander cure sleep apnea?
No. Sleep apnea should be diagnosed and managed by a physician or sleep specialist.
When is the best age to treat a posterior crossbite?
For most children, treatment is often most effective during the mixed dentition years when both baby teeth and permanent teeth are present.
Do all posterior crossbites require treatment?
Not always. Some can be monitored, while others benefit from correction due to their impact on growth, function, or oral health.
Concerned About a Posterior Crossbite?
If you've noticed your child's upper back teeth biting inside the lower teeth, a jaw shift when chewing, or a narrow upper arch, an orthodontic evaluation can help determine the cause and whether treatment is needed.
Dr. Martinez and the Smile Squad team have extensive experience diagnosing and treating posterior crossbites. Together, we'll evaluate your child's growth, bite development, and overall oral health to determine the right treatment at the right time.