A crossbite is a common dental misalignment, or malocclusion, where one or more of the upper teeth fit inside the lower teeth when the jaws are closed. In a balanced bite, the upper teeth should slightly overlap the lower teeth. This condition affects a significant number of people across all age groups, with some studies estimating its prevalence in children to be around 10%. Correction is necessary primarily to ensure proper chewing function and to prevent long-term strain on the teeth and jaw joint. Addressing this issue allows the teeth to meet correctly, distributing the forces of biting and chewing evenly.
Classifying Types of Crossbite
Crossbites are classified based on the area of the mouth they affect, which determines the complexity of treatment. The two primary categories are the anterior crossbite and the posterior crossbite, each presenting a distinct misalignment pattern.
An anterior crossbite involves the front teeth, where one or more upper incisors or canines sit behind the lower front teeth when biting down. This arrangement is sometimes referred to as an underbite. This type of crossbite is often noticeable and can interfere with speech and the ability to incise food.
A posterior crossbite involves the back teeth, specifically the premolars and molars, where the upper back teeth bite inside the lower back teeth. This misalignment can affect a single tooth, a segment of teeth, or an entire side of the mouth. Posterior crossbites often cause the jaw to shift laterally when closing, leading to a functional deviation.
Identifying Underlying Causes
The origin of a crossbite is typically categorized into three main areas: skeletal, dental, or habitual/environmental, and the cause directly influences the required treatment approach. Skeletal causes involve a discrepancy in the size or growth of the upper and lower jaws, which is often genetically determined. For instance, a narrow upper jaw (maxillary hypoplasia) relative to a normal or large lower jaw is a frequent skeletal cause of a posterior crossbite.
Dental causes relate specifically to the incorrect positioning of individual teeth, even if the underlying jaw relationship is balanced. This occurs when a permanent tooth erupts out of alignment due to a lack of space or is blocked by a retained baby tooth. Correcting a dental crossbite usually involves moving the teeth into the correct position within the existing arch structure.
Habitual or environmental factors also play a role, especially in childhood. Prolonged habits like thumb sucking or pacifier use past the age of three can distort the arch form. Other factors include chronic mouth breathing and the premature loss of a baby tooth, which may cause adjacent teeth to drift.
Age-Specific Treatment Protocols
The approach to crossbite correction varies depending on the patient’s age and skeletal maturity. Treatment for growing patients is distinct from that for adults. Early intervention, often called Phase I treatment, capitalizes on the adaptability of a child’s facial bones.
Treatment for Growing Patients (Phase I)
For children with a posterior crossbite caused by a narrow upper jaw, the Rapid Palatal Expander (RPE) is a common orthopedic intervention. The RPE is a fixed appliance anchored to the upper molars with a central screw mechanism. It applies gentle, continuous pressure to physically separate the mid-palatal suture, the fibrous joint connecting the two halves of the upper jaw.
Parents or patients are instructed to use a small key to turn the screw once or twice daily, achieving approximately 0.25 millimeters of expansion per turn. The active expansion phase usually lasts a few weeks until the desired width is achieved. The appliance is then left in place for a retention period of three to six months to allow new bone to stabilize the widened arch.
For a simple anterior crossbite involving one or two teeth, a removable appliance with an active component is frequently used. These appliances, such as a removable plate with a Z-spring, use mechanical force to push the misaligned upper tooth forward. This correction is often fast and may be combined with a posterior bite plane to temporarily unlock the bite.
Treatment for Skeletally Mature Patients (Adults)
Once the mid-palatal suture has fused, typically after puberty, the jaw can no longer be widened using a standard RPE alone. For adults with a purely dental crossbite, where only the teeth are misaligned, fixed orthodontic appliances like braces or clear aligners can be highly effective. Braces apply continuous force to reposition individual teeth into the correct arch form, a process that can take a year or more depending on complexity.
For moderate to severe skeletal crossbites, a combination of orthodontics and surgery is necessary to achieve a stable result. Surgically Assisted Rapid Palatal Expansion (SARPE) is performed to overcome the resistance of the fused sutures. The procedure involves a surgeon making strategic cuts (osteotomies) in the maxilla and surrounding bones to mobilize the two halves of the upper jaw.
Following the surgery, an expansion appliance is activated, similar to an RPE, to widen the jaw at a controlled rate, often 0.5 millimeters per day. For the most severe cases involving significant jaw size discrepancies that affect facial balance, full orthognathic surgery (jaw surgery) may be required to reposition the upper, lower, or both jaws. This comprehensive procedure corrects both the bite and the underlying skeletal structure.
Long-Term Health Consequences of Non-Treatment
Ignoring a crossbite can lead to a cascade of oral health issues that progress over time and often require more invasive treatment later. One of the most common consequences is abnormal and uneven tooth wear, known as attrition, on the surfaces of the affected teeth. Teeth in crossbite often meet at sharp angles, leading to premature wearing down of the enamel and an increased risk of chipping or fracturing.
The abnormal forces generated by a misaligned bite can also negatively impact the soft tissues supporting the teeth. Excessive pressure on the gums and underlying bone can lead to gingival recession and bone loss around the involved teeth. Furthermore, a posterior crossbite can force the lower jaw to shift sideways upon closing to achieve a maximum bite, resulting in a functional shift.
This compensatory movement of the mandible can lead to facial asymmetry, especially in growing children, influencing the long-term development of the facial skeleton. The strain on the jaw joints from this unnatural movement increases the risk of developing symptoms associated with Temporomandibular Joint Disorder (TMD), such as chronic jaw pain, headaches, and difficulty chewing. Correcting the crossbite removes the source of this strain, protecting the long-term health of the teeth, gums, and jaw joint.