An underbite, clinically known as a mandibular prognathism, occurs when the lower teeth and jaw extend forward past the upper teeth and jaw. This misalignment can affect both appearance and the ability to chew and speak properly. The direct answer to whether braces can correct this condition is yes, but with significant caveats based on the underlying cause. Treatment success relies heavily on whether the issue stems from the positioning of the teeth (dental) or the structure of the jawbones (skeletal). Understanding the distinction between these two types of misalignment is the first step in determining the appropriate and effective treatment plan.
Understanding Class III Malocclusion
The clinical term for an underbite is Class III Malocclusion, which describes a relationship where the lower molar is positioned ahead of the upper molar. This condition often has a strong genetic component, frequently inherited through family lines that predispose an individual to a larger lower jaw or a smaller upper jaw. Early childhood habits, such as prolonged thumb sucking or a tongue thrusting pattern, can also contribute to this misalignment.
The most important distinction is separating a dental underbite from a skeletal underbite. A dental underbite involves misaligned teeth tilting forward or backward, while the jaw structure itself is generally balanced. Conversely, a skeletal underbite involves a true mismatch in the size or position of the maxilla (upper jaw) and the mandible (lower jaw). This differentiation guides the entire treatment strategy, as moving teeth is much simpler than modifying bone structure.
Braces as a Direct Solution for Tooth Alignment
Standard fixed braces, consisting of brackets bonded to the teeth and connected by archwires, are effective when the underbite is primarily dental. These appliances apply continuous, gentle pressure to reposition individual teeth. The goal is to move the upper front teeth slightly forward and the lower front teeth slightly backward, correcting the bite relationship between the arches.
A specific technique often employed involves the use of reverse-pull elastics, sometimes called Class III elastics. These small rubber bands stretch from the upper molars to the lower canines or premolars. The elastic force exerts a forward pull on the upper arch and a backward pull on the lower arch, working to resolve the anterior crossbite.
This approach is sometimes referred to as dental compensation or camouflage, where the teeth are tipped to mask a mild underlying skeletal issue. By changing the angle of the teeth, the orthodontist can achieve an acceptable bite without altering the jawbones. This technique has limitations and is reserved for mild cases where the skeletal discrepancy is minimal. If the jaw bones are severely mismatched, simply tipping the teeth may not create a stable or functional result.
Orthodontic Devices for Jaw Modification
When the underbite is skeletal and diagnosed in a child who is still growing, specialized orthodontic devices are used to modify the developing jaw structure. These appliances leverage the child’s growth potential to guide the bones into a more favorable relationship. Early intervention, often starting around age seven or eight, is the best time to influence skeletal growth effectively.
One prominent device is the reverse-pull face mask, also known as protraction headgear, which encourages the forward growth of the maxilla (upper jawbone). This appliance uses external support resting on the forehead and chin, connecting via elastics to an internal appliance cemented onto the upper teeth. The sustained forward force applied to the upper jaw can stimulate bone deposition and correct a deficient maxilla.
Palatal expanders may also be used if the upper jaw is recessed and too narrow. These devices widen the upper jaw by gently separating the suture in the palate, creating necessary space. By widening and advancing the upper jaw, these appliances improve the skeletal foundation before transitioning to fixed braces for final tooth alignment.
Surgical Intervention for Severe Skeletal Issues
For severe skeletal underbites in adult patients, whose growth plates have fully fused, non-surgical methods are no longer viable. In these instances, the definitive treatment involves orthognathic surgery, commonly known as corrective jaw surgery. This procedure is necessary when the size discrepancy between the upper and lower jaws is too large to be masked by moving the teeth.
The surgery is performed by an oral and maxillofacial surgeon to physically reposition the jawbones. This may involve setting the mandible back, advancing the maxilla forward, or a combination of both movements to create a harmonious bite relationship. Braces are used before surgery to align the teeth within their respective arches so they fit together perfectly once the jaws are repositioned. Braces are then worn after the surgery for several months to fine-tune the bite and ensure long-term stability.