An underbite, clinically known as a Class III malocclusion or mandibular prognathism, is a condition where the lower teeth close visibly in front of the upper teeth. This misalignment occurs because the lower jaw (mandible) is positioned too far forward relative to the upper jaw (maxilla). The condition can interfere with the proper function of biting and chewing and may also impact speech clarity. Correcting an underbite is a common goal in orthodontics, and treatment often involves a combination of specialized braces and appliances to reposition the teeth or modify jaw growth. The approach taken depends heavily on the patient’s age and the underlying cause of the jaw discrepancy.
Defining the Types and Severity of Underbites
Orthodontists first determine whether the underbite is primarily dental or skeletal in nature. A dental underbite involves teeth that are simply tipped or positioned incorrectly, while the underlying jaw bones are generally well-aligned. These cases are typically the easiest to correct using only standard braces and tooth movement.
A skeletal underbite presents a more complex challenge because the misalignment stems from the jaw structure itself. This usually means the mandible is overgrown (prognathic) or the maxilla is underdeveloped (retrusive). Diagnosis is confirmed using lateral cephalometric X-rays, which measure the angular relationship between the skull base, maxilla, and mandible.
The severity of the skeletal discrepancy determines the treatment plan. Mild to moderate skeletal issues in growing children may still be managed with orthodontics that modify bone growth. Severe skeletal underbites, especially in adults whose growth plates have fused, often require physically repositioning the jaw bones.
Non-Surgical Correction Using Braces and Appliances
For patients with dental underbites or mild skeletal issues, particularly those still growing, a non-surgical approach using braces is often successful. Brackets and wires are fixed to the teeth to apply continuous, light force, initiating the movement of teeth through the alveolar bone. This process allows the teeth to be properly aligned within their respective arches, correcting minor tipping that contributes to the underbite.
Standard braces are often augmented with specialized appliances to address the jaw position. One effective tool for younger patients is the reverse pull headgear, also known as a facemask. This external device uses elastics to apply orthopedic force to the upper jaw, stimulating forward growth of the underdeveloped maxilla. This action helps close the skeletal gap relative to the lower jaw.
Another common component is the use of Class III elastics, which are small rubber bands worn between the upper and lower braces. These elastics connect from the back of the upper arch to the front of the lower arch. The continuous tension applies a reciprocal force, pulling the upper teeth forward (mesializing) and the lower teeth backward (distalizing) to correct the bite relationship.
In borderline skeletal cases, where the jaw discrepancy is noticeable but not severe enough for surgery, orthodontists may employ a technique called dental camouflage. This involves using the braces to significantly tip the lower front teeth backward and the upper front teeth forward. The resulting tooth movement effectively masks the underlying skeletal problem by creating a functional bite relationship. This camouflage often requires the extraction of lower premolars to create the necessary space for the backward movement of the front teeth.
When Surgical Intervention Is Necessary
Braces and growth modification techniques have limitations, especially when treating a severe skeletal underbite in an adult whose facial growth is complete. Once the growth plates have fused, the physical size or position of the jaw bones cannot be significantly altered by orthodontic forces. In these cases, the definitive solution is orthognathic surgery, commonly known as jaw surgery.
The criteria for recommending surgery involve a significant measurable discrepancy that cannot be camouflaged without compromising dental health. This treatment is a combined effort between the orthodontist and an oral and maxillofacial surgeon, following a specific three-phase process.
Pre-Surgical Orthodontics
The first phase is pre-surgical orthodontics, where braces are worn to align the teeth within each jaw arch individually. This often makes the underbite appear worse temporarily, as the teeth are positioned correctly to fit together only after the jaws are moved. This phase can take between 12 and 18 months, ensuring the teeth are perfectly aligned over the basal bone.
The Surgery
The second phase is the surgery itself, where the surgeon performs osteotomies to reposition the jaw bones. This involves moving the mandible backward, the maxilla forward, or both. The segments are secured in their new position using titanium plates and screws, immediately resolving the skeletal misalignment.
Post-Surgical Orthodontics
The final phase is post-surgical orthodontics, which begins a few weeks after the operation. Braces are used for an additional six to nine months to fine-tune the bite and ensure the teeth interlock perfectly. Recovery involves an initial period of several weeks where only a soft or liquid diet is possible, with full bone healing taking several months.
Maintaining the Results: The Retention Phase
Following the completion of active orthodontic treatment, the retention phase is required for long-term stability. This step is important for underbite correction because the strong musculature of the lower jaw can exert forces that encourage the teeth to relapse.
Patients must wear retainers to hold the teeth and jaws in their newly corrected positions. Two types are commonly used: fixed retainers and removable retainers. Fixed retainers consist of a thin wire bonded to the tongue-side surface of the front teeth, providing continuous stabilization.
Removable retainers, such as a clear thermoplastic aligner or a Hawley appliance, are worn full-time initially and then transitioned to nighttime-only wear. Orthodontists often recommend lifetime retainer wear for the lower arch, given the propensity for teeth to shift back toward their original positions. Consistent use of these devices protects the investment in time and treatment against relapse.