Facial asymmetry, involving the jaw structure, is common when the left and right sides of the face do not perfectly mirror each other. While some asymmetry is universally present, a noticeable jaw deviation affects both appearance and the functionality of the bite and chewing mechanism. Correcting this unevenness depends on accurately identifying the underlying cause and the extent of skeletal, dental, or muscular involvement. Treatment ranges from non-invasive therapies to complex surgical procedures.
The Causes of Jaw Asymmetry
Jaw asymmetry is categorized as congenital, developmental, or acquired. Skeletal asymmetry involves a discrepancy in the size, volume, or position of the jaw bones (maxilla or mandible). This often results from developmental issues like hemimandibular hyperplasia, where one side of the lower jaw grows excessively, or hemifacial microsomia, where one side is underdeveloped.
Dental or occlusal asymmetry relates to the misalignment of the teeth. This misalignment can cause the lower jaw to shift to one side when biting down, known as a functional shift. Causes include uneven tooth eruption, missing teeth, or prolonged bite interferences. The jaw may be structurally symmetrical, but the way the teeth meet forces the mandible into an asymmetrical position.
Functional or muscular asymmetry stems from imbalances in the surrounding soft tissues, including the facial and chewing muscles. Habits like mouth breathing, tongue thrusting, or favoring one side while chewing lead to uneven muscle tone, influencing the jaw’s resting position. Temporomandibular joint (TMJ) disorders, which cause chronic pain and joint dysfunction, can also lead to jaw deviation.
Acquired asymmetry occurs later in life due to external factors like trauma, tumors, or infections. A jaw fracture, especially during growth, can disrupt normal development, causing a noticeable difference in facial structure. Conditions such as condylar ankylosis (fusion of the TMJ to the jaw bone) severely restrict movement and cause undergrowth of the mandible on the affected side.
Conservative Treatment Options
When asymmetry is caused by dental misalignment, muscle imbalance, or a mild skeletal issue, non-surgical approaches are the first line of treatment. Orthodontic treatment, using traditional braces or clear aligners, corrects occlusal asymmetry and dental midlines. By applying controlled forces, orthodontics straightens the teeth and guides them into a corrected bite alignment, eliminating a functional mandibular shift.
Treatment duration typically lasts one to three years, depending on complexity. For mild skeletal discrepancies, orthodontics can use “camouflage” techniques. This moves the teeth to compensate for the underlying bone difference, providing a satisfactory result without requiring surgery.
Specialized dental appliances, such as mandibular repositioning or occlusal splints, address asymmetry related to TMJ dysfunction. These custom-fitted devices stabilize the jaw joint, reduce muscle tension, and guide the mandible into a more centered position. Splints can be a temporary measure to alleviate pain or a preparatory step before further treatment.
Myofunctional therapy (OMT) is physical therapy that retrains the muscles of the tongue, lips, and face. OMT involves specific exercises to correct improper oral habits, such as tongue thrusting, ensuring surrounding muscles function optimally and preventing relapse. For adolescents with growth potential, specialized functional appliances may be used to guide jaw development, encouraging or restraining growth on specific sides.
Surgical Correction Procedures
For severe skeletal asymmetry or cases unresponsive to conservative treatments, surgical correction is required. Orthognathic surgery, or corrective jaw surgery, involves surgically repositioning the upper jaw (maxilla), the lower jaw (mandible), or both. This procedure addresses significant asymmetry originating from the bone structure itself.
The Bilateral Sagittal Split Osteotomy (BSSO) is common for the lower jaw. It involves precise cuts on the mandible, allowing the jaw to be moved or rotated to correct asymmetry. The segments are secured using titanium plates and screws. For the upper jaw, a Le Fort I Osteotomy separates the maxilla, permitting it to be rotated or moved to level the occlusal plane.
Orthognathic surgery requires a coordinated approach, including pre-surgical orthodontics (decompensation) to align the teeth within each jaw. This preparation ensures that when the jaws are surgically moved, the teeth interlock properly for a functional bite. Post-surgical orthodontics then fine-tunes the final bite and tooth positions.
Genioplasty, or chin reshaping, is often performed alongside jaw surgery to correct residual asymmetry or enhance facial balance. An osseous genioplasty involves cutting and repositioning the chin bone for vertical, horizontal, or rotational adjustments. Alloplastic implants can be used for smaller corrections. In cases of significant bone loss, bone grafting or reconstructive surgery may be required to restore volume and structure before or during jaw repositioning.