Facial asymmetry is a difference in size, shape, or position between the right and left sides of the face. While most people have natural, unnoticeable asymmetry, a painful or noticeable jaw deviation suggests a functional or structural issue. This unevenness occurs when the upper jaw (maxilla) and lower jaw (mandible) do not align correctly. Causes include underlying bone structure, tooth arrangement, or issues with the jaw joints and surrounding muscles.
Causes Related to Growth and Genetics
Jaw unevenness can originate from developmental issues that occur before or during childhood growth. Congenital conditions involve an inherent difference in the development of the facial skeleton. A notable example is hemifacial microsomia, characterized by the underdevelopment of one side of the face, often affecting the jaw, ear, and surrounding soft tissues.
In these cases, the affected mandible may be shorter or smaller, causing the chin to point toward the underdeveloped side. This condition is believed to involve a disrupted process during fetal development, such as an issue with the blood supply to facial structures. While hemifacial microsomia is typically sporadic, some cases suggest a genetic component.
Natural variations in growth can also lead to an uneven jaw if one side of the mandible or maxilla develops at a different rate. Furthermore, prolonged childhood habits influence skeletal development. Habits like chronic thumb-sucking or extended pacifier use past age three exert consistent pressure on developing dental arches, potentially leading to misalignment.
Acquired Dental and Skeletal Misalignment
Many instances of an uneven jaw are acquired later in life due to dental and skeletal changes, rather than genetics. The most common acquired factor is malocclusion, or a “bad bite,” where the upper and lower teeth do not fit together correctly. This misalignment can range from simple shifting of individual teeth to a significant discrepancy between the dental arches.
Missing teeth significantly contribute to acquired jaw unevenness. When a tooth is lost, remaining teeth shift into the empty space, disrupting the bite and forcing the lower jaw to shift its resting position. Over time, the jawbone in the area of the missing tooth can resorb, further contributing to an uneven foundation and asymmetrical appearance.
Uneven tooth wear (attrition), often caused by chronic teeth grinding (bruxism), can also destabilize the bite. If a person consistently chews predominantly on one side, those teeth wear down faster, creating an uneven plane that forces the jaw off-center when closing. Significant facial trauma, such as a fracture, is another cause; improper healing can permanently alter the jaw structure’s alignment.
Temporomandibular Joint (TMJ) Dysfunction
A common cause of jaw unevenness relates to problems with the temporomandibular joints (TMJs), the hinges connecting the jawbone to the skull. Temporomandibular joint dysfunction (TMD) encompasses issues with the joint, surrounding muscles, and ligaments. This condition frequently causes the jaw to deviate upon opening or closing, resulting in visible and functional asymmetry.
Muscular imbalance is one factor, where chronic tension or overuse on one side leads to hypertrophy (enlargement) of chewing muscles like the masseter. This uneven muscle development can make one side of the face appear fuller. Conversely, the joint can suffer internal derangement, often involving displacement of the articular disc, the cushion between the jawbone and the skull.
If the disc is displaced or worn away, the joint may lose height on that side, causing the jaw to slant or shift laterally. This displacement often leads to the clicking, popping, or grating sounds associated with TMD. Arthritis in the jaw joint can also cause degenerative changes, leading to structural loss and a shift in the jaw’s position.
Determining the Root Cause
Determining the specific cause of jaw unevenness requires a methodical diagnostic process by a specialist (dentist, orthodontist, or oral and maxillofacial surgeon). The initial step is a thorough clinical examination. This involves visually assessing facial symmetry, examining the dental occlusion (bite), and palpating the TMJs and masticatory muscles for tenderness or abnormal movement. The specialist also observes the jaw’s range of motion, noting any deviation or locking.
Patient history is essential, covering past facial trauma, chronic pain, and habits like teeth grinding. Imaging techniques are then employed to visualize underlying structures. Standard panoramic X-rays provide a broad view of the jaw, teeth, and TMJs, often used to screen for fractures or tumors.
For detailed visualization of bone structure, a Computed Tomography (CT) scan is effective for evaluating bony elements and skeletal discrepancies. Magnetic Resonance Imaging (MRI) is the standard for soft tissue assessment, allowing the specialist to view the articular disc and surrounding muscles. Combining clinical findings with imaging results helps accurately differentiate between skeletal, dental, and joint-related origins.
Corrective and Management Strategies
Treatment for an uneven jaw is highly individualized and depends on the underlying cause identified during diagnosis. For issues related primarily to dental alignment, orthodontics is the most common intervention. Braces or clear aligners apply consistent pressure to shift teeth into a corrected position, which can realign the lower jaw if the unevenness is minor.
When the cause is Temporomandibular Joint Dysfunction (TMD) or muscle issues, management focuses on reducing strain and restoring balance. Physical therapy is effective, involving exercises to improve jaw mobility and strength, and techniques to release muscle tension. Dental splinting, using a custom oral appliance, stabilizes the jaw joint, prevents teeth grinding, and encourages muscles to relax into a balanced position.
For severe skeletal discrepancies, such as those caused by developmental differences or improperly healed trauma, orthognathic surgery (corrective jaw surgery) is often necessary. This procedure involves an oral and maxillofacial surgeon physically repositioning the maxilla, mandible, or both, to achieve proper skeletal alignment. Surgical correction is typically coordinated with pre- and post-operative orthodontics to ensure teeth align perfectly with the newly positioned jawbones.