The experience of the lower jaw moving off-center when opening or closing the mouth is known as mandibular deviation or shift. This abnormal tracking means the jawbone (mandible) is not following its intended straight path, resulting in noticeable lateral movement. This symptom signals an underlying mechanical or functional problem within the complex system of joints, muscles, and teeth that govern jaw movement.
Temporomandibular Joint Derangements
The most common reason for the jaw to shift laterally involves internal issues within the temporomandibular joint (TMJ). This joint acts as a hinge connecting the lower jawbone to the skull and contains the articular disc, a small piece of cartilage. The disc functions as a cushion and smooth-gliding surface between the lower jaw’s condyle and the skull’s socket.
When the articular disc slips out of its normal position, often moving forward, it creates a physical obstacle to the condyle’s smooth movement, known as disc displacement. As the jaw opens, the condyle may suddenly slip under the disc, causing a noticeable pop or click as the jaw shifts back toward the center. This specific scenario is termed disc displacement with reduction.
The shift is a direct mechanical consequence of the condyle being forced to track around the displaced disc until it snaps back into place. If the disc remains displaced and does not return to its proper position, the condition is called disc displacement without reduction. In this scenario, the disc acts as a permanent barrier, severely limiting how wide the jaw can open and forcing the jaw to deflect toward the affected side.
Chronic inflammation or degenerative conditions like osteoarthritis can also impede the joint’s smooth function, leading to a mechanical shift. Joint swelling (capsulitis) can restrict the movement of the condyle within the joint capsule. When movement on one side is physically restricted by structural changes, the unrestricted side continues its normal movement, causing the lower jaw to deviate toward the side with the mechanical problem.
The Role of Muscle Imbalance and Dental Alignment
Beyond the joint’s internal structure, the forces applied by the muscles and the final contact of the teeth influence how the jaw tracks. The muscles of mastication, particularly the lateral pterygoid, guide the jaw forward and side-to-side. Uneven tension or spasm in these muscles can physically pull the jaw off its midline path.
Habits like teeth clenching or grinding (bruxism) often contribute to uneven muscle load by overworking one side. This sustained, asymmetrical muscular activity can lead to hypertrophy (enlargement) of the muscle on one side, resulting in a functional imbalance that pulls the mandible laterally. Stiffness and soreness in the facial muscles then perpetuate the asymmetrical movement pattern.
The way the teeth meet, known as dental alignment or occlusion, influences mandibular tracking. If the upper and lower teeth do not align correctly, malocclusion occurs. Premature tooth contact on one side can force the lower jaw to shift laterally to achieve maximum tooth contact when the mouth closes.
This forced lateral shift, known as a functional posterior crossbite, allows the teeth to interdigitate fully. The jaw shifts to avoid occlusal interference, using the teeth as a ramp that guides the mandible into an asymmetrical position. This repeated guidance is a common cause of a shift most noticeable at the very end of the closing movement.
When to Seek Professional Evaluation
If a jaw shift is accompanied by persistent pain or severely limited function, seeking professional evaluation is the next step. Symptoms that warrant immediate attention include the jaw locking in an open or closed position, severe pain that interferes with eating or speaking, or a recent shift following trauma.
A professional can accurately diagnose the cause, which may involve a complex interplay of joint, muscle, and dental factors. The initial evaluation is typically performed by a general dentist. Specialized care may involve a TMJ specialist, an oral and maxillofacial surgeon, or a physical therapist.
Diagnosis involves a physical examination, including palpation of the joints and muscles, and an assessment of the range and quality of jaw movement. Imaging studies are often used to confirm the diagnosis and visualize the underlying structures. Panoramic X-rays offer a general view of the joint and bone structure, while Magnetic Resonance Imaging (MRI) is used to show the position and condition of the soft tissues, particularly the articular disc.