Working And Nonworking Side Of Mandible

In the study of dental occlusion and mandibular movement, the concepts of the working side and nonworking side of the mandible are fundamental. These terms refer to the sides of the jaw that perform distinct roles during lateral (side-to-side) mandibular movements, especially during chewing or grinding food. Understanding these differences helps dentists, orthodontists, and students analyze functional occlusion, diagnose disorders of the temporomandibular joint (TMJ), and develop appropriate treatment plans for patients experiencing jaw dysfunction or malocclusion.

Understanding Mandibular Movements

Lateral Excursion of the Mandible

Lateral excursion refers to the movement of the mandible to the left or right from its resting or centric position. This motion is essential for mastication, as it allows the teeth to grind food efficiently. During this motion, one side of the jaw becomes the working side, while the opposite becomes the nonworking or balancing side.

Role of Temporomandibular Joint

The temporomandibular joint allows the mandible to move in multiple directions: opening and closing (hinge motion), protrusion and retrusion (forward and backward), and lateral excursions. The TMJ is involved in coordinating the activities of both sides of the jaw during chewing, speech, and other functional activities. The distinction between working and nonworking sides is based on the direction of lateral movement relative to the TMJ.

The Working Side of the Mandible

Definition and Function

The working side is the side toward which the mandible moves during lateral excursion. For example, if the jaw moves to the left, the left side is the working side. This side bears the primary occlusal load during chewing and is typically where the functional contacts between maxillary and mandibular teeth occur during mastication.

Muscular and Joint Activity

On the working side:

• The condyle (rounded end of the mandible that articulates with the skull) rotates slightly and shifts minimally within the glenoid fossa.
• The muscles involved in mastication, such as the masseter and medial pterygoid, contract to facilitate chewing.
• The occlusal surfaces of posterior teeth make contact to grind food.

Clinical Significance

The working side is essential for normal chewing function. Improper alignment, loss of molars, or interference on this side can affect masticatory efficiency and lead to muscle fatigue or TMJ disorders. Dental restorations must restore proper working side contacts to ensure patient comfort and function.

The Nonworking Side of the Mandible

Definition and Movement

The nonworking side, also known as the balancing side, is the side opposite to the direction of mandibular movement. Continuing the example above, if the mandible moves to the left, the right side is the nonworking side.

Joint Mechanics

On the nonworking side:

• The condyle moves downward, forward, and medially in a more complex and pronounced path compared to the working side.
• This movement is more extensive and crucial for enabling the mandible to shift laterally and for opening the occlusal table for chewing.

Occlusal Contacts

Ideally, there should be minimal or no contact between upper and lower teeth on the nonworking side during lateral movements. Unwanted contact on this side, known as nonworking interferences, can lead to increased muscle activity, joint strain, and long-term wear or dysfunction.

Occlusal Considerations

Working vs Nonworking Side Contacts

In a healthy occlusion:

• The working side may exhibit ‘group function,’ where multiple posterior teeth contact to share occlusal forces.
• Alternatively, canine guidance may dominate, where only the canine teeth guide lateral excursions and disclude the posterior teeth.
• The nonworking side should ideally be free of contacts to prevent joint stress or muscle overcompensation.

Nonworking Interference

Nonworking side interferences can disrupt smooth mandibular function. These are occlusal contacts that occur where none should exist, often causing:

• TMJ discomfort or clicking sounds
• Headaches or facial muscle pain
• Tooth wear or fracture due to uneven force distribution
• Difficulty in chewing or lateral movement of the jaw

Correction of these interferences is part of occlusal adjustment therapy in restorative and orthodontic treatments.

Muscle Activity During Mandibular Movement

Coordinated Muscle Function

During lateral movement, different muscles on the working and nonworking sides perform distinct actions:

• The working side masseter and temporalis muscles contract to stabilize and elevate the mandible.
• The nonworking side lateral pterygoid muscle contracts to pull the condyle forward and medially.

Implication in Bruxism

In individuals who grind their teeth (bruxism), abnormal forces may develop on both working and nonworking sides. This can exaggerate muscle activity and lead to long-term joint or dental problems. Occlusal splints may help redistribute forces and protect structures from damage.

Diagnostic and Treatment Applications

Assessment in Dentistry

Dentists often assess working and nonworking side function during:

• Occlusal analysis with articulating paper or digital systems
• TMJ evaluation for abnormal joint sounds or restricted movement
• Orthodontic and prosthodontic treatment planning

Restorative Dentistry

In designing crowns, bridges, and dentures, maintaining or restoring proper working side contacts is essential. Ensuring the absence of nonworking interferences supports joint stability and functional longevity of restorations.

Orthodontic Treatment

Occlusion correction in orthodontics takes into account the balance between working and nonworking sides to achieve a functional and esthetic bite. Proper alignment reduces the risk of TMJ dysfunction and enhances masticatory efficiency.

Educational and Anatomical Importance

Learning Tools

Dental students learn about working and nonworking sides using models, occlusion simulators, and patient cases. Understanding these principles is a foundation for developing effective clinical skills in restorative and functional dentistry.

Anatomical Landmarks

The mandible, TMJ, and surrounding musculature form an intricate system that supports mandibular excursions. Awareness of condylar paths and muscle attachments is necessary to appreciate the biomechanical aspects of working and nonworking side behavior.

The working and nonworking sides of the mandible play distinct yet complementary roles in facilitating mandibular movement, especially during chewing. The working side bears the functional load and guides occlusion, while the nonworking side allows for the dynamic shifting of the jaw. Understanding their anatomical and functional differences is crucial in dental practice, from diagnosis to restorative planning. Proper balance between these two sides ensures healthy joint function, efficient chewing, and long-term oral comfort. By recognizing and respecting the biomechanical principles governing the mandible, dental professionals can help maintain optimal occlusion and patient well-being.