Three-dimensional dynamical capabilities of the human masticatory muscles

Area of Science:

• Biomechanics
• Human Physiology
• Dental Mechanics

Background:

• Human jaw movements, especially non-symmetrical ones, involve complex interactions between muscles and temporomandibular joints.
• The relative contribution of active muscle control versus passive guidance (ligaments, muscle elasticity) to these movements remains unclear.

Purpose of the Study:

• To investigate the interplay between active muscle control, ligamentous guidance, and passive muscle elasticity in non-symmetrical human jaw movements.
• To determine the primary drivers of jaw laterodeviation.

Main Methods:

• Utilized a six-degrees-of-freedom dynamical biomechanical model of the human masticatory system.
• Simulated non-symmetrical jaw movements via unilateral muscle activity, with and without temporomandibular ligaments and passive muscle elastic properties.
• Analyzed forces, torques, and condylar loading relative to the lower jaw's center of gravity.

Main Results:

• Unilateral muscle contractions effectively generated natural-looking laterodeviations.
• Lower incisor movement was minimally impacted by the absence of passive elastic muscle properties or temporomandibular ligaments.
• Condylar movement was significantly influenced by temporomandibular ligaments, but overall jaw motion was primarily muscle-orientation dependent.

Conclusions:

• Human jaw movements are predominantly governed by the orientation of active masticatory muscles relative to the jaw's center of gravity.
• Temporomandibular ligaments and passive muscle properties play secondary roles in guiding jaw motion, particularly condylar movement.