Mandibular helical axis pathways during mastication

Area of Science:

• Biomechanics
• Craniofacial Kinesiology
• Dental Mechanics

Background:

• Condylar trajectories are commonly used to study mandibular movements but can be misinterpreted due to reference point dependency.
• Helical axis analysis offers an unambiguous method for describing rigid body kinematics, making it suitable for complex biological movements.

Purpose of the Study:

• To analyze the mandibular helical axis during mastication using an opto-electronic system.
• To compare the helical axis behavior during the opening and closing phases of unilateral mastication.

Main Methods:

• Utilized the Jaws-3D opto-electronic system to record mandibular movements in seven subjects with Class I occlusion during unilateral mastication.
• Computed the helical axis every 14 ms with a 1° rotation threshold, calculating parameters of its spatial orientation and position relative to condyles.

Main Results:

• The helical axis exhibited more pronounced changes in orientation and position during jaw closing than opening.
• Significant orientation variation was observed from the beginning to the end of jaw closing, but not during opening.
• The distance between the helical axis and the reference condylar point varied significantly on the working side compared to the balancing side.

Conclusions:

• The helical axis continuously changes its position and orientation throughout the masticatory cycle.
• The balancing condyle translates backward during closing, while the working condyle primarily rotates, as indicated by the helical axis pathway.
• Helical axis analysis provides a more precise understanding of mandibular kinematics during mastication than traditional trajectory methods.