Dynamic mechanics in the pig mandibular symphysis

Area of Science:

• Biomechanics
• Mammalian Jaw Function
• Computational Modeling

Background:

• Mastication involves complex biomechanical events at the mammalian jaw symphysis.
• Previous studies analyzed static conditions or surface bone strains, lacking direct measurement of dynamic forces and torques.
• Directly demonstrating forces and torques during dynamic muscle tension changes has been a challenge.

Purpose of the Study:

• To modify a dynamic pig jaw model to predict forces and torques at the symphysis.
• To correlate these forces and torques with simulated muscle tensions and other bite-related forces.
• To investigate dynamic loading patterns at the jaw symphysis during mastication.

Main Methods:

• A dynamic pig jaw model was modified with an artificial rigid joint at the symphysis.
• Tri-axial forces and torques at the symphysis were measured using the model.
• Simulated masticatory muscle tensions, bite, joint, and food bolus forces were incorporated.

Main Results:

• The model confirmed three previously postulated symphysis loading patterns: dorsoventral shear, medial transverse bending, and lateral transverse bending (wishboning).
• Dorsoventral shear correlated with balancing-side adductor forces and working-side bite reaction forces.
• Medial transverse bending was linked to lateral pterygoid tensions during jaw opening, while wishboning involved masseter actions during the power stroke.

Conclusions:

• Dynamic modeling provides a powerful method for studying jaw biomechanics, especially for in vivo unmeasurable parameters.
• The study identified specific muscle actions associated with distinct symphysis loading patterns during mastication.
• The largest predicted force was dorsoventral shear, and the largest torque was a 'wishboning' torque.