A three-dimensional method to calculate mechanical advantage in mandibular function : Intra- and interexaminer...

Area of Science:

• Biomechanical analysis
• Craniofacial anatomy
• Dental research

Background:

• Masticatory muscle performance is influenced by skeletal features, muscle size, and neuromuscular control.
• Current methods for assessing masticatory mechanical advantage are limited to 2D cephalometric analysis.
• A reliable 3D method is needed to accurately evaluate the biomechanics of the masticatory system.

Purpose of the Study:

• To determine the reliability and measurement errors of a novel three-dimensional (3D) method for calculating the mechanical advantage of masticatory muscles.
• To establish a more accurate and comprehensive approach to analyzing jaw biomechanics.

Main Methods:

• Cone-beam computed tomography (CBCT) images from teenage orthodontic patients were used.
• Thirty-six craniofacial landmarks were identified to determine moment arms and load moment arms for seven masticatory muscles.
• Three examiners repeated measurements, with reliability assessed using intraclass correlation coefficient (ICC) and error analysis (CV).

Main Results:

• Landmark identification demonstrated excellent intra- and interexaminer reliability (ICC 0.998-1.000).
• Biomechanical variables showed high intraexaminer reliability (ICC 0.919-1.000, CV < 7%) and good interexaminer reliability (ICC 0.750-1.000, CV < 10%).
• The lateral pterygoid muscle group showed lower reliability (ICC < 0.500) and higher variability (CV < 30%).

Conclusions:

• The proposed 3D method for calculating masticatory system mechanical advantage is reliable and exhibits acceptable measurement errors.
• This 3D approach offers a viable and more accurate alternative to existing 2D methods for biomechanical analysis of the masticatory apparatus.
• Further refinement may be needed for specific muscles like the lateral pterygoid.