Figure 4.

Theoretical analysis of muscle orientation effects on lateral pterygoid muscle forces. 3D plots of MJL (A,C) and MME (B,D) predicted lateral pterygoid muscle forces for molar (A,B) and incisor (C,D) biting, each with a unique color scale. Orientation ranges for each muscle found in the sample were used in two models to identify key combinations of muscle orientations resulting in the highest predicted muscle forces during biting. Lateral pterygoid muscle forces are expressed relative to a 100 unit bite-force (%). Step-wise regression analyses confirmed that x-coordinates of masseter, temporalis, and lateral pterygoid muscles accounted for ≥60% of predicted lateral pterygoid muscle force variability for molar and incisor biting in both models. Lateral pterygoid muscle forces increased when: i) masseter muscles were more upright; ii) temporalis muscles were more posteriorly directed; and iii) lateral pterygoid muscles were less anteriorly directed.