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DYNAMICS OF THE HUMAN MASTICATORY SYSTEM

Department of Functional Anatomy, Academic Centre for Dentistry Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, the Netherlands; j.h.koolstra{at}amc.uva.nl

View larger version (19K): [in a new window]   Figure 1. Six degrees of freedom for jaw movement. Dashed lines: principal axes. a: (linear) accelerations. F: (linear) forces. m: mass. : angular accelerations. M: torques. I: moments of inertia.

View larger version (21K): [in a new window]   Figure 2. Helical axis. (A) Rotations about and translations along a hypothetical helical axis during a non-midline jaw movement (dashed line). (B) Subsequent helical axes during jaw closure (after Gallo et al., 2000).

View larger version (20K): [in a new window]   Figure 3. Force and torque generated by a muscle (arrow) with respect to the center of gravity of the lower jaw.

View larger version (24K): [in a new window]   Figure 4. Overview of the masticatory system. Ventro-lateral view. Continuous lines: muscle lines of action. Cross-bar: muscle origin. Circle: muscle insertion. MAS_S: superficial masseter. MAS_P: deep masseter. MPT: medial pterygoid. TEM_A: anterior temporalis. TEM_P: posterior temporalis. LPT_S: superior lateral pterygoid. LPT_I: inferior lateral pterygoid. DIG: digastric. GEH: geniohyoid. MYH: mylohyoid. Dots: position of centers of right and left condyle and incisor point.

View larger version (26K): [in a new window]   Figure 5. Forces acting on the lower jaw in the sagittal plane. Cross-hairs: center of gravity. Fclosers: mean force of the jaw-closing muscles. Fopeners: mean force of jaw-opening muscles. Fjoint: joint force. Fbite: bite force. a: moment arm of the different forces.

View larger version (25K): [in a new window]   Figure 6. Dynamic muscle properties. Total force is the sum of the forces produced by the sarcomeres (Fsarcomeres) The active force (Factive) is dependent on the activation through the activation dynamics, the instantaneous sarcomere length, and contraction velocity. The parallel elastic force (Fpassive) is dependent on the instantaneous sarcomere length.

View larger version (14K): [in a new window]   Figure 7. Schematic overview of the possible actions generated by force Fm of the superficial masseter or anterior temporalis muscle viewed in the horizontal plane. (A) Possible rotations: Rg, about center of gravity; Rr, about a vertical axis behind the right joint for a latero-deviation to the right; and Rl, about a vertical axis behind the left joint for a latero-deviation to the left. (B) Influence of joint forces: am, moment arm of muscle force; Frj, right joint force; arj, moment arm of right joint force; Fjl, left joint force; and ajl, moment arm of left joint force.

View larger version (28K): [in a new window]   Figure 8. Rotations about vertical and horizontal axes during a latero-deviation movement.