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Human Masticatory Muscle Forces during Static Biting

¹ University of Nebraska Medical Center College of Dentistry, Departments of Growth and Development and
² Oral Biology, 40th and Holdrege Streets, PO Box 830740, Lincoln, NE 68583-0755, USA;
⁴ Private Practice, 3200 North Dobson Rd., Building A, Chandler, AZ 85224, USA;
⁵ University of Manitoba, Faculty of Engineering, Department of Civil Engineering, Winnipeg, MB R3T 2N2, Canada; and
⁶ University at Buffalo School of Dental Medicine, Department of Oral Diagnostic Sciences, 355 Squire Hall, Buffalo, NY 14214-3008, USA;

View larger version (53K): [in this window] [in a new window]   Figure 1. Mechanical schemes. (A) Force vectors involved in numerical models of isometric biting in humans. Forces on the mandible (e.g., vertical bite force), at the joints (Fcondyle, R = right, L = left), and representing 5 muscle pairs (m1,2 = masseter, m3,4 = anterior temporalis, m5,6 = lateral pterygoid, m7,8 = medial pterygoid, m9,10 = anterior digastric muscles), plus the axis system, are shown. (Modified from Smith et al., 1986). (B) Equivalent moments for in vivo (1) and modeled (2) molar (+ Mx) and incisor (+ Mz) biting tasks. Line diagrams illustrate mesial views of mandibular right first molar (top) and left central incisor (bottom) with acrylic crowns in place, where: CR is the center of resistance of the tooth/teeth, r is the moment arm vector, y is the angle away from vertical, and xz is in a plane parallel to the occlusal plane.

View larger version (42K): [in this window] [in a new window]   Figure 2. Effective TMJ eminence results. (A) Eminence height (mm), predicted by the model vs. measured, for a given postero-anterior position from 0 to 5.0 mm anterior to a retruded condylar position, in 0.5-mm increments, for subject m1 ("worst-case", ) and subject m4 ("best-case", *). (B) Sagittal morphology of the effective TMJ eminence in each of the six subjects. The vertical axis represents the eminence height (mm) relative to a retruded condylar position and perpendicular to the occlusal plane, and the horizontal axis represents condylar protrusion (mm) from the retruded position. Function beyond 5 mm of protrusion was unlikely, since this placed mandibular incisors anterior to maxillary incisors in all subjects.

View larger version (34K): [in this window] [in a new window]   Figure 3. Examples of model results for biting tasks. (A) Predicted I/C muscle force ratios for molar biting tasks at a range of bite force angles that created moments equivalent to in vivo biting at lateral, center, and medial positions. MJL model predictions for masseter () and anterior temporalis () muscles and MME model predictions for masseter () and anterior temporalis (X) muscles are shown for subject f1. Please note the discontinuity of scale in the vertical axis. (B) Predicted normalized muscle forces for incisor biting tasks at a range of bite force angles that created moments equivalent to in vivo biting at posterior, center, and anterior positions. Masseter muscle force predictions from MJL model ( subject f1, subject m5) and from MME model ( subject f1, subject m5), and anterior temporalis muscle force predictions from MJL model ( subject f1, subject m5) and from MME model ( subject f1, • subject m5).

Journal of Dental Research, Vol. 82, No. 3, 212-217 (2003)
DOI: 10.1177/154405910308200312


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