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Jaw Clenching: Muscle and Joint Forces, Optimization Strategies

¹ Research Group Biomechanics, Faculty for Mathematics, University of Karlsruhe, D-76128 Karlsruhe, Germany;
² Department of Reconstructive Dentistry and Temporomandibular Disorders, Dental School, University of Basel, Switzerland;
³ Department of Prosthodontics, University of Heidelberg, Germany; and
⁴ Department of Prosthodontics, Dental School, University Hospital Freiburg, Germany

View larger version (23K): [in this window] [in a new window]   Figure 1. Exerimental set-up and fundamentals for the muscle and joint force calculations. (A) Scheme of intra-oral force-measuring device used in the experiments: x', y', z' = coordinates of the occlusal plane; sg = strain gauge; bp = base plate; cp = contact plate; ms = metal splints bearing bp and cp. (B) Reference planes and their orientation to the location of force measurement: x, y, z = coordinates of the Frankfort horizontal plane; Jr, Jl = right and left joint reaction forces; Fres,maxilla = resultant force acting on the maxilla; Fres,mand = resultant force acting on the mandible; = circumferential angle; = cranial angle.

View larger version (37K): [in this window] [in a new window]   Figure 2. Group means and standard deviations of the muscle and joint forces illustrated for the participants’ right side. Data for identical tasks (see text) of the left and right sides are pooled. Best-fitting () and worst-fitting () cases are also depicted. (A) Muscle and joint forces calculated with in vivo data (n = 10). (B) Muscle and joint forces computed with minimization of elastic energy as an objective function (n = 10). For (A) and (B): lFl/lFresl = forces as a fraction of the resultant force Fres = 150 N; = angle of the resultant force in the horizontal plane; different shades of bar plots (left to right) encode angle = 0°, 20°, 40°, 60°; motor task = 180°/ = 60° is not illustrated (see text).

View larger version (42K): [in this window] [in a new window]   Figure 3. Joint reaction forces generated during different motor tasks at Fres = 150 N. (A) Frequency distribution of the joint force angles found for the different resultant force directions defined by angle and angle (n = 10). (B) Range of joint reaction forces in the sagittal plane: J = force exerted by the condyle onto the articular eminence; = joint force angle in the sagittal plane (n = 10).