Control of Jaw-Clenching Forces in Dentate Subjects

Aims: To characterize the control of jaw-clenching forces by means of a simple force-matching exercise. Methods: Seventeen healthy subjects, provided with visual feedback of the exerted force, carried out a unilateral force-matching exercise requiring developing and maintaining for 7 seconds a jaw-clenching force at 10%, 30%, 50%, and 70% of the maximum voluntary contraction. The task was repeated three times in each of two sessions. Motor performance was assessed, for both left and right sides, by different indices quantifying mean distance (MD), offset error (OE), and standard deviation (SD). Their dependence on force intensity, side, and time was assessed by ANOVA. Results: All error indices increased with the intensity of contraction in absolute terms. After normalization with respect to force level, the average performance in the second session was characterized by MD of 8.1% ± 2.6, OE 4.8% ± 2.9, and SD 12.7% ± 6.7 (mean ± standard deviation). Assessment of performance exhibited good reliability for all indices (intraclass correlation coefficient ranging from 74% to 88%). The motor performance improved with repetition (P .01), varied considerably between subjects, was not correlated with gender or age (P > .05) but was highly correlated between left and right side (P .01). Conclusion: The adopted approach is adequate to provide for an objective assessment of individual force control, although the presence of a learning phase must be taken into account. Keywords: accuracy, force transducer, masseter muscle, motor control, precision