Quantifying work load in neck, shoulders and wrists in female dentists

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Abstract

Objective: To assess the work load in neck and upper limbs of dentists. Methods: Twelve right-handed female dentists (six with and six without a history of definite neck/shoulder disorders, pair-wise matched for age) were studied when performing authentic dental work. Electromyography (EMG) was used to quantify the muscular load of the shoulders bilaterally and of the right forearm. Positions and movements of the head and wrists were measured, using inclinometers and electrogoniometers. Results: During work, the median load for the right upper trapezius muscle was 8.4% of the maximal voluntary EMG activity (MVE); during 90% of the time the load was ?3.3% MVE (“static” load). The figures were somewhat lower on the left side (7.0% and 2.5% MVE, respectively). Subjects with disorders had over all lower load levels for the trapezius muscles, although not statistically significant at <0.05, than those without disorders. During a standardized reference contraction for the trapezius, the load was 17% MVE, and the quotient between MVE and torque [normalized to maximal voluntary torque (MVC)] was 0.5. These figures may be used for transformations. The muscular load on the right forearm was similar to the loads on the trapezius. The head was, on average, forward tilted ?39°, and during 10% of the time ?49°. The left hand was held in more static positions, with palmar flexion and ulnar deviation, also reflected by lower angular velocities and repetitiveness, as compared with the right one, which was dorsiflexed. Conclusions: Dentists are exposed to high load on the trapezius muscles bilaterally, and steep, prolonged forward bending of the head. Further, for the wrists the postures were constrained, but the dynamic demands were low.

Received: 14 June 1996/Accepted: 16 October 1996