A biomechanical study of occupational loads in the shoulder and elbow in dentistry

Objective. The aim was to demonstrate that when electromyographic (EMG) recordings are supplemented by biomechanical calculations more detailed information on shoulder loads are produced. Design. Shoulder and elbow moments were calculated for three work situations of arm abduction (> 30 °, < 30 ° and < 30 ° with force on the hand) and were related to EMG. Background. Prolonged arm elevation may result in shoulder pain and information on shoulder loads is needed to avoid development of musculoskeletal disorders. Methods. Three-dimensional coordinates from video recordings of eight working dentists were used in a static link segment model based on orthopaedic axes. Moments and EMG (trapezius muscle) were related. Results: Working with the upper arm abducted more than 30 ° produced 1.7 Nm (440%) higher moments of shoulder abduction, 0.5 Nm (100%) higher moments of outward upper arm twisting and 0.3 Nm (18%) smaller moments of elbow flexion than working with the upper arm abducted less than 30 °. Trapezius muscle activity did not increase with increased arm abduction. Force on the hand (20 N) recorded during cavity filling altered moments of the shoulder and elbow but not the activity level of the trapezius muscle. Conclusion. Supplementing EMG with biomechanical calculations of moments results in more detailed information on shoulder loads. This is important for over-all risk identification.