Variability of musculoskeletal strain on dentists: an electromyographic and goniometric study.

INTRODUCTION Dentists and hygienists are strongly affected by musculoskeletal disorders (MSDs). As workstation concepts are supported by subjective arguments only, the aim of this study was to use objective measurements to compare the variability of strain in various concepts: a dental chair equipped with a cart or an over-the-patient delivery system without an assistant, and Dr Daryl Beach's concept with an assistant. METHODS Goniometric and electromyographic recordings were made on 8 subjects, during a scaling operation. The electrical activity of their trapezius and lumbar muscles was compared, as were their cervical and lumbar ranges of motion. RESULTS The results showed that there was a wide variability depending on the workstation. However, the Beach concept tended to reduce physical strain on most parameters: duration of left lumbar muscle activity (2% compared to 15% of time spent in > 10% maximal voluntary contraction, MVC), time spent in cervical side bending (4% compared to 30%), cervical flexion of > 20° (9% compared to 40%), and left trapezius activity (9% of time spent > 10% MVC compared to 28%). CONCLUSION Practitioners and students should adjust their workstations to reduce the prevalence of MSDs.