Comparison of instantaneous and cumulative loads on the low back and neck in orthodontists

Background. Musculoskeletal disorders of back and neck among orthodontists are prevalent. Due to low instantaneous load they have not been investigated. The present study aimed to quantify and compare instantaneous and cumulative loads on low back and neck in orthodontists. Methods. The sample included nine graduate orthodontic students from the University of Alberta and one practicing orthodontist to validate the generalization from student to professional group. The subjects were videotaped performing regular duties and the recorded postures were printed for biomechanical analysis of compression and shear loads and exposure time. Instantaneous loads were calculated using a biomechanical model developed specifically for this study and cumulative loads were calculated from the resultant loads. Findings. The average instantaneous low back compression loads for men and women were found to be 1383 N and 936 N respectively. The average daily cumulative load on the other hand were found to be 16.2 MN s and 9.9 MN s for males and females respectively. Interpretation. The study demonstrates that smaller loads cannot be ignored due to their magnitude if their duration is long because the time dependent properties of the tissues become modulating factor. Thus the measurement of instantaneous loads on tasks in orthodontists is not indicative of the amount of cumulative stress experienced by them.