Work related musculoskeletal disorders (WMSDs) are common among dentists and possibly caused by
prolonged static load. The aim of this study was to assess the contraction pattern of neck and shoulder
muscles of orthodontists in natural environments.
Electromyographic (EMG) activity of right sternocleidomastoid and trapezius muscles were recorded
by means of portable recorders in eight orthodontists during working conditions, and both active and
resting non-working conditions. Recordings were analysed in terms of contraction episode (CE) count,
amplitude, and duration.
The sternocleidomastoid and trapezius muscles contracted about 40–70 times per hour in the natural
environment. Their EMG activity pattern mainly consisted of short-lasting, low-amplitude CEs. The
counts and amplitude of sternocleidomastoid CEs did not differ across vocational and non-vocational
conditions. The number and amplitude of trapezius CEs were slightly but significantly higher during
the vocational condition. There were highly significant (p < 0.001) differences in duration of CEs across
conditions, with two to threefold increase in the average duration of trapezius muscle contractions found
in the vocational setting.
During orthodontic work, operators commonly hold muscular contractions for significantly longer periods
than are encountered in non-vocational settings. This behaviour may be associated causally with the
increases seen in WMSDs through proposed pathophysiological mechanisms occurring at the motor unit
level. Our findings may also be valid for other occupations characterised by seated static postures with
precision hand and wrist movements