| Sensory perception testing
Sensory perception thresholds were determined using a
full set of SWM in handsets of five consecutive filaments
(0.04–0.6 g-f; 1.0–6.0 g-f; 8-60 g-f) supplied by Connecti-
cut Bioinstruments, New York, USA. Bend forces were
guaranteed by the manufacturer within 15% tolerance. The
filaments were checked at three monthly intervals by the
investigators to make sure they were still in tolerance by way
of a jig and Mitutoyo height gauge, which applied each fila-
ment at right angles to a pressure plate of a fast-responding
Precisa digital balance. After a short period of familiarisa-
tion of the technique with the subject, filaments were gen-
tly applied perpendicular to the surface of the pulp of each
digit in sequence, avoiding any obvious callosities, from lit-
tle finger to thumb, by the investigator until they buckled.
The subject was asked to close their eyes during testing. No
more than 10 subjects were tested per day. The filament was
International Archives of Occupational and Environmental Health
1 3
held in contact with the digit for about a second. They were
applied in ascending order of bend force using the ‘two out
of three’ method. That is, the smallest filament to be felt
twice out of a maximum of three applications was taken as
the sensory threshold for the digit being tested. The time to
test all digits in one hand is about 5 min and for this reason
this method was thought to be the most practical for busy
practitioners in a clinic.
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