Measurement of silent period durations by hand and by commercial device

Silent period durations obtained from the masseter muscle in response to taps to the chin during a clench were measured by the commercially available MDM device and by hand measurement from polygraph tracings. Of the 160 pairs of silent periods, 15 were measurable by polygraph but not by MDM, 20 were not measurable by polygraph but were measured by MDM, and 125 were measured by both. Of the 125 silent periods, the MDM gave a shorter reading in 112. Within-subject correlation coefficients between the two measurement methods ranged from - 0.038 to +0.95; the average (0.75) was significantly different from zero. The among-subject correlation coefficient was +0.26 and was not significant. These data raise questions about the reliability and validity of silent period durations measured by the MDM device.