Dependence of psychophysical threshold on rate of applied force to the upper first molar in humans

Objective: The study aims to investigate the dynamic perception of a force applied to the upper first molar for different rates of force increase. Design: Six volunteers (four male and two female; mean age, 27.2 ± 2.4 years) with full natural dentition (except for the third molars) participated in this study. The psychophysical threshold for a force applied to the right maxillary first molar and the reaction time corresponding to each threshold were measured for rate of force increase of 103.74, 236.23, 354.58, 478.22 and 584.63 mN s^-1. The physical impulse, which is the integral of force over time, was calculated for each threshold. Results: Psychophysical thresholds in the upper first molar increased with the rate of force increase. The reaction time corresponding to each threshold decreased with increasing force rate. Impulses corresponding to each threshold were independent of force rate. Conclusions: In the present study, the psychophysical threshold for a force applied to a molar tooth was shown to change depending on the rate of increase of the exerted force. From the viewpoint of the impulse, the dissipated energy necessary to reach the psychophysical sensation threshold was almost constant, regardless of the rate of force increase.