Influence of the rate of force application on the absolute psychophysical threshold level of periodontal mechanoreceptors in man.

In seven volunteers, controlled small forces were applied in an axial direction to a maxillary central incisor. The forces were generated by a stimulating device supported by the maxillary molars. The stimuli had a symmetrical triangular shape; force-application rates were varied from 1.88 to 960 mN/s. Threshold levels of sensation were determined at the various force-application rates. The relation between force-application rate and threshold level was negative, using 1.88, 3.75 and 7.5 mN/s stimuli. This trend was interrupted as threshold levels were higher at 15 than at 7.5 mN/s. In the range of more rapidly applied forces, 15-960 mN/s, the relationship was also negative, consistently, with a slope of -0.22 of the linear regression line after logarithmic transformation. It was concluded that the periodontal mechanoreceptive unit, as far as conscious functioning is concerned, may be described as a relatively inaccurate static force-detector when small magnitude forces are applied at low rates. Some rate sensitivity appears with more rapidly-applied stimuli.