ABSTRACTThe oral perception of the hardness of plastic deformable products was investigated. Differential sensitivity was studied over a large range of hardness during psychophysical tests in which bite forces were recorded with small intra‐oral load cells. The mechanical properties of 21 products obtained from dental waxes and modelling clays were measured. They covered a stress range from 19N/cm2to 265N/cm2when the plastic deformation plateau was reached. For psychophysical experiments, these products were divided into four series according to their hardness. For each series, a differential threshold was obtained for 10 individuals who were asked to make hardness comparisons by biting the samples with the incisors. During each bite, forces were recorded from an intra‐oral load cell placed beneath the sample. Differential thresholds varied between 6 and 13% depending on the series. For the 21 products taken together, a significant correlation (R = 0.98) was found between bite forces and stresses. Furthermore, significant correlations were also found within each series of comparisons except for the series of the softest products. Bite forces appeared therefore to play the main role in hardness perception of products exhibiting plastic deformation, except for the softest products for which developed forces might not correspond to the normal field of forces activated during masticat