The influence of density and material on oral perception of ball size with and without palatal coverage.

The size of a bolus determines how it will be manipulated in the mouth and swallowed. Ten healthy individuals assessed the size of ball bearings of five sizes (4-11 mm diameter) and four materials with different densities in order to investigate the effect of weight on oral size perception. To study the role of the tongue and palate, the experiment was performed with and without a custom-made plastic palate. The results revealed that size itself determines size perception, and that material and weight are negligible factors. An illusional effect in the direction of under-estimation was found for the ball bearings, especially for the small sizes up to 8 mm diameter. While wearing a plastic palate a significant improvement (P<0.05) occurred; the participants performed better and there was less under-estimation. An explanation for this could be that only a minor part of the total area of the ball bearing touches the palate and is hence detected, while the tongue alone is more compliant and thereby able to sense the ball's whole size.