Geometrical resolution limits and detection mechanisms in the oral cavity.

The objective of this work is to gain more insight into the processes of oral perception of food texture. Particularly, the limits for detectable thickness differences of objects, which are evaluated in the human mouth, are investigated. In a sensory study small, flexible circular disks (diameter in mm range) of varying thickness (in microm range) and material properties are evaluated between tongue and palate in human subjects. The thicker sample is identified in pair comparison tests. Experimental evidence suggests the existence of one detection process (attempt to align tongue and palate and the disk between them) to which the tongue-palate system reacts in two different ways: (1) by bending the disk (thickness below 125 microm, Young's modulus of 480 MPa) and (2) by impressing the disk into the tongue (thickness above approximately 200 microm, Young's modulus of 480 MPa), whereas the first reaction is necessarily followed by the second if the first one fails. For both ranges, differences in thickness of 25 microm can be detected. The two reaction processes cover isolated ranges and leave an insecure detection range in between them, for which neither one of the processes applies. Since deformation and load distribution on the disk are supposed to play a major role in the first detection process (the loads exerted on the disk in order to bend it are compared), we formulate a mathematical model to quantify these mechanical effects. The model is employed to identify parameter constellations (thickness, material properties) for which the insecure range is omitted or the range is enlarged. Theoretical findings are confirmed by further experiments. Their results are consistent with the characteristics and functioning of the mechanoreceptors in-mouth.