Bite force displayed during assessment of hardness in various texture contexts

The relationship between mastication pattern, mechanical properties of the food bolus and texture perception are not fully understood, though the mastication process is known to adjust to different textural properties of foods. This study investigated the role of the bite force as one major aspect in hardness assessment of materials exhibiting simple mechanical properties over a wide hardness range. Elastic, plastic and brittle materials (silicone elastomers, waxes and pharmaceutical tablets, respectively) were tested. The rheological characteristics of these products were measured. For each product, one to four differential thresholds were determined at different points on a hardness scale by 10 individuals free of dental pathology. Bite forces were recorded by placing a small intraoral load cell under each sample. To assess the influence of the nature of the applied force, bites were made either directly on to the sample or on a metal disc placed between the teeth and the sample. As the individuals had to break the brittle products to perceive any hardness difference, bite forces were very closely correlated with the hardness of the products (r = 0.99). For plastic products, bite forces again correlated with the hardness (r = 0.96), even though individuals could stop biting at any time during the plastic deformation. Hardness perception of brittle and plastic products depends directly on sensory information about the bite force. However, hardness assessment of elastic products was obtained under constant bite force; here, the resulting deformation may provide sensory information about hardness.