Method: Ten subjects with normal dentition aged 36.7±9.5 years were selected for the study. Six foods, 3 dry nuts and 3 moist raw vegetables, were tested (peanut, almond, pistachio, cauliflower, radish and carrot). Each subject masticated dry nuts (portions of 2.5 to 3.5g) and cylindrical samples of vegetables (3g) and then spat the sample out after a self-estimation of mastication completion. Two replicates were obtained for each food boli. Particles size distribution was measured by sieving and laser diffraction.
Results: Particles were much larger in vegetables than in nuts. 70% of vegetable particles were bigger than 2mm whilst 70% of nuts particles were less than 0.4mm. Particles size distributions were similar within nuts and within vegetables. After spitting the weights of the boli were approximately 40% of the initial food weight. This was similar within subjects and within foods. Surprisingly, no statistical inter-individual variability was observed in the particles distributions for the six foods. This contrasted with what was known for the physiological parameters of mastication and can be examplified as follows : the masticatory frequency of the 10 subjects ranged from 1.2 to 2.5 Hz and the number of necessary strokes to complete mastication ranged from 13 to 52 cycles/sequence.
Conclusion: These results suggest that the wide variation observed between subjects in the physiological mastication parameters is caused by the need of different individuals to prepare a bolus with common and accurate physical properties.