The effects of food fragmentation index on mandibular closing angle in human mastication.

Jaw movements were recorded using a three-dimensional magnetic sensing system (Sirognathograph, Siemens) in 10 human volunteers while chewing standardized volumes of 15 food types, ranging from soft cheeses to hard nuts. The maximum horizontal amplitude inside the chewing loop (width of the loop), the height of the loop (vertical amplitude) and the closing angle made by the jaw during the late closing phase of the cycle relative to the vertical were calculated. The most highly significant correlation was between the closing angle and the square root of the ratio of two mechanical properties of the food - the toughness (R) and modulus of elasticity (E)(r = -0.85, p<0.001). The width of the chewing loop was also significantly correlated with the above combination of food properties (r = -0.75, p<0.01) whereas the vertical amplitude was not. Thus, the mechanical properties of foods appear to influence the pattern of mandibular movements in human mastication similarly to their reported effect on food breakdown rates and anterior temporalis activity during mastication.