Purpose: To develop an objective and quantitative method of evaluating the characteristics of masticatory laterality. Methods: Seven test foods (chewing gum, boiled fish paste, gummy jelly, pickled radish, dried cuttlefish, peanut, giant corn) were used. Ten subjects with normal occlusion were asked to chew the test food freely for 20 seconds. The mandibular incisal point was recorded by theSirognathograph Analyzing System III. The number of chewing strokes (on either side) was counted,and the

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... symmetry index (AI) was calculated. This test was carried out three times. The median and the range of the Al in the three trials were also calculated. Results: (1) Masticatory laterality was represented quantitatively by calculatingthe Al. (2) Subjects were classified into three types : unilateral type (U type), omnilateral type (O type), and variable type (V type), by the median and range of AI. O Masticatory laterality tends to be influenced by the hardness rather than the property of the test food. Conclusions: The method of objective and quantitative evaluation of masticatory laterality was discussed using several foods. The results suggested that this method was objective and quantitative, that each subject showed a characteristic pattern of masticatory laterality, and that masticatory laterality was influenced by the hardness of the test food.