The frontal, sagittal, horizontal and velocity patterns of mandibular incisor-point movements during mastication in patients with TM Joint internal derangements have been well documented in the dental literature. OBJECTIVE: To detect any significant change in these patterns induced by changing the bolus hardness. METHODS: We 1) randomly selected 30 TMD patients with at least one verified TM Joint internal derangement, 2) recorded each subject's chewing movements with a soft and a hard bolus and 3) calculated 12 intra-subject average parameters (lateral width, +/- SD, vertical height, +/- SD, Lateral Turning point, +/- SD, Cycle time, Frontal shape, Sagittal shape, Horizontal shape, Opening Velocity shape, Closing velocity shape) that are currently used to describe the frontal, sagittal, horizontal and velocity characteristics of mastication. RESULTS: After applying a paired difference statistic to the 12 parameters, we found that three parameters exhibited no significant change (Sagittal shape, Horizontal shape and Opening Velocity shape). Of the remaining nine parameters that did change significantly (p < 0.05), only the Lateral Turning Point value became more negative with a hard bolus. The remaining eight parameters all increased significantly in value with a hard bolus when compared to a soft one. We interpreted this result as indicative that a hard bolus probably increases the “demand” on the masticatory system. CONCLUSION: From our study we conclude that mastication of a hard bolus, by increasing the demand on the stomatognathic system, significantly changed nine of the twelve masticatory patterns tested, compared to the same subjects' soft bolus recordings.

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