Recent studies suggest the usefulness of electroencephalogram (EEG) as index to evaluate the effect of prosthetic treatment. Musha, et al. (2000) established the Emotion Spectrum Analysis Method (ESAM) which quantifies the psychological state by EEG in the time series. However, estimation of the psychological state on EEG has not yet been applied to the field of dentistry. Objective: The purpose of this study is to estimate the psychological state changes caused by the changes of oral cavity sensation with ESAM. Method: Four subjects were selected and mandibular movement and EEG before and after mastication of gum with occlusal interferences were recorded assuming a negative change of oral sensation. Closing phase, occlusing phase, opening phase, and cycle time were calculated from the mandibular movement and examined how the change of oral sensation effect the time related element of the mastication rhythm. We used four emotional levels based on ESAM: stress (N1), sadness (N2), joy (P1) and relaxation (R) to compare the psychological state changes caused by the occlusal interference. Result: When the interference was set, every mastication phase except occlusing phase was significantly shortened at 0.1% level of significance. This result suggests that the occlusal interference causes the change of the oral cavity sensation and effects mastication rhythm. Analysis of ESAM indicated the increase of N1 and N2 and decrease of P1 and R after mastication with interference. This result suggests that the negative change of oral sensation made by the occlusal interference is the factor. Conclusion: The result indicates that it is possible for the emotional levels based on ESAM to estimate the psychological effect caused by the change of oral sensation.

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