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The status of dental caries prevalence in the child patients, having visited the pedodontic clinic of Ohu University Dental Hospital, was surveyed longitudinally for 2 years (between 3 and 5 years of age) or 3 years (between 2 and 5 years). Also the dental caries attack patterns used at the dental health examination in infants aged 3 years, were investigated longitudinally. The surveyed child patients were 132 boys and 143 girls who had 20 deciduous teeth in their mouth through the surveyed period. The results were as follows: 1. The dental caries prevalence rate in the child patients was high at each age. 2. B and C caries attack patterns showing extensive caries increased remarkably at 3 or 4 years of age, and O patterns decreased with advanced age. 3. The child patients having no change in the caries attack patterns for 3 years decreased about 70%, and the severe type group transmitted to C caries attack patterns increased with advanced age. 4. Most of O caries attack patterns at 2 years of age changed to other patterns between 3 and 4 years of age, and they were few at 5 years.

A high voltage electric pulse was applied to DNA cleavage. The DNA cleavage reaction was dependent on the voltage amplitude, pulse number and pulse width. Radical scavengers and ESR data indicated the possibility that active species such as OH radical were strongly related to DNA cleavage.