This study was undertaken to explore the site-specific retention rate and the possibility of shortening fluoride (F) mouthrinsing time of kindergarten children. Fluoride retention after 10-, 20- and 30-second mouthrinsing was determined in 43 kindergarten children aged 4–5 years. Tooth surfaces were sampled by a paper point method. Fluoride concentrations in the salivary film on tooth surfaces increased from primary molars to primary incisors in the maxilla and decreased from primary molars to primary incisors in the mandible. The fluoride solution reached the primary molars even after a 10-second rinse, but F concentrations were higher after 20 s than after 10 s and significantly higher after 30 s than after 10 s. No significant difference was observed between 20 and 30 s. The average total F retained in the mouth was 0.13 mg after 20 s and 0.17 mg after 30 s. It was concluded that 30-second mouthrinsing, which is used extensively in Japanese kindergartens, can be shortened to 20 s.

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With the object of studying the relationship between the self cleaning ability of deciduous teeth and the tooth locations where dental caries tend occur most frequently, glucose clearance was tested in young children. The subjects were 38 kindergarten children aged 3 to 4 years. One by one, the subjects were asked to rinse their mouth with 10ml of a 0.5M glucose solution for 15 seconds before spitting it out. Three minutes after they put the solution in their mouth, a paper point was used to collect samples of saliva from the labial and buccal surfaces of the upper and lower deciduous teeth. The concentration of residual glucose in the small amounts of saliva collected was measured with a Sugar Analyzer.The study led to the following conclusions.1) The residual glucose concentration was significantly higher on certain deciduous teeth than on others in 3-and 4-year-old children: it was higher for the upper central incisors (upper A) than for the upper first molars (upper D), but lower for the lower central incisors (lower A) than for the lower first molars (lower D). In other words, the highest residual glucose concentrations were found on the upper central incisors and the lowest on the lower central incisors. 2) In 3-year-old children the tooth with the highest residual glucose concentration was the upper central incisor (upperA). The types with the lowest residual glucose concentration were the lower central and lateral incisors (lower A and B). In descending order, the residual glucose concentrations were upper A>upper D>upper B>lower E, lower D, upper E>upper C>lower C>lowerA, lower B.3) I deduce from the above data that the upper front deciduous teeth are in an environment that makes them the most susceptible to dental caries, the molars are intermediate in susceptibility, and the environment of the lower central incisors is the most caries resistant.