Water contamination from conventional dental units is serious problem. Health, Labour and Welfare Ministry of Japan set recommended water quality standard as 100 CFU/ml (common bacteria) and 2,000 CFU/ml (heterotrophic bacteria). However, there are no reports on dental units meeting this standards in Japan. The purpose of this study was to develop a dental units without a water supply pipe, and meet water quality standards of Japan.
We removed the water supply pipe from a dental unit, installing a built-in removable water supply tank. We grew common bacteria on standard agar at 36°C for one days and heterotrophic bacteria on R2A agar at 20°C for 7 days, and measured bacterial numbers in the conventional type and the tank type. The results of the conventional type ranged from 180 to 31,000 CFU/ml in common bacteria, and 2,000 to 86,000 CFU/ml in heterotrophic bacteria. The results of the tank type ranged from 30 to 50 CFU/ml in common bacteria, and 30 to 1,500 CFU/ml in heterotrophic bacteria achieving the water quality standard of Japan. The conventional type has a water supply pipe 6-7 m long. In contrast, the tank type has 26cm.

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