A pilot study of three methods for the reduction of bacterial contamination of dental unit water systems in routine use

Three different methods for minimizing the bacterial contamination of the water system in a SIRONA C2 type dental unit were investigated sequentially. Without any decontamination method, water from the hand piece, air-water-jet and mouthwash were continuously contaminated by 10(3) to 10(5) colony forming units (cfu) of aerobic mesophilic bacteria per milliliter. A reduction to below 100 cfu/ml was achieved by continuous adding of a chemical microbicide based on hydrogen peroxide and silver ions. However, this was only possible after rinsing the system thoroughly for at least two minutes after interruptions of the treatment. Long-lasting low counts of below 100/ml were obtained by means of an in-line bacteria filter, in connection with the provision of a thermo-chemical or thermal decontamination of the water pipes and hand pieces after the filter. The electrolyte release of chlorine from the dental unit tap water by anodic oxidation without addition of any chemical disinfectant also resulted in continuously low colony numbers of the water. In this case, regular decontamination of the end parts of the pipes and hand pieces was not necessary.