Contamination of dental unit cooling water with oral microorganisms and its prevention

Each time the handpiece turbine is stopped while the bur is still in the patient's mouth, almost 1 ml of microbe-laden oral fluids may be aspirated into the average dental unit water line by the retraction valve present in the dental unit. This fluid may contain an average in excess of 54,000 microorganisms per milliliter, including both facultative and obligate anaerobic bacteria of medium to high virulence. Other infectious agents including hepatitis, herpes, influenza, and other upper respiratory viruses may also be present. This germ-laden water may then be sprayed into the mouth of the next patient, possibly initiating an oral or upper respiratory tract infection. Sterilizing the handpiece between appointments, although of great significance in the prevention of disease transmission, will not totally eliminate the problem discussed here as almost 95% of the oral fluid aspirated into the dental unit went past the handpiece and into the handpiece cooling water line. Complete elimination of the retraction valve in the unit is the most effective means of solving this problem, but, with present dental unit designs, this may result in water dripping onto the patient. A viable alternative is the installation of a check valve (anti-retraction valve) downstream from the retraction valve. Installation of a check valve resulted in an almost 4,000-fold decrease in this contamination. The attachment of a check valve will have no effect on normal less virulent bacteria already present in tap water. These bacteria colonize the water lines of the dental unit and are then continually shed into the water in numbers often as high as 1,000,000 CFU/ml.(ABSTRACT TRUNCATED AT 250 WORDS)