[Design-dependent transmission of bacteria by internal infection of dental turbines (author's transl)].

The results of the present investigation point to an up to now little recognized possibility of bacterial transmission by dental turbines, namely, the intake of spray water by reverse suction from the turbine hand piece into the cooling water system on turning off the unit. Reverse suction is provided in most modern dental turbine units to prevent after-drip and the cooling of the pre-warmed spray. As a consequence, microorganisms of the oral flora and possibly disease-producing bacteria may be carried into the cooling water system and thus be transmitted to the next patient when using the same turbine. In carefully planned experiments employing E. coli as test organisms it could be shown both in simulated manipulation in the oral cavity as well as in in vitro experiments that transmission of bacteria is possible in up to 10 ml of spray water ejected (equivalent to 10 spray water fractions of 1 ml each). In older model turbines without spray water reverse suction, bacteria were absent after ejection of no more than 6 ml of cooling water (in fractions of 1 ml each). In order to avoid transmission of bacteria in spray water of dental turbines it appears necessary to subject the turbine hand piece or the turbine head, resp., to rigorous disinfection and to allow delivery of at least 20 ml of spray water - corresponding to about 20 second's operation - before reusing the unit.