[The contamination of airturbine handpieces and the disinfecting effect of ultraviolet rays].

Abstract

It has been reported by various investigators that a greater proportion of the contamination on the part of dentists and their clinics is due to drilling with high-speed air-turbine handpieces. It is not only the dentist or his clinic that is contaminated, but also the handpieces themselves that probably become contaminated. For this reason, some kind of countermeasure is needed. But, because of their structure it is difficult to disinfect these instruments and, therefore, we must search for an easy method of disinfection in clinical environments.In the belief that ultraviolet ray, if it could be proved sufficiently effective for bacteriocidal purposes, would provide one easy means of disinfection, I carried out the following research. For study purposes, 3 different types of dental clinics were selected:1) those clinics where handpieces were not disinfected at all dnring dental treatment, 2) those clinics where handpieces were occasionally disinfected, and 3) those clinics where handpieces were disinfected every time they were employed.In these 3 different types of dental clinics, efforts were made to wipe off the handpieces for 5 days prior to the treatment in the first week and at the end of treatment daily in the second week.The number of bacterial coloneis between these two-week intervals were measured and analyzed.By way of determining the disinfecting effects of ultraviolet ray on different bacteria, Escherichia coli, Staphylococcus aureus and Bacillus subtilis were selectivly used to establish the density of ultraviolet ray and the time of bacteriocidal effect.In the last phase of the study, an apparatus was devised so that the entire surface of handpieces could be disinfected and the different bacteriocidal effects were comparatively examined.As a result of the present sudy, I arrived at the following salient conclusions.1. In dental clinics where handpieces were not routinely disinfected, the degree of bacterial infection was much larger than in other dental clincis where handpieces were regularly disinfected.2. Even in dental clinics in which handpieces were disinfected after every dental treatment, they were not always free from bacterial infection.3. The time required for disinfection of Escherichia coli, Staphylococcus aurens, and Bacillus subtilis by an application of ultraviolet ray could be much reduced by increasing the intensity of the ultraviolet ray.4. The bacteriocidal effects of ultraviolet ray were most prominently observed with Escherichia coli, followed by Staphylococcus aurens, and Bacillus subtilis.5. An ultraviolet disinfecting apparatus, devised by me for this study, was effective in killing the bacteria on handpieces within 5 minutes.