Application of Electrolyzed Neutral Water to Sterilization of Metallic Instruments

Objectives: Electrolyzed strong and weak acid waters have been widely used in clinical dentistry because of their excellent bactericidal activities. Recently, electrolyzed neutral water developed as an improved type in the stability of the bactericidal efficacy and corrosiveness to metals. The present study was scheduled to compare the three types of electrolyzed waters in terms of sterilization effect and corrosion on metallic instruments. Methods: Several burs and impression trays with their surfaces being contaminated with the level of 10⁶ bacteria (Staphylococcus aureus 209P) were immersed in the electrolyzed water with or without ultrasound. After treatment, the surviving bacteria were shifted from each instrument to fresh saline solution and the solution was added to the agar culturing media. The total number of the surviving bacteria was calculated from the number of the colonies in the media after incubation. The surface corrosion was macroscopically and scanning electron microscopically observed for the instruments. Results: Only 1-minute immersion in each electrolyzed water could sufficiently sterilize all the burs under ultrasonic and all the trays even under no ultrasonic. After 24-hour immersion in the electrolyzed acid water, especially strong type, a marked corrosion was found on the overall surface of the steel burs and a localized loss occurred at the brazed area between the blade and shank of the carbide burs. The neutral water was less corrosive than the acid waters. Significant damages appeared on the trays made of Sn alloy, Al or stainless steel during 24-hour immersion in the strong acid water. Conclusions: The sterilization efficacy foe metallic instruments were found to be excellent with no significant differences among the three types of electrolyzed waters. It was suggested that the neutral water might be the most proper for sterilization treatment because it showed the least corrosiveness. yuki-naga@kyu-dent.ac.jp