Letters in Applied Microbiology 1998, 27, 292–296 Evaluation of the efficacy of glutaraldehyde and peroxygen for disinfection of dental instruments I.F. Angelillo, A. Bianco, C.G.A. Nobile and M. Pavia Medical School, University of Catanzaro, Italy 1752/98: received 16 July 1998 and accepted 23 July 1998 I.F. ANGELILLO, A. BIANCO, C.G.A. NOBILE AND M. PAVIA. 1998. The antimicrobial and sporicidal activities in vitro and in vivo of 1% peroxygen (Virkon) and 2% alkaline glutaraldehyde (Asporin) were evaluated on dental instruments before and after cleaning. The in vitro antimicrobial activity against vegetative bacteria, bacterial spores and fungi indicated that glutaraldehyde is more active against these organisms than peroxygen. Asporin killed all vegetative bacteria within 1 min after cleaning, whereas Virkon was active, in the majority of cases, within 15 min and obtained a greater than 10 5 -fold reduction in count before killing for the vast majority of instruments, and for all micro-organisms. The spores of Bacillus subtilis were killed by Asporin within 4–5 h after cleaning, whereas Virkon required almost 20 h. A meticulous instrument cleaning process followed by an appropriate disinfection treatment assures a shorter disinfection time. Asporin should be recommended for chemical sterilization or high-level disinfection of dental instruments, and Virkon, if only disinfection is required, would seem to be a possible alternative, even if used with a higher exposure time. INTRODUCTION Within the practice of dentistry, much attention must be given to infection control procedures in order to reduce the chances of cross-contamination that may lead to several infec- tious diseases. Case reports confirm that dental procedures may cause cross-infection and because of the continued threat of HIV and hepatitis B infection, as well as the possibility of serious disease transmission, the dental profession is advised to adhere strictly to recommended infection control strategies in health care settings. Although these risks can be eliminated by the use of effective disinfection and sterilization tech- niques, the processing of contaminated equipment remains a critical issue and must be performed by personnel who adhere strictly to established protocols. The term ‘disinfection’ is defined as a process which kills only vegetative organisms, whereas, sterilization kills spores as well. Over the past decade, the efficacy of chemical and physical disinfectants on contaminated dental instruments (D’Errico et al. 1986 ; Martina et al. 1988), the microbiological con- tamination level of dental unit water lines and its control Correspondence to : Italo F. Angelillo, Chair of Hygiene, Medical School, University of Catanzaro, Via Tommaso Campanella, 88100 Catanzaro, Italy. © 1998 The Society for Applied Microbiology (Angelillo et al. 1988), the microbiological contamination level of air in dental environments (Angelillo et al. 1990), and the degree of compliance with the recommended infection control procedures (gloves, masks, protective eye-wear) by the dis- tribution of a questionnaire to a sample of Italian dentists (Angelillo et al. 1994), have been evaluated. Recently, a new type of chemical agent based on the acid peroxygen system (Virkon) has been widely studied with regard to its antimicrobial activity towards several strains of organisms (Coates and Wilson 1992 ; Broadley et al. 1993 ; Holton et al. 1994 ; Gasparini et al. 1995 ; Coates 1996 ; Ares- Maza `s et al. 1997). The purpose of this study was to evaluate the bactericidal and sporicidal activities of Virkon on dental instruments. MATERIALS AND METHODS Disinfectants Asporin (Farmec, Verona, Italy) is an aqueous solution of 2% glutaraldehyde activated by the addition of sodium phenate solution (final pH 7·9–8·0) at the time of testing. Virkon (Antec International, Sudbury, UK) is a balanced, stabilized