Failure Rate Among Three Types of Dental Office Sterilizers

Purpose: This study was to determine the failure rates of sterilization cycles comparing autoclave, Chemiclave, and dry heat methods of sterilization using data collected from the subscribers of a sterilization monitoring service. Methods: 25,876 commercial biological indicators (BIs) from SPS Medical, Rochester, NY containing spores of Bacillus subtilis and Bacillus stearothermophilus (dual strips) were sent out to customers over a twelve-month period to be processed in regular loaded cycles and returned for evaluation. The BIs were aseptically transferred into sterile Trypticase Soy Broth tubes and incubated for seven days at 37oC to grow B. subtilis in dry heat sterilizer challenges or at 56oC for B. stearothermophilus in steam or chemical vapor sterilizer challenges. The tubes were inspected daily for turbidity and results recorded. Random samples showing positive growth were confirmed by Gram stain and microscopy. Results:There were 247 (1.46%) failures in the Autoclaves out of 16,924 spore strips tested. Of the 4652 spore strips from the Chemiclaves, 68 (1.46%) showed failures. The Dry Heat sterilizers showed 48 (1.12%) failures out of a total of 4300 spore strips. Although the required frequency for monitoring sterilizers is weekly, about 84% of the subscribers to the sterilization monitoring service monitored their sterilizer on a weekly basis. About 4.5% monitored their sterilizers on a fortnightly basis, while 11.5% monitored on a monthly basis. Conclusions: Sterilization failure among process types showed only minor variations. Failures could often be attributed to mechanical problems or improper sterilization techniques. This study was supported by Comprehensive Dental Monitoring Services of Baylor College of Dentistry.