Effects of handling and storage on sterile dental instruments

The microbial contamination post-sterilization of dental instruments has been the object of permanent study. The aim of the present study was to evaluate factors affecting long-term sterility of dental instruments sterilized in the dry-oven or autoclave at the Central Sterilizing Service of the School of Dentistry, University of Buenos Aires stored under room temperature and humidity conditions. Half of the 192 samples were placed in standard closed metal containers and sterilized in a dry-oven (D.O), and the remaining half were placed in perforated metal containers and sterilized in an autoclave (A). All the samples were placed in sterilizing paper bags for medical use. Post sterilization, each group (DO and A) was divided into: Group I: minimal handling (control); Group II: wrapping torn mechanically (1 cm); Group III: wrapping torn manually (1 cm). All the samples were stored a closed cabinet. Contamination was evaluated at 30 and 180 days, by seeding under aerobic and anaerobic conditions. Temperature was monitored throughout the experiment, and ranged between 20 degrees C and 31 degrees C (x: 24 degrees C +/- 3.9). Humidity was measured with a digital hygrometer, and ranged between 40% and 60% (x: 54% +/- 10). Group I evidenced no microbial contamination, unlike Groups II and III. Our results evidence that 1) dry oven or autoclave sterilized material that is handled properly during storage remains sterile regardless of variations in temperature and humidity; 2) improper handling affects sterility, and contamination is time-dependent.