Differential Sterilization of Dental Handpiece Turbines

Dental handpieces may take up saliva or blood containing microorganisms from patients, and induce cross contamination between patients during treatment. Therefore, steam sterilization of handpieces is recommended by the CDC after treatment of each patient. In general handpieces contain two turbine designs, canister- and open wheel-style. However, the efficacy of the steam sterilization may not be equivalent between the two turbine types. Objectives: This study compared the efficacy of steam sterilization on turbine design in the absence of lubricant. Methods: Using the same autoclave, testing was performed according to ANSI/AAMI ST55:2003 with three different brands of canister-style and two different brands of wheel-style turbines. Sterilization tests for handpiece turbines were performed by inoculating non-lubricated turbines with spore suspension in blood containing 1.0 x 10⁶ Geobacillus stearothermophilus. After steam sterilization, turbines were aseptically transferred and incubated in trypic soy broth (TSB) for 7 days at 55^oC. Results: ST55 performance standard requires that biological indicators processed in half cycles shall show no spores growth. In this study (N = 14), three different brands of handpiece canister-style turbines demonstrated spore growth in 28.5%, 21.4% and 7.14%, respectively, with a mean of 18.93 ± 6.26 (SEM)%. However, two different brands of handpiece turbines with wheel-style demonstrated 0% and 7.14% of spore growth, respectively, with a mean of 3.57 ± 3.57 (SEM)%. Spore germination occurred in all non-sterilized positive controls, and no growth was detected in negative controls (sterile TSB). Conclusions: This study indicates that canister-style turbines may have a higher chance of failing the performance standard for ST55 than those containing open wheel-style turbines. Since these failures may be more a function of handpiece design rather than of an autoclave deficiency, ST55 should be amended to specify a standard test handpiece or allow handpiece lubrication before steam sterilization as recommended by handpiece manufacturers.