Hygiene & Medizin 12/2017
The influence of lubricating oil on the efficay of steam sterilization processes used to decontaminate dental handpieces
Sandra Winter*, Andrew Smith, Brian Kirk, David Lappin
Hyg Med 2017; 42(12): D148–D154.
Keywords: steam sterilization · steam penetration · dental handpieces · narrow lumens · hollow load · biological indicators
Background: Dental handpieces pose a risk of cross infection due to contamination with patient material. Cleaning and sterilization of dental handpieces is challenging, due to a complex design. A further limiting, factor influencing achievement of sterilization conditions, is the presence of oil used to lubricate internal components. If moisture is absent then the process takes place in “dry heat” conditions and the time and temperature of exposure must be significantly increased (e.g. 160 °C for 2 h). Lubricating oils can be hydrophobic in nature and therefore, if present, prevent moisture in steam from reaching surfaces and thereby affect microbial kill (sterility).
Aim: The aim of this study was to investigate the effect of handpiece oil in dental handpieces on the inactivation of Geobacillus stearothermophilus spores during steam sterilization.
Methods: Handpieces were inoculated with a spore solution dried onto stainless steel wires, which were then placed into spray channels, followed by inoculation of handpiece oil (W&H, Austria). In order to investigate kill rates of different sterilization cycle profiles a Biological Indicator Evaluation Resistometer (BIER vessel) was used. Three different sterilization processes were investigated (two vacuum and one non-vacuum process). Spores were recovered by sonication of wires in phosphate buffer saline (PBS), filtration and plating on Tryptone Soy Agar (TSA). Recovered spores were expressed as colony forming units (cfu).
Results and Conclusions: Spores were recovered in only one type of process (with one pre-vacuum pulse) from 4 out of 12 processed handpieces. In conclusion this study suggests that it would be prudent to validate sterilization cycles with equipment and conditions that are likely to be encountered in clinical practice. Making assumptions that all bacteria are killed during sterilization processes, despite the overkill of three minutes at 134 °C in terms of integrated lethality, is not necessarily correct.