CFD simulation of the inactivation of Geobacillus stearothermophilus on dental handpieces

Abstract

Steam sterilization processes are used to sterilize dental handpieces before reuse. Computational Fluid Dynamics (CFD) simulations can be a useful tool to investigate the various physical phenomena that occur within steam sterilizers. In this paper, a CFD model with three significant modifications compared to current state-of-the-art simulations of steam sterilizers was developed. The simulated values of the CFD model were validated by measuring the pressure and the fluid temperatures in eight different locations. Both the measured and simulated pressure, as well as the measured and simulated fluid temperatures, were in very good accordance. (I) The steam quality inside the steam sterilizer was investigated for both wrapped and unwrapped loads. The paper wrapping of the load was modelled using a time-efficient porous media approach. Condensation effects on cold surfaces were simulated using a heat transfer model that was developed in-house. The results showed that the lowest steam qualities were found near the wrapped load and in the bottom region of the steam sterilizer. (II) The load temperature and the F0 values were investigated on the surface of two different dental handpieces. The simulated surface average F0 value on the dental handpieces was approximately 155 min. (III) A first order reaction kinetic approach was added to the CFD code to predict the inactivation of the bacteria type Geobacillus stearothermophilus in the steam sterilizer, as well as on the surface of wrapped and unwrapped dental handpieces. The steam sterilizer investigated in this work was able to inactivate approximately 22 log-ratios of Geobacillus stearothermophilus on the surface of the dental handpieces.