Effect of sterilization techniques prior to antimicrobial testing on physical properties of dental restorative materials.

OBJECTIVES: The aim of this study was to investigate any changes to the microstructure and surface properties of selected dental materials after sterilization carried out prior to subjecting them to antimicrobial testing. Initial microbial contamination on the material, as well as other possible sources of contamination were also assessed. METHODS: The materials investigated included dentine replacement materials Chemfil Superior(®), Ionoseal(®), Dyract Extra(®) and SDR(®). The materials were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The test materials were sterilized using alcohol, steam, ultraviolet light (UV) and ethylene oxide and any changes to these materials were then assessed by SEM, microhardness testing and Fourier transform infrared (FT-IR) spectroscopy. Material microbial levels before treatments were assessed by plate counting technique and turbidity tests. Possible contamination through dispensers was assessed by analysing the CFU/sample. RESULTS: Ethylene oxide affected the microstructure of the Chemfil, Ionoseal and Dyract, resulting in flattening of the SiO stretching vibrations and deposition of chlorine and calcium respectively in Chemfil and Dyract. Varied contamination was demonstrated on all materials when incubated in anaerobic conditions. CONCLUSIONS: The different sterilization techniques affected the microstructure of the materials under investigation. Samples of materials produced in sterile conditions could also be contaminated with bacteria, either from the material itself or through the dispensing apparatus. CLINICAL SIGNIFICANCE: Results of antimicrobial studies cannot be extrapolated clinically as the material sterilization treatment results in changes to material chemistry and microstructure, which could in turn affect the materials' antimicrobial activity.