Investigating best practice for specimen preparation for biological testing of root canal sealers

Introduction : Biological characterization of root canal sealers is important as it assesses the ability of the root canal sealer to exert antimicrobial properties thus avoiding treatment failures caused by microbial challenge and also assess the cytotoxic effect on the periapical tissues. Assessment of the biological testing of root canal sealers necessitates the sterilisation of the materials prior to evaluation. This study aims to analyse the influence of various sterilisation techniques conducted prior to biological testing on the microstructure and surface properties of endodontic sealers. Assessment of the initial microbial contamination on the material was also undertaken. Methods: Four commercial sealers were investigated. The sealers were either prepared in a laminar flow cabinet or on a laboratory bench top under ambient conditions. Each group was further divided into 5 groups (n = 3) based on the sterilization technique:1) ethanol-10 mins, 2) ultraviolet-1 h, 3) ethanol-10 mins + ultraviolet-1 h, 4) autoclave, and 5) no sterilisation (control). Microbial levels in the materials were assessed by plate streaking technique. The materials were characterized by scanning electron microscopy and energy dispersive spectroscopy, and Fourier transform infrared spectroscopy, before and after sterilisation, to assess any changes in microstructure and chemical composition. Results: All the materials did not exhibit contamination when prepared in laminar flow chamber in sterile conditions compared with sealers prepared on the bench top. Three of the commercial materials showed changes in microstructure while one (TotalFill) was not affected by the sterilisation. AH Plus and BioRoot RCS exhibited alterations in water and alcohol peaks in FT-IR while the single syringe sealers (TotalFill and BioRoot Flow) showed no changes. Conclusions: Sterilisation methods cause physical and chemical alterations to sealers. Material preparation should be performed in a laminar flow cabinet and a test for sterility should be performed prior to any biological testing being undertaken. If the materials are not sterile, assessment of the effects of the sterilization methods is recommended.