Effect of Various Concentrations of Sodium Hypochlorite on the Microhardness of Bulkfill Restorative Composite Resin used as a Pre-endodontic Restoration

Abstract

Introduction: A four-walled access cavity plays a vital role in successful endodontic treatment. The materials used for preendodontic restoration are flowable composites, restorative composite resins, packable composite resins, silver amalgam, or glass ionomer cement. Researchers have claimed that exposure of composite resins to low pH liquids and root canal irrigants can have a deleterious effect on their physical and mechanical properties. Aim: To evaluate the microhardness of a bulk-fill restorative composite resin material before and after being exposed to distilled water, 1% sodium hypochlorite, 3% sodium hypochlorite, and 5% sodium hypochlorite. Materials and Methods: This was an in-vitro experimental study that was conducted at the Department of Conservative Dentistry and Endodontics, M.G.M Dental College and Hospital, Mumbai, Maharashtra, India, over a period of eight months from January 2021 till August 2021. Total 32 disc-shaped samples were made from a bulk-fill restorative composite resin, 3MTM Filtek Bulk fill posterior restorative composite resin (3MTM, St. Paul, MN, USA). Each disc was prepared using polytetrafluoroethylene (Teflon) molds of 10 mm inner diameter and 4 mm depth. The bulkfill composite resin discs were randomly divided into four main groups, group 1 (distilled water), group 2 (1% NaOCl), group 3 (3% NaOCl), and group 4 (5% NaOCl), with eight samples in each group. Baseline Vickers hardness testing was performed for each group using a 100 gram load and a dwell time of 10 seconds before being immersed in the irrigation solution. Pre and post immersion microhardness measurements were done on the same surface of each sample (top surface). Data obtained were subjected to normality tests. Further statistical analysis was done using one-way Analysis of Variance (ANOVA) followed by the Games-Howell test for pair-wise comparisons. Results: Irrespective of the different concentrations of sodium hypochlorite irrigant, all samples showed a reduction in microhardness of bulk-fill composite restorative resin. The post immersion microhardness mean values were highest in group 1 (63.06) and lowest in group 4 (58.42), and the difference was statistically significant (p<0.001). No statistical difference was seen between group 3 and group 4. On intragroup comparison, all the groups show statistically highly significant difference between pre and post immersion microhardness values {Paired-t test (p<0.05)}. Conclusion: Microhardness of bulk-fill composite restorative resin was lowered by different concentrations of sodium hypochlorite irrigant.