Effect of Different Concentrations of Sodium Hypochlorite on the Compressive Strength of Endodontically Treated Roots

Introduction: The aim was to compare the compressive strength of dentin after irrigation with different concentrations of sodium hypochlorite (NaOCl). Methods: A total of 259 extracted human tooth roots with no root caries or previous endodontic treatment were collected. They were sorted by size and length, and assigned to 7 groups (n = 37): negative control (no instrumentation, no irrigant), positive control (saline irrigant), 1%, 2.5%, 4%, 5.25%, and 10% NaOCl. A total of 13 mL NaOCl or saline (in 1-mL increments) was used per canal while being instrumented to #35 files (approximately 13 minutes). EDTAC (15%) was then used to remove the smear layer (2 minutes), followed by NaOCl as a final rinse. The roots were sectioned into 2-mm-thick disks and subjected to compression testing. Results: There was a significant difference between the negative control group and all instrumented groups (P <.05). The positive control group was significantly different from the 5.25% group (P <.05) and had a low P value when compared with the 2.5% group and the other higher concentrations (P ≅.1). When the NaOCl groups were compared with each other, there was a significant difference between 1% NaOCl and all higher concentrations (P <.05), but no significant difference when 2.5% NaOCl was compared with higher concentrations. Conclusion: A concentration of 1% NaOCl had the least effect on the compressive strength of dentin and this was significantly different from all higher concentrations tested. Therefore, the use of concentrations of NaOCl above 1% should be reconsidered.