Impact of irrigant sequence on mechanical properties of human root dentin

To get the root canal system free of organic debris and the smear layer, it has been recommended to irrigate with a NaOCl solution during instrumentation, followed by a rinse with a chelating agent such as ethylenediaminetetraacetic acid (EDTA) and a final irrigation with NaOCl. However, both hypochlorite and EDTA weaken dentin through dissolution of its organic and inorganic components, respectively. EDTA exposes the organic dentin matrix, which could then be attacked more easily by hypochlorite. It was the aim of this study to assess the impact of different irrigation sequences of NaOCl (2.5% w/v; total exposure time, 24 minutes) and EDTA (17%; 3 minutes) on the elastic modulus and flexure strength of standardized human root dentin bars (n = 11 per group). Exposures to solely EDTA (3 minutes), NaOCl (24 minutes), and water were used as control treatments. Specimens were subjected to 3-point bending tests; modulus of elasticity and flexure strength values were compared between groups with one-way analysis of variance followed by Fisher probable least-squares difference test. The alpha-type error was set at .05. The 24-minute exposure to the hypochlorite solution caused a significant drop in flexure strength compared with water- or EDTA-treated controls (P < .05), whereas the elastic modulus remained unaffected. In contrast, the short exposure to EDTA as is clinically recommended did not affect the mechanical dentin parameters under investigation, regardless of the irrigant sequence that was used.