Effect of different irrigation protocols and calcium hydroxide dressing on the microhardness of root canal dentin

Aim: This study aimed to evaluate the effect of different irrigation protocols and calcium hydroxide dressing on the microhardness of root canal dentin.

Methodology: Thirty human teeth were decoronated and root segments were obtained from pre-established cuts made below the cemento-enamel junction. After specimen’s preparation, the initial dentin microhardness (H0) was measured with a Vickers indenter, on the coronal surface, at 150 µm and 500 µm from the root canal lumen. Next, the specimens were randomly distributed into three groups (n=10), according to the different irrigation protocols: 1% NaOCl; 1% NaOCl + 17% EDTA; and 5% NaOCl. After irrigation, the hardness measurement was repeated (H1), in another quadrant. Then, Ca(OH)₂ dressing was applied and left for 30 days, until it was removed and a new microhardness measurement (H2) was made, in a third quadrant. The data were statistically analyzed using the three-way analysis of variance (ANOVA) and Tukey tests, set at α=0.05.

Results: The factors analyzed (moment of VH, distance from the canal lumen and irrigation protocol) were statistically significant (p<0.05). There was a significant decrease of dentin microhardness after the irrigation protocols (H1<H0, p<0.05), however, with no significant difference after Ca(OH)₂ dressing (H2~H1, p>0.05). The 5% NaOCl group shown the greatest difference between H0 and H1 measurements (p<0.05).

Conclusions: All irrigation protocols promoted significant decrease of the dentin microhardness. The Ca(OH)₂ dressing for 30 days did not significantly affect the microhardness of the root canal dentin.