Effect of exposing dentine to sodium hypochlorite and calcium hydroxide onits flexural strength and elastic modulus

Aim The aim of this study was to evaluate the effect of sodium hypochlorite (NaOCl) solutions (3%, 5%) and saturated calcium hydroxide (Ca(OH)(2)) sol ution, individually and consecutively, on the flexural strength and modulus of elasticity of standardized dentine bars, Methodology Standardized piano-parallel dentine bars (n = 121) were divided into five test groups and one control group. The control group 1 consisted of dentine bars, stored in normal saline until testing. The dentine bars i n the five test groups were treated by exposure to the following solutions; group 2 - 3% NaOCl, 2 h; group 3 - 5% NaOCl, 2 h; group 4 - saturated Ca(O H)(2) solution, 1 week; group 5 - 3% NaOCl, 2 h and then saturated Ca(OH)(2 ) solution 1 week; group 6 - 5% NaOCl, 2 h and then saturated Ca(OH)(2) sol ution 1 week, The dentine bars were then loaded to failure in a three-point bend test, Results The data revealed a significant (P < 0.001) decrease in the modulus of elasticity and flexural strength of the dentine bars treated with 3% an d 5% NaOCl. There was no significant difference in the flexural strength an d the modulus of elasticity between the 3% and 5% NaOCl groups. Exposure to Ca(OH)(2) significantly (P < 0.001) reduced the flexural strength but had no significant effect on the modulus of elasticity. The groups treated with sodium hypochlorite followed by calcium hydroxide did not have moduli of e lasticity and flexural strengths that were significantly different from tho se treated only with sodium hypochlorite. Conclusions NaOCl (3 & 5%) reduced the modulus of elasticity and flexural s trength of dentine. Saturated Ca(OH)(2) reduced the flexural strength of de ntine but not the modulus of elasticity. Sequential use of NaOCl and Ca(OH) (2) has no additional weakening effect.