Introduction: The use of chelating agents removes smear layer, increasing the access of irrigants to allow disinfection, and also reduces microhardness. Microhardness is an indirect evidence of mineral changes in dentin. Its reduction facilitates the instrumentation throughout the canal but, it may weaken the root and increases permeability of dentin. Therefore, finding a biocompatible chelating agent with better chelating ability is mandatory.
Objective: To evaluate the effect Phytic acid (IP6) with different concentrations and ethylene diamine tetra-acetic acid (EDTA) solution on microhardness of radicular dentin.
Materials and method: This study was conducted on 30 single rooted permanentmaxillary anteriors. Teeth were instrumented using rotary files and irrigated in between using 2ml 2.5% NaOCl, then were sectioned longitudinally into halves giving 60 specimens that were embedded in acrylic resin leaving the dentin exposed. After polishing, the microhardness values of the untreated dentin were recorded by Vicker's microhardness tester. The root halves were  divided  into 4 groups composed of  15 samples each  and immersed for 5 minutes with one of the chelating solutions, Group I:  Immersed in 10ml of (IP6) 0.5% followed by 10ml of 2.5% (NaOCl), Group II:  Immersed in 10ml of (IP6) 1% followed by 10ml of 2.5% NaOCl, Group III:  Immersed in 10ml of 1.5% (IP6)  followed by 10ml of 2.5% NaOCl, Group IV:  Immersed in 10ml of 17% EDTA solution followed by 10ml of 2.5% NaOCl. Then microhardness values were recorded, and calculation of the difference between baseline values and post-application values were calculated.
Results: Tested chelators reduced microhardness of the dentin. 17% EDTA reduced the microhardness more significantly than 0.5%, 1% and 1.5% IP6.
Conclusion: Using IP6 with different concentrations had less detrimental effect on dentin microhardness than EDTA.