Aim: The present in vitro study was undertaken to check the effect of the different irrigating solutions with surfactants, i.e., sodium hypochlorite-(Naocl)-Extra, chlorhexidine (CHX)-Ultra, ethylenediaminetetraacetic acid (EDTA), QMix, and BioPure MTAD on the microhardness and smear layer removal of root canal dentin. Materials and Methods: A total of 120 straight rooted lower premolars were collected and were randomly divided into 2 equal groups of 60 each ( n = 60). The microhardness of the samples was evaluated by Vickers hardness tester and the removal of smear layer by scanning electron microscope after irrigation of the samples with the tested solutions. Results: CHX-Ultra showed the least microhardness reduction, and EDTA showed the maximum microhardness reduction in all the tested groups. BioPure MTAD showed the maximum removal of smear layer in the apical third, and CHX-Ultra showed the minimal smear layer removal in the apical third. Conclusion: During smear layer removal, irrigating solutions cause alterations in the chemical composition of dentin, which may decrease the microhardness of the root dentin causing erosion and affecting the clinical performance of the endodontically treated teeth. Irrigating solution with maximum smear layer removal with minimum changes in microhardness should be used.

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