Effect of sodium hypochlorite, chlorhexidin and EDTA on dentin microhardness

*Department of conservative, college of dentistry, Hawler Medical University, Erbil, Iraq. **Department of P.O. P, college of dentistry, Hawler Medical University, Erbil, Iraq. Introduction The aim of root canal treatment is to remove bacteria and debris from the root canal space. This goal is achieved by using irrigant solution. Irrigation flushes away the loose, necrotic and contaminated materials outside the canal before they are pushed deeper into the apical direction. Sodium hypochlorite (NaOCl) has been recommended to remove the organic tissues (necrotic and vital tissues) from the root canals because of its solvent activity. Chlorhexidin (CHX) has antibacterial effect and no cytotoxicity. The different concentrations of EDTA are also used for debridement of root canal by improving the removal of smear layer because act as chelating agent. Dentin microstructure and its properties are very important in restorative dentistry. Knowledge of mechanical properties of human root canal dentin would help restorative treatment. Microhardness de-fine as the resistance to local deformation and it tests based on the induced permanent surface deformation that remains after removal of load. Hardness measurement can be correlated with the other mechanical properties such as fracture resistance. After the use of chemical irrigants, which are capable of altering the proportion of organic and inorganic components of root canals, the structural properties of dentin may be Background and objective: The use of chemical irrigants solution in root canal therapy is capable of altering the proportion of organic and inorganic components of root canals. The structural properties of dentin may be changed such as permeability, solubility and microhardness. The aim of this study was to evaluate the effects of root canal irrigants on the microhardness of root canal by using three types of irrigant solutions with different concentration and normal saline used as control group. Methods: Root halves were prepared by longitudinal splitting of the roots of 56 freshly extracted caries free maxillary second premolars and embedded in autopolymerizing acrylic resin, leaving the dentin surface exposed. The root halves were randomly divided to seven groups composed of 16 samples each and treated for five minutes with one of the following irrigants: normal saline (control group), 0.2 % chlorhexidin, 2% chlorhexidin, 2.5% sodium hypochlorite, 5.25%, 5% Ethylene dimetha tetra hydrate EDTA and 17% EDTA. After surface treatment, the dentin microhardness of the root samples were recorded at the mid-root level by using a vicker microhardness tester. The data were statistically analyzed by using one-way analysis of variance, followed by Duncans test with a significant difference test at P ≤0.05. Results: EDTA, sodium hypochlorite, and 2% chlorhexidin significantly decreased the microhardness of root dentin compared with controls (P <0.05), while 0.2% chlorhexidin had no significant effect on the microhardness of root dentin. Conclusion: The irrigant solutions affect the microhardness of the samples except 0.2%.