Effect of different irrigant solutions on microhardness and smear layer removal of root canal dentin

Aim: To compare the effect of different irrigants on root dentin microhardness and smear layer removal. Materials and methods: A total of 50 roots were equally divided into two halves to measure dentin microhardness and to evaluate the amount of smear layer. One hundred root halves were divided into five equal groups 20 sample each according to the final irrigants used: Group 1: 2.5% NaOCl, Group 2: 2.5% sodium hypochloride (NaOCl) followed by 7% malic acid (MA), Group 3: 2.5% NaOCl followed by 17% ethylenediamine tetraacetic acid (EDTA), Group 4: 2.5% NaOCl followed by mixture of tetracycline, acid and detergent (MTAD) and Group 5: saline. Ten root halves from each group were prepared to measure dentin microhardness at baseline measurement and after treatment to determine the change in microhardness, while the remains 10 root halves were prepared for scanning electron microscope to evaluate the amount of smear in the coronal, middle and apical thirds. Results: Data were analyzed using one-way ANOVA and Student s t-test for microhardness and Kruskul-Wallis and Mann-Whitney for smear layer. Malic acid showed the greatest significant reduction in dentin microhardness (P 0.05), followed by EDTA, MTAD, NaOCl and saline (control). EDTA, malic acid and MTAD efficiently removed smear layer, respectively, in the coronal and middle thirds of root canal. However, in the apical region, malic acid showed more efficient removal of the smear layer than the other irrigants. Conclusion: Malic acid is the most efficient final irrigant solution after NaOCl irrigation throughout instrumentation.