Effect of various concentrations of sodium hypochlorite on primary dentin: an in vitro scanning electron microscopic study.

Sodium hypochlorite solutions have been evaluated for their effects in bonding procedures as they are found to deplete or remove the organic portion of the dentin, particularly the collagen fibrils. The aim of this in vitro study was to assess and compare the efficacies of 1%, 2.5%, 5% and 10% NaOCl at 30, 60 and 120s on etched primary dentin. 84 primary anterior teeth were ground to expose a flat dentin area on the buccal surface. The specimens were divided into fourteen groups of six each based on the dentin surface treatment (35% phosphoric acid etching for 7 seconds-AE and/or NaOCl application), NaOCl solution concentrations (1%, 2.5%, 5% and 10%) and time of application (0, 30, 60 and 120s). Specimens were prepared for SEM and photomicrographs were taken of the surface and were scored against a five point scale, based on the smear layer and amount of collagen removed. The scores were submitted to Kruskal-Wallis and Mann Whitney tests. This study showed the presence of smear layer in the control group. The group treated with Acid Etchant showed a demineralized pattern of dentin with exposure of dentin tubules and collagen fibrils network on the intertubular and peritubular dentin which was not significantly different from the groups treated with 1% and 2.5% NaOCl. Groups treated with 5% NaOCI were not statistically different from each other the surface was corroded but collagen fibrils were not completely depleted. Groups treated with 10% NaOCl were not statistically different from each other and showed complete removal of collagen fibrils with wider tubular apertures and several secondary tubules on peritubular and intertubular dentin. Higher concentrations of NaOCl solutions (5% and 10%) produced significant changes in the etched primary dentin. The higher the concentration of the NaOCI solution, the lower can be the time for the application of the solution for the complete removal of collagen fibrils.