A New Weak Chelator in Endodontics: Effects of Different Irrigation Regimens with Etidronate on Root Dentin Microhardness

This study investigated the effect of sodium hypochlorite (NaOCl), ethylenediaminetetraacetic (EDTA), etidronic (HEBP), and citric acid (CA) associated in different irrigation regimens on root dentin microhardness. Forty-five root halves of single-rooted teeth were sectioned into thirds that were embedded in acrylic resin, polished, randomly assigned into 3 groups, and treated as follows: G1: saline solution; G2: 5% NaOCl + 18% HEBP, mixed in equal parts; and G3: 2.5% NaOCl. After measurements, the G3 samples were distributed into subgroups G4, G5, and G6, which were submitted to 17% EDTA, 10% CA and 9% HEBP, respectively. Following the new measurements, these groups received a final flush with 2.5% NaOCl, producing G7, G8, and G9. Microhardness was measured with Knoop indenter under a 25？g load for 15 seconds, before and after treatments. The data were statistically analyzed using paired Student’s t-test ( ) to compare values before and after treatments and analysis of variance (ANOVA) ( ) to detect any differences among thirds. Except G1, all tested irrigation regimens significantly decreased the microhardness. There were no differences between root thirds before treatments, and all root thirds exhibited equal responses to same treatment. Except saline, all tested irrigation regimens reduced the root dentin microhardness. 1. Introduction During endodontic therapy, chemical solutions are used to assist the action of endodontic instruments in the process of cleaning and shaping the root canal system. The lubrication of dentinal walls by these solutions would lower mechanical stress on rotary root canal instruments preventing instrument separation [1]. Despite the fact that these solutions facilitate the root canal instrumentation, they can also increase the possibility of occurrence of root canal deviation during biomechanical preparation [2], because they interfere in chemical structure of dentin, modifying the calcium/phosphorus (Ca/P) ratio of the surface [3, 4], which may decrease microhardness [5] facilitating the dentin cutting. These changes can also affect the sealing ability and adhesion of root canal sealers [6, 7]. Studies indicated that sodium hypochlorite (NaOCl), the most commonly used irrigating agent, decreases the microhardness of dentin at all concentrations [8–10]. With regard to chelating agents, the decalcification effects depend heavily on the irrigant used, the application time, and the solution pH and concentration [11, 12]. The association of different solutions with capability to dissolve organic and inorganic components is