Acido citrico y fosforico

Basic Research—Technology

Scanning Electron Microscopic Investigation of the Effectiveness of Phosphoric Acid in Smear Layer Removal When Compared with EDTA and Citric Acid
Mara Prado, DDS, MSc,* Heloisa Gusman, DDS, MSc, PhD,† Brenda P.F.A. Gomes, DDS, MSc, PhD,‡ ı and Renata A. Sim~ o, DSc, MSc, PhD* a
Abstract
Introduction: The smear layer adheres to dentinal surface, thus occluding thedentinal tubules. Because this layer disfavors the penetration of irrigant solutions and root canal fillings, it should be removed. The aim of this study was to compare the effectiveness of 37% phosphoric acid with that of 17% EDTA and 10% citric acid in the removal of smear layer. Materials and Methods: Fifty-two maxillary single-rooted human canines were accessed and instrumented. Between eachinstrument used, the canals were irrigated with sodium hypochlorite. After instrumentation, the teeth were irrigated with distilled water and then divided into groups according to the time and substances employed. The substances used were 17% EDTA, 10% citric acid, and 37% phosphoric acid solution and gel. The experimental time periods were of 30 seconds, 1 minute, and 3 minutes. The samples wereprepared and observed by means of scanning electron microscopy. Three photomicrographs (2,000Â) were recorded for each sample regarding the apical, middle, and cervical thirds. A score system was used to evaluate the images. Results: None of the substances analyzed in this study was effective for removing the smear layer at 30 seconds. In the 1-minute period, the phosphoric acid solution showedbetter results than the other substances evaluated. In the 3minute period, all the substances worked well in the middle and cervical thirds although phosphoric acid solution showed excellent results even in the apical third. Conclusions: These findings point toward the possibility that phosphoric acid solution could be a promising agent for smear layer removal. (J Endod 2011;37:255–258)

D

uringthe cleaning and shaping of the root canal system, dentin chips are created by instrument action. These chips associated with organic materials, microorganisms, and irrigant solutions form the so-called smear layer. This layer adheres to the dentinal surface and occludes the dentinal tubules (1, 2). Many researchers believe that the smear layer should be removed. This layer contains bacteria andnecrotic tissue (3). It forms a barrier between the filling material and sound dentin that inhibits the penetration of irrigants into dentinal tubules, increases microleakage with commonly used sealers, and decreases the bond strength of resin based materials (4–10). Some chemical agents such as EDTA solutions at concentrations ranging from 15 to 17%, citric acid (5%-50%), and phosphoric acid(5%-37%), therefore, are used to remove this layer (11). Despite the relevant literature available concerning the effect of these agents on the smear layer removal, the small number of studies with similar methodologies and comparable time intervals and concentrations limits the ability to make valid comparisons between these treatments, especially when considering the use of phosphoric acid. Thischemical agent has been extensively used to remove the smear layer from coronal dentin (12–14), and only a few studies have analyzed its performance in root dentin (15–17). Therefore, the aim of this study was to compare the effectiveness of 37% phosphoric acid with that of 17% EDTA and 10% citric acid in removing the smear layer by means of scanning electron microscopy (SEM).

Materials and MethodsSmear Layer Production and Irrigation Protocols This study was approved by the Ethics Committee of the Federal University of Rio de Janeiro. Fifty-two single-rooted maxillary human canines, extracted because of periodontal or prosthetic reasons, were used. The teeth were randomly selected from known patients. All patients signed an informed consent document to take part of this research. Their...