Presence of endodontic sealer remnants in the pulp chamber may result in gradual coronal discoloration of variable intensity (Parsons et al., 2001). Despite the low rate of diffusion through dentin tubules, the sealer itself may undergo discoloration, compromising the translucency of the dental crown and posing esthetic concerns for the patient (Davis et al., 2002; Plotino et al., 2007).
The bond strength of dentin adhesives is negatively affected when the dentin surface is impregnated by oil, hemostatic agents, temporary filling material, or endodontic sealer residues (Matos et al., 2008; Roberts et al., 2009; Chaiyabutur and Kois 2011). A recent study showed that persistence of AH Plus sealer (Dentsply Caulk, Milford, DE) residues in the pulp chamber significantly reduces the microtensile bond strength of self-etching adhesives and appears to interfere with the achievement of effective coronal seal (Roberts et al., 2009). Several solutions containing ethanol, ethyl acetate, acetone, or chlorhexidine digluconate have been recommended for removal of debris and residues from the dentin surface (Saraç et al., 2008).
Cleaning protocols using formamide and 2-phenylethanol (Endosolv R; Septodont, New Castle, DE) and 95% ethanol have been evaluated for removal of AH Plus from the dentin of the pulp chamber. Endosolv R was able to remove most of the AH Plus sealer from the dentin surface and did not affect the ability of bonding agents to create hybrid layers in intact dentin (Roberts et al., 2009). Although this product appears to be clinically effective (Vranas et al., 2003; Shokouhinejad et al., 2010), according to the manufacturer, its main ingredient is formamide, a potential teratogen (National Toxicology Program, 2008).
Acetone is frequently used as a solvent in dental products (Abate et al., 2000; Garcia et al., 2010), and is recommended by the manufacturers of AH Plus to clean the instruments used for mixing the material. This solvent is one of the components of several dentin-cleaning agents for removal of temporary restorative material remnants (Demiryürek et al., 2009). Despite its cleaning potential, no studies evaluating its efficiency in removing epoxy resin-based sealer residues from the dentin of the pulp chamber are found in the literature.
Amyl acetate is a liquid mixture of the isomeric forms of pentyl acetate and methyl-1-butyl acetate, used as a volatile organic solvent (Ballantyne et al., 1986). It is commercially available, combined with ethanol, as a nail polish solvent. However, similarly to acetone, its efficiency in removing residual epoxy resin-based sealer from the dentin of the pulp chamber is also unknown.
The goal of this study was to evaluate the efficacy of different solvents in the removal of residual epoxy resin-based sealer (AH Plus) from the dentin walls of the pulp chamber. Dentin surfaces impregnated with sealer were analyzed under scanning electron microscope (SEM) after cleaning with amyl acetate solution, acetone solution, 95% ethanol, or isopropyl alcohol.
Materials and Methods
Forty-four freshly extracted bovine permanent mandibular incisors, stored in a solution of 0.1% thymol for 1 month at 4°C, were used. Forty-four tooth fragments with flat dentin surfaces, measuring 1.0 cm × 1.0 cm, were obtained from the buccal surface of dental crowns using a slow-speed Isomet precision saw (Buehler Ltd, Lake Bluff, IL) under irrigation with water. Next, 17% EDTA (Biodinâmica Ind. Com, Ibiporã, PR, Brazil) was applied to the dentin surfaces for 3 min. Specimens were then washed with 2.5 ml of 2.5% NaOCl and dried with an air stream.
The specimens received a layer of mixed AH Plus sealer (Dentsply, DeTrey, Germany), which was spread evenly over the dentin surface with a microbrush (Microbrush Int., Grafton, WI) and left undisturbed for 5 min. The sealer was handled equally by mixing 1 g of base paste with 1 g of catalyzer. The prepared specimens were randomly divided in four groups (n = 10), according to the cleaning solution used: G1—isopropyl alcohol (Farmácia Científica, Santa Fé do Sul, SP, Brazil), G2—95% ethanol (Rioquímica, São José do Rio Preto, SP, Brazil), G3—acetone solution (acetone + ethanol—Farmax Dist. Quim., Divinópolis, MG, Brazil), and G4—amyl acetate solution (amyl acetate + ethanol—Farmax Dist. Quim., Divinópolis, MG, Brazil). The dentin surfaces were wiped using cotton pellets saturated with the solutions evaluated, until the surface appeared visibly clean. No additional rinsing with water was performed. Negative control specimens (n = 2) did not receive AH Plus, and positive controls (n = 2) received AH Plus but the sealer was not subsequently removed. All specimens were prepared by the same operator.
For SEM analysis, the specimens were dried at room temperature for 7 days, dehydrated in silica for 24 h, mounted onto aluminum stubs with silver paint, sputter coated with gold, and examined under a DSM 940 A SEM (Carl Zeiss, Oberkochen, Baden-Wurttemberg, Germany) operating at 10 kV. Each fragment was initially visualized at 100×, and for assessment of the amount of AH Plus sealer remnants, further observations under 500× were conducted in four different fields. A representative image of each specimen at 500× was used for evaluation. Evaluation of the amount of AH Plus remnants on the dentin surface was carried out by attributing scores, as follows: (i) clean dentin surface with few small debris particles; (ii) few small agglomerations of debris; (iii) several agglomerations of debris covering less than 50% of the dentin surface; (iv) more than 50% of the dentin surface covered with debris; and (v) complete or nearly complete surface coverage with debris (Hülsmann et al., 1997). SEM evaluations were performed by two examiners who were blind to the experimental groups. The examiners were initially calibrated using the reference SEM images. The scores were compared, and when a difference was found, the evaluators jointly examined the sample. Data were analyzed statistically by nonparametric Kruskal–Wallis and Dunn's tests at 5% significance level.
The positive controls showed that AH Plus sealer was uniformly present on the dentin surfaces. The negative controls showed that the dentin of the pulp chamber was free of debris, ensuring that analysis of the clean surfaces did not yield false positive results for remaining debris.
None of the cleaning solutions was able to completely remove AH Plus from the dentin surface. Figure 1 presents the distribution of scores, median score, and comparisons among the experimental groups. The amyl acetate solution was significantly better than 95% ethanol and isopropyl alcohol (p < 0.05), but not different from the acetone solution (p > 0.05) in removing AH Plus from dentin. There was no difference among the efficacy of acetone solution, 95% ethanol, and isopropyl alcohol (p > 0.05). SEM images representative of AH Plus residues on the dentin surfaces of the experimental groups are shown in Figure 2.
SEM is used for ultrastructural analysis of dentin subjected to different treatments (Hüllsman et al., 1997; Ferreira et al., 2011). This method allowed visualization of AH Plus sealer remnants on dentin surfaces that clinically appeared clean after using different cleaning solutions The rationale for using flat dentin fragments (1 cm × 1 cm) from the pulp chamber as a substrate was to avoid analysis of curved areas, which may adversely affect interpretation of the results.
AH Plus, an epoxy resin-based sealer, has been recommended as a root canal filling material due to its biological (Miletic et al., 2005; Sousa et al., 2006) and physical–chemical properties (Flores et al., 2011). This sealer is presented commercially as two pastes: paste A (bisphenol-A epoxy resin, bisphenol-F epoxy resin, calcium tungstate, zirconium oxide, silica, and iron oxide pigments) and paste B (dibenzyldiamine, aminoadamantane, tricyclodecane-diamine, calcium tungstate, zirconium oxide, silica, and silicone oil). Bisphenol-A and bisphenol-F epoxy resins are polar substances (Goswami et al., 2004).
Persistence of residual AH Plus may negatively interfere with the bond of dentin adhesives, allowing bacterial leakage into the pulp chamber. This occurs because epoxy resin-based sealers are chemically distinct from adhesive methacrylate resins, and these two classes of resin monomers do not copolymerize (Roberts et al., 2009).
In the present study, the amyl acetate solution was significantly better than 95% ethanol and isopropyl alcohol, but not better than the acetone solution in removing the AH Plus from dentin.
The efficacy of a solvent in dissolving a solute or softening a polymer may be explained by the concept “like dissolves like” (i.e. polar solvents are better at dissolving polar compounds) (Roberts et al., 2009). Therefore, it may be assumed that ethanol and isopropyl alcohol are either immiscible or incompletely miscible with the epoxy resin component in the AH Plus sealer. Conversely, epoxy resin is probably miscible or partially miscible with amyl acetate and acetone solutions, enabling its dissolution by these solvents.
The most commonly used solvent for removal of debris from the pulp chamber after root canal filling is 95% ethanol (Gutman and Witherspoon 2002). The presence of water in 95% ethanol may have contributed for the permanence of sealer residues on the dentin surface, due to the fact that water is immiscible or incompletely miscible with epoxy resin (Roberts et al., 2009). Previous studies have shown that epoxy resin-based endodontic sealers present low solubility in water (Kaplan et al., 1997; Donnelly et al., 2007).
Amyl acetate is an ester soluble in ether and ethanol, and partially soluble in water (Verschueren, 2001). It is commercially available combined with ethyl acetate, acetone (Elder, 1988), or ethanol. This solution is used as a solvent in cosmetics, as well as in the chemical and pharmaceutical industry (Clayton and Clayton, '93; Elder, 1988). Amyl acetate presents good solvent action on resins (Lewis, 1993), which may explain its greater efficacy in removing the epoxy resin-based sealer when compared with 95% ethanol and isopropyl alcohol.
Acetone is used as solvent in dentin adhesives (Abate et al., 2000; Garcia et al., 2010). The acetone solution tested in the present study was mixed with hydrated ethanol at a 2:1 ratio, since the sale of pure acetone is prohibited in Brazil (Agência Nacional de Vigilância Sanitária, 2003). The presence of hydrated ethanol in the acetone solution may have contributed for the similar scores attributed to specimens cleaned with acetone, in relation to the 95% ethanol group.
Regardless of the good results of amyl acetate, all samples presented remnants of AH Plus sealer on the dentin surfaces. This led to the conclusion that the solvents tested are unable to completely remove epoxy resin, which may interfere with the bond of restorative materials and/or result in undesirable esthetic effects. Further, in vitro studies and clinical trials should be undertaken in order to develop more efficacious cleaning protocols for removal of epoxy resin-based sealers from dentin.
Although none of the solvents used in this study was able to completely remove the epoxy resin-based sealer from dentin, amyl acetate and acetone may be considered as good alternatives for cleaning the pulp chamber after root canal filling with AH Plus.