Results - Discussion - References.
Data regarding coronal microleakage measured in millimetres are presented in Table 1. The teeth from Group II had the least leakage (mean 2.62 mm) followed by Group III (mean 2.78 mm); there was no significant difference between the two groups. The mean coronal microleakage of teeth from Group I irrigated with 1% NaOCl (mean 3.51mm) was significantly greater than in Groups II and III (P < 0.05). Group IV had the most leakage (mean 9.36mm) that was significantly deeper (P < 0.05) even when compared to the teeth irrigated with distilled water (6.10 mm).
During irrigation of Group IV teeth, the formation of a marked dark-brown precipitate was observed, resulting from the combination of 2% chlorhexidine gel with 1% NaOCl. Even after the fifinal flush with distilled water the precipitate could be observed staining the dentine.
Table 1. Coronal linear dye penetration after irrigation regimes and obturation.Discussion.
The main aim of this study was to evaluate the influence of different irrigation protocols on the sealing of root fifillings.
One of the desirable properties of irrigants is smear layer removal (Goldberg & Abramovich 1977). Many authors have demonstrated that canal surfaces without a smear layer permit penetration of fifilling materials into patent dentinal tubules, increasing the contact surface, improving mechanical retention (White et al.1997) and reducing the possibility of microleakage through the filled canal (Cergneux et al. 1987, Behrend et al. 1996) independently of the obturation technique (White et al. 1984, Saunders & Saunders 1994). An important factor in smear layer removal is the proximity of the irrigation needle to the apical debris. Abou-Rass & Piccinino (1982) showed that the needle must deliver the solution close to the debris to be most effective.
In the present study, the teeth irrigated with 1% NaOCl combined with 17% EDTA and those irrigated with EndogelTM had the least mean coronal microleakage after obturation and exposure to India ink. Previous studies demonstrated that both irrigation methods are highly efficient in smear layer removal (White et al. 1984, Ferraz et al. 2001), a fact that may have influenced the results.
Previously studied viscous irrigants, including those containing chlorhexidine gluconate, were less soluble substances, leaving residues on the root-canal surfaces which impared fifinal obturation (Tucker et al.1976). The chlorhexidine gel employed in the present study did not produce this effect. The gel base used was Natrosol, a biocompatible carbon polymer (Miyamoto et al. 1998) that is a water-soluble substance, and therefore can be easily removed from the root canal with a fifinal flush of distilled water (Ferraz et al.2001).The present results also showed that the chlorhexidine gel (viscous form) did notinterfere with the sealing ability of the sealer. Previous studies have shown that it maintains almost all the dentinal tubules open because its viscosity keeps the debris in suspension reducing smear layer formation. Moreover, such viscosity increases the mechanical removal of the organic tissues, which compensates for the inability of the chlorhexidine gel to dissolve them (Ferraz et al. 2001).The properties of chlorhexidine gel, such as broad spectrum of antimicrobial activity, substantivity, low toxicity, water solubility and smear layer removal have increased interest in its use as an endodontic irrigant (Gomes et al. 2001).
The combination of 1% NaOCl with 2% chlorhexidine gel showed the worst results in the present study. Kuruvilla & Kamath (1998) fifirst suggested this combination to obtain the optimal properties of both irrigants. The authors suggested that chlorhexidine chloride would form, increasing the ionizing capacity of the chlorhexidine molecule and consequently its antimicrobial activity. In that reaction, sodium hypochlorite dissociates into H+, O_2 and Cl- ions, the chloride group then reacts with the chlorhexidine molecule in the guanine group (NH), resulting in chlorhexidine chloride (N+Cl-). However, the authors did not mention the precipitate that forms during this reaction and was frequently observed in the present study. The viscous dark-brown precipitate material stained the dentine and adhered to the root-canal walls. It could not be completely removed from the root canals, probably acting as residual film, damaging the seal of the root-canal fifilling and favouring coronal microleakage.
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