Introduction - Materials and methods.
N.Vivacqua-Gomes, C. C. R. Ferraz, B. P. F. A. Gomes, A. A. Zaia, F. B.Teixeira & F. J. Souza-Filho School of Dentistry of Piracicaba, University of Campinas, Piracicaba, Brazil.Introduction.
Cleaning and shaping root canals are essential steps in root-canal treatment. Unfortunately, the mechanical action of instruments is unable to reach areas of the root-canal system due to anatomical complexities. As a result, irrigating solutions have an important role in chemo-mechanical preparation (Bystrom & Sundqvist 1983).
Sodiumhypochlorite (NaOCl), a widely used endodontic irrigant, is efficient in dissolving organic tissues as well as eliminating microorganisms. However, NaOCl is cytotoxic when in contact with periapical tissues and is unable to completely remove the smear layer (Ciucchi et al. 1989). Formed onto the root-canal surfaces by the action of endodontic instruments, the smear layer consists of pulpal tissue remnants, bacteria, and dentine debris (Ciucchi et al. 1989). The smear layer can be forced 1-5 mm into the dentinal tubules, to create a smear plug that reduces dentine permeability up to 78% (Pashley 1984). This layer is acid labile and can be dissolved by fluids with pH between 6.0 and 6.8 (Pashley1990). Some bacteria may degrade the smear layer via proteolytic enzymes that eliminate the collagen component rather than the hydroxyapatite component (Pashley 1990). Therefore, by acting as a substrate for bacterial growth, the smear layer is susceptible to bacterial penetration. The removal of the smear layer provides more efficient disinfection and improves the seal of root fifillings due to penetration of sealer into the open dentinal tubules, decreasing microleakage (Behrend et al.1996,Taylor et al. 1997).
Two percent chlorhexidine gel used as an endodontic irrigant has been shown to have antimicrobial activity against microorganisms commonly found in endodontic microflora (Ferraz et al. 2001). However, it has no effect on dissolving pulpal tissue remnants (Kuruvilla & Kamath 1998). The action of chlorhexidine gel in the removal of organic and inorganic remnants from smeared surfaces is enhanced by its viscosity (Ferraz et al.2001).Moreover, chlorhexidine gel has shown better antimicrobial action against Enterococcus faecalis when compared to its liquid form. One of its advantages is that the biocompatible carbon polymer used as the gel base, Natrosol, is highly water-soluble, being easily removed from the root canal by a fifinal flush with distilled water (Ferraz et al. 2001).
When used as an endodontic irrigant, EDTA has an efficient chelating action, dissolving mineralized tissues and promoting smear-free surfaces (Ciucchi et al.1989). According to Yamada et al. (1983), to obtain a maximum cleansing effect after instrumentation, it is necessary to use chelating agents (EDTA) followed by a tissue solvent (NaOCl).
The aim of the present study was to assess in vitro coronal microleakage in extracted human teeth after root-canal treatment, using different endodontic irrigants. Materials and methods.
Fifty single-rooted maxillary central incisors and mandibular premolars with similar root curvatures of 0- 108 (Schneider 1971) were stored in 10% formalin. The teeth were instrumented using a hybrid hand preparation technique (Valdrighi et al.1998).The teeth had their crowns removed and were then divided into 5 groups (n =10) made up of five maxillary central incisors and five mandibular premolars. Canal preparation.
The coronal two-thirds of each canal was prepared initially using files up to size 35. A size 2 Gates-Glidden bur (GG) was then used with gentle force up to this length, followed by a size 3 GG 1mm shorter. A size 10 file was used to recapitulate the canal 1mm beyond this length between each file and bur, in order to maintain patency. A size 15 K-file (Dentsply Maillefer, Ballaigues, Switzerland) with a rubber stop was introduced carefully into each canal until it was just visible in the apical foramen. This length was noted and 1mm was subtracted to give the working length of the root. Apical instrumentation commenced with a straight file of the same size as the apical foramen. The instrument was used with a half turn reaming action until the file became loose within the canal. A size 35 or 45 file was used to establish the apical stop for the mandibular and maxillary teeth, respectively. Step-back flaring of the canal was performed using larger files at 1mm intervals manipulated in a filing action. The file used to prepare the apical stop was used to recapitulate; step-back preparation was completed after the use of three files larger than the file used to prepare the apical stop. Irrigation.
Irrigation was performed using a BD-5needle coupled to a 5-mL Luer-Loc syringe as follows:
- Group I : 1mL of1% sodium hypochlorite (1% NaOCl) between each file.
- Group II : 1mL of1%NaOCl between each file and 5 mL of EDTA for 3 min at the end of the instrumentation.
- Group III : 0.5 mL of 2% chlorhexidine gel (Endogel, Endosupport, Hapetininga, Brazil) between each file.
- Group IV: Alternate 1mL of 1% NaOCl and 0.5 mL of Endogel between each file.
- GroupV : 1mL distilled water between each file.
In all groups, a final flush with 5 mL of distilled water was performed to remove debris and the irrigants.
Root canals were filled using standardized guttapercha points (Tanari, Manaus, Brazil) and Endomethasone sealer (Septodont, Saint-Maur, France) using the lateral condensation technique. Excess gutta-percha was seared off with a hot instrument (Paiva plugger, Dentsply Industriale Comercio Ltda, Petro. polis, Brazil) 1mm below the canal orifice. The cervical portion of the warm gutta-percha was vertically condensed firmly using a Paiva No. 2 plugger.
The teeth were then incubated for10 days at 37 8C to allow the sealer to set. Two layers of nail polish were placed on the entire extent of the root (except on the coronal surface of the gutta-percha), and cyanacrylate was used to seal the foramen before placing the teeth in human saliva at 37,8C for10 days. The specimens were kept in India ink for 10 days (John Faber Castel, Saâ¹ o Paulo, Brazil) and then washed with tap water to remove excess ink. The nail polish layers were then removed with a scalpel.
The roots were decalcified in asks containing 30 mL of 5% hydrochloric acid for 48 72 h at 37 8C under constant agitation in an automatic shaker (TE - 420Tecnal, Piracicaba, Brazil) and then washed with tap water for 12 hto remove remaining acid. After that, the roots were dehydrated in increasing alcohol concentrations and immersed in methyl salicylate until the time for image analysis.
The images were taken with a digital video camera (LG Colour Camera - CCD, Seoul, Korea) connected to a stereomicroscope (Lambda, Hong Kong, China) and analysed with a computer (PC - Intel Pentium 200 MHz, 32 MB RAM, Manaus, Brazil) using Image Lab software version 2.4 (Saftium Informatica, Sao Paulo, Brazil) in order to measure coronal leakage up to the most apical India ink mark . Each tooth was evaluated on the buccal, mesial, lingual and distal surfaces (Fig.1).
All data were organized in a contingency table and the Kruskal-Wallis test was applied for statistical analysis, with the level of significance set at 5% (P < 0.05).
Figure 1. The coronal leakage measurements were taken in millimetres from the top of the gutta-percha obturation to the deepest extent of ink penetration.