In vitro evaluation of the antimicrobial activity of endodontic sealers Avaliação in vitro da atividade antimicrobiana de cimentos endodônticos

The purpose of this study is to evaluate the antimicrobial activity of the endodontic sealers: N-Rickert, Sealapex, AH Plus, Mineral Trioxide Aggregate (MTA) and portland cement. The Agar diffusion method was used in plates previously inoculated with the following microorganisms: C. albicans, S. aureus, E. faecalis, E. coli. The diameters of microbial inhibition zones were measured after 24 hours of incubation in kiln at 37 degrees C. According to the methodology used, it was possible to conclude that only the sealers AH Plus and N-Rickert presented antimicrobial activity against C. albicans, S. aureus, and E. coli; no antimicrobial activity in MTA, Sealapex and portland cement was observed. N-Rickert presented the largest inhibition zones varying from 8 to 18 mm, and the microorganism E. faecalis was resistant against all sealers tested.


INTRODUCTION
The main purpose of endodontic therapy is to clean and shape the root canal by means of instruments and chemical irrigation substances, in order to eliminate or reduce the amount of microorganisms, when the pulp is necrosed. 8,10,14owever, infection may persist in canals with high anatomic complexity, with a great number of bacteria, especially facultatively anaerobic bacteria. 15n chronic pulpar necrosis, apical cement erosion may occur as well as the presence of bacteria in periradicular tissues, which are resistant against the organic defense of the host and the chemical solutions used in the root therapy. 1 Most endodontic infections are mixed and polimicrobial, with predominance of strict anaerobes, some facultative anaerobes and rarely aerobes. 9In addition, recent studies have associated the presence of fungi with therapy-resistant endodontic infections. 7,16,20fter disinfection, the canal is sealed with a root filling, and one of its main properties is to have antimicrobial activity, with potential to eliminate residual microorganisms unaffected by the effects of both chemo-mechanical preparation and intracanal medication. 12Besides, the root filling should also help prevent a recurrent root canal infection and aid the repair process of apical and periapical tissues. 19tudies reported that only an initial microbial inhibition exists, probably because the highest reactivity of the cement happens during the cure. 5,13herefore, the aim of this study was to evaluate the antimicrobial activity of the following endodontic sealers: AH Plus, Portland cement, N-Rickert, Pro Root MTA and Sealapex; in the presence of microorganisms commonly isolated from infected root canals, such as Candida albicans, Enterococcus faecalis, Escherichia coli and Staphylococcus aureus.Brazil, 2003), in the necessary volume to obtain five (5) mm of thickness.On each dish, five (5) perforations were made with a metal tube with four (4) mm of diameter to receive the testing materials.Each microorganism was scattered on the dishes with a swab.The sealers under study were handled according to the manufacturer's instructions and placed in the wells immediately after mixing.After the sealers setting, the agar plates were incubated at 37°C for 24 hours to allow the microorganisms to grow and reagents to diffuse through the culture medium.After incubation, the inhibition zones formed around the wells containing the sealers were measured.All experiments were made three times, and the results were the average values of the three records.

RESULTS
The results obtained according to the methodology used are presented in Figures 1 and 2 and Table 1.
The sample distribution was not normal and a non-parametrical test was required.
The results of the statistical analysis revealed significant differences (5%) when comparing AH-Plus with MTA, Portland and Sealapex.
No difference was found when comparing AH-Plus with N-Rickert.
When comparing N-Rickert with MTA, Portland and Sealapex, the mean difference was significant (1%).

DISCUSSION
In this study, we used the agar diffusion test, which is the most widely used in vitro method for the evaluation of antimicrobial activity. 6This method allows direct comparisons between materials and also indicates which sealers are more likely to have antimicrobial activity within the root canal system. 12Besides that, its results are highly influenced by the diffusibility of the material across the medium. 4ost endodontic sealers possess antimicrobial components that need to be released from the sealer matrix to be effective.The test sealers showed no permanent residual antibacterial effects. 12ur results showed that the most resistant microorganism to the antimicrobial activity of all sealers tested was Enterococcus faecalis.This is one of the most resistant species usually found in root canal infections. 10It is usually persistent and difficult to treat. 2 It is frequently associated with failure of the root canal treatment. 16he existence of antimicrobial activity in Portland cement and MTA was not observed, even though their pH reached 12.5, similar to that of calcium hydroxide, which could lend some antimicrobial properties to them, according to Torabinejad et al. 17,18 (1995).
The results of the present study agree with those obtained by Estrela et al. 3 (2000).
The same result obtained with MTA also applies to Portland cement, with no significant difference.The fact that the main components of MTA are also found in Portland cement can justify why the results of their antimicrobial activity tests were similar. 3he N-Rickert sealer presented the best antimicrobial activity among the sealers tested, probably due to its components, such as oil of cloves, aristol and silver.
The AH-Plus sealer presented antimicrobial activity too because of the components of the epoxy resin and due to the discreet liberation of formaldehyde.As for Sealapex, no antimicrobial activity was observed, as it depends on ionization that releases hydroxyl ions, increasing the medium pH.However, it requires an adequate time for its effective action against microorganisms. 6iqueira, de Uzeda 11 (1997) reported that the culture medium can influence the solubility, liberation of ions and alkalinity of calcium hydroxide, which are essential conditions for the antimicrobial effect.

CONCLUSION
According to the methodology used, it was possible to conclude that none of the materials tested presented antimicrobial activity against E. faecalis.The sealers AH-Plus and N-Rickert presented antimicrobial activity against C. albicans, S. aureus, and E. coli.No antimicrobial activity was observed in MTA, Sealapex and Portland cement.

TABLE 1 -
In