Avaliação de bactérias redutoras de sulfato no processo de corrosão de limas endodônticas

Abstract

Several methods have been employed in order to remove broken endodontic files in the radicular canal. This study presents a new alternative that can facilitate the removal of broken fragments by biocorrosion performed by sulphate-reducing Bacteria (SRB). Thus, the goal of this study was to investigate the corrosion in vitro by environmental SRB and oral Desulfovibrio spp. in endodontic files. The SRB oral strains were obtained from the samples of saliva of 118 patients of the oral Diagnosis Clinic of the University Hospital Antônio Pedro. One of these positive samples to BRS was isolated in order to determinate the oral species. Sixteen new files were analyzed in a stereomicroscope, and from these files were prepared 53 specimens (Cps) for preliminary analysis in Alicona Infinite Focus Microscope. Subsequently, these Cps were distributed in 15 groups, immersing them in: G1- modified Postgate E medium; G2- artificial saliva; G3- sodium hypochlorite; G4- without immersion in medium; G5- artificial saliva inoculated with Desulfovibrio desulfuricans; G6- artificial saliva inoculated with Desulfovibrio fairfieldensis; G7- modified artificial saliva inoculated with Desulfovibrio fairfieldensis; G8- modified artificial saliva inoculated with Desulfovibrio fairfieldensis; G9- modified artificial saliva inoculated with Desulfovibrio desulfuricans; G10- modified Postgate E medium inoculated with Desulfovibrio fairfieldensis; G11- modified Postgate E medium inoculated with Desulfovibrio desulfuricans; G12- artificial saliva inoculated with Desulfovibrio fairfieldensis; G13- artificial saliva inoculated with Desulfovibrio desulfuricans; G14- modified artificial saliva inoculated with Desulfovibrio fairfieldensis, and G15- modified artificial saliva inoculated with Desulfovibrio desulfuricans. After 28 days of incubation, the groups were again analyzed in Alicona Microscope for identifying modifications on the metal surface. A group of endodontic files was submitted to chemical analysis (Rx spectrometry) in order to analyze the features of the chemical constituents of instrument and correlate with the degree of corrosion made by BRS. Of the 118 samples, 35 samples were positive to BRS, being a sample identified as Desulfovibrio fairfieldensis. The 16 endodontic files analyzed showed structural changes on the surface. The artificial saliva and modified artificial saliva medium were unable to maintain the BRS active. Cps showed pitting corrosion, and the biggest corrosion was observed in G10 and G11 groups, followed by G12, G13, G14 and G15, while the G5, G6, G8 and G9 demonstrated the smallest corrosion. In other groups the images remained unchanged. These data indicated that both the environmental strain Desulfovibrio desulfuricans as oral Desulfovibrio fairfieldensis species were able to promote biocorrosion on the steel of the endodontic files. In addition, the biocorrosion carried out by both species of BRS occurred preferentially in interface (border) and in areas with pre-existing structural defects.