Evaluation of methods for removal of filling material in endodontic retreatment and assessment of antimicrobial action of solutions used in final irrigation

• Ano de defesa: 2017
• Autor(a) principal: Rodrigues, Clarissa Teles
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Biofilm; Biofilmes; Endodontia; Endodontics; Microtomografia por Raio-X; Nanoparticles; Nanopartículas; Retratamento; Retreatment; X-Ray microcomputed tomography
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/25/25147/tde-29112021-103557/

When endodontic treatment fails, an alternative could be root canal retreatment. During this procedure, all filling material should be removed to allow a new root canal preparation and new obturation of the root canal system. Bacteria are the main cause of endodontic treatment failure, and persistent infection may be related to microorganism ability to penetrate into dentinal tubules. Therefore, this requires the use of irrigating solutions with antimicrobial action and low toxicity. The aim of this study was to evaluate the performance of instruments made of different alloys in root canal re-instrumentation during endodontic retreatment of lateral incisors with apical curvature, using computed microtomography and assessment of these samples by scanning electron microscopy after irrigant activation. Furthermore, the antimicrobial action of a root canal irrigant containing silver nanoparticles, 2% chlorhexidine and 2.5% sodium hypochlorite was evaluated against Enterococcus faecalis biofilm and dentin infected with this microorganism. Thirty extracted maxillary lateral incisors with apical curvature were selected. The teeth were instrumented, filled and divided into three different groups according to the protocol for removal of filling material: Group 1: re-instrumentation with Reciproc R25 instruments, Mtwo 40 and ProDesign Logic 50.01; Group 2: re-instrumentation with ProDesign R, ProDesign Logic 40 and ProDesign Logic 50.01; Group 3: re-instrumentation with Gates-Glidden drills and manual instruments K-file and Hedstroem files. For filling material removal analysis, the samples were scanned in a microtomograph device SkyScan 1174, for comparison of images taken before and after removing the root canal filling, and in each sample the volume was calculated at four levels (apical 1, apical 2, middle and cervical). These samples were split and analyzed by scanning electron microscopy to visualize filling material residues before and after irrigant activation with an ultrasonic device and with the EasyClean system used in continuous rotary motion. Statistical analyses were performed using Kruskal-Wallis, Friedman, Wilcoxon and Dunn tests. Furthermore, the minimum inhibitory concentration of an irrigating solution containing silver nanoparticles was determined against strains of Enterococcus faecalis, by using the microdilution method. Additionally, the antimicrobial activity of silver nanoparticle solution, 2% chlorhexidine and 2.5% sodium hypochlorite was tested against Enterococcus faecalis biofilm in vitro. For biofilm formation, bovine dentin blocks were placed in 24-well culture plates and Enterococcus faecalis biofilm was developed for 21 days. The dentin blocks were divided into 9 experimental groups of 5 blocks each, according to the irrigating solution used and the time in contact with the irrigant (5, 15 and 30 minutes). The samples were stained with Live/Dead reagent for analysis by confocal laser scanning microscopy (CLSM). Finally, the antimicrobial action of these solutions was tested after dentinal tubules were contaminated with Enterococcus faecalis. Dentin tubes were made from bovine incisors, taken to a centrifuge and infected with Enterococcus faecalis. The dentin tubes were treated with silver nanoparticle solution, 2% chlorhexidine and 2.5% sodium hypochlorite, and analyzed by CLSM to assess the antimicrobial activity of these solutions against bacteria in the dentinal tubules. The results showed that residues of filling material were found after root canal reinstrumentation in all groups. No significant difference was observed in removal of filling material between the reciprocating instruments Reciproc and ProDesign R and between rotary instruments Mtwo 40 and ProDesign Logic 40. The ProDesign Logic 50/.01 instrument significantly improved the removal of filling material compared with the use of Reciproc and ProDesign R instruments. The apical levels presented greater amount of remnant filling material compared with middle and cervical levels. After canal reinstrumentation, the passive ultrasonic irrigation and irrigant agitation with EasyClean significantly improved the removal of residual filling material in all root canal thirds. There was no significant difference between the performance of ultrasonics and EasyClean regarding the removal of residual filling material, as well no significant difference was observed in the removal of these residues when comparing apical, middle and cervical thirds. Regarding the action of the irrigating solutions against Enterococcus faecalis, the minimum inhibitory concentration of silver nanoparticle solution capable of eliminating this microorganism in broth and agar plates was 94 ppm. After the irrigation of Enterococcus faecalis biofilm, the silver nanoparticle solution was significantly less effective in killing bacteria compared with chlorhexidine when used for time of contact of 5 minutes. The sodium hypochlorite solution presented antimicrobial activity significantly higher compared with the silver nanoparticle solution and chlorhexidine. This solution also presented higher ability to dissolve biofilm in all times tested, whereas the silver nanoparticle solution presented higher ability to dissolve biofilm compared with chlorhexidine in times of 5 and 15 minutes. In infected intratubular dentin with Enterococcus faecalis, the sodium hypochlorite solution presented significant higher effectiveness than the silver nanoparticle solutions and chlorhexidine, especially in middle third and deep areas of the root canal. When comparing the antimicrobial activity of these solutions in biofilm and infected intratubular dentin, it was shown that when the silver nanoparticle solution was used for shorter periods of time, it was more effective in intratubular dentin compared with biofilm. On the other hand, with longer time of 30 minutes, the number of viable bacteria was higher in intratubular dentin than in biofilm, which was also observed when using the sodium hypochlorite solution in this time of action. It was concluded that to increase the rate of success in endodontic retreatment, the combination of the use of reciprocating and rotary instruments in the removal of filling material, the agitation of irrigants and the use of antimicrobial agents could be used in an attempt to eliminate bacteria that resisted to endodontic treatment.