The use of microcomputed tomography in the evaluation of accumulation and removal of the hard- tissue debris from root canal system with isthmuses

Aims During biomechanical preparation of the root canal system, the cutting action of instruments on dentine result in the formation of hard-tissue debris, which can be packed in some areas of the root canal system, mainly in anatomical variations as isthmus, branches and flattening (1, 2). Accumulated hard-tissue debris in the root canal system may compromise thorough disinfection and filling favoring the reinfection and failure of root canal treatment (3, 4). In this regard, irrigation procedures are fundamental in cleaning up the root canal, removing debris from within the root canal space, during and after the root canal preparation. Traditionally, the debridement and cleaning of the root canals has been evaluated by means of histology, scanning electron microscopy and sectioning methods (5-7). However, they are destructive methodologies which during its processing, promotes the specimens decalcification with inorganic tissue removal, as well as section procedures that may result in the deposition of smear or changes in the location of debris (8). Microcomputed tomography (micro-CT) is a non-destructive method that allows sequential analysis of endodontic treatment steps. Recent studies has also been quantified the hardtissue debris accumulated after different biomechanical preparation protocols using micro-CT (9, 10, 11, 12, 13, 14). Even though there is accumulating evidence on the efficacy of several irrigating methods using conventional methodologies, a comprehensive knowledge regarding the activation of irrigants in different final irrigation protocols, aiming to remove hard-tissue debris from the isthmus area by means of micro-CT technology is still lacking. Thus, the aim of this study was to evaluate, quantitatively and qualitatively, the accumulation and removal of the hard-tissue debris from root canal system with isthmuses of mesial roots of mandibular molars subjected to different final irrigation, using microcomputed tomography analysis.