Microscopic Evaluation of The Remaining Gutta-Percha/ Sealer on Root Canal Wall Following Retreatment with the New ProTaper Retreatment and Mtwo R Files

One of the most important reasons of endodontic failure is the persistence of microbial factors in the root canal system. Therefore, three-dimensional cleaning of the root canal space is very important to eliminate or reduce the irritant factors and microorganisms. To evaluate the effectiveness of Mtwo R and ProTaper Retreatment files as compared with Mtwo and ProTaper files in retreatment of the gutta-percha filled root canals. In this in-vitro study, fifty extracted single root premolars with approximately straight and similar root lengths were selected. Primary preparation of the root canals was performed by ProTaper rotary system and all of the roots were filled by lateral condensation technique. Then, the teeth were randomly divided into five groups, and each group was retreated with one of the ProTaper, ProTaper Retreatment, Mtwo, Mtwo R systems and hedstrom hand files. Following the longitudinal splitting of the roots with diamond discs and evaluation of amount of the gutta-percha/ sealer on the root canal walls with stereomicroscope. Obtained results were analyzed with kruskal-wallis and Mann- Whitney u tests. Complete removal of gutta-percha/ sealer did not occur with any of the investigated systems. There is significant statistical differences between test groups at the apical and middle thirds of canals(P=0.849, P=0.315 respectively).In Hedstrom group, significantly less filling material was observed in the coronal third of canals. Regardindg the duration of retreatment, all of the rotary systems were significantly more rapid than hand files. Rotary files that were specifically designed for retreatment, were significantly more rapid than universal ProTaper. Despite this fact that neither of used techniques in this study were able to remove the filling material completely, but regarding to higher speed and probability of less fracture of the files specifically designed for retreatment (Mtwo R and ProTaper Retreatment) as compared with universal rotary files (Mtwo R and ProTaper), we suggested that these files can be appropriate choice for root canal retreatment.