Comparative evaluation of dentinal crack formation after root canal preparation using proTaper universal, protaper next, reciproc and reciproc blue

Introduction: Currently the popularity of NiTi rotary files is increasing because of their superiority over stainless steel files; despite the benefits of rotary files, there is a risk of cracking in the root canal walls when using these files. The aim of this thesis was to compare the rate of dentin cracking during tooth canal preparation using Protaper universal, Protaper next, Reciproc and Reciproc blue rotary files in vitro. Materials and Methods: In this in vitro study, 75 human mandibular premolar teeth with equal root length, without developmental anomaly and without spherule were selected and randomly divided into 5 groups (n = 15). Teeth of 4 groups were cleaned and shaped according to the manufacturer's instructions using one of the protaper universal, protaper next, Reciproc and Reciproc blue files and one group was selected as a control group. In all the files, 2.5% sodium hypochlorite was used as washing liquid between each device during channel preparation. After preparation, all roots were sectioned perpendicular to the longitudinal axis of the tooth at distances of 3, 6 and 9 mm from the apex with a diamond saw and water as a coolant. Each section was examined by stereo microscope to examine the presence of dentin defects. The obtained data were analyzed by SPSS software version 23 using chi-square and Fisher exact tests at the 0.05 level of error. Results: Maximum dentin crack was observed in Protaper Universal in 6 and 9 mm in Apex group and protaper next in 3 mm; no dentin crack was observed in 3, 9and 9 mm sections in control group where no preparation was done. The results also showed that rotary files of protaper universal, protaper next, Reciproc, Reciproc blue are effective in the formation of dentin crack during endodontic treatment. The amount of crack created by Protaper universal was significantly higher than Reciproc blue (P <0.05). Also, the overall dentin crack rate by the Next protaper rotary file was significantly (P