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ePaper created 2017-11-24, 11:00:53 | version 1.38.0
defects after preparation study | Switzerland). The main feature of these files is that they are manufactured via an electro-discharge ma- chining (EDM) process. The EDM is a non-contact ma- chining procedure used in engineering for manufac- turing the parts that would be difficult to machine with conventional techniques. The removal of mate- rial is performed by pulsating electric current dis- charges that flow between an electrode and the work piece are immersed in a dielectric medium. The elec- tric current partially melts and evaporates small por- tions of the material in a well-controlled and repeat- able manner. The material is therefore superficially removed, leaving an isotropic surface, characterised by regularly distributed craters (Pirani et al. 2015). In our comprehensive literature review, no study examining the dentinal defects caused by HEDM NiTi files during root canal shaping procedure was found. For this purpose, the aim of this in vitro study was to compare the incidences of dentinal defects that HEDM, WOG and PTG NiTi files create during shaping the mesial canals of mandibular molar teeth. The null hypothesis of present study was that there would be no difference between the dentinal defect formation incidences of HEDM, WOG and PTG NiTi files. Material and methods Specimen selection After obtaining the ethical committee approval, 80 mandibular molar teeth that were extracted due to periodontal reasons and had < 20° of canal curvature (Schneider 1971) and two separate mesial canals were involved in this study. The soft and hard tissues around the teeth were mechanically removed using “Under water-cooling the roots of 80 specimens were cut perpendicular to the tooth axis at 3, 6, and 9 mm distant from the apex, and 3 slices were obtained from each specimen.” a periodontal curette. Moreover, the distal roots of teeth were removed under water-cooling. The crowns of teeth were removed from the enamel-cement junction under water-cooling, allowing 16 mm of root length. The radiographic images of teeth were taken in mesio-distal and bucco-lingual directions. Teeth that were found to have calcification, history of previous root canal treatment, involving internal and/or external resorption, or were fractured and/or had immature roots were excluded. The selected teeth were kept in distilled water at 4 °C for the ex- perimental procedures. The roots of teeth were wrapped with aluminum foil and then embedded into acrylic resin (Imicryl, Konya, Turkey) (Capar et al. 2014). After the acrylic set, the teeth were taken out from the resin, and the foils were removed. To simulate the periodontal ligament, the resin blocks were filled with viscous silicon im- pression material (Express XT Light Body Quick; 3M ESPE, Neuss, Germany) and the specimens were then placed into the resin blocks again. Root canal preparation The canals of teeth were penetrated using a #10 K-file (Dentsply Maillefer) until the tip of file was seen from the apex. The working length was set to 1 mm shorter than this length. For all of the speci- mens, the glide path was created ensuring the apical diameter of 0.20 mm. For every specimen, 20 ml 1 % sodium hypochlorite (NaOCl) was used during the preparation. The entire procedure was executed by the same endodontist, having 5 years of experience. The teeth were randomly divided into 4 groups, 20 teeth in each. And then, the following procedures were performed. Group 1: HyFlex EDM Using the torque-controlled endodontic motor (X-Smart; Dentsply Maillefer), the root preparation of the specimens in this group was performed by using a HEDM 25/.~ NiTi single-file system according to the manufacturer’s instructions at 500 rpm and 2.5 Ncm torque. Group 2: WaveOne GOLD Using the torque-controlled endodontic motor (VDW Reciproc GOLD; VDW, Munich, Germany), the root preparation of the specimens in this group was performed by using a WOG Primary (25/.07) NiTi sin- gle-file system according to the manufacturer’s in- structions in “WaveOne ALL” programme. Group 3: ProTaper GOLD Using the torque-controlled endodontic motor (X-Smart; Dentsply Maillefer), the root preparation of the specimens in this group was performed by us- ing a PTG NiTi rotary file system’s S1 (18/.02), S2 (20/.04), F1 (20/.07) and F2 (25/.08) files according to the manufacturer’s instructions at 300 rpm and 3 Ncm torque. Group 4: Negative control No intervention was made to this group and they were assigned to the negative control group. roots 4 2017 25