Please activate JavaScript!
Please install Adobe Flash Player, click here for download
ePaper created 2017-11-24, 11:00:53 | version 1.38.0
| study defects after preparation The Number and Percentage of Slices with Defects at Each Level (n = 20) Table 1 3 mm n (%) 4 (20 %) 8 (40 %) 6 (30 %) 5 (25 %) 6 mm n (%) 8 (40 %) 10 (50 %) 9 (45 %) 10 (50 %) 9 mm n (%) 6 (30 %) 8 (40 %) 8 (40 %) 7 (35 %) Total of specimens of presenting defects n (%) 11 (55 %) 14 (70 %) 12 (60 %) 11 (55 %) In many in vitro studies, the dentinal defects cre- ated by the NiTi file systems during root canal prepa- ration were investigated using single- and straight- rooted teeth (Karata et al. 2015b, Kfir et al. 2017). However, the increasing root canal curvature would increase the stress on the files, which were used in preparation, and consequently on the dentine. An in- crease in the stress on dentine would cause increas- ing irregularities (transportation, straightening, etc.) within the canal and lead to thinner dentinal structure in certain regions. Thinner dentine would weaken the root structure and prepare the ground for vertical root fracture formation (Kim et al. 2013). In previous stud- ies, it has been reported that the highest level of stress occurred on the curved root canals during the root ca- nal preparation by NiTi rotary files (Kim et al. 2013, Medha et al. 2014). For this reason, the mesial canals of mandibular molar teeth were used in present study. NiTi file manufacturers generally recommend using the files on single. Based on four-canal maxillary first molar tooth in present study, the files were discarded after use in four canals (two specimens) in order to prevent the deformation from influencing the results (Hin et al. 2013). It has been reported that use of larger files in shap- ing the root canals increase the incidence of dentinal defect formation (Capar et al. 2015). For this reason, in the present study, the apical diameter of files was de- termined to be 0.25 mm, and no larger file was used. Moreover, in order to protect the dentine microstruc- ture, 1 % NaOCl was used as an irrigation solution. Thus, it was ensured that most of the dentinal defects to be related with the mechanic preparation. It has been reported that the forces applied while ex- tracting the teeth, and the stress during storing the teeth and obtaining the slices might cause dentinal de- fects (De-Deus et al. 2014). This may explain the forma- tion of dentinal defects in the negative control group, where no intervention was made. Studies using con- ventional methods of sectioning have failed in deter- mining these defects in negative control groups (Capar et al. 2014, Karata et al. 2015b, Li et al. 2015). When il- lumination was applied on the obtained dentine slices, the light moved along the dentine, but stopped at the point of any crack on dentine and thus the presence of crack and/or fracture could be determined (American Association of Endodontists, 2008). In Coelho and col- leagues’ study (2016a, 2016b), dentinal defects could be determined in many specimens in negative control groups by employing light-emitting diode (LED) trans-illumination. Moreover, Arslan et al. (2014) have also used methylene blue in order to determine dentinal defects, and they reported non-significant differences between the experimental group and negative control group in terms of dentinal defects. Arias et al. (2014) reported in their study that mask- ing is important for eliminating observer bias because of observing which of the specimens had been shaped or not. For this reason, the canal-masking method was used in the present study in order to eliminate any bias. The movement kinematic of NiTi files may affect the amount of dentinal defects during canal root shaping by files. Under favour of the reciprocation movement in clockwise and counterclockwise directions, the file is protected from being stuck within the canal while shaping the root canals (Yared 2008). Some of the studies have reported WaveOne files to cause less den- tinal defects than ProTaper Universal files (Kansal et al. 2014, Li et al. 2015), while some other studies have re- ported that reciprocation systems create more den- tinal defects (Bürklein et al. 2013). Besides that, in some studies, no statistically significant difference between the reciprocation systems and rotary systems has been reported (Arias et al. 2014, Karata et al. 2015a, Coelho et al. 2016b). Li et al. (2015) have examined the dentinal defect formation incidences of ProTaper Universal, ProTaper Next and WaveOne files in curved root canals of molar teeth. The researchers have reported that ProTaper Next file system created less dentinal defects than other files. El Nasr and El Kader (2014) have re- ported ProTaper Universal F2 files operating based on the same movement kinematic with WaveOne system Group Control ProTaper GOLD WaveOne GOLD HyFlex EDM * There were no statistically differences in each level at P = .05. 28 roots 4 2017