BV6 The data collected was statistically

The data collected was statistically analyzed to compare the presence of defective BV6 between various experimental groups. Each group was compared with control groups and it was found that WaveOne did not produce any significant dentinal cracks. ProTaper and K3XF rotary systems produced significant dentinal cracks as compared to control groups but when were compared with each other no significant difference was found (Tables 2 and 3).

Discussion
Rotary endodontics was developed with the aim of reducing the treatment time, increasing efficiency and accuracy of root canal preparation. Currently, there are many different NiTi rotary systems available in the market. Root canal preparation with different rotary NiTi endodontic instruments may cause stress and strain which can lead to micro cracks or craze line formation in root dentin [14]. Tip design, cross-sectional geometry, taper, pitch and flute form of NiTi instruments may contribute to the extent of these defects [15].
The total volume of dentin removed from root canals is significantly greater with NiTi engine driven systems when compared to hand filing, this may contribute for the formation of the defects. These small defects can extend to the external surface thus breaching the intact root dentin. Also defects shown in one section might communicate with defects in another section [16].
Control group B samples also showed no crack formation, even after using Gates Glidden burs for coronal flaring as their use was limited to coronal one-third only. This was in accordance with the earlier studies which concluded that use of Gates Glidden burs for coronal flaring does not induce cracks in the root dentinal wall [17]. Less crack formation with hand filing can be because of the slower speed, better tactile sensation and less stress generated as compared to rotary instruments. However, this must be balanced against the better efficiency of motor driven systems in cleaning and shaping the root canal.
Group C samples prepared with ProTaper files showed the most root dentinal crack formation among all the groups, in 33.3% of samples. This could be attributed to continuous rotating motion and design of the file having triangular or modified triangular cross section resulting in less space for collection of dentine chips, thus generating stresses on the root dentinal wall. Its 7–9% taper of various files from F1 to F3 can also cause more stresses. Bier et al. also found cracks in horizontal section of 16% of roots instrumented with the ProTaper system [18]. Liu et al. observed cracks at apical root surface in 25% of roots instrumented with the ProTaper system [19].
Group D samples prepared with K3XF files showed crack formation in 16.7% of samples. Decrease in incidence of crack formation with this continuous rotating system could be due to its peripheral blade relief design of the file which claimed to reduce friction, facilitating its smoother operation. This feature controlled the depth of cut which prevented the files from over-engagement thus, protecting the root dentin from getting more damaged [20].
The present study showed more crack generation at coronal third as compared to middle or apical third. Versluis et al. also concluded that the stresses generated at 1mm short of the apical foramen were one third of stresses at more coronal levels. This may be due to increase in taper of various files towards the coronal third [21].
Other reasons that can contribute to the root dentinal crack formation beside different type of systems are operator skill, storage conditions and the absence of periodontal cushioning in prepared samples. Clinical procedures that can further lead to propagation of these cracks are stresses induced by obturation methods or postspace preparation techniques [22, 23]. In addition, simple masticatory forces, parafunctional habits like bruxism and occlusal loading can also contribute to progression of incomplete cracks to complete fracture of root.