comparison of dentinal defects formation in straight, moderate and severely curved canals by three distinctive nickel titanium instruments: an in vitro study

Statement of the problem: it is stated that engine-driven instruments might cause dentinal defects during root canal preparation. these defects might spread and progress into greater fractures or vertical root fracture. purpose: this study aimed to compare the incidence of dentinal defects that might arise all through preparation of root canals, using one shape, race, and waveone systems in canals with a curvature (0-20°) and (20-40°). materials and method: in this in vitro study, 150 mandibular first molars were enrolled. based on the degree of curvature in the mesial roots, the samples were divided into two groups (n=75) of straight and moderately curved canals (0-20º), and severely curved canals (20-40°). then each group was randomly divided into four sub-groups. in subgroups 1 to 3 from each group, canals were prepared using waveone, one shape, and race. then all roots were sectioned at 3, 6 and 9-mm distances from the apex. the slices were evaluated using stereomicroscope at 12× magnification. the data were analyzed using the chi-square and fisher’s exact tests and the level of significance was set at 0.05. results: fracture and other defects were not found in the control groups. in canals with curvature (0-20°), waveone caused the maximum dentinal defects and race produced the least. moreover, in canals with curvature (20-40°), one shape caused the maximum dentinal defects while waveone and race caused equal dentinal defects approximately. conclusion: there was a statistically significant relationship between the performance of race and one shape in canals with curvature (0-20º) and (20-40º), (p value< 0.05) while no statistically significant difference was observed in connection to the performance of waveone (p> 0.05).