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), (pValue< 0.05) while no statistically significant difference was observed in connection to the performance of WaveOne (p> 0.05).