Reciprocation and rotation nickel-titanium file systems’ cyclic fatigue and centering ability in premolars accessed by ultraconservative and traditional access cavities: An in vitro study

Abstract

Introduction: With the importance of restricted access cavities, this study aimed to compare the cyclic fatigue and the centering ability of TruNatomy rotary file versus R-motion reciprocating file systems in premolars accessed by traditional versus ultraconservative access cavity preparations. Materials and Methods: Forty extracted intact maxillary first premolars were divided into two groups (n = 20/group) according to the access cavity design (traditional or ultraconservative). Each group was then subdivided according to the type of file used for instrumentation (TruNatomy [26/0.04] or R-motion [30/0.04] [n = 10 teeth/subgroup]). Cone-beam computed tomography (CBCT) scans were obtained for all the teeth before and after instrumentation. The teeth were accessed and instrumented by three in-and-out pecking motions repeated two times until the instrument reached the working length. Every instrument was only used to prepare one canal. For cyclic fatigue assessment, the used files, in addition to 10 brand-new TruNatomy and R-motion files that were used as control groups, were tested in stainless-steel artificial canals, and the time to fracture was used to determine the number of cycles to fracture (NCF). After obtaining and analyzing the before and after instrumentation CBCT images, the centering ability of the buccal roots was calculated at 3, 5, and 7 mm from the apex. Data were statistically analyzed. Results: There were no differences in NCF and centering ability of each file in both access cavities (P > 0.05). There were higher NCF values of the R-motion file compared to the TruNatomy file (P < 0.05). The R-motion file showed significantly higher centering than the TruNatomy file in the traditional access cavity at the 3 and 5 mm levels and the 3 mm level in the ultraconservative access cavity (P < 0.05). Conclusion: The R-motion file had significantly higher cyclic fatigue resistance and centering ability than the TruNatomy file. The ultraconservative access cavity had no unfavorable influence on the cyclic fatigue resistance and the centering ability of R-motion and TruNatomy files.