INTRODUCTION: This study investigated the fatigue and fracture modes of RaCe and ProTaper rotary Instruments.MATERIALS & METHODS: Fatigue resistance was evaluated by rotating the files 30o or 60o and with 2 or 5mm radius of curvature. RaCe taper 06 size 25 and ProTaper F1 files (n=40) were used. The number of rotations to failure was analyzed by two-way ANOVA and independent sample t-test. Fracture surfaces were examined under a scanning electron microscope.RESULTS: Both files exhibited significantly more resistance to fracture when angle severity was reduced and increase in curvature radius (P=0.000). ProTaper demonstrated higher number of cycle of failure (P=0.0029) in one group (r=5mm, 60o). SEM observation revealed fatigue mark/features in 17 specimens, shear characteristics in 37 samples, and tensile overload in 26 samples.CONCLUSION: Radius of curvature was the main factor in torsional and fatigue failures.

Background. The aim of this study was to compare the cyclic fatigue resistance of XP-endo Shaper, HyFlex CM, FlexMaster and RaCe rotary Instruments at body temperature (37± 1° C). Methods. Twenty XP-endo Shaper (#30/. 01), 20 HyFlex CM (#30/. 04), 20 FlexMaster (#30/. 04) and 20 RaCe (#30/. 04) Instruments were tested at body temperature (n=20). The Instruments were evaluated in artificial canals with a 3-mm radius of curvature and 60° angle of curvature to the center of the 1. 5-mm-wide canal. Each instrument was rotated until fracture occurred and the number of cycles to failure (NCF) recorded. Data were analyzed using one-way ANOVA and Tukey HSD tests (P<0. 05). Results. The difference in the NCF of all the Instruments was statistically significant (P<0. 05). The order of the Instruments from the highest to the lowest NCF was as follows: XP-endo Shaper (3064. 0± 248. 1), HyFlex CM (1120. 5± 106. 1), FlexMaster (569. 8± 48. 4) and RaCe (445. 5± 53. 5). Conclusion. Under the limitations of the present study, XP-endo Shaper Instruments were more resistant to cyclic fatigue than the #30/. 04 nickel-titanium rotary Instruments immersed in water at simulated body temperature.

Introduction: Success of root canal treatment depends on several factors; among which, maintaining the original canal path during mechanical preparation is extremely important. This in vitro study aimed to compare apical transportation using RaCe NiTi rotary system and precurved stainless steel (SS) hand files in a reciprocating handpiece. Methods and Materials: Mesiobuccal canals of 40 extracted human mandibular first and second molars with 20 to 45° curvatures and 3 to 7 mm curve radius were chosen for this study. After working length determination, the teeth were divided into two groups (n=20). Root canals were prepared with RaCe in group 1 and NSK handpiece and precurved SS hand files in group 2 up to #30 with 2% taper in both groups. Radiographs were taken of teeth before and after instrumentation from buccolingual and mesiodistal directions. The images were superimposed using Adobe Photoshop CS3 software. Degree of straightening and amount of apical transportation at 0, 0. 5, 1, 2, 3, 4 and 5 mm levels short of the working length were determined using digital subtraction radiography. The student’ s t test was used to compare the degree of straightening and Mann Whitney test was applied to compare apical transportation (millimeters) between the two groups. Results: No significant difference was noted between the two groups on buccolingual or mesiodistal views in degree of straightening and apical transportation on buccolingual view (P>0. 05). However, on mesiodistal view, NSK reciprocating handpiece caused greater apical transportation at 0. 0. 5 and 1 mm levels (P<0. 05). Conclusion: The RaCe system and precurved SS files in reciprocating handpiece were highly similar in terms of degree of straightening and apical transportation. Thus, engine-driven NSK reciprocating handpiece can be used as an efficient adjunct for root canal preparation.

Introduction: The most important aims of root canal preparation are the removal of vital pulp tissue, remaining necrotic debris and infected dentin, eliminating the bulk of bacteria present in the root canal system. The aim of this study was to compare the cleaning efficacy of hand K-Flexofiles and rotary RaCe and K3 Instruments in root canal preparation.Materials and Methods: A total of 60 single rooted teeth with maximum curvature of <20o were selected and divided into three groups of 20 teeth each. Canals were prepared with KFlexofiles, K3 and RaCe Instruments using crown down preparation technique, up to size #30. After instrumentation, the root canals were flushed with 5 mL of 2.5 % NaOCl solution. The mount of debris and smear layer was quantified on the basis of Hulsmann method using a scanning electron microscope. The data were statistically analyzed with one-way ANOVA test at a significance level of P<0.05.Results: None of the three groups achieved completely debrided root canals.. In general, KFlexofiles were able to achieve cleaner canals compared to K3 and RaCe Instruments (P<0.05). There were no significant differences between three groups in smear layer removal throughout the root canal walls (P<0.05).Conclusion: K-Flexofiles group had less remained debris when compared to K3 and RaCe Instruments.

Introduction: The aim of this study was to compare centering ability and dentin removal of three rotary systems in curved root canals of extracted teeth.Materials and Methods: Sixty root canals of mandibular first molars with curvatures ranging between 25-35o were divided into three groups of 20 teeth each. Based on pre-instrumentation radiographs that assessed the angle and the radius of canal curvatures, teeth with curvatures were equally spread between the three groups. The root canals were sectioned horizontally at two levels before preparation and then remounted onto the muffle. All root canals were prepared using a low-torque control motor with Mtwo or Medin or RaCe Instruments. Cross sectional images were obtained before and after instrumentation. Cross-sectional area and centering ability were evaluated. The data were analyzed using the one-way ANOVA and Tukey tests.Results: Neither instrument fracture nor permanent deformation occurred during preparations. The best centering ability was obtained by Mtwo Instruments compare to RaCe and Medin Instruments. In the coronal and middle sections, Mtwo removed less dentin than RaCe and Medin; while the difference in the apical section was not significant.Conclusion: Under the conditions of this study, the debridement of root canals was more conservative with Mtwo. The canals prepared with these Instruments were better centered in all three regions of the root.