Victor Talarico Leal Vieira

Effects of Electropolishing Surface Treatment on the Cyclic Fatigue Resistance of BioRace Nickel-Titanium Rotary Instruments

INTRODUCTION This study evaluated the influence of electropolishing surface treatment on the number of cycles to fracture of BioRace rotary nickel-titanium endodontic instruments. METHODS BioRace size BR5C instruments with or without electropolishing surface treatment were used in an artificial curved canal under rotational speed of 300 rpm until fracture. Fractured surfaces and the helical shafts of fractured instruments were analyzed by scanning electron microscopy (SEM). RESULTS Polished instruments displayed a significantly higher number of cycles to fracture when compared with nonpolished instruments (P < .001). Actually, the number of cycles to fracture of a polished BR5C instrument was 124% higher than that of a nonpolished instrument. SEM analysis showed that the fractured surface of both polished and nonpolished BR5C instruments had ductile morphologic characteristics. Evaluation of the separated fragments after cyclic fatigue testing showed the presence of microcracks near the fracture surface. Polished instruments exhibited fine cracks that assumed an irregular path (zigzag crack pattern), whereas nonpolished instruments showed cracks running along the machining grooves. CONCLUSIONS Electropolishing surface treatment of BioRace endodontic instruments significantly increased the cyclic fatigue resistance.

Fatigue Life of Reciproc and Mtwo Instruments Subjected to Static and Dynamic Tests

INTRODUCTION This study evaluated the influence of flexibility and reciprocating movement on the fatigue life of endodontic instruments subjected to static and dynamic tests. METHODS The rotary nickel-titanium instruments used in this study were Reciproc and Mtwo. The instruments were initially subjected to a cantilever-bending test and then to static and dynamic fatigue tests. Reciproc instruments were operated in reciprocating movement, whereas Mtwo instruments were worked in continuous rotation. RESULTS The means of bending resistance (maximum load in grams) of the instruments were 274.9 for Reciproc and 429 for Mtwo. The mean times (in seconds) to fracture of the instruments subjected to static and dynamic tests were 214.5 (static) and 286.3 (dynamic) for Reciproc and 38.9 (static) and 99 (dynamic) for Mtwo. The Students t test revealed significant differences in all tests (P < .05). CONCLUSIONS The results of the present study showed longer fatigue life for instruments with higher flexibility, driven by reciprocating movement, and in the dynamic testing model. These findings reinforce the assumption that use of reciprocating movement is a means to prolong the fatigue life of rotary nickel-titanium endodontic instruments during instrumentation of curved canals.

Influence of different manufacturing methods on the cyclic fatigue of rotary nickel-titanium endodontic instruments.

INTRODUCTION The aim of this study was to evaluate, by static and dynamic cyclic fatigue tests, the number of cycles to fracture (NCF) 2 types of rotary NiTi instruments: Twisted File (SybronEndo, Orange, CA), which is manufactured by a proprietary twisting process, and RaCe files (FKG Dentaire, La Chaux-de-Fonds, Switzerland), which are manufactured by grinding. METHODS Twenty Twisted Files (TFs) and 20 RaCe files #25/.006 taper instruments were allowed to rotate freely in an artificial curved canal at 310 rpm in a static or a dynamic model until fracture occurred. RESULTS Measurements of the fractured fragments showed that fracture occurred at the point of maximum flexure in the midpoint of the curved segment. The NCF was significantly lower for RaCe instruments compared with TFs. The NCF was also lower for instruments subjected to the static test compared with the dynamic model in both groups. Scanning electron microscopic analysis revealed ductile morphologic characteristics on the fractured surfaces of all instruments and no plastic deformation in their helical shafts. CONCLUSIONS Rotary NiTi endodontic instruments manufactured by twisting present greater resistance to cyclic fatigue compared with instruments manufactured by grinding. The fracture mode observed in all instruments was of the ductile type.

Blue Thermomechanical Treatment Optimizes Fatigue Resistance and Flexibility of the Reciproc Files

Introduction: The aim of the present study was to evaluate the influence of Blue thermal treatment on the bending resistance and cyclic fatigue of conventional M‐Wire Reciproc files (VDW, Munich, Germany). The roughness pattern and the microhardness of the files were also assessed. Methods: Flexibility of standard Reciproc R25 files and the corresponding Blue prototypes was determined by 45° bending tests according to the ISO 3630‐1 specification. Instruments were also subjected to cyclic fatigue resistance, measuring the time to fracture in an artificial stainless steel canal with a 60° angle and a 5‐mm radius of curvature. The fracture surface of all fragments was examined with a scanning electron microscope. The roughness of the working parts was quantified by using a profilometer, and the microhardness test was performed using the Vickers hardness tester. Results were statistically analyzed using the Student t test with a level of significance set at P < .05. Results: Reciproc Blue instruments presented a significantly longer cyclic fatigue life and significantly lower bending resistance than the original Reciproc instrument (P < .05). Regarding the roughness pattern, there was no significant difference between Reciproc Blue and the original Reciproc instruments (P > .05), whereas Reciproc Blue revealed significantly lower microhardness than the original Reciproc instrument (P < .05). Conclusions: Reciproc Blue nickel‐titanium showed improved all‐around performance when compared with conventional M‐Wire superelastic nickel‐titanium, demonstrating improved flexibility and fatigue resistance, and reduced microhardness while maintaining similar characteristics of the surface. HighlightsSo far, Blue thermal treatment was not assessed regarding cyclic fatigue and other mechanical features.Reciproc Blue showed overall improved performances when compared with conventional Reciproc, demonstrating improved flexibility and fatigue resistance, and reduced microhardness while maintaining similar characteristics of the surface.

Bending resistance and dynamic and static cyclic fatigue life of Reciproc and WaveOne large instruments.

INTRODUCTION The aim of the present study was to evaluate the bending resistance and the dynamic and static cyclic fatigue life of Reciproc R40 and WaveOne large instruments. METHODS A sample of 68 nickel-titanium instruments (25 mm in length) for use under reciprocation movement (Reciproc and WaveOne) from 3 different lots was tested. Reciproc R40 and WaveOne Large files, both of which had a nominal size of 0.40 mm at D0, were selected. The bending resistance was performed in 10 instruments of each system by using a universal testing machine. Dynamic and static models for cyclic fatigue testing were performed by using a custom-made device. For these tests, an artificial canal measuring 1.4 mm in diameter and 19 mm total length was fabricated from a stainless steel tube. Scanning electron microscopy analysis was performed to determine the mode of fracture. Statistical analysis was performed by using parametric methods, 1-way analysis of variance. Post hoc pair-wise comparisons were performed by using Tukey test for multiple comparisons. RESULTS WaveOne instruments presented significantly higher bending resistance than Reciproc (P < .05). Moreover, Reciproc revealed a significantly longer cyclic fatigue life (P < .05) in both static and dynamic tests (P < .05). CONCLUSIONS Reciproc R40 instruments resisted dynamic and static cyclic fatigue significantly more than WaveOne Large instruments. Furthermore, WaveOne instruments presented significantly less flexibility than Reciproc.

Influence of the Geometry of Curved Artificial Canals on the Fracture of Rotary Nickel-Titanium Instruments Subjected to Cyclic Fatigue Tests

INTRODUCTION This study evaluated the influence of different features of canal curvature geometry on the number of cycles to fracture of a rotary nickel-titanium endodontic instrument subjected to a cyclic fatigue test. METHODS BioRaCe BR4C instruments (FKG Dentaire, La Chaux-de Fonds, Switzerland) were tested in 4 grooves simulating curved metallic artificial canals, each one measuring 1.5 mm in width, 20 mm in total length, and 3.5 mm in depth with a U-shaped bottom. The parameters of curvature including the radius and arc lengths and the position of the arc differed in the 4 canal designs. Fractured surfaces and helical shafts of the separated instruments were analyzed by scanning electron microscopy. RESULTS The Students t test showed that a significantly lower number of cycles to fracture values were observed for instruments tested in canals with the smallest radius, the longest arc, and the arc located in the middle portion of the canal. Scanning electron microscopic analysis of the fracture surfaces revealed morphologic characteristics of ductile fracture. Plastic deformation was not observed in the helical shaft of the fractured instruments. CONCLUSIONS Curvature geometry including the radius and arc lengths and the position of the arc along the root canal influence the number of cycles to fracture of rotary nickel-titanium instruments subjected to flexural load.

Torsional properties of pathfinding instruments

INTRODUCTION This study compared the torsional properties of 2 stainless steel endodontic pathfinding instruments: C-Pilot (VDW, Munich, Germany) and C(+) files (Maillefer/Dentsply, Ballaigues, Switzerland). Stainless steel conventional K-type instruments (KCC(+), VDW) were used as controls. METHODS File sizes 10 were subjected to a torsional assay in clockwise rotation. The 2 parameters evaluated were maximum torque and angular deflection at failure. The fractured surfaces and the helical shafts of the fractured instruments were then examined by scanning electron microscopy (SEM). RESULTS The results indicated that the angular deflection to fracture decreased in the following order: KCC(+) > C-Pilot > C(+). As for the maximum torque values, the results revealed the following descending order: C(+) > KCC(+) > C-Pilot. SEM analysis revealed that plastic deformation occurred along the helical shaft of the fractured instruments and that the fractured surfaces were of the ductile type. CONCLUSIONS The instruments tested showed different torsional behavior depending on the parameter evaluated. Considering that high angular deflection values may serve as a safety factor for instruments used as pathfinders, the conventional K file showed significantly better results than both C-Pilot and C(+) files.

Cyclic and Torsional Fatigue Resistance of XP-endo Shaper and TRUShape Instruments

Introduction: The purpose of this study was to evaluate the cyclic and torsional fatigue resistance of the XP‐endo Shaper (FKG Dentaire, La Chaux‐de‐Fonds, Switzerland) and TRUShape (Dentsply Tulsa Dental Specialties, Tulsa, OK) instruments. Methods: Twenty XP‐endo Shaper (30/0.01) instruments and 20 TRUShape (30/0.06v) instruments were used. Cyclic fatigue resistance was tested by measuring the number of cycles and time to fracture in an artificial stainless steel canal with a 60° angle and a 5‐mm radius of curvature (n = 10). The torque and angle of rotation at failure of new instruments (n = 10) were measured according to ISO 3630‐1. The fracture surface of all fragments was examined with a scanning electron microscope. Results were statistically analyzed using the Student t test at a significance level of P < .05. Results: The XP‐endo Shaper instruments showed a significantly longer number of cycles to fracture and time to failure in seconds than the TRUShape instruments (P < .05). The XP‐endo Shaper also presented a lower maximum torque load (P < .05) but a significantly higher angular rotation to fracture than TRUShape (P < .05). Conclusions: The XP‐endo Shaper instruments showed a higher cyclic fatigue resistance and angle of rotation to fracture but lower torque to failure than TRUShape instruments. HighlightsCyclic and torsional fatigue resistance of the newly launched XP‐endo Shaper and TRUShape instruments was assessed.The XP‐endo Shaper instruments showed a significantly longer cyclic fatigue life than TRUShape instruments.The XP‐endo Shaper presented a lower maximum torque load but a higher angular rotation to fracture than TRUShape.

Bending resistance and cyclic fatigue of a new heat-treated reciprocating instrument

The current study aimed to evaluate the bending resistance and the cyclic fatigue life of a new heat-treated reciprocating instrument (ProDesign R). Untreated ProDesign R, Reciproc R25, and WaveOne Primary instruments were used as reference instruments for comparison. The bending resistance was performed in ten instruments of each system by using a universal testing machine and a proper apparatus. The cyclic fatigue resistance was tested measuring the number of cycles to failure in an artificial stainless steel canal. Scanning electron microscopy analysis was performed to determine the mode of fracture and possible deformations at the helical shaft. Statistical analysis was performed by using parametric methods; one-way analysis of variance plus post hoc pair-wise Tukey test for multiple comparisons (p < 0.05). Untreated ProDesign R presented significantly higher bending resistance than the other tested systems (p < 0.05). No differences were observed between ProDesign R and Reciproc files regarding the bending resistance (p > 0.05). Moreover, ProDesign R revealed a significantly longer cyclic fatigue life (p < 0.05). In contrast, Untreated ProDesign R and WaveOne instruments presented significantly lower cyclic fatigue life than Reciproc (p < 0.05). The new heat-treated reciprocating instrument ProDesign R have higher cyclic fatigue resistance than Untreated ProDesign R, Reciproc, and WaveOne instruments. ProDesign R and Reciproc were significantly more flexible than Untreated ProDesign R and WaveOne files. SCANNING 38:837-841, 2016.

Torsional Fatigue Resistance of Blue-treated Reciprocating Instruments

Introduction: The aim of the present study was to evaluate the influence of blue thermal treatment on the torsional resistance behavior of M‐Wire Reciproc files (VDW, Munich, Germany). Methods: Ten M‐Wire Reciproc R25 (25/0.08v) and 10 Reciproc Blue R25 (25/0.08v, VDW) instruments were used. The torque and angle of rotation at failure of new instruments (n = 10) were measured according to ISO 3630–1. Three millimeters of each instrument tip was clamped to a small load cell by a lever arm linked to the torsion axis. The fracture surface of all fragments was examined with a scanning electron microscope. Results were statistically analyzed using the Student t test at a significance level of P < .05. Results: The maximum torsional strength of M‐Wire Reciproc was higher than Reciproc Blue instruments (P < .05). Reciproc Blue instruments showed significantly higher angular rotation to fracture than M‐Wire Reciproc instruments (P < .05). Scanning electron microscopy of the fracture surface showed similar and typical features of torsional failure for the 2 types of instruments, including concentric abrasion marks and the fibrous dimple marks at the center of rotation. Conclusions: Reciproc Blue instruments showed a higher angle of rotation to fracture but a lower torque to failure than M‐Wire Reciproc instruments. HIGHLIGHTSThe aim of the present study was to evaluate the influence of blue thermal treatment on the torsional fatigue behavior of M‐Wire Reciproc files (VDW, Munich, Germany).The maximum torsional strength of M‐Wire Reciproc was lower than Reciproc Blue (VDW) (P < .05).Reciproc Blue instruments showed significantly higher angular rotation to fracture than M‐Wire Reciproc instruments (P < .05).