RESUMEN
INTRODUCTION: The purpose of this study was to evaluate the effect of various degrees of cyclic fatigue on torsional failure and torsional preloading on the cyclic fatigue life of heat-treated K3XF nickel-titanium (NiTi) instruments (SybronEndo, Orange, CA). METHODS: The mean number of cycles until failure (Nf) of K3XF and K3 NiTi instruments was examined in a 3-point bending apparatus with a 7-mm radius and 45° curve. Torque and distortion angles at failure of new instruments and instruments stressed to 25%, 50%, and 75% of the Nf were measured according to ISO 3630-1. Other new files were preloaded at 25%, 50%, and 75% of the mean distortion angles before the fatigue test. After torsional preloading, the Nf was examined. The fracture surface of each fragment was examined with a scanning electron microscope. RESULTS: The fatigue resistance of K3XF instruments was 2 times higher than that of K3 instruments (P < .05). The torque and angle of rotation at fracture of K3XF instruments were similar to those of K3 instruments. The 25%, 50%, and 75% torsional preloading significantly lowered the Nf of both K3 and K3XF instruments (P < .05). In the fatigue prestressed groups, K3 instruments with 75% preloading had significantly lower torque and distortion angles than unused K3 instruments (P < .05). The fractographic patterns corresponded to the pattern defined by the last stage test. CONCLUSIONS: A low amount of torsional preloading reduced the fatigue resistance of K3 and K3XF instruments. A high amount of precycling fatigue significantly reduced the torsional resistance of K3 instruments. The torsional resistance of K3XF instruments was less affected by previous load cycling even after extensive precycling.
Asunto(s)
Equipo Dental , Falla de Equipo , Níquel , Estrés Mecánico , Titanio , Torsión MecánicaRESUMEN
INTRODUCTION: The purpose of this study was to understand how fatigue affects the torsional properties of both traditional nickel-titanium (NiTi) and NiTi controlled memory (CM) files. METHODS: Typhoon (TYP; Clinician's Choice Dental Products, New Milford, CT) 25/.04 and 40/.04 rotary files in both NiTi and CM were tested to obtain the mean number of cycles of failure (Nf) using a 3-point bending apparatus. New files were then precycled to 4 conditions (0%, 25%, 50%, and 75% of the Nf), and torsional resistance tests were performed. Each file was exposed to torsional stress until failure, and at that point the torque and distortion angles were measured. The fracture surface of each fragment was examined with a scanning electron microscope. RESULTS: TYP CM files had an Nf 7 times higher than that of TYP files (P < .05). No difference in torque between the CM files and the conventional NiTi files of either file size was detected (P > .05). The torque of the size 40/.04 files was significantly higher than the torque of the size 25/.04 files (P < .05). In the 40/.04 files group, TYP files in the 75% precycling group had a significantly lower torque than files in the group with no precycling (P < .05), whereas slight precycling (25%) significantly reduced the distortion angle on TYP CM files (P < .05). The CM files of both sizes had a significantly higher distortion angle than the corresponding NiTi files (P < .05). The fractured files in the precycling groups showed the typical pattern of torsional failure. CONCLUSIONS: Within the same amount of precycling (25%, 50%, and 75%), the cyclic fatigue life of TYP CM instruments was significantly higher than that of the TYP instruments. However, the torque value of TYP CM was similar to TYP files. The larger instruments were not only less resistant to cyclic fatigue but were affected most by prestressing of both TYP and TYP CM files.
Asunto(s)
Aleaciones Dentales/química , Níquel/química , Preparación del Conducto Radicular/instrumentación , Titanio/química , Diseño de Equipo , Falla de Equipo , Humanos , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Docilidad , Estrés Mecánico , Propiedades de Superficie , Temperatura , Torque , Torsión Mecánica , Agua/químicaRESUMEN
INTRODUCTION: The bending and torsional properties of thermomechanically treated K3XF (SybronEndo, Orange, CA) nickel-titanium instruments in relation to their phase transformation behavior were evaluated. METHODS: NiTi instruments K3 (SybronEndo) and K3XF, both in sizes 25/.04 and 40/.04, were examined by differential scanning calorimetry and X-ray diffraction. The metal composition was determined by scanning electron microscopy with X-ray energy-dispersive spectrometric analyses. The bending property of K3 and K3XF instruments was measured in a cantilever-bending test with a maximum deflection of 4.00 mm. A torsional test of the instruments was evaluated according to the American National Standards Institute/American Dental Association Specification No. 28. RESULTS: K3 and K3XF instruments had approximately the same chemical composition with a nickel content of 48-49 atomic %. The differential scanning calorimetry analyses showed that each segment of the K3XF instruments (24.89°C ± 1.98°C) had a higher austenite finish temperature than the K3 instruments (17.63°C ± 1.76°C) (P < .05). The bending load values were significantly lower for K3XF than for K3 in the superelastic ranges (P < .05). There was no statistically significant difference between K3 and K3XF in the maximum torque or maximum angular deflection before failure. The torque at fracture values of K3 and K3XF increased significantly with the diameter (P < .05). CONCLUSIONS: K3XF exhibited different phase transformation behavior and flexibility when compared with K3, which may be attributed to the special heat treatment history of K3XF instruments.
Asunto(s)
Aleaciones Dentales/química , Níquel/química , Preparación del Conducto Radicular/instrumentación , Titanio/química , Rastreo Diferencial de Calorimetría , Fenómenos Químicos , Elasticidad , Diseño de Equipo , Calor , Humanos , Ensayo de Materiales , Fenómenos Mecánicos , Microscopía Electrónica de Rastreo , Docilidad , Espectrometría por Rayos X , Temperatura , Torque , Torsión Mecánica , Difracción de Rayos XRESUMEN
INTRODUCTION: To improve the fracture resistance of nickel-titanium (NiTi) files, manufacturers have introduced new alloys and developed new manufacturing processes for the fabrication of NiTi files. This study aimed to examine the phase transformation behavior and microstructure of NiTi instruments from a novel controlled memory NiTi wire (CM wire). METHODS: Instruments of EndoSequence (ES), ProFile (PF), ProFile Vortex (Vortex), Twisted Files (TF), Typhoon (TYP), and Typhoon™ CM (TYP CM), all size 25/.04, were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). Microstructures of etched instruments were observed by optical microscopy and scanning electron microscopy with x-ray energy-dispersive spectrometric (EDS) analyses. RESULTS: The DSC analyses showed that each segment of the TYP CM and Vortex instruments had an austenite transformation completion or austenite-finish (A(f)) temperature exceeding 37°C, whereas the NiTi instruments made from conventional superelastic NiTi wire (ES, PF, and TYP) and TF had A(f) temperatures substantially below mouth temperature. The higher A(f) temperature of TYP CM instruments was consistent with a mixture of austenite and martensite structure, which was observed at room temperature with XRD. All NiTi instruments had room temperature martensite microstructures consisting of colonies of lenticular features with substantial twinning. EDS analysis indicated that the precipitates in all NiTi instruments were titanium-rich, with an approximate composition of Ti(2)Ni. CONCLUSIONS: The TYP CM and Vortex instruments with heat treatment contribute to increase austenite transformation temperature. The CM instrument has significant changes in the phase transformation behavior, compared with conventional superelastic NiTi instruments.