RESUMO
OBJECTIVE: To investigate the effects of reversing the coiling direction of nickeltitanium closed-coil springs (NiTi-CCSs) on the force-deflection characteristics. METHODS: The samples consisted of two commercially available conventional NiTi-CCS groups and two reverse-wound NiTi-CCS groups (Ormco-Conventional vs. Ormco-Reverse; GAC-Conventional vs. GAC-Reverse; n = 20 per group). The reverse-wound NiTi-CCSs were directly made from the corresponding conventional NiTi-CCSs by reversing the coiling direction. Tensile tests were performed for each group in a temperature-controlled acrylic chamber (37 ± 1â). After measuring the force level, the range of the deactivation force plateau (DFP) and the amount of mechanical hysteresis (MH), statistical analyses were performed. RESULTS: The Ormco-Reverse group exhibited a significant shift of the DFP end point toward the origin point (2.3 to 0.6 mm), an increase in the force level (1.2 to 1.3 N) and amount of MH (1.0 to 1.5 N) compared to the Ormco-Conventional group (all p < 0.001), which indicated that force could be constantly maintained until the end of the deactivation curve. In contrast, the GAC-Reverse group exhibited a significant shift of the DFP-end point away from the origin point (0.2 to 3.3 mm), a decrease in the force level (1.1 to 0.9 N) and amount of MH (0.6 to 0.4 N) compared to the GAC-Conventional group (all p < 0.001), which may hinder the maintenance of force until the end of the deactivation curve. CONCLUSIONS: The two commercially available NiTi-CCS groups exhibited different patterns of change in the force-deflection characteristics when the coiling direction was reversed.
RESUMO
The aim of this study was to investigate the effect of thermomechanical treatment on mechanical and metallurgical properties of nickel-titanium (NiTi) rotary instruments. Eight kinds of NiTi rotary instruments with sizes of ISO #25 were selected: ProFile, K3, and One Shape for the conventional alloy; ProTaper NEXT, Reciproc, and WaveOne for the M-wire alloy; HyFlex CM for the controlled memory- (CM-) wire; and TF for the R-phase alloy. Torsional fracture and cyclic fatigue fracture tests were performed. Products underwent a differential scanning calorimetry (DSC) analysis. The CM-wire and R-phase groups had the lowest elastic modulus, followed by the M-wire group. The maximum torque of the M-wire instrument was comparable to that of a conventional instrument, while those of the CM-wire and R-phase instruments were lower. The angular displacement at failure (ADF) for the CM-wire and R-phase instruments was higher than that of conventional instruments, and ADF of the M-wire instruments was lower. The cyclic fatigue resistance of the thermomechanically treated NiTi instruments was higher. DSC plots revealed that NiTi instruments made with the conventional alloy were primarily composed of austenite at room temperature; stable martensite and R-phase were found in thermomechanically treated instruments.
Assuntos
Ligas/química , Instrumentos Odontológicos , Humanos , Estresse MecânicoRESUMO
The purpose of this study was to compare fracture resistances of K3 nickel-titanium files made from different thermal treatments. K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and experimentally heat treated K3 (K3H) were used. For the cyclic fatigue test, the samples were rotated with up-and-down motion in the artificial canal with the curvature of 60 degrees until the fracture occurred. The number of cycles to fracture (NCF) was measured. For the torsional fracture test, the samples were tightly bound and rotated until the fracture occurred. Elastic modulus (EM), ultimate torsional strength (UTS), and angle of rotation to fracture (ARF) were measured. The results were statistically analyzed by one-way ANOVA. The NCF of K3H was higher than those of K3 and K3XF (P < 0.05). The EM of K3XF and K3H was lower than that of K3 (P < 0.05). There was no significant difference in UTS. The ARF of K3XF was higher than that of K3 (P < 0.05). K3XF and K3H showed more flexibility than K3. The maximum torsional angle of K3XF was higher than that of K3, but there was no significant difference on the UTS in all three groups.
RESUMO
OBJECTIVE: The aim of this study was to investigate the effect of heat treatment on the cyclic fatigue resistance, thermal behavior and microstructural changes of K3 NiTi rotary instruments. MATERIALS AND METHODS: Twelve control (as-received) and 12 experimental (heat-treated) K3 NiTi rotary instruments were compared in this study. Those experimental K3 instruments were heated in a furnace for 30 min at 450°C and then quenched in water. The cyclic fatigue resistance was measured with a fatigue tester. The thermal characteristic and the microstructures of both instruments were investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), respectively. RESULTS: There was a significant increase in the cyclic fatigue resistance between the heat-treated instruments and the as-received instruments (T-test, p < 0.05). DSC showed that the as-received and heat-treated samples were different, with an increased Af (austenite-finish temperature) for the latter. TEM analysis revealed that both as-received and heat-treated instruments were composed mainly of an austenite phase. However, the heat-treated samples had an increased appearance of larger grains, twinning martensite, TiO2 surface layer and a Ni-rich inner layer. CONCLUSIONS: Heat treatment increased the cyclic fatigue resistance of NiTi files and changed the thermal behavior of the instruments without marked changes in the constituting phases of NiTi alloy.
