ABSTRACT
OBJECTIVE@#To compare the effects of autoclave on surface microstructure and cyclic fatigue resistance of K3XF and K3.@*METHODS@#Forty-eight size 25, 0.06 taper 25 mm-long K3XF or K3 were randomly divided into 4 groups (n=12). The instruments from group 1 were not autoclaved, and the groups 2 to 4 underwent autoclave for 10 cycles, 20 cycles, and 30 cycles, respectively. The surface microstructure of two instruments randomly selected from each group was observed using scanning electron microscope (SEM). The remaining 10 instruments were submitted to the cyclic fatigue test by using a simulated metal root canal with curvature of 60° and radius 3.5 mm. The time till fracture was recorded, the number of cyclic fatigue (NCF) calculated, the fragment length evaluated, and the topographic features were analyzed using SEM. The data were analyzed using the two-way ANOVA analysis by SAS 9.3 software at a significance level of P<0.05.@*RESULTS@#SEM observation identified rough features on the surface of K3XF with micropores existing evenly. K3 was characterized by machining grooves, which located specifically in the flute, leaving a smooth cutting edge. After autoclave, SEM observation indicated that the micropores in the surface of K3XF became larger and more, whereas the machining grooves in the surface of K3 were squeezed, out of shape and flaking. As far as the NCF was concerned, new K3XF was 210±59, and no significant difference was found after 10, 20, and 30 cycles of autoclave for K3XF, values being 178±37, 208±48, and 227±43, respectively (P>0.05). For K3, the new one was 145±38, and no significant difference in NCF was demonstrated after 10 and 20 cycles of autoclave, with the values of 128±43 and 124±46, respectively (P>0.05). However, after 30 cycles of autoclave of K3, significant increase to 216±38 was identified (P<0.05). Topographic features demonstrated typical cyclic fatigue for all the groups.@*CONCLUSION@#The surface roughness of K3XF was increased after autoclave, while the cyclic resistance remained stable after up to 30 cycles.
Subject(s)
Dental Alloys , Dental Instruments , Disinfection , Equipment Failure , Hot Temperature , Materials Testing , Nickel , Root Canal Preparation/instrumentation , TitaniumABSTRACT
OBJECTIVE@#To compare the surface microstructures and cyclic fatigue resistance of HyFlex EDM with HyFlex CM and HyFlex NT.@*METHODS@#Twelve 25 mm-long 25#/- HyFlex EDM and twelve 25 mm-long 25#/0.06 taper HyFlex CM or HyFlex NT were selected. The surface microstructure of the 2 instruments which were randomly selected from each group was observed by using scanning electron microscope (SEM). The remaining 10 instruments from each group were submitted to the cyclic fatigue test by using a simulated stainless steel root canal with 60° angle of curvature and curvature radius of 3.5 mm. The time till fracture was recorded, the number of cyclic fatigue (NCF) was calculated, the length of fracture fragment was evaluated, and the topographic features were analyzed by using SEM. The data were analyzed by using one-way analysis via SPSS 23.0 software. The statistical significance level was set at 0.05.@*RESULTS@#SEM observation of the surface and microstructural characterization revealed peculiar melting appearance and evenly distributed micropores on the surface of HyFlex EDM while observations of the surface of both HyFlex CM and HyFlex NT demonstrated machining grooves and irregularities. The NCF of HyFlex EDM was 838±223, which was significantly higher than not only that of HyFlex CM (582±99), but also that of HyFlex NT (81±20) (P<0.05), and the difference between the latter two groups was significant, as well (P<0.05). The length of fractured fragments of HyFlex EDM was (7.27±0.28) mm, which was significantly longer than the HyFlex CM and HyFlex NT, with values of (6.72±0.26) mm and (6.62±0.37) mm, respectively (P<0.05). Topographic features demonstrated typical cyclic fatigue for all the three groups while the region of crack origins was more for HyFlex EDM and HyFlex CM than that of HyFlex NT. As far as the dimple area was concerned, that of HyFlex EDM was deeper and larger than that of HyFlex CM and HyFlex NT.@*CONCLUSION@#Within the limitations of this study, electro-discharge machining leads to peculiar melting appearance with micropores instead of machining grooves and irregularities on the surface of HyFlex EDM, which may be the reason why HyFlex EDM exhibits significantly better cyclicfatigue resistance than HyFlex CM and HyFlex NT.