Thesis:the Effect Of Irrigation On The Surface Roughness And Fatigue Resistance Of Controlled Memory Wire Nickel-titanium Instruments

Part oneThe effect of irrigation on the surface roughness of controlled memory wire nickel-titanium instruments[Abstract]The effect of irrigation on the surface roughness of controlled memory(CM)wire nickel-titanium(NiTi)instruments was investigated.[Methods]Two new files of both HyFlex and M3 NiTi files were chosen,and then 15 points were scanned randomly along a 2-4 mm section of the tip of each file by atomic force microscopy(AFM).Each brand files were subdivided into 2 subgroups,then;the instruments were dynamically immersed in either 5.25%sodium hypochlorite(NaOCl)or 17%ethylene diamine tetraacetic acid(EDTA)solution for 10 min,respectively.After being removed from the immersion,all the files were rinsed with distilled water and dried,followed by AFM analysis again.The surface roughness and three-dimensional(3D)images(512*512 line)were preceding using AFM analysis software.The roughness average(Ra)and the root mean square value(RMS)values were selected to investigate the vertical surface roughness of the NiTi files.The Ra and RMS values were analyzed statistically using an independent sample t-test.The level of significance was set at p<0.05.[Results]For M3 files,the Ra and RMS values significantly increased after the 5.25%NaOCl and 17%EDTA immersion(p<0.05).For the HyFlex file,the Ra and RMS values significantly increased only in 17%EDTA solution(p<0.05),but not in 5.25%NaOCl solution(P>0.05).[Conclusions]The surface roughness of 5.25%NaOCl and 17%EDTA immersed M3 files significantly increased compared to the control groups.The roughness of 17%EDTA immersed HyFlex files significantly increased compared to the new file,but the file was not affected by 5.25%NaOCl for 10 min.Part twoThe effect of irrigation on the fatigue resistance of controlled memory wire nickel-titanium instruments[Abstract]The effect of irrigation on the fatigue resistance of controlled memory(CM)wire nickel-titanium(NiTi)instruments was investigated.[Methods]36 new files of both HyFlex and M3 NiTi files were randomly assigned to three groups(n = 12).Group 1(the control group)was composed of new instruments not immersed in solutions.Groups 2 was dynamically immersed in 5.25%sodium hypochlorite(NaOCl)solutions for 10 min,and Groups 3 was dynamically immersed in 17%ethylene diamine tetraacetic acid(EDTA)solutions for 10 min.Then the instruments were subjected to rotate freely in a simulated curved root canal with curvature of 45°and 3-mm radius until fracture occurred.The timing of rotating from beginning to fracture was recorded using a stopwatch.The time was then converted into the number of revolutions to fracture(Nf).The length of the fractured tip was measured using a digital caliper.The fracture surfaces of all instruments were examined under the scanning electron microscope(SEM).The number of rotations to failure for various groups and the length of the fractured tip were analyzed using the one-way analysis of variance software.The significance level was set at p<0.05.[Results]The resistance to cyclic fatigue of both HyFlex and M3 files did not significantly decrease by immersing in 5.25%NaOCl and 17%EDTA solutions for 10 min.The fracture fragment length of HyFlex and M3 NiTi instrument was between 5-6 mm,there was no significant difference in the mean length of the fractured fragments of the two brands tested.SEM of the fracture surface showed similar and typical features of cyclic fatigue failure for the two brands.[Conclusions]The change in the surface tomography of CM wire instruments caused by contacting with irrigations for 10 min did not enough trigger the decrease of their cyclic fatigue resistance.The length of the fractured fragment of HyFlex and M3 NiTi instruments is consistent with the length of the bent part that the files deep into the simulated curved root canals.SEM of the fracture surface showed similar and typical features of cyclic fatigue failure for the two brands.