Fatigue Behavior Of Grinding On The Y-TZP Zirconia Ceramics After Cyclic In Vitro

Objectives In this experiment,the zirconia specimens were adjusted by grinding to simulate the effect of clinical grinding.Then the zirconia specimens after grinding were subjected to different cyclic fatigue properties of zirconia.Methods FPreparation of zirconia specimens: 120 zirconia ceramics specimens were prepared.After sintering,30 specimens with a size of 20mm×4mm×2mm were sintered,and 90 specimens with a size of 20mm×4mm×2.4mm were used(with an error of no more than 0.01mm).120 specimens of zirconia ceramics were divided into 4 groups(A?B?C and D)with 30 in each group.Group A:without surface treatment;Group B: grinding with a speed of 105 rpm;Group C: grinding with a speed of 2×105 rpm;Group D: grinding with a speed of 3×105 rpm.Afer the grinding is completed,it is required to fully rinse.Specimens A,B,C and D were randomly divided into 3 groups(n=10)using a random number table method.The fatigue tester was used to perform no cyclic loading,105 cyclic loadings,and 106 cyclic loadings.The test machine uses a 4mm diameter tungsten carbide ball to align with the centre of test piece.Preload 8N,eliminate sinusoidal loading after loading,load force 40N-230 N,frequency 2HZ,experiments are performed at room temperature of 25?.After different cycles of cyclic loading,XRD test were performed on X-ray diffractometers for each set of specimens that were not loaded,105 loaded,106 loaded,and the percentage of monoclinic phase relative content in each set of specimens was measured.The SEM was used to observe the changes in microstructure of each set of specimens.The universal test machine was used to measure the three-point bending strength of each set of specimens.Weibull analysis was performed on the threepoint bending strength of each set of specimens to obtain the zirconia specimens after cyclic loading.Weibull modulus m and Weibull characteristic intensity?0 value.The SPSS 17.0 software package was used to analyze the experimental data,and the one-way analysis of variance was performed on the bending strength values of the sopecimens of the grinding group and the non-trimming group after cyclic loading of different times.The test standard was ?=0.05.Results After the different rotation speeds were adjusted,the zirconia specimens showed a certain amount of monoclinic phase changes;the content of monoclinic phase after cyclic loading did not change significantly.The SEM observation showed that the zirconia specimens had a certain amount of wear after conditioning,and there were some scratches on the surface that were parallel to each other and different shades,and scattered particles were attached between the scratches.Undisturbed specimens after cyclic loading of different times,no significant changes in the surface,showing a clear arrangement of irregular grains.With the increase of the number of cycles,the zirconia specimens after tempering will have exfoliation and microcracks,and the more the loading times,the more exfoliative and microcracks will become.The three-point bending strength test results showed that there were no significant differences regarding the three-point bending test of any group between no loading cyclic and 105 cyclic loadings(P>0.05).However,group A?group B?group C and group D showed significant three-point bending strength decrease after 106 cyclic loading(P<0.05),and there were no significant difference with group B?group C and group D(P>0.05).Weibull analysis indicated the Weibull modulus and characteristic strength of zirconia were increased compared to the control group after the grinding of zirconia.After 105 cyclic loading,the Weibull modulus and characteristic intensity decreased;after 106 loading,the Weibull modulus and characteristic intensity decreased significantly.Conclusions Under the experimental condition,the strength of zirconia after tempering is not reduced,but as the number of loadings increases to a certain amount,the strength decreases,but the speed of the grinding does not affect it.The experimental results suggest that after long-term chewing,the clinical trial of zirconia prosthesis on the occlusal surface to a certain degree.Terefore,the long-term perspective of the prosthetic body will be used.Clinically,excessive adjustment of zirconia restorations should be minimized.