Effect Of Cyclic Loading On The Compressive Strength Of Full-contour Zirconia Crowns

Objective: To evaluate and compare the resistance level of full-contour zirconia crowns under cyclic loading.Methods: Cast 18 metal dies of the standard first molar of the left mandibular.The principle was: the axial degree was 6,the width of chamfer was 0.8mm.There was no under cuts and stress concentration area.The computer aided design and computer aided manufacturing(CAD/CAM)system was used to prepare 18 full-contour zirconiacrowns of the occlusal surface to1.0mm.All the crowns were bonded to the metal dies using 3M glass ionomer cement,pressed the crowns for 10 minutes with the strength of 20 N by fingers,moved away the exceeded cement,put the 18 full-contour zirconia crowns in the 37?constant temperature box with distilled water for 24 h.Randomly divided these crowns into A,B,C three groups randomly,six for each group.Group A and group B was respectively fixed on the biomechanical test machine for cyclic loading,with a frequency of 8 Hz,300000 cycles.The loading force of group A was 300 N,and group B was500 N.Place the full-contour zirconia crowns after Hertzian indenation test sequentially on a universal testing machine for compression test.The loading head was loaded at a constant speed of 0.5 mm / min on the crowns until the all-ceramic crown was damaged.Then recorded the date.Used SPSS 21.0software to analysis the data.Results: The compressive strength of full-contour zirconia crown in different groups: group A:(4501.00±812.84)N,groupB:(4193.33±335.68)N,group C:(4416.00±156.25)N.The compressive strength of crowns showed no significant differences between different Hertzian indenation(P>0.05).And there was no significant differences between each two groups(P>0.05).Conclusion: Using different loaded force for 300000 cycles on thezirconium crown load had no significant effect on its resistance to compressive strength.