Effect of cyclic loading on the mechanical properties of CADCAM ceramic materials & on the survivability of VM9YZ crowns
Ashkar, Hanaa Hamzah A
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Objectives: This in-vitro study was designed to determine the residual strength of single layer all-ceramic crowns after being subjected to simulate oral fatiguing and to establish a fatigue limit curve of veneered zirconia crowns. Materials and Methods: for the first part of the study,40 crowns from Mark II, ProCAD and Paradigm C ceramics were milled using CEREC inLab machine and cemented on epoxy dies using RelyXTM Unicem Self-Adhesive Resin Cement, 10 crowns from each material were subjected to load to failure test on a universal testing machine. 30 crowns from each material were subjected to cyclic loading force of 450N for 30,000 cycles, 60,000 cycles and 120,000 cycles respectively. After cyclic loading,residual strength of the crowns determined using the universal testing machine. One-way ANOVA and Tukey HSD tests were used to analyze the data at significant level of alpha =0.05. For the second part of the study, 50 standardized VM9/In-Ceram YZ veneered crowns were fabricated and subjected to cyclic fatiguing under various loads for different times. A fatigue limit graph was created to show the lifespan of the crowns. Binary logistic regression and Cochrane- Mantel Hanzel (CMH) tests were used to analyze the data. Results: load to failure of Mark II (1.045[plus or minus]0.118 KN) was significantly lower than ProCAD (1.253[plus or minus]0.0989KN) and Paradigm C (1.185[plus or minus]0.1799 KN) while there was no significant difference in the load to failure between ProCÅD and Paradigm C. There was no significant diffence in the load to faillure of Mark II crowns before (1.045[plus or minus]0.118 EN) and after cyclic loading of the crowns for 30,000(0.984[plus or minus]0.159 KN), 60,000 (1.091[plus or minus]0.128 KN) and 120,000 (1.034[plus or minus]0.23 KN) cycles. The load to failure of ProCAD crowns was significantly decreased from baseline (1.253[plus or minus]0.0989 KN) to 30,000(1.012[plus or minus]0.279 KN) cycles but there was no significance difference between 30,000, 60,000 (0.988[plus or minus]0.15 KN)and 120,00 (0.98[plus or minus]0.256) cycles. The load to failure of Paradigm C crowns was significantly decreased from baseline (1.1 85[plus or minus]0.1 799 KN) to 30,000 (0.945[plus or minus]0.13KN) cycles but there was no significance difference between 30,000 , 60,000 (0.981[plus or minus]0.347KN) and 120,000 (0.889[plus or minus]0.221 KN) cycles. Logistic regression showed for each unit of load increase, there is 3% less likely to be categorized as not fail. However, this was not statistically significant at alpha 0.05. Cochrane-Mantel Hanzel (CMH)t est showed there was a strong association between fail / not fail and number of cycles after adjusting for load. Conclusions: There were statistically significant differences in the mean load to failure of the materials tested Paradigm C mean load to failure was statistically lower than ProCAD and Mark II. There was no statistical difference in the load to failure of Mark II before and after cyclic Ioading for 30,000, 60,000 and 120,000 cycles. There was a statistical difference in the load to failure of Paradigm C and ProCAD before and after cyclic loading for 30,000 cycles. But there were no difference in the load to failure between fatiguing for 30,000, 60,000 and 120,000 cycles. There was a strong statistical association between increasing the load and number of fatigue cycles and crack formation in VM9/YZ crowns.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact email@example.com.Dissertation (DScD) --Boston University, Goldman School of Dental Medicine, 2012 (Department of Restorative Sciences and Biomaterials).Includes bibliographic references: leaves 87-90.
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