Effect of crystallization cycle on static and cyclic failure load of lithium disilicate hybrid abutment crowns
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Objectives: This in vitro study was designed to test the static and fatigue load at failure of CAD-CAM fabricated lithium desilicate hybrid abutment crowns, and to compare the efforts of a shorter crystallization cycle with the cycle recommended by the manufacturer. Materials and Methods: Nineteen IPS e.max CAD hybrid abutment crowns were designed and milled in the Sirona inLab MCXL milling machine to fit over a 4.3 mm Nobel Biocare Replace Select (NB RS 4.3 mm) implant for tooth number 14. Nine crowns were individually fired in the Programat CS furnace using the "Normal (P1)" firing cycle and ten crowns were individually fired in the same furnace using the "Fast or Characterization (P3)" firing cycle. The crowns were cemented with Multilink Implant resin cement to Ti bases (Sirona)that serve as the connection to the NB RS implant and then screwed into NB RS 4.3 mm lab analogs. The screws of the hybrid abutment crowns were tightened at a final torque of 35 N.cm and the screw access holes were blocked with a light curing composite resin. Then the specimens were mounted in a customized Delrin fixture by embedding the lab analog stubs in epoxy resin. After the resin fully set, four normal fired and four fast fired specimens were subjected to a static load to failure test in a universal mechanical testing machine (Instron 5566A). Five normal fired and six fast fired hybrid abutment crowns were subjected to 50,000 cycles of cyclic loading fatigue under water with a maximum load of 700 N, which was approximately 30% of the mean static load at failure value. After cyclic loading fatigue the residual static load at failure of the survivors was determined using the universal testing machine. The differences of load at failure among the four groups were analyzed by JMP Pro 11.0 and IBM SPSS 20.0 using ANOVA with post hoc Tukey-HSD test with a significance level of 0.05 and confidence interval of 0.95. Selected failed specimens were subjected to fractographic analysis and Energy Dispersive Spectroscopy(EDS) using a Field Emission Scanning Electron Microscope (FESEM). Results: Mean load at failure values were 2203.4 [plus or minus] 337.23 N for the Normal Static group, and 1631.46 [plus or minus] 274.33 N for the Normal Fatigued group, 2319.93 [plus or minus] 367.14 N for the Fast Static group, and 1590.21 [plus or minus] 179.55N for the Fast Fatigued group. There is a statistically significant difference between the following groups: - Normal Static group and Normal Fatigued group (p = 0.040) - Normal Static group and Fast Fatigued group (p = 0.020) - Fast Static group and Normal Fatigued group (p = 0.012) - Fast Static group and Fast Fatigued group (p = 0.006) Conclusions: Cyclic loading fatigue of IPS e.max CAD hybrid abutment crowns significantly lowered the load at failure values for both crystallization cycles. Crystallization cycle had no significant effect on the load at failure.
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 (MSD) --Boston University, Henry M. Goldman School of Dental Medicine, 2015 (Department of Restorative Sciences and Biomaterials).Includes bibliography: leaves 96-99.
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