Browsing by Subject "Zirconia"
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Item Effect of a screw-access channel on the fracture resistance of monolithic zirconia crowns(2019-06) Loeb, MitchellPurpose This in-vitro study was designed from a clinical case and investigated the effect of the presence of a screw assess channel, created either during the milling phase or following cementation, on the fracture strength of a monolithic zirconia cement-retained implant-supported fixed prosthesis (ISFP). Material & Methods A definitive cast from a clinical case restoring a mandibular right first molar implant was utilized to fabricate three different styles of monolithic zirconia cement-retained ISFP. Group 1 had no screw-access channel (CR), Group 2 had a screw-access channel milled in the green phase (MA), and Group 3 had a screw-access channel created by hand preparation after cementation (HA). With 3 groups and 5 samples in each group, there were a total of 15 monolithic zirconia crowns fabricated on custom abutments in preparation for testing. The maximum force required for crown fracture was measured using a universal testing machine. Results The mean loads to fracture from highest to lowest were: the milled screw-access channel group (MA), followed by the hand-made screw-access channel group (HA), and lastly by the cement-retained group without a screw-access channel (CR). One-way ANOVA analysis indicated the fracture strength of the MA was statistically significantly different than the cement-retained samples (P<0.05). No statistically significant differences were found between the milled screw-access channel and the access channel created by hand. Conclusion The presence of a screw-access channel, whether milled or prepared by hand, does not negatively affect the fracture strength of a monolithic zirconia ISFP.Item The Influence of Cutback Design on the Fracture Strength of Zirconia Crowns with Minimal Porcelain Veneering(2022-12) Rainville, LouisThe purpose of this study is to compare designs of partially veneered 3Y-TZP zirconia crowns, quantify the fracture and ultimate compressive loads and define the failure patterns. A premolar was prepared with a 1mm reduction. The die was duplicated, 30 specimens were fabricated and divided in 3 groups (n=10): Group A – Control (PFZ), Group B – Experimental #1 (Veneer) and Group C – Experimental #2 (Window). Zirconia copings were fabricated with manually layered porcelain. The crowns were cemented onto the dies using resin cement and the specimens were tested under axial loading. The mean FL were 1538.40N (A), 2025.33N (B) and 2266.03N (C), and the mean UCL were 1554.42N (A), 2032.85N (B) and 2279.39N (C). 26/29 specimens underwent core fracture, and 3/29 specimens experienced adhesive veneer fracture. In conclusion, there were statistical differences between the control and the experimental groups, but not between the experimental groups.Item Nanostructured zirconia as a strain relief interlayer - A study of microstructure and its evolution in plasma sprayed coatings.(2010-01) Guru, Dwijendra NathNanostructured zirconia as a strain relief interlayer - a study of microstructure and its evolution Thermal barrier coatings (TBC) for the next generation gas turbines and jet engines need to work at higher temperature gradients and better accommodate strain across their thickness. The research undertaken is an effort to understand whether the morphological characteristics of coatings prepared using nanostructured material could lead to strain accommodation within a TBC. TBCs of nanostructured partially stabilized zirconia (n-PSZ) were prepared using the Triple Torch Plasma Reactor, a reduced pressure plasma spray deposition system. A shutter mechanism was designed to capture individual splats of the spray particles. Scanning electron microscope (SEM) images of the splats were analyzed to identify morphological characteristics such as circularity and crack density. Samples of proto-coatings, i.e. samples with two to five splats deposited one on top of the other were also prepared. Reference coatings were prepared using a commercial atmospheric pressure plasma spray deposition system. The coatings were subjected to isothermal testing at different temperatures. Cross sections of representative coatings were prepared and imaged using a SEM. Image analysis techniques were used to extract the porosity information of the coatings. A database of morphological parameters of the splat samples as a function of the plasma spray parameters was compiled. It was confirmed that the defining characteristic of a n-PSZ TBC is the presence of semi-molten feedstock particle. Cross sectional samples of these semi-molten structures were prepared and imaged. The distribution of peak heights of these semi-molten n-PSZ structures in the splat samples were found to be strongly influenced by the plasma spray deposition conditions. The peak heights are, on an average, smaller when the percentage of hydrogen in the plasma gas is increased, and even smaller in the case of a deposition with an increased arc current, indicative of stronger melting of the agglomerated feedstock particles. Heat treatment of the coating samples indicated that a n-PSZ under-layer within a multilayered TBC had a stabilizing influence on the porosity across the coating. Thus the morphology of a n-PSZ interlayer is conducive for strain accommodation within a multi-layered TBC in plasma sprayed coatings.