The effect of different surface and heat treatments on Y-TZP zirconia ceramics and their bond to their corresponding veneering ceramics
Ishgi, Adnan A.
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Statement of the problem: Zirconia ceramics can be affected by surface and heat treatments. Additionally, the overall performance of the bilayer zirconia restoration is determined by their weakest parts, which are the veneering porcelain and its bond to the Y-TZP. Objectives: To test the effect of various surface and heat treatments on zirconia ceramics and their corresponding veneering porcelains; test the effect of the transformation mechanism on the hardness, of the zirconia; evaluate the failure modes of bilayered specimens. Materials and methods: Disc specimens of VITA YZ[R] & LAVA[TM] (zirconia ceramics) were prepared and subjected to grinding, polishing, sandblasting, or repeated firing, and then loaded to failure. Disc specimens of zirconia ceramics veneered with VITA VM[R] 9 & LAVA[TM] CERAM (veneering porcelains) were prepared. Zirconia cores were subjected to grinding and sandblasting and veneering porcelains we prepared under different veneering protocols (wash layer and different firing temperatures). Specimens were loaded to failure using Instron machine. All failed specimens were evaluated by PHOTOSHOP[R] software for delamination. The hardness of VITA YZ[R] and LAVA[TM], and VITA VM[R] 9; LAVA[TM] CERAM were evaluated by MICROMET 2003 microhardness tester. Statistical analyses were performed using ANOVA and Tukey HSD. Materials' microstructure was investigated (CTE, surface roughness, X-ray diffraction, EDS, SEM and optical microscope). Results: Sandblasting and polishing increased the flexural strength of zirconia ceramics, while grinding followed by heat treatment decreased it. LAVA[TM] CERAM had high delamination percentage compared with VITA VM[R] 9. Delamination of LAVA[TM] CERAM was improved significantly by the application of wash layer and increasing the firing temperature to 840 degrees C. VITA VM[R] 9 prepared on untreated zircona cores had the lowest delamination percentage. The hardness of VITA YZ[R] and LAVA[TM] were similar. Stressed zirconia surfaces had the highest hardness values, while stressed surfaces followed by heat treatment had the lowest. VITA VM[R] 9 had higher hardness values than LAVA[TM] CERAM. Conclusions: Surface treatment improved or didn't change the flexural strength of the material, however, monoclinic crystals were detected (i.e. stresses); releasing these stresses by a heat treatment reduced the strength of the material. Surface treatments of the zirconia core didn't improve the bond of veneering porcelains.
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 firstname.lastname@example.org.Thesis (DScD) --Boston University, Goldman School of Dental Medicine, 2009 (Department of Restorative Sciences and Biomaterials).Includes bibliographic references: leaves 188-193.
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