Effect of multiple firings on the mechanical and physical properties of dental porcelain
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This study aimed to evaluate the alterations in flexural strength and fracture toughness of five different porcelains (Vitadur alpha dentine, Omega 900 dentine, VMK 95 dentine, Finesse dentine, Dsign deutine) after multiple firing cycles. Forty bars (24.0mm x 3.0mm x 2.0mm) were fabricated for each material, and assigned to two different tests: four-point and three-point bending test to determine respectively the flexural strengths and the fracture toughness of the specimens. X-ray diffraction analysis was performed on Omega 900 dentine and VMK 95 dentine porcelains, to determine the general behavior of leucite during the firing cycles. For each test, there were five specimens for each material in each group: one, three, five, and seven firing cycles prior to testing, with a total of 200 specimens. Surface texture and roughness were evaluated qualitatively by scanning electron microscopy (SEM). The results were evaluated by using an analysis of variance (ANOVA), 2-tailed t test at a significance level of 0.01, and post hoc test (SPSS 10.01 for Windows, SPSS Inc. and Microsoft Excel 1997). After ANOVA was performed, multiple means comparison within sample groups and between groups of the same firing was conducted with Tukey test at a significant difference probability level of O.05. All data were assumed parametric. Results from X-ray diffraction indicated a clearly noticeable trend in the amount of crystalline component (leucite), which steadily increased with each firing. A correlation at the 0.05 level of significance between firing cycles and flexural strength values for Finesse and Dsign porcelain with a negative slope was detected (i.e., the more these materials were fired the weaker they became). The correlation had a positive slope for Vitadur alpha porcelain (i.e., the more it was fired, the stronger it became). VMK 95 porcelain showed a correlation between the firing cycles and the flexural strengths at the 0.05 level of significance with a negative slope. Omega 900 porcelain showed no correlation between flexural strengths and firing cycles. For the fracture toughness tests, at the 0.05 level of significance, there was a correlation with the firing cycles for VMK 95 and Dsign porcelains with a positive slope. For Vitadur porcelain there was a correlation at the 0.05 level of significance between firing cycles and fracture toughness with a positive slope. For Finesse porcelain there was a correlation at the same 0.05 level of confidence but with a negative slope. Omega 900 porcelain showed no correlation between fracture toughness and firing cycles. Multiple firings increased leucite content in Omega 900 and VMK 95 porcelains, two ceramics used in the fabrication of PFM crowns, which ranked the strongest and most resistant to fracture in both tests. Finesse porcelain, which has a low content of leucite (8-10%), and Dsign porcelain, which contained fluoroapatite crystals rather then feldspathic leucite crystals, were the weakest and least resistant to fracture in these same tests.
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 (MSD)--Boston University, Goldman School of Dental Medicine, 2005 (Prosthodontics).Includes bibliographical references: leaves 81-85.
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