Translucency of monolithic ceramics and the effect of surface condition on their flexural strength and enamel wear
Basunbul, Ghadeer Islem
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Objectives: New block materials have been developed to fabricate full-contour restorations. Typically, zirconia and lithium disilicate (IPS e.max CAD) are s milled to full contoured restorations and then subjected to various grinding and polishing procedures in the dentist hand to improve the fit. Various finishing procedures may affect physical and mechanical properties of the material. The purposes of this study are (1) to evaluate the wear resistance and the abrasiveness of zirconia and lithium disilicate with different surface finish against dental enamel, (2) to evaluate the flexural strength of zirconia and lithium disilicate restorative materials subjected to various finishing procedures and (2) to compare the translucency of three different brands of zirconia. Materials and methods: (1) 190 ceramic specimens (3 x5 x12 mm) - 10 from each group: IPS e.max CAD polished, glazed, ground and repolished, BruxZir polished, glazed, ground and repolished, Zirlux polished, glazed, ground and repolished, Zenostar polished, glazed, ground and repolished, Vita Mark II polished, Ceramco 3 polished and Unipack Prismatic porcelain polished were subjected to 600,000 strokes of enamel wear in a wear machine under a constant 400g load. Enamel specimens were prepared from sound, caries-free, extracted teeth. Measuring height and weight loss and then calculating volume loss determined the amount of enamel wear. The amount of ceramic wear was determined by measuring weight loss and calculating volume loss. Before and after 60,000, 120,000 and 600,000 strokes of wear testing; surface roughness was measured for each ceramic specimen using a portable surface roughness tester. (2) 150 bars (2 x 4 x 20 mm) of IPS e.max CAD, BruxZir, old Zirlux, new Zirlux and Zenostar were randomly divided into 15 groups of 10 specimens each. Experimental groups are polished (Buehler Ecomet 250 polisher, 45, 15, 6, 1 micron diamond grit), ground (coarse grit diamond bur grinding) and repolished (medium and fine grit diamond bur finishing and Dialite diamond-impregnated polishers). A 3-point-bending test, span 1 5 mm, was used to measure the flexural strength of materials using an Instron machine at a crosshead speed of 0.5 mm/min with a 10 kN load cell. The surfaces of few random specimens were examined in the SEM. (3) Spectrophotometer coIor i5 was used to measure the translucency of O.5 mm thick specimens: 30 BruxZir, 30 Zenostar and 30 Zirlux. All data was transferred to an excel sheet and translucency parameter was calculated. Statistical analysis was conducted using t-test, one-way and two-way ANOVA and Bonferroni’s post hoc test at p = 0.05 1evel of significance. Results: (1) Statistical analysis revealed a significantly less enamel abrasion and greater wear resistance for the Zirconia materials than any other group. The most abrasive materials are Ceramco 3 and Unipack prismatic porcelain. Vita Mark II and IPS e.max CAD exhibit an intermediate position. Glazing and coarse grinding significantly increase the abrasiveness of Zirconia to enamel while only glazing increases the abrasiveness of IPS e.max CAD. On the ceramic level, only glazed zirconia exhibited volume loss by enamel wear. (2) Two-Way ANOVA demonstrated significant difference in flexural strength between the test groups (p[less than] 0.05). IPS e.maX CAD demonstrated lower flexural strength than any Zirconia material tested. Surface finish did not alter the flexural strength of IPS e.max CAD. The new Zirlux flexural strength was also Iower than the old Zirlux, BruxZir and Zenostar which did not differ significantly. Bonferroni’s post hoc multiple comparison tests demonstrated that coarse grinding significantly lower the flexural strength of the zirconia materials while finishing and repolishing raise it back to its starting level except in Zenostar where repolishing cause further reduction in the flexural strength. (3) Translucency testing demonstrated significant difference between the different brands of zirconia in the study: BruxZir is slightly less translucent than Zirlux and Zenostar. Conclusions: Despite the limitations of this study, less wear of antagonist teeth was shown with Zirconia than with feldspathic porcelain. Polishing of zirconia full-contoured restoration is recommended for the best results in term of wear behavior and flexural strength.
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, 2013 (Department of Restorative Sciences and Biomaterials).Includes bibliographic references: leaves 195-204.
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