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Finite element analysis of the failure mechanism of porcelain applied on zirconia (Y-TZP) frameworks

Grant number: 09/06266-7
Support Opportunities:Scholarships abroad - New Frontiers
Effective date (Start): August 16, 2010
Effective date (End): August 10, 2011
Field of knowledge:Health Sciences - Dentistry - Dental Materials
Principal Investigator:Josete Barbosa Cruz Meira
Grantee:Josete Barbosa Cruz Meira
Host Investigator: Michael V. Swain
Host Institution: Faculdade de Odontologia (FO). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Research place: University of Sydney, Australia  


In vivo and in vitro studies have attested the superior performance of yttrium - oxide paritally-stabilized tetragonal zirconia polycrystals (Y-TZP) compared to other frameworks ceramics. Recently, however, clinical reports describing chipping of the overlaying porcelain applied on the zirconia structure has increased substantially. The overall objective of this project is to develop a numerical model that could help to explain this failure mechanism in all-ceramic crowns cemented to the tooth structure or fixed to an implant. The hypothesis is that chipping occurs due to the association of residual thermal stresses with stresses resultant from occlusal loading. Moreover, it can be hypothesized that in cases the porcelain is applied on the abutment, the risk of chipping is higher because the porcelain layer presents a large volume without infra-structure support. The geometries will be generated in CAD ("computer-aided design") software and exported to the finite element analysis software. MSC.Patran will be used for pre- and post-processing, and MSC.Marc will be used for processing. Thermal residual stresses will be analyzed by simulating the cooling of the overlaying porcelain after sintering (between 900oC and room temperature). Two cooling rates will be studied: 10oC/s and 50oC/s. The change in porcelain coefficient of thermal expansion as it passes through its glass transition temperature (Tg) and its viscoelastic behavior above Tg will be taken into consideration. Occlusal contact will be simulated in two different ways: by applying the load directly on the external nodes of the ceramic crown and by contact bodies (non-linear analysis). The risk of porcelain chipping will be evaluated by analyzing the magnitude, location and direction of the maximum principal stress (s1) in this material. The model will be considered representative when the location and direction of s1 are coherent with fractography data found in the literature. Based on the results, new modeling conditions will be simulated as an attempt to reduce the risk of chipping. (AU)

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Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
MEIRA, JOSETE B. C.; REIS, BRUNO R.; TANAKA, CARINA B.; BALLESTER, RAFAEL Y.; CESAR, PAULO F.; VERSLUIS, ANTHEUNIS; SWAIN, MICHAEL V.. Residual stresses in Y-TZP crowns due to changes in the thermal contraction coefficient of veneers. Dental Materials, v. 29, n. 5, p. 594-601, . (09/06266-7)

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