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Fracture behaviour of zirconia FPDs substructures: fractographic analysis of zirconia
Umeå University, Faculty of Medicine, Department of Odontology, Dental Materials Science. Umeå University, Faculty of Medicine, Department of Odontology. (Biomaterial)
Umeå University, Faculty of Medicine, Department of Odontology, Dental Materials Science. (Biomaterial)
2010 (English)In: Journal of Oral Rehabilitation, ISSN 0305-182X, E-ISSN 1365-2842, Vol. 37, no 4, 292-299 p.Article in journal (Refereed) Published
Abstract [en]

 The purpose of this study was to evaluate the occurrence of superficial flaws after machining and to identify fracture initiation and propagation in three-unit heat-treated machined fixed partial dentures (FPDs) substructures made of hot isostatic pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) after loaded to fracture. Four three-unit HIPed Y-TZP-based FPDs substructures were examined. To evaluate the occurrence of superficial flaws after machining, the surfaces were studied utilizing a fluorescent penetrant method. After static loading to fracture, characteristic fracture features on both mating halves of the fractured specimens were studied using a stereomicroscope and a scanning electron microscope. Grinding grooves were clearly visible on the surfaces of the machined FPDs substructures, but no other flaws could be seen with the fluorescent penetrant method. After loading to fracture, the characteristic fracture features of arrest lines, compression curl, fracture mirror, fracture origin, hackle and twist hackle were detected. These findings indicated that the decisive fracture was initiated at the gingival embrasure of the pontic in association with a grinding groove. Thus, in three-unit heat-treated machined HIPed Y-TZP FPDs substructures, with the shape studied in this study, the gingival embrasure of the pontic seems to be a weak area providing a location for tensile stresses when they are occlusally loaded. In this area, fracture initiation may be located to a grinding groove.

Place, publisher, year, edition, pages
Blackwell Publishing Ltd , 2010. Vol. 37, no 4, 292-299 p.
Keyword [en]
ceramics, fixed partial denture, fractographic analysis, machined surface, Y-TZP, zirconia
National Category
Research subject
URN: urn:nbn:se:umu:diva-31637DOI: 10.1111/j.1365-2842.2009.02057.xISI: 000275206600009PubMedID: 20085616OAI: diva2:293637
Available from: 2010-02-12 Created: 2010-02-12 Last updated: 2010-10-08Bibliographically approved
In thesis
1. On dental ceramics and their fracture: a laboratory and numerical study
Open this publication in new window or tab >>On dental ceramics and their fracture: a laboratory and numerical study
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background Surface treatments and irregularities in the surfaces may affect the fracture of ceramics. The effects of various treatments on the surface texture of different types of ceramic cores/substructures was therefore qualitatively, quantitatively and numerically evaluated. Since fractures in ceramics are not fully understood, the fracture behavior in dental ceramic core/substructures was also studied using both established laboratory methods and newly developed numerical methods.

Methods The surfaces of dental ceramic cores/substructures were studied qualitatively by means of a fluorescence penetrant method and scanning electron microscopy, quantitatively evaluated using a profilometer and also numerical simulation. In order to study fracture in zirconia-based fixed partial denture (FPD) frameworks, fractographic analysis in combination with fracture tests and newly developed two-dimensional (2D) and three-dimensional (3D) numerical modeling methods were used. In the numerical modeling methods, the heterogeneity within the materials was described by means of the Weibull distribution law. The Mohr–Coulomb failure criterion with tensile strength cut-off was used to judge whether the material was in an elastic or failed state.

Results Manual grinding/polishing could smooth the surfaces on some of the types of dental ceramic cores/substructures studied. Using the fluorescence penetrant method, no cracks/flaws apart from milling grooves could be seen on the surfaces of machined zirconia-based frameworks. Numerical simulations demonstrated that surface grooves affect the fracture of the ceramic bars and the deeper the groove, the sooner the bar fractured. In the laboratory tests the fracture mechanism in the FPD frameworks was identified as tensile failure and irregularities on the ceramic surfaces could act as fracture initiation sites. The numerical modeling codes allowed a better understanding of the fracture mechanism than the laboratory tests; the stress distribution and the fracture process could be reproduced using the mathematical methods of mechanics. Furthermore, a strong correlation was found between the numerical and the laboratory results.

Conclusion Based on the findings in the current thesis, smooth surfaces in areas of concentrated tensile stress would be preferable regarding the survival of ceramic restorations, however, the surfaces of only some of the ceramic cores/substructures could be significantly affected by manual polishing. The newly developed 3D method clearly showed the stress distribution and the fracture process in ceramic FPD frameworks, step by step, and seems to be an appropriate tool for use in the prediction of the fracture process in ceramic FPD frameworks.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2010. 53 p.
Umeå University odontological dissertations, ISSN 0345-7532 ; 113
Dental ceramics, Finite element analysis, Fixed partial denture, Fracture, Numerical modeling, Surface treatment
National Category
Biomaterials Science
Research subject
urn:nbn:se:umu:diva-36590 (URN)978-91-7459-037-1 (ISBN)
Public defence
2010-10-29, Sal 260, byggnad 3A, Norrlands universitetssjukhus, Umeå, 13:00 (Swedish)
Available from: 2010-10-08 Created: 2010-10-05 Last updated: 2011-10-11Bibliographically approved

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Kou, WenSjögren, Göran
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