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On dental ceramics and their fracture: a laboratory and numerical study
Umeå University, Faculty of Medicine, Department of Odontology, Dental Materials Science.
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.
Series
Umeå University odontological dissertations, ISSN 0345-7532 ; 113
Keyword [en]
Dental ceramics, Finite element analysis, Fixed partial denture, Fracture, Numerical modeling, Surface treatment
National Category
Biomaterials Science
Research subject
Odontology
Identifiers
URN: urn:nbn:se:umu:diva-36590ISBN: 978-91-7459-037-1 (print)OAI: oai:DiVA.org:umu-36590DiVA: diva2:354929
Public defence
2010-10-29, Sal 260, byggnad 3A, Norrlands universitetssjukhus, Umeå, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2010-10-08 Created: 2010-10-05 Last updated: 2011-10-11Bibliographically approved
List of papers
1. Fracture behaviour of zirconia FPDs substructures: fractographic analysis of zirconia
Open this publication in new window or tab >>Fracture behaviour of zirconia FPDs substructures: fractographic analysis of zirconia
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
Keyword
ceramics, fixed partial denture, fractographic analysis, machined surface, Y-TZP, zirconia
National Category
Dentistry
Research subject
Odontology
Identifiers
urn:nbn:se:umu:diva-31637 (URN)10.1111/j.1365-2842.2009.02057.x (DOI)000275206600009 ()20085616 (PubMedID)
Available from: 2010-02-12 Created: 2010-02-12 Last updated: 2017-12-12Bibliographically approved
2. Surface roughness of five different dental ceramic core materials after grinding and polishing
Open this publication in new window or tab >>Surface roughness of five different dental ceramic core materials after grinding and polishing
2006 (English)In: Journal of Oral Rehabilitation, ISSN 0305-182X, E-ISSN 1365-2842, Vol. 33, no 2, 117-124 p.Article in journal (Refereed) Published
Abstract [en]

In clinical practice, core materials can be exposed after adjustments are made to previously-luted all-ceramic restorations. The purpose of this study was to evaluate the surface roughness of five different dental ceramic core materials after grinding and polishing. Five different ceramic core materials, Vita In-Ceram Alumina, Vita In-Ceram Zirconia, IPS Empress 2, Procera AllCeram, and Denzir were evaluated. Vita Mark II was used as a reference material. The surface roughness, Ra value (mum), was registered using a profilometer. The measurements were made before and after grinding with diamond rotary cutting instruments and after polishing with the Sof-Lex system. The surface of representative specimens was evaluated qualitatively using scanning electron microscopy (SEM). Results were statistically analysed using analysis of variance (anova) supplemented with Scheffe's and Bonferroni multiple-comparison tests. Before grinding, Procera AllCeram and Denzir had the smoothest surfaces, while IPS Empress 2 had the coarsest. After grinding, all materials except IPS Empress 2 became coarser. Polishing with Sof-Lex provided no significant (P > 0.05) differences between Denzir, Vita Mark II and IPS Empress 2 or between Procera AllCeram and In-Ceram Zirconia. There were no significant differences (P > 0.05) either between the ground and the polished Procera AllCeram or In-Ceram Alumina specimens. Polishing of Denzir, IPS Empress 2 and In-Ceram Zirconia made the surfaces smoother compared with the state after grinding, whereas the polishing effect on Procera AllCeram and In-Ceram Alumina was ineffective. The findings of the SEM evaluation were consistent with the profilometer readings.

Keyword
all-ceramic crowns, alumina, dental ceramics, dental polishing, finishing, lithium disilicate, Y-TZP, zirconia
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-12427 (URN)10.1111/j.1365-2842.2006.01546.x (DOI)16457671 (PubMedID)
Available from: 2007-12-13 Created: 2007-12-13 Last updated: 2017-12-14Bibliographically approved
3. Numerical modeling of the fracture process in a three-unit all-ceramic fixed partial denture
Open this publication in new window or tab >>Numerical modeling of the fracture process in a three-unit all-ceramic fixed partial denture
2007 (English)In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 23, no 8, 1042-1049 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVES: The main objectives were to examine the fracture mechanism and process of a ceramic fixed partial denture (FPD) framework under simulated mechanical loading using a recently developed numerical modeling code, the R-T(2D) code, and also to evaluate the suitability of R-T(2D) code as a tool for this purpose. METHODS: Using the recently developed R-T(2D) code the fracture mechanism and process of a 3U yttria-tetragonal zirconia polycrystal ceramic (Y-TZP) FPD framework was simulated under static loading. In addition, the fracture pattern obtained using the numerical simulation was compared with the fracture pattern obtained in a previous laboratory test. RESULTS: The result revealed that the framework fracture pattern obtained using the numerical simulation agreed with that observed in a previous laboratory test. Quasi-photoelastic stress fringe pattern and acoustic emission showed that the fracture mechanism was tensile failure and that the crack started at the lower boundary of the framework. The fracture process could be followed both in step-by-step and step-in-step. SIGNIFICANCE: Based on the findings in the current study, the R-T(2D) code seems suitable for use as a complement to other tests and clinical observations in studying stress distribution, fracture mechanism and fracture processes in ceramic FPD frameworks.

Keyword
Numerical modeling; Dental ceramic; Fracture; Zirconia; Fixed partial denture
National Category
Biomaterials Science
Identifiers
urn:nbn:se:umu:diva-6508 (URN)10.1016/j.dental.2006.06.039 (DOI)17109952 (PubMedID)
Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2017-12-14Bibliographically approved
4. A 3D numerical simulation of stress distribution and fracture process in a zirconia-based FPD framework
Open this publication in new window or tab >>A 3D numerical simulation of stress distribution and fracture process in a zirconia-based FPD framework
Show others...
2011 (English)In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 96B, no 2, 376-385 p.Article in journal (Refereed) Published
Abstract [en]

In this study, a numerical approach to the fracture behavior in a three-unit zirconia-based fixed partial denture (FPD) framework was made under mechanical loading using a newly developed three-dimensional (3D) numerical modeling code. All the materials studied were treated heterogeneously and Weibull distribution law was applied to describe the heterogeneity. The Mohr-Coulomb failure criterion with tensile strength cut-off was utilized to judge whether the material was in an elastic or failed state. For validation, the fracture pattern obtained from the numerical modeling was compared with a laboratory test; they largely correlated with each other. Similar fracture initiation sites were detected both in the numerical simulation and in an earlier fractographic analysis. The numerical simulation applied in this study clearly described the stress distribution and fracture process of zirconia-based FPD frameworks, information that could not be gained from the laboratory tests alone. Thus, the newly developed 3D numerical modeling code seems to be an efficient tool for prediction of the fracture process in ceramic FPD frameworks.

Place, publisher, year, edition, pages
John Wiley & Sons, 2011
Keyword
ceramics, finite element analysis, fixed partial denture, fracture process, numerical simulation
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-38966 (URN)10.1002/jbm.b.31782 (DOI)000286169600023 ()
Available from: 2011-01-12 Created: 2011-01-12 Last updated: 2017-12-11Bibliographically approved

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