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Zirconia as a biomaterial for odontological applications: effects of composition and manufacturing processes on fracture resistance
Umeå University, Faculty of Medicine, Department of Odontology, Dental Materials Science.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: Ceramics have long been amongst the most biocompatible materials known but their mechanical properties have limited their use. During the past few decades zirconia has aroused particular interest as a biomaterial because of its greater flexural strength, fracture resistance and toughness compared to other bioceramics. Technological inventions and developments have made the processing of zirconia-based ceramics possible and thus also the successful processing of dental restorations constructed from this type of material. The properties of zirconia-based ceramics can, however, be affected by, for example, shape, composition, manufacturing processes and subsequent handling. It was, therefore, of particular interest to study in what way recently introduced zirconia-based ceramics intended for odontological applications could be affected by the shape, manufacturing process, composition, grinding and veneering.

Methods: By means of newly invented and developed CAM-Software systems with improvements in grinding technology and strategy and hardware technology, cores for single crowns, fixed partial denture (FPD) frameworks and implant-supported abutments and copies were manufactured from a hot isostatic-pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic. In addition, zirconia-based ceramics intended for odontological applications but made from other compositions and/or using different manufacturing techniques were studied. The effects were determined of shape, composition, manufacturing process, heat treatment and veneering of the cores/frameworks on the fracture or bending resistance of various types of ceramic single crowns, FPD frameworks and implant-supported abutments and copies.

Results: Different thicknesses in different parts of HIPed Y-TZP cores improved the fracture resistance compared with cores of a uniform thickness resulting in a thicker veneer layer. Machining, heat treatment and veneering affected the fracture resistance of the zirconia-based ceramics studied. In addition, the quality of sintering and composition and type of veneering porcelain used influenced the fracture resistance of zirconia-based ceramics.

Conclusion: The results obtained indicate that zirconia-based ceramics have the potential for use as a material in odontological applications. The mechanical properties of zirconia ceramics are, however, affected by, among other things, the shape, composition, manufacturing processes and subsequent handling of the material. These findings have to be taken in consideration in the production processes of zirconia-based ceramic restorations. To further improve their function more studies are needed to elucidate the effects of various manufacturing and handling techniques on the properties of zirconia-based ceramics.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2010. , 50 p.
Series
Umeå University odontological dissertations, ISSN 0345-7532 ; 114
Keyword [en]
CAD/CAM, ceramics, HIPing, Mg-PSZ, veneering, Y-TZP, zirconia
Identifiers
URN: urn:nbn:se:umu:diva-37578ISBN: 978-91-7459-073-9 (print)OAI: oai:DiVA.org:umu-37578DiVA: diva2:369016
Public defence
2010-12-03, Sal B By1D, Norrlands universitetssjukhus, Umeå, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2010-11-12 Created: 2010-11-09 Last updated: 2010-11-15Bibliographically approved
List of papers
1. A comparison of fracture strength of yttrium-oxide-partially-stabilized zirconia ceramic crowns with varying core thickness, shapes and veneer ceramics
Open this publication in new window or tab >>A comparison of fracture strength of yttrium-oxide-partially-stabilized zirconia ceramic crowns with varying core thickness, shapes and veneer ceramics
2004 (English)In: Journal of Oral Rehabilitation, ISSN 0305-182X, E-ISSN 1365-2842, Vol. 31, no 7, 682-688 p.Article in journal (Refereed) Published
Abstract [en]

The fracture strengths of stylized all-ceramic crowns manufactured using an yttrium-oxide-partially-stabilized (Y-TZP) zirconia ceramic core (Denzir) veneered with lithium disilicate glass-ceramics (IPS Empress 2 or IPS Eris) were evaluated. The Denzir cores were manufactured in two ways: either with different thicknesses in different parts of the restoration, called an ‘adapted Denzir core’; or with a uniform core thickness of 0.5 mm. IPS Empress 2 all-ceramic crowns served as reference. There was no significant difference between the crowns with an ‘adapted Denzir core’ veneered with the two brands of glass-ceramics. No significant difference was seen between the crowns with a 0.5 mm Denzir core veneered with the two brands of glass-ceramics. The crowns with an ’adapted Denzir core’ exhibited significantly higher values than those with a 0.5 mm Denzir core and than the IPS Empress 2 crowns used as reference. No significant differences were seen among the IPS Empress 2 crowns used as reference and the crowns with a 0.5 mm Denzir core. The mode of failure varied among the Empress 2 crowns and the crowns with a core of a Y-TZP zirconia ceramic. Long-term studies are necessary to assess the clinical performance of this restorative system.

Keyword
All-ceramic crowns, CAD/CAM, Dental ceramics, Glass-ceramics, Fracture strength, Y-TZP, Zirconia
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-6431 (URN)10.1111/j.1365-2842.2004.01284.x (DOI)15210030 (PubMedID)
Available from: 2007-12-13 Created: 2007-12-13 Last updated: 2010-11-12Bibliographically approved
2. Fracture resistance of yttrium oxide partially-stabilized zirconia all-ceramic bridges after veneering and mechanical fatigue testing
Open this publication in new window or tab >>Fracture resistance of yttrium oxide partially-stabilized zirconia all-ceramic bridges after veneering and mechanical fatigue testing
2005 (English)In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 21, no 5, 476-482 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVES: Yttria-stabilized zirconia (Y-TZP) ceramic is a high-performance material with excellent mechanical properties suitable for fixed partial dentures. The purpose of this study was to evaluate after fatigue testing, the effect of heat-treatment and veneering on the fracture resistance of frameworks manufactured using sintered and subsequently hot isostatic pressed yttrium oxide partially-stabilized zirconia (Denzir).

METHODS: The specimens were subjected to dynamic loading in water. Thereafter, using a universal testing machine, the fracture resistance of three-unit fixed partial dentures was determined; (i) of the frameworks as delivered after machining, (ii) after the frameworks had been subjected to heat-treatment similar to veneering with a glass-ceramic (Eris) or a feldspar-based ceramic (Vita D) and (iii) after the frameworks had been veneered with these ceramics. In addition, the fracture resistance of frameworks as delivered after machining not subjected to dynamic loading in water was determined.

RESULTS: Cyclic loading in water did not significantly (p>0.05) affect the fracture resistance. The load necessary to fracture the frameworks as delivered after machining was significantly (p<0.001) higher than for the heat-treated and veneered specimens. No significant difference was seen between the specimens veneered with Eris and those veneered with Vita D (p>0.05). For all but three specimens the fractures were located in the loading point and through one of the connectors.

SIGNIFICANCE: Heat-treatment and veneering reduce fracture resistance of hot isostatic pressed zirconia. Nevertheless, the results obtained indicate that it is an interesting material for potential in all-ceramic restorations.

Keyword
All-ceramic bridges; Dental ceramics; FPDs; Fracture load; Y-TZP
National Category
Biomaterials Science
Identifiers
urn:nbn:se:umu:diva-15844 (URN)10.1016/j.dental.2004.07.013 (DOI)15826705 (PubMedID)
Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2010-11-12Bibliographically approved
3. Fracture resistance of all-ceramic zirconia bridges with differing phase stabilizers and quality of sintering
Open this publication in new window or tab >>Fracture resistance of all-ceramic zirconia bridges with differing phase stabilizers and quality of sintering
2006 (English)In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 22, no 8, 778-784 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVES: The mechanical properties of zirconia ceramics are affected of stabilizing oxides and quality of sintering. The purpose of this study was to investigate the fracture resistance of frameworks manufactured using prefabricated zirconia blanks with differing stabilizing oxides and quality of sintering.

METHODS: After dynamic loading in water, the fracture resistance was determined of stylized three-unit fixed partial dentures made of prefabricated homogenous ceramic green-body yttria-stabilized zirconia (Y-TZP) blanks (Vita YZ) or of densely-sintered magnesia partially stabilized zirconia (Mg-PSZ) blanks (Denzir-M); (i) as supplied from the manufacturer, (ii) after subjection to heat treatment in a way similar to veneering, and (Hi) after veneering with a feldspar-based ceramic.

RESULTS: After veneering, the load at fracture of the Vita YZ specimens was significantly higher (p<0.05) than that of Denzir-M. The load necessary to fracture Denzir-M as supplied after machining was significantly (p<0.05) higher than that of heat-treated Denzir-M, Vita YZ as supplied and heat-treated Vita YZ specimens. There was no significant difference (p>0.05) between the heat-treated and veneered Denzir-M specimens. For Vita YZ the load at fracture of the veneered specimens was significantly (p<0.05) higher than of those as supplied or heat-treated, whereas no significant difference (p>0.05) was seen between heat-treated Vita YZ and Vita YZ specimens as supplied.

SIGNIFICANCE: The fracture strength of the Vita YZ specimens increased considerably after veneering. Denzir-M and Vita YZ seem to be interesting alternatives for use as core materials in all-ceramic restorations. Long-term studies are, however, necessary before general clinical recommendations can be issued.

Keyword
CAD/CAM; Dental ceramics; FPDs; Fracture load; Mg–PSZ; PSZ; TZP; Vita In-Ceram 2000 YZ; Y-TZP
National Category
Biomaterials Science
Identifiers
urn:nbn:se:umu:diva-16176 (URN)10.1016/j.dental.2005.11.006 (DOI)16414111 (PubMedID)
Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2010-11-12Bibliographically approved
4. A study of the bending resistance of implant-supported reinforced alumina and machined zirconia abutments and copies
Open this publication in new window or tab >>A study of the bending resistance of implant-supported reinforced alumina and machined zirconia abutments and copies
2008 (English)In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 24, no 5, 611-617 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVES: The purpose of the present study was to evaluate the bending resistance of implant-supported CAD/CAM-processed restorations made out of zirconia or manually shaped made out of reinforced alumina.

METHODS: Units of abutments and copies made of (i) a prefabricated hot isostatic pressed (HIPed) yttrium oxide partially-stabilized zirconia (Y-TZP) (Denzir), (ii) a prefabricated densely-sintered magnesia partially stabilized zirconia (Mg-PSZ) (Denzir-M) or, copies made of (iii) a prefabricated partially-sintered, porous reinforced alumina ceramic (RN synOcta-In-Ceram) were subjected to static loading perpendicularly at the long axis. The abutments were attached to either stainless steel analogs or titanium implant fixtures. The Y-TZP and Mg-PSZ copies were bonded onto the ceramic abutments with a dual-cured resin composite (Rely-X Unicem). Units of titanium abutment attached to a titanium implant fixtures were used as reference.

RESULTS: The units comprising Denzir abutments as delivered (p<0.05) and heat-treated Denzir copies bonded to the Denzir abutments as delivered (p<0.01) and attached to stainless steel analogs exhibited significantly higher bending resistance than the control. The heat-treated Denzir copies bonded to the heat-treated Denzir M abutments attached to titanium implant fixtures and the In-Ceram specimens attached to stainless steel analogs showed significantly (p<0.05) lower bending resistance than the heat-treated Denzir copies bonded to the Denzir abutments as delivered and attached to stainless steel analogs. No statistically significant (p>0.05) differences were seen among the other groups studied.

SIGNIFICANCE: All the ceramic abutments and copies exhibited values that were equal or superior to that of the control and exceeded the reported value, up to 300 N, for maximum incisal bite forces. To assess the clinical behavior long-term clinical studies should be conducted.

Keyword
CAD/CAM, Dental ceramics, Dental implants, Mg-PSZ, Titanium, Y-TZP
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-16922 (URN)10.1016/j.dental.2007.05.021 (DOI)17681595 (PubMedID)
Available from: 2008-03-21 Created: 2008-03-21 Last updated: 2010-11-12Bibliographically approved

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