Fractographic analyses of zirconia-based fixed partial dentures

Taskonak, Burak; Yan, Jiahau; Mecholsky, John J.; Sertgöz, Atilla; Koçak, Ayşe

doi:10.1016/j.dental.2007.12.006

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Volume 24, Issue 8 , Pages 1077-1082, August 2008

Fractographic analyses of zirconia-based fixed partial dentures

Burak Taskonak
- Department of Restorative Dentistry, Indiana University School of Dentistry, Indianapolis, IN, USA
- Corresponding author at: Department of Restorative Dentistry, Division of Dental Biomaterials, Indiana University School of Dentistry, 1121 West Michigan Street, Indianapolis, IN 46202, USA. Tel.: +1 317 274 3725; fax: +1 317 278 7462.
Jiahau Yan
- Department of Restorative Dentistry, Indiana University School of Dentistry, Indianapolis, IN, USA
John J. Mecholsky Jr.
- Department of Materials Science and Engineering, College of Engineering, University of Florida, Gainesville, FL, USA
Atilla Sertgöz
- Department of Prosthodontics, Marmara University College of Dentistry, Istanbul, Turkey
Ayşe Koçak
- Department of Prosthodontics, Marmara University College of Dentistry, Istanbul, Turkey

Received 22 June 2007; received in revised form 10 December 2007; accepted 24 December 2007.

Abstract

Objectives

Advances in ceramic processing techniques enable clinicians and ceramists to fabricate all-ceramic fixed partial dentures (FPDs) for posterior regions using high-strength yttria-stabilized tetragonal zirconia polycrystals (Y-TZP). However, failures occur in ceramic FPDs due to their design. The objectives of this study were to determine the site of crack initiation and the causes of fracture in clinically failed zirconia-based ceramic FPDs.

Methods

Five clinically failed four-unit Y-TZP-based FPDs (Cercon^® ceramics, DeguDent GmbH, Hanau, Germany) were retrieved and analyzed. The fragments containing the fracture origins in the veneers (Cercon^® Ceram S Veneering Ceramic, DeguDent GmbH, Hanau, Germany) of two samples were missing but the rest of veneer structures were present. The other three samples had their veneers intact. Fracture surfaces were examined using fractographic techniques, utilizing both optical and scanning electron microscopes (SEM). Quantitative fractography and fracture mechanics principles were used to estimate the stresses at failure.

Results

Primary fractures initiated from the gingival surfaces of connectors at veneer surfaces in four out of the five samples. However, critical flaw sizes could be measured in three of the five cases since fracture origins were lost in the remaining two due to local fragmentation at the crack initiation site. Delaminations between glass veneer and zirconia core were observed in Y-TZP-based FPDs and a secondary fracture initiated from the zirconia core. Secondary fracture controlled the ultimate failure. Failure stresses of the fixed partial dentures that failed due to zirconia fracture ranged from 379 to 501MPa. Fractures that had origins on the glass veneer surface had failure stresses between 31 and 38MPa.

Significance

Primary fractures in clinically failed Y-TZP-based FPDs initiated from the veneer surfaces. Interfacial delamination in glass veneer/zirconia core bilayer dental ceramic structures controlled the secondary fracture initiation sites and failure stresses in Y-TZP-based fixed partial dentures.

Keywords: Dental ceramic, Fracture surface analysis, Fractography, Zirconia, Fracture mechanics