| 1831 Fractographic techniques in evaluating ceramic crown clinical failures | ||
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J.B. QUINN, American Dental Association Foundation, Gaithersburg, MD, USA, G.D. QUINN, National Institute for Standards and Technology, Gaithersburg, MD, USA, J.R. KELLY, University of Connecticut, Farmington, USA, and S.S. SCHERRER, University of Geneva, Geneva 4, Switzerland Ceramic dental restorations are increasingly popular due to superior biocompatibility and esthetics, but are subject to brittle failure. One advantage of brittle failure is retention of the fracture surfaces without ductile deformation, enabling much information to be obtained through fractographic examination. Objectives: Develop successful fractographic techniques to perform failure analyses of ceramic crowns, and apply them to clinically failed restorations. Methods: Three clinical crown failures of different ceramic materials (Procera, Cerestore and Empress 2) were studied. Classical techniques were applied, and some new approaches were invented. Both optical and scanning electron microscopes were utilized independently and in group examination by four fractographers. Results: All three restorations, although of different materials, displayed many common fractographic features, the most important of which was wake hackle. Wake hackle occurs when an approaching crack front sweeps by a small bubble or other discontinuity in a brittle material. The crack procedes on slightly different planes as it passes the discontinuity on either side, and forms a trail or wake as the crack rejoins past the discontinuity. The resulting trails can be used to trace back crack progression from an intitial starting area. Wake hackle was found to be particularly common in the veneers, and the crack paths were traced from a core area outward in all three restorations. Another helpful fracture feature was compression curl, indicating flexural stress configurations. Some expected features such as fracture mirrors were not detected. Both types of microscopes were helpful, although more information was gained through optical microscopes because of the ability to use different lighting configurations. Conclusions: Fractographic failure analyses can be fruitfully performed on failed ceramic crowns utilizing a variety of techniques. Wake hackle and optical examination were the most helpful, and implicated hoop stresses as a major concern in restoration crown failures. | ||
| Seq #205 - Ceramics: Stresses, Geometry, Fractography 10:15 AM-11:30 AM, Friday, 12 March 2004 Hawaii Convention Center Exhibit Hall 1-2 | ||
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