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Thursday, August 26, 2004 - 2:20 PM
SES 6A.3

Lifetime of All-Ceramic Dental Crowns

Y. Zhang, New York University College of Dentistry, New York, NY; B. R. Lawn, National Institute of Standards and Technology, Gaithersburg, MD

The full potential of esthetic ceramic-based dental restorations has not yet been realized. Processing and surgical induced damage, exacerbated by fatigue damage during normal chewing, can reduce the initial strength of inherently brittle materials. The present research aims to develop a fundamental understanding of damage initiation and accumulation in all-ceramic dental crowns and hence to predict reliability and lifetime of these components as a function of materials and fabrication variables. Five clinical relevant dental ceramics were selected for study as monolithic crown materials: a dense fine-grain alumina, an yttria-stabilized zirconia (Y-TZP), a potential crown material alumina-matrix composite (AMC), an Empress II and a d-sign porcelain. Hertzian contact tests, sphere indenter on ceramic crown/dentin-like polycarbonate substrate, were utilized to simulate the essential elements of occlusal function. Two modes of fatigue testing – dynamic and cyclic were conducted on ceramics with polished and sandblasted surfaces. In polished samples, the cyclic and dynamic data overlap each other, consistent with the slow crack growth model. The sustainable stress levels in Y-TZP and AMC are over twofold higher than alumina, Empress II and porcelain. In sandblasted samples, a reduction up to 30% in sustainable stress was observed under cyclic fatigue. The above analysis is then extended to a more complex veneer/core/dentin system, where porcelain veneer is fused onto strong ceramic core for aestheticism. By utilizing the preliminary single-cycle loading data, the cyclic fatigue behaviour of these trilayers can be predicted. Competing damage modes are expected in respect to different stages over 10-yr time span.