Graded Zirconia Structures for Resistance to Chipping, Delamination, and Fatigue

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DESCRIPTION (provided by applicant): Ceramics are widely used in dental and orthopedic applications because of their esthetic value and chemical inertness. However, ceramics are vulnerable to fracture which accounts for millions of dollars annually in replacement costs and can cause significant patient discomfort and loss of productive lifestyle. Despite improvements in material properties, the performance of all-ceramic restorations still fails to match the 'gold standard' of metal-ceramic restorations. Our previous investigations have established relations between failure modes and restoration thickness, surface conditions, ceramic properties, and loading conditions. These findings indicate that monolithic glass-ceramic and veneered-alumina restorations are vulnerable to both occlusal sliding-contact damage and cementation bulk fracture, while the veneered zirconia restorations are prone to veneer chipping and delamination. These findings are consistent with clinical reports. Recent advances in theoretical and experimental work from our current NIDCR-supported project have demonstrated that veneer failure and bulk fracture may be substantially mitigated by controlled compositional gradients within the restoration layer. Such graded structures exhibit significantly higher resistance to sliding- contact damage and flexural bulk fracture relative to their homogeneous counterparts. In this competing renewal application we propose to elucidate enhanced resistance to chipping, veneer/core delamination, and mouth-motion fatigue of graded glass-zirconia materials with and without a thin veneer (0.3 mm) in both flat model structures and anatomically-correct geometries. This will bring us closer to a solution of a clinical problem-chipping, delamination, and fracture of ceramic restorations. Additionally, we propose to establish a simple but powerful edge-indentation technique to assess the toughness properties of graded laminates, a problem area that lies beyond the scope of current fracture testing protocols. We propose to achieve these objectives through three specific aims: 1. Quantify increased resistance to edge-chipping of graded zirconia structures using a novel edge-indentation technique; 2. Elucidate crack-interface interaction of graded zirconia structures using a novel crack growth technique and a conventional shear bond test; and 3. Determine resistance to fatigue damage of anatomically-correct glass/zirconia/glass graded structures with or without a thin porcelain veneer relative to commercial veneered and monolithic zirconia systems using a mouth-motion simulator in wet environments. Knowledge generated from this investigation will facilitate the development of smart glass-zirconia graded structures for next-generation dental and orthopedic prostheses with improved damage-tolerance, esthetics, and cementation properties. These improvements will lead to reduced morbidity of dental prostheses and cost of replacement to the public.