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Materials Design of Ceramic-based Layer Structures for Crowns

¹ Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8500;
² Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD 20742-2115; and
³ University of Medicine and Dentistry of New Jersey, Dental School, 110 Bergen Street, Newark, NJ 07103-2400;

View larger version (29K): [in a new window]   Figure 1. Schematic of brittle layer of thickness d and modulus EC on a compliant substrate of modulus ES, depicting sphere indenter of radius ri. (Specimen radius rc in general relation Eq. 1a is effectively infinite in the flat layer structure depicted here.) Damage modes: surface cone cracks (C); quasi-plastic yield zone (Y); inner-surface flexural radial cracks (R).

View larger version (152K): [in a new window]   Figure 2. Radial crack sequence in glass-infiltrated alumina layer, thickness d = 155 µm, on polycarbonate substrate, from indentation with WC sphere of radius r = 3.96 mm. Sequence during loading cycle at (a) P = 15.1 N (critical), (b) P = 35.1 N (intermediate), (c) P = 56.6 N (peak), and (d) P = 0 N (fully unloaded).

View larger version (24K): [in a new window]   Figure 3. Critical load for first damage as function of layer thickness d, for ceramic/polycarbonate bilayers indented with WC spheres. (a) Results for zirconia, alumina, and porcelain specimens, fixed sphere radius r = 3.96 mm. Filled symbols are PR data (R), unfilled symbols are PC data (C) or PY data (Y). Minimum n = 5 indentations each data point, standard deviation limits shown (some less than the size of the symbol). Solid lines are theoretical first-damage predictions for radial and cone cracking or quasi-plasticity. (Regression fits not shown.) (b) Predictions from Eq. 4 for hypothetical Dicor/polycarbonate bilayers, sphere radii r = 4 mm and 2 mm. Inclined lines—radial cracking (R); horizontal lines—cone cracking (C) or quasi-plasticity (Y). Shaded line represents a nominal occlusal load of 100 N, dashed vertical line indicates the corresponding thickness ( 0.3 mm) at which this load will induce flexural radial cracking.