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Fracture of Porcelain-veneered Structures in Fatigue

B. Kim, Y. Zhang*, M. Pines, and V.P. Thompson

Department of Biomaterials and Biomimetics, New York University College of Dentistry, 345 East 24th Street, New York, NY 10010, USA


Figure 1
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  		Figure 1. Schematic diagram of crack geometry for cyclic contact loading with a tungsten carbide (WC) spherical indenter on porcelain-veneered layered structure cement bonded to dentin: (a) porcelain layer fused to metal coping, and (b) porcelain layer fused to ceramic core. Indenter radius r at load P, contact radius a, for number of cycles n, in water. Occlusal surface crack modes, outer cone cracks (O), inner cone cracks (I), and median-radial cracks (M). Porcelain veneer internal surface radial cracks (R), resulting from yield of metal coping (YM) and dentin support (YD); and cementation ceramic core internal surface radial cracks (R), owing to yield of dentin support (YD).

 

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  		Figure 2. Optical micrographs illustrating damage sustained in d.SIGN porcelain layers (both translucent and opaque) fused to metal copings, cement-bonded to dental composite support (Z100) following P = 200 N cyclic loading with a sphere indenter (r = 3.18 mm) in water. Specimens were sectioned through the indentation site and polished for cross-sectional examination. d.SIGN porcelains on gold alloy coping after (a) n = 15,000, and (b) n = 25,000. d.SIGN porcelains on palladium-silver alloy coping following (c) n = 50,000, and (d) n = 400,000. Note inner cone cracks (I) and radial cracks (R).

 

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  		Figure 3. Cross-section of optical micrographs illustrating damage modes in (a) LAVA porcelain fused to LAVA zirconia core (n = 550,000). Thickness of the ceramic core is ~ 0.5 mm. Note inner cone cracks (I). Scanning electron micrograph of (b) a clinically fractured metal-ceramic crown abutment after 16 yrs in service, showing fracture initiated within the occlusal contact area, and (c) a similar failure in a 19-year-old bilayer ceramic crown (Cerestore, Coors, Boulder, CO, USA). In both (b) and (c), the crack extends to the gingival margin in these lingual views. SEM images were supplied by Susanne Scherrer and were prepared from clinical polyvinyl siloxane impressions of the crowns, which were cast with epoxy resin. The resulting replica samples were sputter-coated and examined in the SEM.

 




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