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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.
