OBJECTIVES: Ceramics are attractive dental crown materials because of their superior aesthetics, bioinertness, etc. However, ceramics are brittle and subject to premature failure, especially in repeated contact loading and moist environments. In order to design longer-lasting ceramic crowns, there is a need to understand the fracture mechanism of these materials. METHODS: Two types of model crown systems were fabricated. To simulate the monolithic glass-ceramic crowns, soda-lime glass plates (d=1mm) were epoxy bonded to 12.5mm thick polycarbonate substrates. To simulate the veneer/core systems, soda-lime glass slides (d=1mm) were fused onto fine-grain alumina cores (d=0.5mm) and then epoxy bonded to polycarbonate substrates. Contact fatigue tests were accomplished by loading the specimen top surface with WC and glass spheres (r=1.6mm) in water. The entire crack evolution within the sample - from first sighting to ultimate failure - was recorded using a macro-video camera system. RESULTS: Damage initiation map and failure maps for the model crown systems have been constructed. Such maps have significant importance to identify the fracture modes in ceramic restorations. In the nominal biting force range (35–200N), classical cone cracks form before any other damage modes. These cracks do not propagate very deep into the material. Conversely, the inner cone cracks and occlusal-surface radial cracks, although forming much later, all have potential to penetrate the entire ceramic layer. In addition, cementation radial cracks can form in the thin crowns (d<1mm). CONCLUSION: Different damage modes dominate under given testing conditions. A mode which initiates first may not continue to dominate in prolonged cyclic loading. Occlusal-surface cracks, both radial and cone, are contact induced and can be suppressed by increasing the contact area. Cementation radial cracks are suppressed by using strong ceramic cores. Supported by NIDCR PO1 DE10976.

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