Use of contact testing in the characterization and design of all-ceramic crownlike layer structures: A review

Ceramic-based crowns, particularly molar crowns, can fail prematurely from accumulation of fracture and other damage in continual occlusal contact. Da mage modes depend on ceramic types (especially microstructures), flaw state s, loading conditions, and geometric factors. These damage modes can be sim ulated and characterized in the laboratory with the use of Hertzian contact testing on monolayer, bilayer, and trilayer structures to represent import ant aspects of crown response in oral function. This article reviews the cu rrent dental materials knowledge base of clinically relevant contact-induce d damage in ceramic-based layer structures in the context of all-ceramic cr own lifetimes. It is proposed that simple contact testing protocols that ma ke use of sphere indenters on model flat, ceramic-based layer structures-ce ramic/polymer bilayers (simulating monolithic ceramic crowns on dentin) and ceramic/ceramic/polymer trilayers (simulating veneer/core all-ceramic crow ns on dentin)-can provide useful relations for predicting critical occlusal loads to induce lifetime-threatening fracture. It is demonstrated that rad ial cracking from the lower core layer surface is the dominant failure mode for ceramic layer thicknesses much below I mm. Such an approach may be use d to establish a scientific, materials-based foundation for designing next- generation crown layer structures.