Edge-chipping Resistance of Zirconia, Glass-ceramic, and Porcelain

Objectives: Brittle materials are notoriously susceptible to edge-chipping fracture. The objective of this study is to quantify the resistance to edge-chipping of three major ceramic classes using a well controlled edge-chipping technique.
Methods: Monolithic bar-shaped specimens of zirconia, lithium disilicate and porcelain were prepared. They were first polished to 3µm finish. Then, the specimens were loaded at prescribed distances for edge-chipping test, using a Vickers indenter with its pyramid diagonals approximately parallel and perpendicular to the specimen edges. A constant loading rate of 0.1mm/min was utilized. Each specimen was chipped approximately twenty times; the corresponding critical loads were recorded as a function of indentation distance from the specimen edge. Mean force and standard deviation were calculated for each distance. The relationship between mean critical force (Fc) and edge distance (da) was plotted. Finally, edge toughness was determined using the slope of the linear portion on these graphs.
Results: Two significant results were obtained; (i) zirconia revealed over 5 and 4 times higher resistance to edge-chipping compared to lithium disilicate and porcelain, respectively; (ii) edge-toughness of these classical brittle materials can be accurately determined using sound fracture mechanics criteria.
Conclusions: The results of the current study have allowed us to have a better understanding of resistance to edge-chipping of various dental ceramics, providing design guidelines for ceramic dental prostheses.