Marginal toughness of bonded dental ceramics evaluated by determination of the crack length

Objectives The objective of this study was to evaluate the toughness of dental ceramics near a bonded interface using indentation microfracture. Methods The ceramics used in the present study were two leucite-reinforced ceramics (IPS Empress and Finesse), one lithia-based ceramic (IPS Empress 2) and one mica-based ceramic (OCC). The ceramic discs were processed according to the manufacturers instructions and were bonded to resinous discs using a resin composite cement. The bonded specimens were sectioned perpendicularly, and micro-Vickers indentations were imprinted at several distances from the bonded interface in the polished ceramic sections. The lengths between the two ends of the radial cracks along the bonded interface were measured. Results Crack lengthening was recognized when the distance was within 70 μm. In each ceramic, the indentation crack length at 40 μm from the interface was significantly longer than the length at the inner point of the ceramic material (p<0.05). The order of the mean indentation crack lengths at 40 μm was OCC>Finesse>IPS Empress 2>IPS Empress, while the order at 490 μm was Finesse>OCC>IPS Empress>IPS Empress 2. There was a difference between the orders at 40 μm and at 490 μm. Significance The behaviour of the indentation crack near the interface differs from that which is distant from the interface. Therefore, it is impossible to estimate the marginal toughness of the ceramic based on the indentation microfracture at the inner point of the ceramic.