Fracture Of Ceramic Materials For Dental Applications

All ceramic materials for dental applications still have a great interest among researches in dentistry and clinicians. The first ceramic materials were conventional feldspathic porcelains. Theimmense volume of amorphous phase in porcelains gives them outstanding optical properties to mimic the dental structure.
Nevertheless, the biggest problem of dental porcelains are brittle materials whichhave low values of fracture toughness and are extremely sensitive to slow crack growth phenomenon. [1]
In order to determinate how sensitive is these materials fracture analysis are performed. Thevalue of fracture toughness is calculated with the following formula:

KIC=η·EH18·σf·P1334

Where η is a geometrical constant, which depends upon crack and indenter shape, E is Young´s modulus, Pis impression load and H is hardness. [1]
The lower the fracture toughness is the bottom clinical reliability of the ceramic restoration because the KIC value defines the level of critical stressintensity at which catastrophic failure occurs due to micro fault. Thus there are several methods to measure the fracture toughness of different ceramic materials.
One way of analyzing the fracturetoughness can be looking indentation cracks, for example Vickers indentation cracks. During charging and discharging of a Vickers indenter two perpendicular cracks are initiated from location deeperdeformation zone that spread the material surface. So, the evidence seems very suitable indentation, particularly for the dental field, because measurements of the fracture toughness can be done directlyin the finished component, i.e. ceramic inlays, crowns and bridges.
In the table 1, we can see the fracture toughness evaluated by the bending test with different ceramic materials. With thatmethod we can be evaluated, from the maximum load and the dimensions of the specimen and the notch, the fracture toughness. [2]

Table 1. Results of the indentation method. [1]
Another method, which...