Ceramics

Dental Ceramics

Ceramic materials have the ability to emulate natural teeth, and they are some of the oldest dental materials, going back to 1792, when complete dentures were made from them. In 1996 they are used to create inlays, veneers, and crowns, as facings on metal substrates, and even as bridges, which can be made completely from high-strength ceramics. Restorations in ceramics are generally made by building up the correct aesthetic combinations of prefired, pigmented particles, and then re-firing under vacuum to sinter them together and eliminate voids.

Defeat of Brittle Nature of Ceramics

The developers are aware of their inherent brittle nature and have discovered many ways of interfering with the propagation of cracks within them. To this end, dispersion strengthening with alumina was the first approach. However, because of the opaque nature of the alumina, it is limited to the inner most structure of a crown, known to the dentist as a core. The cracks, which lead to catastrophic failure, nucleate at the internal interface between the prepared tooth and the ceramic crown. A high strength core can prevent the growth of these cracks and the strongest cores are currently made from either alumina. The toughest all-ceramic core produced so far actually infills any cracks in a high alumina base with molten glass during a firing stage in its production.

Glass Ceramics:

Glass ceramics are also used in several CAD/CAM applications in dentistry. In one of these a restoration is designed on a video image of a prepared tooth. It is then machined from a pre-fired block of glass ceramic. All of this takes place in front of the patient. As with all types of ceramic restoration, the machined unit is then coated with a silane bonding agent and cemented to the tooth with a resin-based cement. The tooth itself is also coated with an enamel/dentine bonding agent.