Porcelain (ceramics)
All-ceramic Dental Onlay for a molar tooth[5]
Full-porcelain dental materials include Dental porcelain (porcelain meaning a high-firing-temperature ceramic), other ceramics, sintered-glass materials, and glass-ceramics as indirect fillings and crowns or metal-free "jacket crowns". They are also used as in-lays, on-lays, and aesthetic veneers. A veneer is a very thin shell of porcelain that can replace or cover part of the enamel of the tooth. Full-porcelain restorations are particularly desirable because their color and translucency mimic natural tooth enamel.
Another type is known as porcelain-fused-to-metal, which is used to provide strength to a crown or bridge. These restorations are very strong, durable and resistant to wear, because the combination of porcelain and metal creates a stronger restoration than porcelain used alone.
One of the advantages of computerized dentistry (CAD/CAM technologies) involves the use of machinable ceramics which are sold in a partially sintered, machinable state that is fired again after machining to form a hard ceramic. Some of the materials used are glass-bonded porcelain (Viablock), "lithium disilicate" glass-ceramic (a ceramic crystallizing from a glass by special heat treatment), and phase stabilized zirconia (zirconium dioxide, ZrO2). Previous attempts to utilize high-performance ceramics such as zirconium-oxide were thwarted by the fact that this material could not be processed using the traditional methods used in dentistry. Because of its high strength and comparatively much higher fracture toughness, sintered zirconium-oxide can be used in posterior crowns and bridges, implant abutments, and root dowel pins. Lithium disilicate (used in the latest Chairside Economical Restoration of Esthetic Ceramics CEREC product) also has the fracture resistance needed for use on molars.[6] Some all-ceramic restorations, such as porcelain-fused-to-alumina set the standard for high aesthetics in dentistry because they are strong and their color and translucency mimic natural tooth enamel. Not as aesthetic as porcelain-fused-to-ceramic, many dentists will not use new machine-made "monolithic" zirconia and lithium disilicate crowns on anterior (front) teeth.[7]
Cast metals and porcelain-on-metal are currently the standard material for crowns and bridges. The demand for full ceramic solutions, however, continues to grow.
Comparison
Composites and Amalgam are used mainly for direct restoration. Composites can be made of color matching the tooth, and the surface can be polished after the filling procedure has been completed.
Amalgam fillings expand with age, possibly cracking the tooth and requiring repair and filling replacement. But chance of leakage of filling is less.
Composite fillings shrink with age and may pull away from the tooth allowing leakage. If leakage is not noticed early, recurrent decay may occur.
Fillings have a finite lifespan: an average of 12.8 years for amalgam and 7.8 years for composite resins.[8] Fillings fail because of changes in the filling, tooth or the bond between them. Secondary cavity formation can also affect the structural integrity the original filling. Fillings are recommended for small to medium sized restorations.
Inlays and onlays are more expensive indirect restoration alternative to direct fillings. They are supposed to be more durable, but long-term studies did not always detect a significant lower failure rate of ceramic[9] or composite [10] inlays compared to composite direct fillings.
Porcelain, cobalt-chrome, and gold are used for indirect restorations like crowns and partial coverage crowns (onlays). Traditional porcelains are brittle and are not always recommended for molar restorations. Some hard porcelains cause excessive wear on opposing teeth.