there will be times when one of these materials is better than the other but that is dependant upon the clinical situation. However in most cases the ease of use is deciding factor. Compomer Dental compomers are another type of white filling material although their use is not as widespread. Compomers were formed by modifying dental composites with poly-acid in an effort to combine the desirable properties of dental composites, namely their good aesthetics, and glass ionomer cements, namely their ability to release fluoride over a long time. Whilst this combination of good aesthetics and fluoride release may seem to give compomers a selective advantage, their poor mechanical properties (detailed below) limits their use. Compomers have a lower wear resistance and a lower compressive, flexural and tensile strength than dental composites, although their wear resistance is greater than resin-modified and conventional glass ionomer cements. Compomers cannot adhere directly to tooth tissue like glass ionomer cements; they require a bonding agent like dental composites. Compomers may be used as a cavity lining material and a restorative material for non-load bearing cavities. In Paediatric dentistry, they can also be used as a fissure sealant material. The luting version of compomer may be used to cement cast alloy and ceramic-metal restorations, and to cement orthodontic bands in Paediatric patients. However, compomer luting cement should not be used with all-ceramic crowns. Porcelain (ceramics) 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 inlays, onlays, 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 (Vitablock), lithium disilicate glass-ceramic (a ceramic crystallizing from a glass by special heat treatment), and