Glass ionomers Cements

First aesthetic, tooth-coloured filling materials appeared in 1930s. These were the silicate cements, which were formed when phosphoric acid displaced metal ions from a glass made from alumina, silica and several other metal oxides and fluorides. They set when aluminium phosphate was precipitated between the glass particles. These cements were used by dentists for half a century to fill cavities in front teeth, for not only did they match the colour and translucency of enamel and dentine, but they also acted as a source of fluoride. It was unusual to see dental decay recurring in any tooth they were used to fill. Similar cements also form when variations on this type of glass are exposed to polymeric acids which possess carboxylate groups. The acids displace metallic ions from the glasses and these cross-link the polymeric acid chains causing the cement to set. The acids also undergo ion exchange reactions with the apatite (calcium phosphate) crystals, which form part of both dentine and dental enamel. These glass ionomer cements, as they are known, thus form direct chemical bonds to teeth, without the need for the primers described above.
The basic cements lack the strength and resistance to wear that the dental composites have, and recent research has come up with resin-modified versions. These possess not only the carboxylate groups needed to form bonds to teeth, but also the light-curable dimethacrylate components present in the composite resins. Their durability is thus considerably enhanced.