Composite Fillings

These filling materials have reached a high degree of sophistication since their appearance on the dental scene in the early 1960s. A modern dental composite consists of a paste created by combining a mixture of dimethacrylate monomers and cross-linking agents with up to 80% by weight of silane coated, ceramic particles, whose sizes range from 0.04-4 microns. This composite paste is packed into a dental cavity and the dentist exposes it for about 30 seconds to intense visible blue light. The light activates a chemical initiator within the composite and the resins undergo free radical addition polymerisation via their vinyl groups, turning the paste into a durable, solid filling.

Composite Fillings Disadvantages:

These fillings have similar strengths to amalgam but they tend to wear away more rapidly. They also shrink as they polymerise, and efforts have to be made to prevent gaps forming between the composite and the tooth. Incremental packing and curing helps, but the dentist uses other techniques and other materials to help form a seal.

Bond between Resins and Teeth:

If enamel is present, its prismatic structure of apatite can be etched with phosphoric acid to produce mini chasms, into which the resin matrix material of a composite will flow. When this sets, it results in strongly retentive mechanical bonds. However, materials scientists have spent many hours seeking to produce a bond to the dentine, which exists below the layer of protective, inorganic enamel. Dentine is a wet, porous and sensitive combination of organic and inorganic materials, and current approaches to bond formation involve the use of primers containing bifunctional compounds. These have hydrophilic molecules at one end and hydrophobic ones at the other. The hydrophilic ends infiltrate the wet dentine and the hydrophobic ends form links with the resins in the composite, and so the composite is bonded to the dentine.