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Silanes are good at promoting adhesion between resin composites and dental

Silane coupling agents are used in dental restoration, such as ceramic repairs of onlays, inlays, crowns and bridges. For most patients, repair is more economical and time-saving than the fabrication of new restorations, unless damage due to a fracture is beyond repair. The clinical procedure for repairing ceramic restoration usually involves the following steps: roughening the surface with diamond burs, sand-blasting the surface, acid etching, silanisation and finally bonding to resin composite.

A relatively new group of dental biomaterials, the glass fibre-reinforced composites, is used in fixed partial dentures, removable prosthodontics, periodontal splints and retention splints. The adhesion between the glass fibre and resin composite is improved by adding a silane coupling agent. The silane forms siloxane linkages with the surface hydroxyl groups of glass fibre. The organo-functional groups of silane react with the functional group in the resin composite. Thus, the bonding strength is increased between resin composite and glass fibre.

Nowadays, dental resin composites are composed of a resin matrix that contains monomers and cross-linking monomers, as well as a free-radical initiator, an inhibitor, colouring pigments, filler materials such as barium glass, silica, apatite and a silane coupling agent.The latter enhances the bonding between the filler particles and the resin matrix.The filler particles added to the resin matrix also improve the physical and mechanical properties of the resin composite. Moreover, the addition of fillers reduces volume shrinkage after polymerisation, and improves the aesthetic appearance and radiopacity.

Silanes are good at promoting adhesion between resin composites and dental restorative materials but there are some limitations to silane coupling agents.

The adhesion of silane coupling agents and non-silica-based restorative materials such as alumina, zirconia or metals is weaker than the silica coating of these materials.Therefore, a surface pretreatment with silica coating is required so that durable bonds (siloxane bonds) are formed between silane and silica-coated restorative materials. For noble metals or noble metal alloys, thione or thiol-based coupling agents are used to promote adhesion.These coupling agents have different bonding mechanisms with various dental restorative materials.