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 The interface can be dramatically enhanced with a coupling agent

Silane coupling agents, which are synthetic hybrid inorganic-organic compounds, are used to promote adhesion between dissimilar materials. They are good at promoting adhesion in silica-based materials such as porcelain. However, adhesion in non-silica-based restorative materials such as zirconia, metals and metal alloys is not satisfactory.

A solution to this problem may be surface conditioning of the restorative materials. Currently, a widely used surface-conditioning method in dentistry is tribochemical silica coating. After this treatment, a silica layer is formed on the surface so that the silane coupling agent can react chemically to form a durable bond with non-silica-based materials. Moreover, this treatment increases surface roughness, which will enhance micromechanical interlocking for bonding.

This review will discuss surface-conditioning methods and some new surface-conditioning techniques, silane chemistry, silane application in dentistry, and the limitations of silanes in adhesion promotion. The silane monomer most commonly used in clinical commercial products is 3-methacryloxypropyltrimethoxysilane. This is pre-hydrolysed in a solvent mixture usually consisting of ethanol and water that is acidified with acetic acid.

The shelf life for a single-bottle silane solution is relatively short. The solution will turn cloudy over time and cannot be used for adhesion. Two-bottle silane systems have been developed to offer a more stable system. One bottle contains an unhydrolysed silane in ethanol and the other one contains an aqueous acetic acid solution.[1] The two solutions are mixed for silane hydrolysis before use.