cosmetic dentistry_ beauty & science

_In dental restorations, it is desirable to have durableandstrongbondingbetweenresincompos- ite and dental restorative materials. Weak bonding at the interface can be dramatically enhanced with a coupling agent. Silane coupling agents, which are synthetic hy- brid inorganic-organic compounds, are used to promote adhesion between dissimilar materials. Theyaregoodatpromotingadhesioninsilica-based materials such as porcelain. However, adhesion in non-silica-based restorative materials such as zir- conia, metals and metal alloys is not satisfactory. A solution to this problem may be surface con- ditioning 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 ma- terials. 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. Thisispre-hydrolysedinasolventmixture 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 anunhydrolysedsilaneinethanolandthe otheronecontainsanaqueousaceticacid solution.1 The two solutions are mixed for silane hydrolysis before use. _Surface-conditioning methods The surface conditioning of restorative materi- als is an important preliminary step in clinical prac- tice to modify surface properties for durable and hydrolyticallystableadhesion.Thesurfacepretreat- ment methods widely used in dental technology are grit blasting, tribochemical silica coating and hydrofluoric acid etching, which will be discussed briefly in the following section. Gritblasting The surface of materials such as metals, alloys and some ceramics is sand-blasted with alumina particles of 110 µm in size at a perpendicular dis- 30 I I review _ surface-conditioning cosmeticdentistry 2_2013 Fig. 1_Thesilane hydrolysis mechanism. Silane coupling agents and surface conditioning in dentistry Authors_Drs Christie Ying Kei Lung & Jukka Pekka Matinlinna, Hong Kong