cosmetic dentistry_ beauty & science

review _ surface-conditioning I tance of 10 mm under an air pres- sure of 380 kPa for ten to 15 sec- onds.2 This process is intended to increase the surface roughness of the materials. It also enhances micromechanical retention for bonding.3 Pyrochemicalsilicacoating Over the years, several silica- coating systems have been used in dental laboratories. Briefly, they are Silicoater Clas- sical,SilicoaterMDandSiloc(allHeraeusKulzer)and PyrosilPen (SURA Instruments).2 In these systems, a tetraethoxysilane solution is injected into a flame and burned with butane in oxygen. The silane decomposes and forms reactive SiOx-C fragments, which are deposited on the substrate surface. A glass-like silica layer is thereby formed on the surface.4 The use of this surface treatment is not popular in clinical practice. Tribochemicalsilicacoating The tribochemical Rocatec system (3M ESPE) that uses silica-coated alumina particles was intro- duced in 1989. It isindicated for silica coating of ceramic and metal surfaces.5 It enhances the ad- hesion of a silane coupling agent to a silica-coated materialbyformingadurablesiloxaneSi-O-Sibond. This surface treatment also increases the surface roughness that provides micromechanical reten- tion for resin bonding, that is, for the resin to pen- etrate pores on the surface.6, 7 Hydrofluoricacidetching Hydrofluoricacidisnormallyusedtoetchporce- lain veneers and for intra-oral repair of fractured porcelain restorations before cementation.1 Low concentrations of 4 to 10 % hydrofluoric acid are usedinclinicalpractice.Whenaporcelainsurfaceis etched with hydrofluoric acid etching gel, the acid dissolves the glassy matrix of the porcelain. A mi- croscopically porous and micro-retentive surface is thus produced and micromechanical interlocking for resin bonding is enhanced.9 _New surface-conditioning methods The quest for enhanced and durable bonding continues.Severalnewsurface-conditioningmeth- odsarecurrentlyunderinvestigationglobally.These includelasersurfacetreatment9,10,selectiveinfiltra- tion etching11, nanostructured alumina coating12, internal coating14, chemical vapour deposition14 and plasma fluorination.16 Lasersurfacetreatment Laser stands for light amplification by stimulated emission of radiation and the technology was intro- ducedinthe1950s.Er:YAG,Nd:YAG,andCO2 lasersare used in dentistry for soft-tissue surgery and hard- tissuetreatmentandsurfacetreatment.10 Laserirradi- ation of a ceramic surface produces irregularities on thesurface,whichincreasethesurfaceroughnessfor mechanical retention.16 The main problem, however, of this surface treatment method is the formation of surface cracks owing to thermal effects of laser irra- diation at high power settings.10,16 Therefore, appro- priate laser settings for different ceramic surfaces is important to prevent formation of surface cracks. Selectiveinfiltrationetching In this method, a thin layer of a glass condition- ing agent is coated onto the zirconia surface and is then heated to above the glass transition tem- perature. The molten glass particles ma infiltrate between the surface grains. After this process, the specimensareallowedtocoolatroomtemperature. Theconditioningagentisthenremovedbyapplying hydrofluoric acid and rinsing it off. This creates a new retentive surface for resin–zirconia bonding.17 Nanostructuredaluminacoating Inthiscoatingmethod,thezirconiaisimmersedin asuspensionofaluminiumnitride.Aluminiumnitride undergoes hydrolysis to form boehmite, which is depositedontothezirconiasurface.Aheattreatment at 900 °C is carried out. Boehmite undergoes a phase transition to d-alumina. Through this treatment, a micro-retentive surface area is created that may increasemechanicalinterlockingforresinbonding.13 Internalcoatingwithporcelain The zirconia surface is sand-blasted with alu- mina particles of 70 µm in size. Then, the surface is coatedwithhighfusingporcelain,whichisprepared by stirring the porcelain powder into an excess amount of distilled water. The porcelain is fired at Fig. 2_The steric effect of alkoxy groups on silane hydrolysis using ball-and-stick models between butoxysilane and methoxysilane. I 31cosmeticdentistry 2_2013