PARTIAL CERAMIC CROWNS . ESTHETIC AND TISSUE CONSERVATIVE RESTORATIONS – PART I : POSTERIOR TEETH occurred most probably due to expansion after water uptake by the hydrophilic material . 26 Extensive experience exists with the use of so-called dual cured luting composite materials together with the etch and rinse ( E & R ) adhesive technique followed by the use of self-adhesive luting materials . Luting composites Dye penetration studies with different luting materials have shown superior results in the critical areas ( approximal cavity floor in dentin ) with the use of a dual curing luting material and an E & R adhesive and of a self-adhesive material 21 , 31 as compared to compomers . The tested self-adhesive materials initially showed a white line along the luting space , which , however , disappeared after water storage . As ceramic thickness for partial crowns is mainly 1.5 mm or higher , dual curing luting composites are recommended . These materials contain a chemical initiating system , which is sensitive to protons 32 and thus dual curing luting composites should not be used with acidic monomers of self-etch ( SE ) adhesives . Exemptions are new universal adhesives ( see below ) or cases in which a separate dual cure activator is used . Luting composites used together with an E & R adhesive are the standard , showing good esthetics , high bond values both to dentin and to enamel and they provide greatest retention . 33 Self-adhesive luting materials These luting materials have been developed and marketed in order to facilitate luting by avoiding a separate pretreatment of dentin or enamel . Laboratory tests had shown that bonding of selfadhesive luting materials to dentin was as good as that with E & R and SE adhesives in combination with a composite luting material , whereas bonding to enamel was compromised . 34-36 Therefore , selective enamel etching was proposed to be used with selfadhesive cements . In a prospective , clinical split mouth study with 34 patients we compared the use of additional enamel etching to that with no separate etching for luting partial ceramic crowns with a selfadhesive luting material . After 6.5 years observation period , additional selective etching of enamel did not offer advantages concerning marginal staining , but revealed better retention rates . 37 However , etching of dentin should be avoided , because bond strength of self-adhesive cements to etched dentin is reduced . 38 Self-adhesive luting materials are comparatively simple to use and they enjoy a great popularity . A practical advantage is that so-called flash curing is possible : the material is cured for 2-3 seconds , then the surplus material can easily be removed and the final light curing is performed . However , appropriate ceramic pretreatment ( etching and silanization ) is still necessary and - as was outlined above – the bond strength to enamel is comparatively low ( selective enamel etch recommended ). Furthermore , desiccation of the dentin before luting should be avoided , because bond establishment and stability are impaired . 27 Universal adhesives Recently , a new group of adhesives has been introduced into the market , which can be used with resin-based composites in an E & R or in a SE mode ( with and without selective enamel etching ), and thus were named “ Universal Adhesives ”. These adhesives are also interesting for luting ceramic to tooth substances as some of the preparations also contain silane substances . The idea is that no separate silane application after ceramic etching is necessary . Universal adhesives contain acidic monomers . These normally interfere with dual cure luting composites ( see above ). However , one product ( Universal Bond , 3M ) was claimed to be compatible if used together with the respective dual cure luting composite from the same company ( RelyX Ultimate , 3M ), because this luting composite contains a proton scavenger . If other luting composites are used , a separate proton scavenger ( dual cure activator ) can be purchased and added . In a prospective clinical split-mouth study with 50 patients we tested the clinical outcome when using this universal adhesive with and without selective enamel etching compared to a self-adhesive luting material . 27 Forty-eight patients were evaluated clinically according to FDI criteria at baseline and 6 , 12 and 18 months . After 18 months , retention rates for the group with selective etching were slightly higher ( 97.6 %) than without ( 95.8 %). For both groups retention rates were significantly higher than for a self-adhesive luting material . From these – relatively short term – data it can be concluded that the new adhesives seem to work properly , especially together with the selective enamel etch technique . For all restorations in situ no difference in the clinical behavior ( e . g . marginal discoloration ) could be observed . The incorporation of a silane into the adhesive and the abandoning of a separate silanization procedure is discussed critically in the literature . Currently , a separate silanization procedure is advocated for . Resin coating technique / Ceramic Pretreatment Coating the cavity floors with a thin layer of a flowable resin-based composites prior to impression taking 31 as well as IDS – immediate dentin sealing – are advocated for to protect the freshly cut dentin
Review Articles
Figure 12 . Overview over luting materials partial ceramic crowns . Polycarboxylate cements and glass ionomer cements must not be used for luting PCCs from silicate / disilicate ceramics .
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