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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