Compendium Supplement Bisco March 2010 : Page 3
Suh et al. Literature studies and unpublished internal research at Bisco Dental Products on pyrochemical and tribochemical bond- ing showed neither method offered improved bonding and they could be prone to degradation. However, other re- search has demonstrated tribochemical bonding with the use of primers improved bonding.19 CEMENTATION TO ZIRCONIA SUBSTRATES Glass ionomer cements have minimal bonding strengths to zirconia (4 MPa) and are susceptible to water degradation due to their chemistry.23-26 Phosphate monomers in self- adhesive cements have been proven to be effective for ad- hering to the non-silica-based polycrystalline materials of zirconia, alumina, and metal. Based on this knowledge, primers specific to zirconia, alumina, and metal were cre- ated. Numerous studies have shown phosphate monomers are promising chemical agents for improving zirconia bonding.17-20,27,28 The possible mechanism is the abil- ity of phosphate monomers to form chemical bonds with zirconia, alumina, and metal surfaces, and have polymer- izable resin terminal end groups (eg, methacrylate), which enable cohesive bonding to appropriate resin cements (Figure 1).28,29 Self-adhesive resin cements, such as BisCem, RelyX Unicem, and SmartCem 2, are dual-cured, contain orga- nophosphate monomers, and can be used when prepara- tion designs are fully retentive; however, these cements are hydrophilic due to the acidic resin components and have lower physical and mechanical properties than resin ce- ments. Self-adhesive resin cements differ in viscosity, smell, and self-curing efficiencies. Bond strengths are lower than those of bonded resin cements (with zirconia primer). How- ever, in retentive preparations, the ease of placement is a compelling benefit (Table 1). Self-adhesive resin cements may not be strong enough to be used alone on both surfaces (tooth and zirconia) when cementing a nonretentive zirco- nia restoration. Primers may be beneficial for improved ad- hesion of self-adhesive cements to zirconia. For slightly retentive or nonretentive designs, traditional adhesive protocols are time-tested and required. Optimiz- ing adhesive performance is the goal in less-than-retentive preparation designs and demands the use of dentin adhe- sives, including self-etch (ACE/All Bond SE, Bisco) or total- etch (All Bond 3), primers specific to zirconia/alumina/ metal (Z-Prime Plus), and the use of dual-cure hydrophobic resin cements (Duo-Link). Zirconia Zirconia Figure 1 Theoretical demonstration of how the hydrogen (-H) group of phosphate monomer interacts with the Zr-O group of zirconia and forms the phosphate monolayer on the zirconia surface. Table 1: Shear Bond Strength (SBS) of Self-Adhesive Resin Cements to Zirconia Cement BisCem SBS (SD), MPa 12.4 (2.6)b RelyX Unicem 6.2 (2.6)c SmartCem2 10.8 (3.0)b Z-Prime Plus/Duo-Link 23.0 (5.3)a Means and standard deviations (n = 8) of shear bond strength tested on sandblasted zirconia using Ultradent (www.ultradent.com) jig method with cement. Cements were self-cured for 10 mins at 37°C, then cured specimens were stored in 37° C water for 2 hours prior to shear bond tested. Results with same letter superscripts are statistically the same (P > .05). Compendium—Volume 31 (Special Issue 1) 3
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