title: A comparison of bond strength of layered veneering porcelains to zirconia and metal.
abstract: BACKGROUND
  High chipping rates of veneering porcelain for zirconia ceramic restorations have been reported in clinical studies. The information on the bonding behavior of veneering porcelain to zirconia frameworks is limited.
  
  
  OBJECTIVE
  This study assessed the relationship between coefficient of thermal expansion (CTE) and shear bond strength of veneering porcelain to zirconia frameworks.
  
  
  METHODS
  Zirconia ceramics (Katana; ZrO(2)), casting gold alloy (DeguDent U; DEG), and feldspathic porcelain (Cerabien ZR; CZR) were used as the bonding substrates. Five types of porcelain (CZR, Cercon ceramkiss (CER), IPS e.max Ceram (EMX), Vintage ZR (VZR), and VITA VM 9 (VM9)) were fired to ZrO(2) discs (n=8). Feldspathic porcelain (Super Porcelain AAA; AAA) designed for metal ceramic systems was fired to DEG discs. To evaluate the strength of veneering porcelain, CZR was veneered on CZR discs. The porcelain with a strong thermal mismatch for each substrate was applied; AAA and CZR were applied to ZrO(2) and DEG substrates, respectively. Shear bond strength was tested after 24 hours of water storage. Debonded surfaces were examined with an optical microscope and SEM. Data were analyzed with 1- and 2-way ANOVA followed by Dunnett and Tukey multiple comparison tests (α=.05).
  
  
  RESULTS
  No significant differences in the mean shear bond strength (MPa) were found between groups ZrO(2)-VZR (24.8), ZrO(2)-CZR (27.0), and ZrO(2)-VM9 (30.9). ZrO(2)-CER (22.0) (P=.017) and -EMX (22.1) (P=.020) groups had significantly lower bond strengths than the ZrO(2)-CZR group. ZrO(2)-CZR, -VM9, -CER, -VZR, and -EMX groups demonstrated cohesive failures in veneering porcelain. There was no significant difference among the groups ZrO(2)-CZR, DEG-AAA, and CZR-CZR. Two-way ANOVA showed that interaction between the 2 factors was significant (P<.001).
  
  
  CONCLUSIONS
  Strong discrepancies in CTE between veneering porcelains and zirconia significantly affect their bond strength.
authors.affiliation: Division of Applied Oral Sciences, Nihon University Graduate School of Dentistry, Tokyo, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Saito
authors.forename: Futoshi
authors.initials: F
authors.lastname: Komine
authors.forename: Markus B
authors.initials: MB
authors.lastname: Blatz
authors.forename: Hideo
authors.initials: H
authors.lastname: Matsumura
mesh_terms: D000704:Analysis of Variance; D003722:Dental Alloys / Q000737:chemistry; D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D003801:Dental Veneers; D006801:Humans; D008669:Metallurgy; D033081:Shear Strength; D018709:Statistics, Nonparametric; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; D003764:Dental Materials; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide