title: The effect of a layer of resin luting agent on the biaxial flexure strength of two all-ceramic systems.
abstract: BACKGROUND
  The influence of a layer of resin luting agent on the longevity of glass-ceramic crowns has been demonstrated in some laboratory and clinical studies. The mechanisms of glass-ceramic crown failure and the influence of the resin luting agent layer are still not clearly understood.
  
  
  OBJECTIVE
  The objectives of this study were to examine the difference in biaxial flexure strength between 2 glass-ceramic dental materials and to examine the influence of a layer of resin luting agent on the characteristic strength of these materials.
  
  
  METHODS
  Thirty-seven disks, 15 mm x 1.5 mm, each of IPS Empress and IPS Empress2, were fabricated according to the manufacturer's recommendations. The surface of each disk underwent acid etching and silanation. The disks from each group were arbitrarily divided into 2 subgroups. One subgroup of each material type was selected to receive a thin (approximately 0.1 mm) layer of resin luting agent (Nexus 2), whereas the other subgroups remained unaltered. Each disk was loaded, with the treated surface down, using a ball-on-ring biaxial configuration in a universal testing machine. The failure loads (N) were recorded, and the biaxial flexure strength for each disk was calculated. Characteristic Weibull parameters and a +/-95% confidence interval were determined. A 2-way analysis of variance (alpha=.05) on transformed fracture strength data was used to determine significant differences between groups.
  
  
  RESULTS
  The Weibull characteristic strength of IPS Empress2 (213 MPa) was 75% higher than IPS Empress (122 MPa). The results also show that the application of a thin layer of resin luting agent significantly increased (P <.001) the characteristic strength of both IPS Empress and IPS Empress2 by 45.6% and 47.6%, respectively. The higher strength of the resin-coated specimens cannot be explained in terms of standard fracture mechanics alone.
  
  
  CONCLUSIONS
  Results suggested that IPS Empress had significantly lower characteristic strength than IPS Empress2. A relatively thin layer of resin luting agent bonded to both IPS Empress and IPS Empress2 significantly increased the characteristic strength of the ceramics.
authors.affiliation: The Ohio State University, College of Dentistry, Department of Restorative and Prosthetic Dentistry, Columbus, Ohio, USA. DublinDentalCare@SBCglobal.net
authors.forename: Roland P
authors.initials: RP
authors.lastname: Pagniano
authors.forename: Robert R
authors.initials: RR
authors.lastname: Seghi
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Rosenstiel
authors.forename: Rentong
authors.initials: R
authors.lastname: Wang
authors.forename: Noriko
authors.initials: N
authors.lastname: Katsube
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D003442:Crowns; D003738:Dental Cements / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D019279:Resin Cements / Q000737:chemistry*; D013718:Tensile Strength
chemical_list: D000538:Aluminum Silicates; D003738:Dental Cements; C075815:IPS-Empress ceramic; D019279:Resin Cements; D003776:Dental Porcelain