title: Evaluation of thermal compatibility between core and veneer dental ceramics using shear bond strength test and contact angle measurement.
abstract: OBJECTIVE
  To test the hypotheses that shear bond strength (sigma(s)) and contact angle (theta) are influenced by the thermal expansion/contraction behavior of bilayered all-ceramic systems.
  
  
  METHODS
  Glass-infiltrated ceramics (A - In-Ceram ALUMINA) and zirconia-reinforced alumina (Z - In- Ceram ZIRCONIA) were veneered with feldspathic ceramics (7 - VM7; 9 - VM9; 13 - VM13), yielding 6 experimental groups. Surface roughness (Ra) of A and Z core ceramic disks (12 mm diameter x 1.2 mm high) was measured to assure that values were similar. A cylinder of veneer (2 mm diameter x 2 mm high) was fired onto the center of all core disks, cooled under identical conditions and tested for sigma(s) to failure (n=20). For the theta evaluation (n=10) similar specimens (veneer 1 mm high) were overfired to develop an equilibrium theta that was then measured from digital images (AutoCAD 2006). Published thermal expansion data were used.
  
  
  RESULTS
  The mean values of sigma(s) (MPa) and theta (degrees) for the core-veneer ceramic groups were, respectively: A7 (19.4+/-4.7; 49+/-4.7); Z7 (23.4+/-6.2; 56+/-4.9); A9 (0.9+/-1.6; 55+/-5.8); Z9 (9.8+/-5.7; 59.8+/-2.9); A13 (0; 70+/-6.0); Z13 (0; 67.2+/-6.3). As the difference in coefficient of thermal expansion (coreveneer) increases, the theta value increases (r=0.95) and the sigma(s) value decreases (r=-0.92), p<or=0.01.
  
  
  CONCLUSIONS
  The contact angle measurement and the shear bond strength test of core-veneer ceramics are influenced by the thermal expansion behavior of these all-ceramic systems.
authors.affiliation: São Paulo State University, Department of Dental Materials and Prosthodontics, São José dos Campos, SP, Brazil.
authors.forename: Paula
authors.initials: P
authors.lastname: Benetti
authors.forename: Alvaro
authors.initials: A
authors.lastname: Della Bona
authors.forename: J Robert
authors.initials: JR
authors.lastname: Kelly
mesh_terms: D000537:Aluminum Oxide; D001840:Dental Bonding; D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D004055:Differential Thermal Analysis; D004548:Elasticity; D006358:Hot Temperature; D008422:Materials Testing; D033081:Shear Strength; D013499:Surface Properties; D014783:Viscosity; D017155:Wettability; D015040:Zirconium
chemical_list: D003776:Dental Porcelain; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide