title: The Schwickerath adhesion test: A fracture mechanics analysis.
abstract: OBJECTIVE
  The Schwickerath three point bending adhesion test is the basis of the International Standard ISO 9693:1999 procedure for assessing porcelain bonding to metals [1]. It has also been used to evaluate the adhesion of porcelain to zirconia. The purpose of this paper is a fracture mechanics analysis of this test, which allows determination of the crack-length load-displacement and toughness dependence of cracks extending along or near the interface.
  
  
  METHODS
  Linear elastic mechanics is used to develop expressions for the strain energy and compliance of Schwickerath geometry specimens as a function of crack extension along or near the interface. From the derivative of the compliance as a function of crack growth the strain energy release rate (G, N/m) is determined.
  
  
  RESULTS
  The energy release rate for interface crack extension of Schwickerath geometry specimens is determined. It is found that a simple relationship between the minima of the force-displacement response and the strain energy release rate G exists. Further development enables the predicted force-displacement response as a function of crack length to be derived for different values of G. Experimental results of porcelain bonded to zirconia with and without notches of various lengths machined along the interface verify the expressions and analysis developed.
  
  
  CONCLUSIONS
  With the fracture mechanics analysis developed in this paper it is possible to determine the quality of adhesion in Schwickerath specimens by the interface toughness in addition to the nominal interface shear bond strength. As the toughness of brittle materials has much less scatter than its strength, the interface toughness characterization of the adhesion should allow for a better distinction between the adhesion quality of bonding.
authors.affiliation: Institute of Advanced Ceramics, Hamburg University of Technology, D 21073, Hamburg, Germany. Electronic address: g.schneider@tuhh.de.
authors.forename: G A
authors.initials: GA
authors.lastname: Schneider
authors.affiliation: Prosthetic Department, Freiburg University, D 29106 Freiburg, Germany; Biomaterials, Faculty of Dentistry, University of Sydney, NSW 2006, Australia.
authors.forename: M V
authors.initials: MV
authors.lastname: Swain
mesh_terms: D001840:Dental Bonding; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000379:methods*; D055119:Elastic Modulus; D008422:Materials Testing; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide
keywords: Adhesion; Dental materials; Fracture mechanics; Interfaces; Porcelain; Reliability; Schwickerath test; Zirconia