title: Residual stresses in porcelain-veneered zirconia prostheses.
abstract: OBJECTIVE
  Compressive stress has been intentionally introduced into the overlay porcelain of zirconia-ceramic prostheses to prevent veneer fracture. However, recent theoretical analysis has predicted that the residual stresses in the porcelain may be also tensile in nature. This study aims to determine the type and magnitude of the residual stresses in the porcelain veneers of full-contour fixed-dental prostheses (FDPs) with an anatomic zirconia coping design and in control porcelain with the zirconia removed using a well-established Vickers indentation method.
  
  
  METHODS
  Six 3-unit zirconia FDPs were manufactured (NobelBiocare, Gothenburg, Sweden). Porcelain was hand-veneered using a slow cooling rate. Each FDP was sectioned parallel to the occlusal plane for Vickers indentations (n = 143; load = 9.8 N; dwell time = 5s). Tests were performed in the veneer of porcelain-zirconia specimens (bilayers, n=4) and porcelain specimens without zirconia cores (monolayers, n = 2).
  
  
  RESULTS
  The average crack lengths and standard deviation, in the transverse and radial directions (i.e. parallel and perpendicular to the veneer/core interface, respectively), were 67 ± 12 μm and 52 ± 8 μm for the bilayers and 64 ± 8 μm and 64 ± 7 μm for the monolayers. These results indicated a major hoop compressive stress (~40-50 MPa) and a moderate radial tensile stress (~10 MPa) in the bulk of the porcelain veneer.
  
  
  CONCLUSIONS
  Vickers indentation is a powerful method to determine the residual stresses in veneered zirconia systems. Our findings revealed the presence of a radial tensile stress in the overlay porcelain, which may contribute to the large clinical chip fractures observed in these prostheses.
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, 345 East 24th Street, New York, NY 10010, United States.
authors.forename: Marta
authors.initials: M
authors.lastname: Baldassarri
authors.forename: Christian F J
authors.initials: CF
authors.lastname: Stappert
authors.forename: Mark S
authors.initials: MS
authors.lastname: Wolff
authors.forename: Van P
authors.initials: VP
authors.lastname: Thompson
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D019245:Compressive Strength; D003442:Crowns; D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000379:methods*; D003801:Dental Veneers; D003830:Denture, Partial, Fixed; D006245:Hardness Tests; D013718:Tensile Strength; D015040:Zirconium
chemical_list: D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide