title: Shear bond strength of zirconia-based ceramics veneered with 2 different techniques.
abstract: BACKGROUND
  Delamination of veneering ceramic is reported as one of the most frequent problems associated with veneered zirconia restorations.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to compare the shear bond strength of sintered lithium disilicate to that of pressed fluorapatite glass-ceramic on a zirconia substrate.
  
  
  METHODS
  Thirty zirconia blocks (20×15×2.5-mm thick) were cut, sintered, and divided into 2 groups. A pressed group, a zirconia liner, was applied and sintered, and the lost-wax technique was used to fabricate fluorapatite glass-ceramic blocks (3×3×3 mm), which were pressed onto the sintered zirconia blocks. A sintered group, lithium disilicate blocks, were cut (3×3×3 mm) and sintered to the sintered zirconia blocks by using a low-fusing glass-ceramic. The thickness of the low-fusing glass-ceramic was standardized to approximately 80 μm prior to sintering. The shear bond strength levels of the specimens were tested using a universal testing machine at a crosshead speed of 1 mm/min until failure. Representative separated specimen surfaces were examined for fracture characteristics, using scanning electron microscopy at ×50 magnification. Debonding data were compared using a 2-tailed, unpaired Student t test (α=.05).
  
  
  RESULTS
  The sintered group demonstrated mean shear bond strength values (41.2 ±6.3 MPa), which were significantly higher (P<.001) than those of the pressed group (21.3 ±4.3 MPa).
  
  
  CONCLUSIONS
  Sintering of computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate ceramic achieved higher shear bond strength values than pressing fluorapatite glass-ceramic to zirconia substructure material.
authors.affiliation: Assistant Professor, Department of Oral Rehabilitation, Dental College of Georgia at Augusta University, Augusta, Ga. Electronic address: azaher@augusta.edu.
authors.forename: Ahmed M
authors.initials: AM
authors.lastname: Zaher
authors.affiliation: Associate Professor and Director, Graduate Prosthodontics, Department of Prosthodontics, Louisiana State University, School of Dentistry, New Orleans, La.
authors.forename: J L
authors.initials: JL
authors.lastname: Hochstedler
authors.affiliation: Professor and Section Director, Dental Materials, Department of Oral Rehabilitation, Dental College of Georgia at Augusta University, Augusta, Ga.
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Rueggeberg
authors.affiliation: Associate Professor, Department of Prosthodontics, Louisiana State University, School of Dentistry, New Orleans, La.
authors.forename: Edwin L
authors.initials: EL
authors.lastname: Kee
mesh_terms: D001031:Apatites; D002516:Ceramics; D003764:Dental Materials; D003776:Dental Porcelain; D003801:Dental Veneers; D008422:Materials Testing; D033081:Shear Strength; D013499:Surface Properties; D015040:Zirconium
chemical_list: D001031:Apatites; D003764:Dental Materials; C493120:lithia disilicate; D003776:Dental Porcelain; C023506:Glass ceramics; D015040:Zirconium; C025105:fluorapatite; C028541:zirconium oxide