title: The effect of graded glass-zirconia structure on the bond between core and veneer in layered zirconia restorations.
abstract: OBJECTIVE
  The aim of this study was to test the hypothesis that a graded glass-zirconia structure can strengthen the core-veneer bond in layered zirconia materials.
  
  
  METHODS
  A graded glass-zirconia structure was fabricated by infiltrating glass compositions developed in our laboratory into a presintered yttria tetrahedral zirconia polycrystal (Y-TZP) substrate by the action of capillary forces. The wettability of the infiltrated glass and Y-TZP substrate was investigated by the sessile drop technique. The microstructures of the graded glass-zirconia structure were examined by scanning electron microscopy (SEM). The phase structure characterization in the graded glass-zirconia structure were identified by X-ray diffraction (XRD) analysis. The elastic modulus and hardness of the graded glass-zirconia structure were evaluated from nanoindentations. Further, the shear bond strength (SBS) of the graded glass-zirconia structure and veneering porcelain was also evaluated.
  
  
  RESULTS
  SEM images confirmed the formation of the graded glass-zirconia structure. Glass frits wet the Y-TZP substrate at 1200 °C with a contact angle of 43.2°. Only a small amount of t-m transformation was observed in as-infiltrated Y-TZP specimens. Nanoindentation studies of the glass-zirconia graded structure showed that the elastic modulus and hardness of the surface glass layer were higher than those of the dense Y-TZP layer. The mean SBS values for the graded glass-zirconia structure and veneering porcelain (24.35 ± 0.40 MPa) were statistically higher than those of zirconia and veneering porcelain (9.22 ± 0.20 MPa) (P<0.05).
  
  
  CONCLUSIONS
  A graded glass-zirconia structure can be fabricated by the glass infiltration/densification technique, and this structure exhibits a strong core-veneer bond.
authors: Department of Stomatology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China.
authors: Ruoyu
authors: R
authors: Liu
authors: The 1st Affiliated Hospital of Jinan University, Guangzhou 510630, China.
authors: Ting
authors: T
authors: Sun
authors: Department of Stomatology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China.
authors: Yanli
authors: Y
authors: Zhang
authors: Department of Stomatology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China.
authors: Yaokun
authors: Y
authors: Zhang
authors: State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Shanghai 200050, China. Electronic address: dyjiang@mail.sic.ac.cn.
authors: Danyu
authors: D
authors: Jiang
authors: Department of Stomatology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China. Electronic address: shaolongquan@smu.edu.cn.
authors: Longquan
authors: L
authors: Shao
mesh_terms: D005898:Glass / Q000737:chemistry*; D008422:Materials Testing; D055595:Mechanical Phenomena; D036103:Nanotechnology; D017155:Wettability; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide; C091417:yttria
keywords: Bonding properties; Dental ceramic; Functionally graded structure; Glass-infiltrated; Zirconia