title: Influence of surface characteristics of four silica-based machinable ceramics on flexural strength and bond strength of a dual-curing resin luting agent.
abstract: OBJECTIVE
  The aim of the present study was to evaluate the crystalline phase and microstructure of 4 commercial machinable ceramic blocks--Cerec Vitablocs Mark II (Vita), ProCAD (Ivoclar/Vivadent), GN-I (GC), and GNCeram (GC)--and compare flexural strength and shear bond strength between a dual-curing resin luting agent and the ceramics treated with a silane coupling agent.
  
  
  METHODS
  Specimens were examined using scanning electron microscopy/energy-dispersive x-ray spectroscopy, and x-ray diffractometry. Three-point bending tests were performed with polished specimens 20 mm long, 4 mm wide, and 1.2 mm thick. Two differently shaped specimens for each of the 4 machinable ceramics were treated with a silane coupling agent. The specimens were then cemented together with a dual-curing resin luting agent. Half of the specimens were stored in water at 37 degrees C for 24 h and the other half were thermocycled 20,000 times.
  
  
  RESULTS
  Chemical composition, crystalline phase, and crystallinity were significantly different between brands. The Vitablocs Mark II material had the significantly lowest flexural strength (101.7 +/- 15.3 MPa), while the GNCeram material had the highest (174.8 +/- 10.3 MPa). The use of a silane coupling agent yielded high shear bond strength after 20,000 thermocycles (Vitablocs Mark II: 37.7 +/- 3.7 MPa, ProCAD: 41.2 +/- 3.1 MPa, GNCeram: 50.2 +/- 2.1 MPa), except with the GN-I material (23.9 +/- 4.4 MPa).
  
  
  CONCLUSIONS
  It appeared that crystal distribution and particle size of leucite crystal, not crystallinity, in the feldspar glass matrix of silica-based machinable ceramics might influence the flexural strength and efficacy of a silane coupling agent in bonding between a dual-curing resin luting agent and machinable ceramics.
authors.affiliation: Division of Applied Prosthodontics, Nagasaki University, Graduate School of Biomedical Sciences, Nagasaki, Japan. keiichi@nagasaki-u.ac.jp
authors.forename: Keiichi
authors.initials: K
authors.lastname: Yoshida
authors.forename: Xiangfeng
authors.initials: X
authors.lastname: Meng
authors.forename: Kohji
authors.initials: K
authors.lastname: Kamada
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Atsuta
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D002516:Ceramics / Q000737:chemistry*; D018583:Pliability; D033081:Shear Strength; D012821:Silanes / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000538:Aluminum Silicates; D012821:Silanes; C078519:leucite