title: Laminated ceramics with elastic interfaces: a mechanical advantage?
abstract: OBJECTIVE
  As CAD/CAM technologies improve we question whether adhesive lamination of ceramic materials could offer mechanical advantages over monolithic structures and improve clinical outcomes. The aim was to identify whether an adhesive interface (a chemically cured resin-cement) would influence the biaxial flexure strength (BFS) and slow-crack growth in a machinable dental ceramic.
  
  
  METHODS
  Monolithic and adhesively laminated (with a chemically cured dimethacrylate resin-cement) feldspathic ceramic discs of identical dimensions were fabricated. BFS testing was performed on the Group A monolithic specimens (n = 20), on Group B laminated specimens with the adhesive interface positioned below the neutral bending axis (n = 20) and Group C laminated specimens with the adhesive interface positioned above the neutral bending axis (n = 20). To study subcritical crack growth additional laminated specimens received controlled indentations and were exposed to thermo-mechanical fatigue. BFS data was analysed using parametric statistics (α = 0.05). Fractographic analyses were qualitatively assessed.
  
  
  RESULTS
  No significant differences between the mean BFS data of Groups A and B were observed (p = 0.92) but the mean BFS of Group C was slightly reduced (p < 0.01). Lamination reduced the stiffness of the structure and fractographic analysis demonstrated that energy consuming crack deflection occurred. Thermo-mechanical fatigue caused subcritical extension of radial cracks associated with indentations adjacent to the adhesive interface. Crack growth was limited to parallel to the interface and was arrested or deflected in a direction normal to the interface.
  
  
  CONCLUSIONS
  Ceramic lamination increased the damage tolerance of the structure and could limit or arrest subcritical crack growth at regions near the 'interlayer'.
  
  
  CONCLUSIONS
  Lamination of a dental ceramic with a polymeric 'interlayer' could offer toughening effects which could potentially delay or arrest sub-critical crack growth at regions near the interface and thereby improve restoration longevity.
authors.affiliation: Biomaterials Unit, University of Birmingham School of Dentistry, St. Chad's Queensway, Birmingham B4 6NN, UK; Dental Materials and Prosthodontics Unit, Sao Jose dos Campos Dental School, Institute of Technology and Science, SP, Brazil.
authors.forename: Anna Karina F
authors.initials: AK
authors.lastname: Costa
authors.affiliation: Biomaterials Unit, University of Birmingham School of Dentistry, St. Chad's Queensway, Birmingham B4 6NN, UK.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Kelly
authors.affiliation: Materials Science Unit, Dublin Dental University Hospital, Lincoln Place, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Garry J P
authors.initials: GJ
authors.lastname: Fleming
authors.affiliation: Dental Materials and Prosthodontics Unit, Sao Jose dos Campos Dental School, Institute of Technology and Science, SP, Brazil.
authors.forename: Alexandre Luiz S
authors.initials: AL
authors.lastname: Borges
authors.affiliation: Biomaterials Unit, University of Birmingham School of Dentistry, St. Chad's Queensway, Birmingham B4 6NN, UK. Electronic address: addisono@adf.bham.ac.uk.
authors.forename: Owen
authors.initials: O
authors.lastname: Addison
mesh_terms: D000268:Adhesiveness; D001696:Biomechanical Phenomena; D003776:Dental Porcelain / Q000737:chemistry; D003801:Dental Veneers; D008422:Materials Testing; D012117:Resins, Synthetic
chemical_list: D012117:Resins, Synthetic; D003776:Dental Porcelain
keywords: Bi-axial flexure strength; CAD/CAM; Elastic interface; Fractography; Lamination