title: Mechanical behavior of a bi-layer glass ionomer.
abstract: OBJECTIVE
  A high-viscosity consistency of the glass-ionomer cement (GIC) may lead to poor adaptation into the cavity. The use of a flowable GIC layer seemed to improve its adaptation in approximal restorations in vitro. In this study we assessed the flexural strength of a two-layered GIC, using a flowable GIC as a liner (two-layer technique). Additionally, finite element analysis on standardized bar-shaped models and on a representative tooth model was performed to rationalize the obtained results.
  
  
  METHODS
  The flexural strength and Young's modulus were calculated from the results of a three-point-bending test. Bar-shaped specimens were prepared either with a conventional GIC, with a flowable GIC (powder/liquid ratio 1:2), or with two-layers (either with the flowable layer down or on the top of the specimen). Three dimensional FEA models of the bar-shaped specimens and a model of tooth 46 provided information on the stress distribution of each component of the specimen and on the restoration.
  
  
  RESULTS
  The apparent flexural strength and Young's modulus of both two-layered groups were significantly lower than that of the conventional group. FEA showed that the layers of the two-layer specimens with the flowable GIC down separated from each other under load. The tooth model showed better stress distribution for the two-layer restorations.
  
  
  CONCLUSIONS
  The two-layer GIC showed inferior flexural strength, which might be explained by the detachment of the layers under load. Nevertheless the tooth model showed that the two-layer GIC provides a lower stress concentration on the occlusal surface of the material.
authors.affiliation: Department of Conservative and Preventive Dentistry, Academic Centre for Dentistry Amsterdam, Amsterdam, The Netherlands. Electronic address: C.Bonifacio@acta.nl.
authors.forename: Clarissa C
authors.initials: CC
authors.lastname: Bonifácio
authors.forename: Niek
authors.initials: N
authors.lastname: de Jager
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Kleverlaan
mesh_terms: D000180:Acrylic Resins; D001696:Biomechanical Phenomena; D003738:Dental Cements; D003793:Dental Restoration, Permanent; D020342:Finite Element Analysis; D012822:Silicon Dioxide
chemical_list: D000180:Acrylic Resins; D003738:Dental Cements; C015897:glass ionomer; D012822:Silicon Dioxide
keywords: Finite element analysis; Flexural strength; Glass ionomer; Young's modulus