title: Evaluation of the interfacial work of fracture of glass-ionomer cements bonded to dentin.
abstract: OBJECTIVE
  The aim of this study was to investigate the interfacial work of fracture of conventional (C-) and resin-modified (RM-) glass-ionomer cements (GICs) bonded to dentin.
  
  
  METHODS
  One hundred and sixty five aries-free human molars were embedded in epoxy resin, sectioned and polished with 300- and 600- grit silicon carbide paper to remove enamel on the occlusal surface. Equilateral triangular-shaped plastic molds (4×4×4×5mm(4)) were clamped to the prepared dentin surfaces by a stainless steel test apparatus. Teflon tape was placed under one internal vertex of the mold to create a 0.1-mm notch at the material-dentin interface. Interfacial work of fracture (γwofint) in tensile fracture mode-I (opening) was determined for six C-GIC, three RM-GIC, and two GIC luting cements at a cross-head speed of 0.1mm/min and a crosshead distance (L) from the interface of 4.3mm. The debonded surfaces were evaluated for the predominant failure mode. SEM analysis of examples showing interfacial and notch areas was performed.
  
  
  RESULTS
  ANOVA and Tukey's post hoc test demonstrated the highest mean γwofint value (90.16±16.6J/m(2)) of one RM-GIC was significantly different (p<0.05) from the other materials. 'High viscosity' GICs achieved lower results with the lowest recorded at 20.4±10.1J/m(2). There was a significant difference observed (p<0.05) between the mean γwofint of luting C-GIC and luting RM-GIC. Although differences were observed between different material mean γwofint, when comparing groups no significant differences (p=0.181) were observed. For all groups, mixed GIC-interface failure (41%) was the most commonly observed, followed by cohesive failure in GIC (25%) and adhesive failure (20%). SEM analysis revealed that specimens generally fractured from the notch initiation point into the GIC or along the dentin-GIC interface.
  
  
  CONCLUSIONS
  Within the limits of this study, significant differences (p<0.05) were observed in the γwofint between different glass-ionomer materials. The null hypothesis that there is no difference in the γwofint among different glass-ionomer materials bonded to human dentin was rejected.
  
  
  CONCLUSIONS
  In the current study, the interfacial work of fracture (γwofint) of glass-ionomer adhesive interfaces has been reported using a simple method that can be used to study the fracture mechanics of an adhesive interface without the need for complicated specimen preparation.
authors.affiliation: Melbourne Dental School, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Australia. Electronic address: j.cheetham@student.unimelb.edu.au.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Cheetham
authors.forename: Joseph E A
authors.initials: JE
authors.lastname: Palamara
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Tyas
authors.forename: Michael F
authors.initials: MF
authors.lastname: Burrow
mesh_terms: D003804:Dentin; D017220:Dentin-Bonding Agents; D005899:Glass Ionomer Cements; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D012117:Resins, Synthetic
chemical_list: D017220:Dentin-Bonding Agents; D005899:Glass Ionomer Cements; D012117:Resins, Synthetic
keywords: Conventional glass-ionomer; Interfacial work of fracture; Resin-modified glass-ionomer; Work of fracture