title: Adhesion of resin-modified glass-ionomer cements may affect the integrity of tooth structure in the open sandwich technique.
abstract: OBJECTIVE
  To study the interfaces between model cavities prepared in teeth and four glass ionomer cements (two conventional and two resin-modified).
  
  
  METHODS
  Ten non-cavitated molars and premolars were used and, in each, two 3mm deep slot preparations were created on opposing sides of the tooth. The teeth were conditioned as appropriate, then restored using the open sandwich technique, using a conventional glass ionomer (Fuji IX, Ketac Molar) or resin modified glass ionomer (Fuji II LC or N100), followed by completion with composite resin. The teeth were then embedded in a transparent acrylic resin and cut parallel to the long axis through both restorations, using a low speed diamond wheel saw. Samples were evaluated using a metallographic light microscope (100×). Three areas were assessed: the axial wall, the axial gingival line angle and the cavo-surface line angle. Bonding was categorized as inadequate or adequate based on the appearance and inadequate bonding was further studied and classified. Data were analysed statistically using the McNamara analysis.
  
  
  RESULTS
  The majority of materials failed to make adequate contact with the axial wall, and there were also flaws at the axial/gingival line angle in several samples. By contrast, the cavo-surface line angle was generally soundly filled and the materials showed intimate contact with the tooth surface in this region. The most serious inadequacy, though, was not lack of intimate contact and/or adhesive bond, but the presence of perpendicular cracks in 30% of the Fuji II LC samples which extended into the underlying dentin.
  
  
  CONCLUSIONS
  The problems of placement and dentin cracking experienced with these materials demonstrate that adhesive bond strength alone cannot be used as the criterion of success for restorative materials. In fact good adhesion can, in certain cases, promote cracking of the dentin due to stresses within the material, an outcome which is undesirable.
authors.affiliation: Department of Biomaterials and Experimental Dentistry, University of Medical Sciences, ul Bukowska 70, 60-812 Poznań, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Czarnecka
authors.affiliation: Department of Biomaterials and Experimental Dentistry, University of Medical Sciences, ul Bukowska 70, 60-812 Poznań, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Kruszelnicki
authors.affiliation: Department of Biomaterials and Experimental Dentistry, University of Medical Sciences, ul Bukowska 70, 60-812 Poznań, Poland.
authors.forename: Anthony
authors.initials: A
authors.lastname: Kao
authors.affiliation: Department of Biomaterials and Experimental Dentistry, University of Medical Sciences, ul Bukowska 70, 60-812 Poznań, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Strykowska
authors.affiliation: School of Sport, Health & Applied Science, St Mary's University College, Twickenham, Middlesex TW1 4SX, United Kingdom. Electronic address: john.nicholson@smuc.ac.uk.
authors.forename: John W
authors.initials: JW
authors.lastname: Nicholson
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000180:Acrylic Resins / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding / Q000379:methods*; D003737:Dental Cavity Preparation / Q000379:methods*; D003743:Dental Enamel / Q000648:ultrastructure*; D003764:Dental Materials / Q000737:chemistry; D003804:Dentin / Q000648:ultrastructure*; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D012117:Resins, Synthetic / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000180:Acrylic Resins; D003188:Composite Resins; D003764:Dental Materials; C444701:Filtek Z250; C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; D019279:Resin Cements; D012117:Resins, Synthetic; C110713:fuji IX; C110712:ketac-molar; C006903:carbopol 940
keywords: Adhesion; Bonding; Glass-ionomer; Tooth fracture