Adhesion of GIC and RMGIC in the open sandwich technique

To study the interfaces between model cavities prepared in teeth and four glass ionomer cements(two conventional and two resin-modified).

Method:

Ten non-cavitated molars and premolars were used and, in each, two 3 mm 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, GC Fuji IX (A) or 3M ESPE Ketac Molar (B) or resin modified glass ionomer, GC Fuji II LC (C) or 3M ESPE N100 (D), followed by composite resin restoration. The teeth were embedded in 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 (x100).   Three areas were assessed: axial wall, axial gingival line angle and 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. 

Result:

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 cavosurface line angle was generally soundly filled and the materials showed intimate contact with the tooth surface in this region.  The most serious inadequacy was not lack of intimate contact and/or adhesive bond, but presence of perpendicular cracks in 30% of group C samples, which extended into the underlying dentin.

Conclusion:

Problems of placement and dentin cracking experienced with these materials demonstrate that adhesive bond strength alone cannot be used as the criterion ofsuccess 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.