Adhesion of resins to Ag-Pd alloys by means of the silicoating technique.

The purpose of the investigation was to study the effect of water storage on the bond strengths between silanized, silicoated Ag-Pd alloys and veneered composites, in comparison with the bond strengths of systems with conventional retention beads. Furthermore, the mechanism of the bonding was examined. The bond strength of silanized, silicoated dry specimens and similar specimens stored in water was measured by four-point bending. Water storage for 90 days at 37 degrees C reduced the bond strength by approximately 30% to about 15-20 MPa. Mechanical retention beads caused bond strengths of approximately 16-18 MPa which were unaffected by water storage. SEM and microprobe investigations showed that sandblasting with AI2O3 prior to silanization caused substantial numbers of cracks and porosities in the surface layer of the alloy, partly filled with Al2O3. Some particles of silicon oxide in these surface defects were produced by the flame-spraying of the so-called silicoating technique. Further painting of the surface with a silane adhesion primer provided chemical bonding to the composite at the densely spaced Si-O-H-containing silica particles. Many cracks were observed in the interfaces between these particles; thus, water is likely to penetrate the interface with time. The bond strength is most likely reduced by reaction between water and the composite/Si-O structure. The silicon oxide particles are probably attached to the alloy substrate by mechanical retention. Without sandblasting, no bonding was obtained by means of the silicoating technique.