New mechanical retention method for resin and gold alloy bonding

Objective. The purpose of this study was to improve adhesion between dental adhesive resins and 14K gold alloy by creating a sponge-like structure on the alloy surface which enhanced mechanical bonding. Methods. The internal oxidation particles of Cu oxides precipitated on a 14K gold alloy surface after high-temperature oxidation at 800 °C in air were removed by pickling with an acid solution to create a sponge-like structure on the alloy surface. A PMMA resin containing 4-META as an adhesive monomer and a self-cured resin without 4-META were used to examine the effects of mechanical and chemical factors on bond strength. A thiophosphate-type metal primer (M-Primer II) was used in combination with 4-META resin to strengthen the chemical bonding of 4-META resin to the porous alloy surface. The surfaces of the alloy specimen treated by oxidation, pickling, and bonding with 4-META resin were analyzed using an electron probe X-ray micro-analyzer. Results. SEM observation showed many resin tags on the resin side of the bond structure after removal of the gold alloy matrix with aqua regia. The bond strength of 4-META resin to the porous alloy surface was 38±3 (mean±SD) MPa whereas that to a flat alloy surface with the same composition was 19±1 MPa. The bond strength of a self-cured resin without 4-META to the porous alloy surface was 24±2 MPa. Significance. A high bond strength was obtained when 4-META resin was bonded to the porous 14K gold alloy surface treated with M-Primer II.