The effect of metal primer application and Nd:YAG laser irradiation on the shear-bond strength between polymethyl methacrylate and cobalt-chromium alloy.

OBJECTIVE

The purpose of this study was to compare the shear-bond strengths (SBSs) of an acrylic resin and a cobalt-chromium (Co-Cr) alloy after applying a metal primer, Nd:YAG laser irradiation, or both to the sandblasted surface of the Co-Cr alloy.

BACKGROUND DATA

The serviceability of a removable partial denture (RPD) is dependent on the bond strength at the resin-alloy interface. No previously published studies exist on the use of Nd:YAG lasers for preparing the surface of a Co-Cr alloy in an RPD to obtain a high-strength bond between PMMA and the alloy.

METHODS

One-hundred twenty Co-Cr alloy specimens were sandblasted and randomly assigned to four equal groups: Group I, sandblasting; Group II, sandblasting + metal primer; Group III, sandblasting + Nd:YAG laser; and Group IV, sandblasting + Nd:YAG laser + metal primer. To establish the most appropriate fluence for modifying the surface of the sandblasted cast specimens, we conducted a preliminary study. Nd:YAG laser irradiation at a fluence of 46.9 J/cm(2) was selected. After the various surface treatments, each alloy specimen was embedded in PMMA to determine the SBS between PMMA and the alloy.

RESULTS

Group II and III specimens exhibited higher SBSs than did those of the Group I specimens (p < 0.05), and Group IV specimens showed higher SBSs than did those of the Group II and III specimens (p < 0.05). A significant difference existed in failure types among groups (p < 0.05). Failure type was predominantly adhesive for groups I and III, but predominantly mixed for groups II and IV.

CONCLUSIONS

Nd:YAG laser irradiation at a fluence of 46.9 J/cm(2) roughens the sandblasted surface of a Co-Cr alloy and increases the strength of the bond between PMMA and the alloy. This bond strength can be increased further by applying a metal primer to the laser-irradiated surface.