Effectiveness of adhesive systems for a Co-Cr removable partial denture alloy

In vitro bond strengths of traditional denture base acrylic resin (Lucitone 199) to a cobalt-chromium partial denture alloy (J.D. Partial Denture Alloy) were tested using two surface pretreatments (sandblast, sandblast and electrochemical etch) with three adhesive primers: Lee Metal Primer, Acrylic Solder, and CR Inlay cement. A sandblasted group with no primer served as the control.

The alloy specimens (8.0-mm bonding diameter) were cast and invested to receive a traditional denture base resin after surface treatments (sandblasted, and sandblasted-electrochemically etched) and application of adhesive primers. The bonded specimens were stored in distilled water at 37 degrees C for 24 hours and divided into two groups. The first group was debonded in tension on a testing machine at a cross-head speed of 0.05 cm/min. The second group was subjected to thermocycling of 1,000 cycles and then tested for tensile bond strength. The force at which the bond failed was recorded, and the bond strength was calculated in megapascals (MPa). The sites of bond failure were examined, quantified under (20x) magnification, and recorded. Ten specimens were evaluated for each experimental condition for a total of 160 specimens. Data were analyzed by ANOVA with a factorial design. Means were compared by Tukey intervals at the 0.05 significance level.

Significant differences in bond strength were observed, with primers being the most important factor, followed by pretreatment and storage and thermocycling with significant interactions. Sandblasted-electrochemically etched alloy with primers more effectively enhanced bond strength of the denture base resin to the treated alloy than sandblasted alloy with primers. Thermocycling had a greater effect on bond strength of the specimens with Acrylic Solder when compared with Lee and CR Inlay primers. The highest bond strengths (> or = 18.0 MPa) were observed for the conditions involving electrochemical etching and the priming with CR Inlay cement (both after 24 hours and thermocycling of 1,000 cycles). For primed specimens, the bond failures occurred cohesively within the primers or the denture resin and adhesively between the primers and the denture base resin, or between primers and alloy. For nonprimed, the bond failures occurred adhesively at the denture base resin-metal interface.

Nonprimed specimens (both sandblasted and electrochemically etched) had lowest bond strength (0.4 +/- 0.1 MPa; 0.3 +/- 0.4 MPa). The bond strengths of the primed treated specimens were improved significantly. The CR Inlay-treated specimens exhibited the highest bond strength (20.6 +/- 6.3 MPa). After thermocycling for 1,000 cycles, the bond strengths of the specimens were significantly lower than the bond strengths of the specimens after 24 hours.