Objectives: Fe-Pt alloys have magnetic properties and can be cast using a dental casting machine. This study evaluated the bonding strengths of prosthetic composite to magnetic Fe-Pt alloy with four adhesive metal primers. Methods: Disk patterns (7.5 mm diameter, 2.0 mm thick) were cast from a custom-made Fe-Pt ingot (Fe-69.4wt%Pt-0.6wt%Nb) using a high-frequency centrifugal casting machine (Jelenko Eagle; Jelenko, NY). Cast discs were heat-treated according to the previous study (Watanabe et. al., JDR 81:172,2002) to obtain hard magnetic properties. After the adhesive surfaces were sandblasted with 50 µm Al₂O₃, they were primed with Metal Primer II (MP) (GC, Japan), Meta Fast Bonding Liner (BL) (Sun Medical, Japan),New Meta Color INFIS Opaque Primer (IN) (Sun Medical), or Epricord Opaque Primer (EP) (Kuraray, Japan). Prosthetic composite (New Meta Color INFIS; Sun Medical) was then polymerized. After the specimens were immersed in 37 °C. water for 24 hrs (Baseline, TC0), the shear bond strengths (n=7) were measured at a crosshead speed of 5.0 mm/min after 10,000 thermocycles (TC 10,000 at 4 °C. to 60 °C.). The data were statistically analyzed by ANOVA/Scheffe's test (a=0.05). Results: The bonding strengths [Mean (SD)] of TC0 and TC10000, respectively, were: MP [15.03 (2.83), 13.19 (2.34)]; BL [14.33 (3.62), 5.71 (2.26); IN [3.52 (1.40), 0.32 (0.47)]; EP [13.54 (3.98), 15.26 (5.54)]. Although IN showed the lowest strengths, there were no significant differences (P>0.05) in bond strengths among the other three primers (MP, BL, EP). The bonding strengths of MP and EP were slightly changed by thermocycling (p>0.05), but BL and IN underwent a significant decrease (p<0.05). Conclusions: The use of Metal Primer II and Epricord Opaque Primer is recommended when prosthetic composite is bonded to Fe-Pt alloy.

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