Methods: Twenty Ni-Cr alloy specimens and twenty porcelain fused metal specimens were fabricated. With the use of Clearfil Repair kits, specimens' surfaces were bonded to composite resin cylinders. Ni-Cr alloy specimens and porcelain fused metal specimens were randomly divided into A1, A2 groups and B1, B2 groups respectively. Then, specimens of group A2 and group B2 were thermocycled at 5°C to 55°C for 5000 cycles. After that, the shear bond strengths between surfaces and resins were measured and the fracture surfaces were evaluated with a stereomicroscope.
Results: Group B1 and group B2 showed significant higher shear bond strength than that of group A1 and group A2, group A1 had significant higher shear bond strength than that of group A2, and the shear bond strength of group B1 didn't statistically show different from that of group B2. Almost all specimens of group A1 and group A2 revealed adhesive failures, whereas those of group B1 and group B2 predominantly revealed cohesive failures in the porcelain layer.
Conclusions: The bonding strength between porcelain surface and resin shows significantly higher than the one between metal surface and resin. Intra-oral thermocycling can significantly decrease the bonding strength between metal surface and resin.