Microstructure and bonding of basic alloys to a resin cement

Objectives: To evaluate the microstructure of basic alloys used for metaloceramic crowns and the micro-shear bond strength [BS] of a dual-cure resin luting cement (Panavia, Kuraray) to some basic alloys. Methods: The basic alloys used in this study were: Suprem Cast V ([SC], Tilite, USA), Tilite Star ([TS], Talladium, USA), Wiron 99 ([W9], Bego, Germany), VeraBond II ([VBII], AalbaDent, USA), VeraBond ([VB], AalbaDent, USA), Remanium ([RM], Dentaurum, Germany) and IPS d.SIGN 30 ([IPS], Ivoclar Vivadent, Liechtenstein). Five wax patterns (13mm in diameter and 4mm high) were invested, and casted in a centrifugal casting machine for each basic alloy. The metal disks were embedded in acrylic resin, polished with a SiC paper (600 grit) and sandblasted with 110 microns aluminum oxide (15s). After cleaning of the metallic surfaces with isopropyl alcohol, five cylinders of the cement were placed to each alloy surface using a tygon tube (0.5mm high and 0.75mm in diameter). Excess resin was removed before light-curing. After storage (24h/37°C), the specimens were subjected to BS testing (0.5mm/min). The data was subjected to a one-way repeated measures analysis of variance and Tukey's test (alfa=0.05). The fracture surfaces were examined in a stereomicroscope (40X). After polishing down the same specimens, their microstructures were revealed with specific conditioners. Results: The highest BS values (mean/standard deviation [MPa]) were observed in the alloys which dendritic structure and eutetic formation with several domains: VB (30.6/1.7), TS (29.8/0.9), SC (30.6/1.7), exception made for IPS (31.1/0.9) which showed high BS but no eutectic formation. The W9 (28.1/1.5), VBII (25.9/2.0) and RM (25.9/0.9) showed the significant lowest BS with no eutetic formation. Most of the fracture modes were mixed (cement/adhesive). Conclusions: It seems that alloys with eutetic formation provide the highest micro-shear bond strength values to a dual-cure resin luting cement.