Bond strength between different bonding systems and densely sintered alumina with sandblasted surfaces or as produced

The traditional zinc phosphate cementation technique for crowns and fixed partial dentures (FPDs) is based on mechanical retention where the geometry of the prepared tooth provides retention for the restoration. In clinical situations where mechanical retention is compromised or regarded insufficient, a bonding system can be used to provide retention. This study investigates whether bond strengths of different bonding systems to densely sintered high-strength alumina ceramics are sufficient. One hundred twenty pairs of industrially manufactured specimens--one block and one cylinder-shaped disc of densely sintered alumina--were used. The cementation surfaces of the blocks were sandblasted with 110-microm aluminium oxide while the cementation surfaces of the discs were left untreated, as produced. The pairs were then bonded with one of six different bonding systems. Each bonding group of 20 samples was randomly divided into thermocycled and non-thermocycled subgroups (n=10). Both subgroups were stored 1 week in distilled water (37 degrees C). During this week, the thermocycled subgroup underwent 5000 thermocycles (5 degrees C-55 degrees C). Following pre-treatment, the specimens were loaded until fracture in a universal testing machine to determine shear bond strength. Data were analysed using student's t-test and a one-way ANOVA. Fractured interfaces were examined under a light microscope to classify the failure mode of the debonded area as adhesive, cohesive, or a combination of the two. The highest bond strengths, achieved with two of the bonding systems, were significantly higher than the remaining bonding systems, irrespective of pretreatment--(p>0.001). The predominant failure mode for both treated and untreated surfaces was adhesive. Two of the six tested bonding systems achieved sufficient shear bond strength to densely sintered alumina. Furthermore, recommendations on whether to use surface-treated or as produced densely sintered alumina must be based on which bonding system is being used.