Enhancement of the adhesion between cobalt-base alloys and veneer ceramic by application of an oxide dissolving primer

Objectives

Uncontrolled formation of an oxide layer on base metal alloy surface impairs adhesion between the alloy and veneer ceramic. The aim of this study was to investigate the influence of an oxide dissolving primer on the adhesion between cobalt-base alloys and a veneer ceramic.

Methods

Combinations of two cobalt-base alloys (Bärlight/BL, Cara Process/CP) and one veneering ceramic (HeraCeram) were investigated. 40 rectangular specimens of each alloy were covered with the veneer ceramic; half of the alloy samples were treated with an oxide dissolving primer (NP-Primer) prior to veneering (n = 20). Subsequently, the veneering surface was ground flat and notched using the single-edge V-notched-beam method. Then specimens were loaded in a four-point bending test and the critical load to induce stable crack extension at the adhesion interface was determined, in order to calculate the strain energy release rate (G, J/m²). Finally, fracture surfaces of the specimens were evaluated by scanning electron microscopy (SEM).

Results

Strain energy release rates averaged between 24.1 J/m² and 28.8 J/m². While application of the primer statistically significantly increased adhesion between alloy and ceramic with the BL specimens (p = 0.035), no significant influence was found for the CP specimens (p = 0.785). For both material combinations, SEM analysis revealed enhanced wetting of the alloy surfaces with ceramic after application of the primer.

Significance

Application of an oxide dissolving primer increases the wettability of cobalt-base alloy surfaces and thus improves adhesion to veneering ceramics. This may enhance the long-term stability of bilayer restorations made from these materials.