Objectives: CoJet
® is a surface treatment system used to improve the bond between resin cements and both metals and ceramics, that can be used at the chairside by dentists. The aim of this study was to clarify the optimal conditions for use of this system with precious and non-precious metals.
Methods: 15 disk shaped specimens were made from each of a Nickel Chrome and a Gold alloy (Nicor and Argenco60S) using a loss of wax casting technique. They were mounted in resin blocks and lapped and finished to a high gloss. CoJet
® was used to sandblast the specimens' surfaces with the distance of the nozzle from the metal surface and the application time as variables. Columns of a resin cement (Nexus) were bonded to the treated metal surface following the manufacturer's instructions. The specimens were stored in distilled water at 37°C for 24 hours before testing. The shear bond strength was tested using an ISO standard test rig in an Instron Universal Testing Machine at a cross head speed of 1.0 mm min
-1. These data were analysed using ANOVA followed by Tukeys comparison of means and Weibull analysis.
Results: There were no significant differences between the bond strengths to either alloy with variation in distance of the nozzle from the metal surface. The highest bond strengths were achieved with 10 seconds blasting for the gold alloy and 20 seconds for the NiCr (p>0.05), extending the blasting time beyond this reduced the bond strength.
Conclusions: Within the limits of this study, the distance between the instrument tip and the specimen surface did not affect bond strengths. The time for blasting did have an effect with a peak bond strength after between 10 and 20 seconds. Extending the blasting time beyond this resulted in reduce bond strength.