Bonding of resin cements to post materials: influence of surface energy characteristics

1) To determine the surface energy characteristics of three variously treated post materials and two resin cements, and 2) to investigate if previously measured bond strengths between cements and treated posts could be related to the surface energy characteristics of the posts and cements.

The post materials were those of ParaPost XH, ParaPost Fiber White, and Cerapost, and the resin cements were ParaPost Cement and Panavia F. The post materials were surface treated by grinding, sandblasting, CoJet, or with Alloy Primer. Droplets of four reference liquids were placed on the surfaces and the contact angles measured. On this basis the dispersive, acid, and base components of the surface free energy of the materials were calculated. Then the thermodynamic work of adhesion between resin cements and treated post surfaces was calculated, as well as its dispersive and polar components.

It was found that the surface energy characteristics varied significantly between the investigated surfaces. The previously measured bond strengths correlated statistically significantly (p < 0.02) to the dispersive component of the work of adhesion between posts and cements (r = 0.53), to the dispersive component of the surface free energy of the posts (r = 0.54), and to the contact angle determined with ethylene glycol as reference liquid (r = -0.52), but not to other surface energy characteristics.

In spite of the significant correlations, the "explained" part of the variation in bond strength did not surpass 30%. This means that factors other than surface energy characteristics of adherend and adhesive play a role in determining the strength of the bond.