New method evaluates coupling agents bonding polymer to tooth mineral.

Polymerized test specimens consist of a Bis-GMA matrix and a filler of synthetic hydroxyapatite previously coated with the coupling agent under investigation. As the concentration of filler increases for a given coupling agent, the specimen's tensile strength decreases. The more effective the coupling agent, the less pronounced is the decrease. Application of the method is proposed for classifying coupling agents as well as providing a means for assessing the weakening effects of environmental exposure.