John W. Kumpula

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 specimens 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.

Application of Diffraction Gratings to Measurement of Strain of Dental Materials

Strains occurring on application of loads to small specimens of dental materials were determined by measuring the changes in the angle of the beams of light diffracted from gratings ruled on the specimens. The method gives a rapid response to stress and is effective over very short gauge lengths.