Polymerization shrinkage of microfilled composites determined by laser beam scanning

An He---Ne scanning laser beam was used to measure for the first time the linear shrinkage of light-cured microfilled composites. A low-power beam, which has a wavelength (632.8 nm) different from the polymerization wavelength (≈ 450 nm), was used. In these conditions no shrinkage is induced by the laser light. This method of measurement makes it possible to analyse small samples with a very low error (±1 μm). Five different materials were tested using 10–20 mg specimens, and the shrinkage process was examined in detail over 2 days. All these materials showed shrinkage of more than 50% of their original length after 1 min of irradiation and approximately 99% of the total shrinkage occurred 4 h after irradiation.