Test methodVideo-controlled characterization of polymerization shrinkage in light-cured dental composites

This study investigated a procedure to measure the intrinsic polymerization contraction of dental resin-based materials. A CCD-camera interfaced with a computer through video-interface hardware measured the coordinates of the centers of gravity of two dot markers stuck on a resin composite cylinder before and after the irradiation. The distances of the centers of gravity, and hence the linear percentage shrinkage, were calculated. The values obtained were compared with those measured by the deflecting disk technique [D.C. Watts, A.J. Cash, Determination of polymerization shrinkage kinetics in visible-light-cured materials: methods development, Dent. Mater. 7 (1991) 281-287.], which assessed polymerization shrinkage through deflection of a glass disk measured by an linear vertical displacement transducer (LVDT). Three resin composites, light-cured for 40 s at 800 mW cm−2, were tested: Solitaire 2 [SOL2], Tetric Ceram [TECE] and Z100 [Z100]. The data were subjected to the Kruskal-Wallis test (p < 0.05). Whatever the experimental procedure, the three resin composites did not present statistically different polymerization shrinkage, and data obtained with the video-controlled technique were statistically higher than with the deflecting disk method.