E20. Identify three key differences in using chemically activated composites and light-activated composites.

Polymerization shrinkage

Light-curable materials shrink toward the light source if thick layer has been placed and the marginal regions closest towards the light have been cured. However, by using very thin layers it is possible to achieve an instantaneous cure, which does not result in shrinkage toward the light source. In this case, a large number pf photons go instantaneously through the entire material thickness.

Cold-curable materials shrink toward the center of gravity

Working time

Light-curable materials "snap-set." Working time is almost unlimited

Cold-curable materials start setting as soon as they are mixed. However, because of the inhibitor (hydroquinone), the resin remains workable for a few minutes.

Air bubbles

Light-curable materials are rather free from air-bubbles because they are not mixed together as pastes. The cold-curable materials contain numerous air bubbles introduced during mixing of the two pastes