Page 4

How is polymerisation affected by the type of initiator system used?

In chemically-activated composite resin, the reaction takes place almost uniformly throughout the bulk of the material. In light-activated systems, the depth to which activation will occur is dependent on a number of factors. It is important to note that much of the resin not activated initially by the light at the time of curing will remain incompletely set. In both systems, a significant proportion of the methacrylate groups remain unreacted even after some hours. “degree of conversion” of double bonds 0.2 mm below the surface of an “optimally” light-cured composite is between 44% and 75%