Surface microhardness of a resin composite exposed to pulse-delayed plasma arc lamp irradiation, in vitro.

Groups of samples of a light-activated resin composite were exposed, using a 3-step pulse-delayed protocol, to a plasma arc unit. Further groups were exposed with the light-curing guide positioned at increasing distances from the composite surface. The pulse-delayed protocol yielded a progressive increase in microhardness number at the end of each step but with a maximum mean value significantly less than the controls. Increasing the irradiation distance yielded a progressive and significant decrease in microhardness number.