Optical density and depth of cure in visible light-cured filled-resin dental restorative materials

Abstract

The identification of the correct exposure (irradiance × time, I.t) of a direct-placement, visible light-cured, filled-resin dental restorative material in order to achieve “complete” reaction is of continuing concern. Essentially, in order to attain the intended set of mechanical properties, and thus (presumably) maximize the service life of the restoration, the degree of conversion of reactable vinyl groups must also be maximized. This involves, typically, a diketone-amine photosensitized free-radical polymerization system, irradiated by light of wavelengths in the region of 400 – 500 nm, and then in which a kinetically-complicated series of processes occur in a highly viscous, non-isothermal medium, approaching the glassy state as reaction proceeds. Reaction does not come to a stop on cessation of irradiation but continues for some time afterwards. There is economic pressure on the dentist to minimize the time spent performing the irradiation, and thus a concomitant drive to increase the irradiance to achieve this, frequently on the erroneous assumptions that total energy is the criterion and that reciprocity holds