The influence of ultraviolet radiation intensity on curing depth of photo-activated composite veneering materials.

Light intensity and wavelength distribution affect post-cure properties of photo-activated composite materials. This study examined curing depth of composite veneering materials polymerized with a laboratory photo-curing unit for the purpose of evaluating the influence of ultraviolet radiation (UV) intensity on depth of cure. Three microfilled composite materials designed for prosthetic veneer were assessed. Two materials (Axis and Thermoresin LC II) were activated by both UV and visible radiation, whereas the other material (Dentacolor) was activated substantially by visible light. The light source of the photo-curing unit was a metal-halide lamp that radiates both UV and visible light. The unit was equipped with a removable UV-elimination filter capable of reducing the UV intensity from 1014.0 mW/cm2 to 574.0 mW/cm2. Each of the three materials was cured with the photo-curing unit for durations of 20, 30, 60 and 90 s both with and without the filter. The depth of cure of the materials was determined using a scraping technique described by the International Organization for Standardization (ISO 4049). Three-factor analysis of variance revealed that the depth of cure was influenced by the type of composite material, by the exposure period and also by the use of the filter (P < 0.01). Curing depth of one material (Thermoresin LC II) was significantly greater when the material was exposed without the filter than when the material was exposed through the filter. Among the three materials, the Axis composite demonstrated the greatest depth of cure regardless of exposure time period or filter use.