Depth of Polymerization in Photo Cured Composites and Microfilled Dental Restoratives: An in Vitro Study

Visible light cured composite and microfilled resins are being used with increased frequency in the dental profession. Several investigators have reported on overall depth of cure of various resin systems and characteristics of the curing lights. The information related to the variation in micro hardness at different locations on the surface and at different levels within the bulk is inadequate. The present investigation concerns itself with these two aspects. In the first part of the study specimens of four commercially available resins were prepared in nylon holders. The diameters of the specimens corresponded to those of their associated light tips. The curing was performed by positioning the light tip concentrically over the specimen. Knoop Microhardness Numbers were obtained at different locations on the surface of each specimen. Analysis of variance indicated that there were highly significant differences between the hardness values exhibited by different resin systems. The hardness values at different locations on the surface were not significantly different for individual resin systems. The second part of the study involved cylindrical specimens, with a diameter greater than those of the light tips, cured to varying depths for the different resin systems. These specimens were sectioned longitudinally and Knoop Hardness Numbers were different levels along their depths. Analysis of Variance indicated that the hardness values decreased with increasing depth for each resin system. The decrease in hardness was more pronounced around the periphery than in the central portion of the specimen