Effect of photopolymerization variables on composite hardness

Statement of Problem. Variations in light-polymerizing parameters, such as light intensity and light-to-material distance, may affect the physical characteristics of polymerized resin. Purpose. The purpose of this study was to characterize the relation between total light energy and the final hardness of 4 composites polymerized under varying conditions. Material and Methods. Four commercial composite restorative resins (Z100, Filtek A110, Tetric Ceram, and Tetric Flow) were used to prepare 4 disk-shaped specimens (6 × 2 mm) for each experimental condition. Photoactivation was carried out with a light device and energy of 22.6, 15.7, 9.0, or 6.7 J/cm2. Either the light-to-material distance (0, 5, 10, 15 mm) or activation time (40, 28, 16, 12 seconds) was varied. Immediately after polymerization, Barcol hardness was determined on the specimen surface that had been exposed to the light. Analysis of variance (P.05) was found for the overall effect of the experimental variables (polymerization time and distance), but significant differences (P