Effect of energy density on color stability in dental resin composites under accelerated aging

The effects of the energy density that is used for polymerization on properties of dental resin composites are well known. However, few studies relate color stability to this factor. The aim of this study was to assess color changes (deltaE*), in vitro, in terms of accelerated aging under UV exposure of specimens prepared with different energy densities. Four commercial dental resin composites were included in the study. Thirty six specimens were prepared for each one of them, following the procedure established by ISO 4049 Standard, and assigned to three groups: A (3.75 J/cm2), B (9 J/cm2), C (24 J/cm2). Each group was further subdivided into four subgroups: 1 (no aging), 2 (500 hours aging), 3 (1000 hours aging) and 4 (1500 hours aging). The results were analyzed by means of ANOVA and Tukey's test (alpha = 0.05) to determine the effect of the factors. Correlation was performed in order to determine the possible relationship among variables. Energy density is not a significant factor in color stability. However aging is directly proportional to color changes. deltaE* depends on filler size; hybrid material presented deltaE* of 2.1(0.5), 2.4(0.6) and 3.3(0.3) at 500, 1000 and 1500 hours of accelerated aging respectively, and nanofilled material showed deltaE* of 3.0(0.6), 4.5(1.2) and 5.9(0.6) at the same times respectively. It can be concluded that deltaE* does not depend on energy density; however other factors are involved in color change. Further studies in this area are warranted.