Influences of composite–composite join on light transmission characteristics of layered resin composites

Objectives The purposes of this study were: (1) to determine the light transmission characteristics (straight-line and diffusion transmission) of bulk-filled and layered resin composites, and (2) to evaluate the effect of layering filling on translucency and color appearance of resin composites. Methods Three light-cured resin composites (EsteliteΣ, Tokuyama Dental; Beautifil II, Shofu and Clearfil Majesty, Kuraray Medical) in A2 and OA2 shades were used in this study. 2 mm-thick resin composite discs were prepared by two methods; bulk filling technique (2 mm filling at one time), layering technique (two layers each 1 mm thickness). The transmitted light intensity of each resin composite disc was measured using a goniophotometer, and diffusion factor (DF), an indicator for diffuse transmission property, and peak gain (G0) for straight-line transmission were calculated from the light distribution graphs. Color was measured according to the CIELAB color scale on a spectrophotometer, and the translucency parameter (TP) and color difference (ΔE(*)) between bulk-filled and layered specimens were calculated. The data were statistically analyzed using three-way ANOVA, and Dunnett's T3 and t-test for post-hoc test. Results Three-way ANOVA revealed that the layered specimens had significantly lower G0 values and higher DF values than the bulk-filled specimens, and significantly reduced TP values. The color differences (ΔE(*)) ranged from 1.07 to 1.85 between the bulk-filled and layered specimens. Significance Resin composite placed in layers exhibited reduced straight-line light transmission and increased diffusion transmission compared with bulk-filled resin composite. The layering technique affected the translucency and color rendition of resin composite.