Influence of nano- and micro-filler proportions on the optical property stability of experimental dental resin composites

This study determined the influence of nano- and micro-filler proportions on the stabilities of color, translucency and opalescence of experimental dental resin composites after wet thermocycling. Silane-coated nano- (mean: 40 nm) and micro-glass fillers (mean: 0.77 μm), in the ratios of 0:6 (N0M6), 1:5 (N1M5), 2:4 (N2M4), 3:3 (N3M3), 4:2 (N4M2), 5:1 (N5M1) and 6:0 (N6M0), were added to 1:1 mixed BisGMA and TEGDMA light curing resin matrix with a total content of 60 wt.% of the resin composites. Reflected and transmitted colors of cured specimens (1 mm in thickness) were measured before and after 5000 cycles of thermocycling with a spectrophotometer. A commercial dental resin composite with a filler content of 65 wt.% was used as a reference. As results, changes in color (ΔEab∗), translucency (ΔTP) and opalescence (ΔOP) were in the range of 1.1–3.6, −4.5 to 0.1 and −3.7 to −0.7 units, respectively, all of which were influenced by the filler proportion (p < 0.05). A hybrid composite (N4M2) and the nano-filled composite (N6M0) showed the smallest color change, while N4M2 alone showed the smallest translucency change (p < 0.05). All the experimental composites showed significant changes in opalescence (p < 0.05). Experimental hybrid composite containing 2:1 mixed nano- and micro- fillers showed the best stabilities in color and translucency. The micro-filled composite (N0M6) always showed higher translucency but lower opalescence than those of the hybrid and nano-filled composites.