The effect of combining photoinitiator systems on the color and curing profile of resin-based composites

Objective To evaluate the effect of combining camphorquinone (CQ) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) on the color and curing profile of resin-based composites. Methods Experimental composites were produced with different CQ and TPO molar concentrations: CQ-only, 3CQ:1TPO, 1CQ:1TPO, 1CQ:3TPO, and TPO-only. Polywave LED was characterized using a beam profiler. Block-shaped samples (5 mm × 5 mm × 3 mm depth) were cured in a custom-designed mold with a polywave LED positioned to compare the regions exposed to the 420–495 nm and 380–420 nm LED emittances. To map the cure profile, degree of conversion (DC) of longitudinal cross-sections from each block were evaluated by FT-NIR. Color, light-transmittance and light-absorption during curing were evaluated on specimens 1–3 mm thick. Data were analyzed using ANOVA/Tukey's test (α = 0.05; β = 0.2). Results Though the polywave LED beam profile was non-uniform, up to a depth of 2 mm no differences in DC were found among the composites containing CQ with TPO added up to 50%, regardless of the position under the curing tip. Composites with higher TPO concentration showed a decrease in DC beginning with a depth of 1 mm, while composites with higher or similar CQ concentrations did not show decreased DC until a depth of 3 mm. Higher TPO concentration reduced initial yellowness and color change after curing; and lower CQ concentration decreased light-absorption at greater depths. Significance The combination of CQ with TPO added up to 50% reduced the yellowness and color change of composites after curing without affecting cure efficiency up to a depth of 2 mm.