Delayed light-curing of dual-cure bulk-fill composites on internal adaptation and depth of cure

To evaluate the effect of delayed light-curing of dual-cure bulk-fill composites on internal adaptation and microhardness (KHN) in depth.

Bulk-fill composites were placed in 35 box-shaped preparations and cured according to the following protocols (n = 5): Filtek Bulk-Fill light-cured immediately after insertion (FBF); Bulk-EZ light-cured immediately after insertion (BEZ-I); Bulk-EZ light-cured 90 s after insertion (BEZ-DP); Bulk-EZ self-cured (BEZ-SC); HyperFIL light-cured immediately after insertion (HF-I); HyperFIL light-cured 90 s after insertion (HF-DP); HyperFIL self-cured (HF-SC). After 24 h, the samples were axially sectioned, and the internal adaptation was evaluated using replicas under a scanning electron microscope. The KHN was evaluated at six depths (0.3 mm, 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm). The statistical analysis was performed using α = 0.05.

The KHN significantly decreased with depth, except in self-curing mode, when it was similar at all depths. Delayed light-curing significantly increased the KHN at higher depths. The internal adaptation was material-dependent. Light-curing did not influence the internal adaptation of HyperFIL, whereas delayed light-curing significantly reduced the internal gaps (%) of Bulk-EZ.

Delayed light-curing improved the depth of cure of dual-cure resin composites. Light-curing did not influence the internal adaptation of HyperFIL, but delayed light-curing improved the internal adaptation of Bulk-EZ.

Light-curing is fundamental for improving the mechanical properties of dual-cure resin composites. Moreover, depending on the dual-cure resin composite, the delay in light-curing can reduce the internal gaps.