The Effect of Photoinitiator Systems on Resin-Composite Containing ZnO-Nanoparticles

Objectives: Zinc oxide (ZnO) possesses antibacterial activity and has a tooth-like color, but it severely reduces the resin-based composite (RBC) depth of cure (DoC). This study investigated the effect of unary and binary photoinitiator systems on the DoC and degree of conversion (DC%) of formulated RBC containing ZnO-nanoparticles.
Methods: Ten formulated RBC (n=3/gp) consisting of 50 wt.% mixture of monomers (Bis-GMA, TEGDMA, and UDMA) and 50 wt.% fillers (inert barium glass and silica nanoparticles). ZnO-nanoparticles were added at 0 (control), 0.5, 1, 1.5 and 2 wt.%. A unary photoinitiator system consists of Camphorquinone (CQ) 1 wt.% and Ethyl 4-(dimethylamino)benzoate (EDAB) 0.75 wt.% or a binary system consisting of Diphenyliodonium hexafluorophosphate (DPI) 1 wt.%, CQ 1 wt.% and EDAB 0.75 wt.% were added to the monomer mixture. To measure DoC, each specimen was prepared in a custom-made mold with a slot (16 mm x8 mm x2 mm) and a top cover plate, irradiated from one end (40 s), stored dry (37°, 1 d) and measured using Vickers hardness (0.5 mm intervals). 1 mm thick specimens were prepared to measure DC% continuously using FTIR, from zero up to 24 h post-irradiation.
Results: Increasing ZnO-nanoparticles wt.% led to a significant reduction of DoC (p<0.05). But, most of binary groups showed significantly higher DoC (p<0.05). Depth at 80% of max VHN of unary groups reduced from 6.8 mm (ZnO 0wt.%) to 2.1 mm (ZnO 2wt.%) and in binary groups from 8.4 mm to 2.3 mm. DC% after 24 h were not influenced by either ZnO-nanoparticles nor the photoinitiator system (p>0.05). However, faster conversions were observed in binary groups. RP_max of binary groups ranged from 8.6-10.1 %/s, and unary groups ranged from 5.6-7.2 %/s.
Conclusions: The addition of DPI resulted in an overall higher curing depth, which is desirable in manufacturing antibacterial RBC containing ZnO.