Lignin-derived new hydrogen donors for photoinitiating systems in dental materials

The aim of this study is to develop amine free photo-initiating system (PIs) for the photopolymerization of dental methacrylate resins, using seven new hydrogen donors HDA-HDG derived from β-O-4 lignin model.

Seven experimental CQ/HD PIs were formulated with Bis-GMA/TEGDMA (70 w%/30 w%). CQ/EDB system was chosen as the comparison group. FTIR-ATR was used to monitor the polymerization kinetics and double bond conversion. Bleaching property and color stability were evaluated using a spectrophotometer. Molecular orbitals calculations were used to demonstrate C-H bond dissociation energies of the novel HDs. Depth of cure of the HD based systems were compared to the EDB based one. Cytotoxicity was also studied by CCK8 assay using tissue of mouse fibroblasts (L929 cells).

Compared to CQ/EDB system, the new CQ/HD systems show comparable or better photopolymerization performances (1 mm-thick samples). Comparable or even better bleaching properties were also obtained with the new amine-free systems. Comparing to EDB, all HDs exhibited significantly lower C-H bond dissociation energies by molecular orbitals calculations. Groups with new HD showed higher depth of cure. OD and RGR values were similar to that of the CQ/EDB group, ensuring the feasibility of the new HDs in dental materials.

The new CQ/HD PI systems could be potentially useful in dental materials, presenting improvements in restorations' esthetic and biocompatibility.