Mapping camphorquinone consumption, conversion and mechanical properties in methacrylates with systematically varied CQ/amine compositions

Objectives. To evaluate conversion, bulk mechanical properties and camphorquinone (CQ)consumption in methacrylate resins, comprising a range of overall initiator concentrationsand CQ/amine ratios.

Methods. BisGMA (Bisphenol-A glycidyl dimethacrylate), TEGDMA (triethyleneglycoldimethacrylate) and UDMA (urethane dimethacrylate) were mixed at a 1:1:1 molar ratio.CQ was used as the visible light photosensitizer, in combination with EDMAB (Ethyl p-dimethylamino benzoate), at 3:1, 2:1, 1:1, 1:2 and 1:3 weight ratios, at 0.5, 1.0, 1.5, 2.0 and3.0 wt% overall initiator concentration. Butylhydroxytoluene was added at 0.05 wt% as aninhibitor. Unfilled resins were photoactivated with a dental light source (VIP Jr, Bisco) for60 s at 600 mW/cm2. Flexural strength/modulus were assessed in 2 × 1 × 10 mm bars, testedin three-point bending. Degree of conversion was assessed at the bottom of the same speci-mens using FT-RAMAN. CQ consumption was measured using a UV-vis spectrometer. Datawere analyzed with two-way ANOVA/Tukey test (α = 5%).

Clinical relevance. Above 1.5 wt% overall initiator concentration, the conversion and gen-eral mechanical properties were independent of the initiator concentration. Therefore,there seems to be no benefit to increasing the initiator concentration above that level. At higher camphorquinone concentrations, light transmission and photosensitizer consumption becomes impaired, which could lead to decreased depth of cure and yellowing of the restoration.

Results. Lower conversion and inferior mechanical properties were observed with loweroverall initiator concentrations and higher amine/CQ ratios. The lowest overall initiator con-centration (0.5%) presented the statistically lowest conversion/properties results, except forthe 1:3 amine/CQ ratio. For overall concentrations equal or greater to 1.5%, the amine/CQratio did not influence conversion or mechanical properties. CQ consumption was less effi-cient for the highest overall initiator concentrations and lower amine/CQ ratios.