Effect of photoinitiators on dynamic mechanical properties of dentin adhesives

Effective bonding at the prepared tooth/composite material interface requires dentin adhesives that provide superior properties and rapid polymerization under clinical conditions.  The reactivity and the mechanical behavior are influenced by the photoinitiator system and curing conditions. Objective: The aim of this study was to determine the effect of photoinitiator systems on dynamic mechanical properties of dentin adhesives. Methods: The adhesive formulation: HEMA, bisGMA 45/55 w/w was cured in the presence of 0 (A0), 8 (A8) and 16 (A16) wt% H₂O to simulate wet bonding. The photoinitiators were: camphorquinone (CQ) as a photosensitizer, 2-(dimethylamin)ethyl methacrylate (DMAEMA) and ethyl-4-(dimethylamino)benzoate (EDMAB) as co-initiator and diphenyliodonium hexafluorophosphate (DPIHP). Beam specimens (1x1x11 mm³) were used for measurement of dynamic mechanical properties (TA Instruments Q800) and degree of conversion (LabRAM ARAMIS Raman spectrometer). The adhesives were cured for 40 s at 25°C with commercial visible-light, (Spectrum® 800, Dentsply, Milford, DE, USA), Intensity=550 mW cm^-2. Results:DC ranged from 75-97% increasing w H₂O content. The CQ/DMAEMA system was gel-like in H₂O, but DPIHP addition led to comparable rubbery moduli in all systems regardless of water content. Tg-^oC and storage moduli in the rubbery region (E_r^'-MPa):

Conclusions: The addition of DPIHP to either the CQ/EDMAB or the CQ/DMAEMA photoinitiator system improved the polymerization conversion, Tg and rubbery moduli of the polymer networks formulated in water to simulate wet bonding.   Supported NIH/NIDCR R01-DE014392.