Objective: Improve photoinitiation efficiency using iodonium initiators combined with other initiators and photosensitizers on rate and degree-of-conversion (DC) and volumetric shrinkage of low-shrinkage liquid-crystal dimethacrylate monomers (LCM) compared to BisGMA-based resins.
Methods: Samples were made with various ratios of photosensitizers (camphorquinone [CQ] and/or 1-phenyl-1,2-propanedione [PPD]) and photoinitiators (p-octyloxy-phenyl-phenyl iodonium hexafuoroantimonate [OPPI]) and/or 2-dimethylaminoethyl methacrylate [DMAEMA]). Half were typical BisGMA resins (BisGMA, TEGDMA, BisEMA (EssTech) 37.5:37.5:25 wt% [GTE]) and half an experimental LCM (1,4(di-4-(methacryloxy-hexyloxy)benzoyloxy)-2-t-butylbenzene).
Samples with 70wt% filler were polymerized using a halogen curing unit (COE LunarTA, GC America, 200 mW/cm/2) for 10s, 20s, 40s, 80s, 120s, 240s. DC was determined at each exposure time with Fourier transform infrared spectroscopy (Nicolet).
For shrinkage, specimens were cured for 180s. After 20m the difference between uncured and cured volumes was determined with an image analyzer (Acuvol, Bisco Inc.).
Results: Samples containing 1% OPPI by mass showed significant increases in polymerization rate and maximum DC for both GTE and LCM resins. OPPI functioned best with an amine and did not significantly affect shrinkage (<1 vol% in LCM). Neither shrinkage nor DC of LCM was affected by CQ/PPD ratio. Conclusions:
• OPPI can be combined with other photoinitiators in both BisGMA- and LCM-based composits to significantly increase both conversion rate and maximum DC, functioning best with an amine coinitator.
• OPPI does not significantly affect polymerization shrinkage.
• Varying CQ and PPD in conjunction with OPPI and/or DMAEMA (while keeping CQ+PPD at 1wt% of monomer) has no significant effect on degree or rate of conversion in GTE and LCM systems, and no significant effect on shrinkage in LCM systems.
• OPPI substantially improves cure characteristics without other adverse effects.
Supported by NIDCR grant P01DE11688