286 Short wavelength absorption of resin composites: Implications for effective curing

Thursday, March 21, 2013: 8 a.m. - 9:30 a.m.
Location: Room 611 (Washington State Convention Center)
Presentation Type: Oral Session
W.M. PALIN, Biomaterials, University of Birmingham, Birmingham, England, C. FELIX, BlueLight analytics inc, Halifax, NS, Canada, and J.G. LEPRINCE, School of dental medicine and stomatology / Institute of condensed matter and nanosciences - Bio and Soft Matter, Universite Catholique de Louvain, Bruxelles, Belgium
Objective: To examine the effect of dual wavelength light transmission and photoinitiator (PI) absorption on the curing extent through depth of light-activated resin-based composite materials

Method: Two wavelengths centred at 400 and 470nm were measured on a MARC® Resin Calibrator (BlueLight analytics inc., Halifax, Canada) and adjusted to deliver approximately 1500 mW/cm2 to cure a variety of commercial and model resin composite formulations that either contained 1) CQ-amine, 2) TPO, or 3) CQ-amine/TPO PI systems. The total transmitted energy within the blue range (420-540 nm) and violet range (360-420 nm) was calculated as well as the percentage of light transmission. Raman spectroscopy was used to explore curing extent through depth.

Result: Light transmission through commercial materials varied significantly between products (p<0.05) with considerable short wavelength absorption at 2mm depth for some materials. Experimental resins containing TPO exhibited significantly increased degree of conversion in the upper 4mm of the specimen compared with CQ-amine and CQ-amine/TPO (P<0.05). The conversion of TPO-based experimental materials decreased more rapidly with depth compared with those containing the CQ-amine system. However, CQ-amine/TPO materials exhibited a significantly increased conversion compared with CQ-amine or TPO at thicknesses greater than 5mm (p<0.05).

Conclusion: Blue wavelengths, absorbed by CQ, scatter less than those of shorter violet wavelengths, absorbed by TPO. Combining both initiators that exhibit large differences in molar absorptivity have synergistic effects that improve conversion through depth compared with using either photoinitiator alone. Resin composite manufacturers should provide more information regarding photoinitiator chemistry and corresponding energy requirement in order to adequately initiate the PI system through to the bottom of the recommended depth of cure.

Keywords: Composites, Photoinitiator, Polymerization and Polymers