dental materials 23 ( 2 0 0 7 ) 655–664 available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/dema Quantum yield of conversion of the photoinitiator camphorquinone Yin-Chu Chen a , Jack L. Ferracane b , Scott A. Prahl c,∗ a Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA b Division of Biomaterials & Biomechanics, Oregon Health Science University, Portland, OR, USA c Department of Biomedical Engineering, Oregon Health Science University, 9205 SW Barnes Road, Portland, OR 97225, USA article info Article history: Received 24 November 2005 Received in revised form 22 May 2006 Accepted 9 June 2006 Keywords: Dynamic absorption coefficient Light-activated polymerization Molar extinction coefficient Curing threshold Reciprocity Radiant exposure abstract The primary absorber in dental resins is the photoinitiator, which starts the photo polymer- ization process. We studied the quantum yield of conversion of camphorquinone (CQ), a blue light photoinitiator, in dental resin composites using a LED lamp (3M FreeLight) and a Quartz Tungsten Halogen (QTH) lamp (VIP) as the light curing units at five different irradi- ances. The molar extinction coefficient, ε 469 , of CQ was 46 ± 2 cm -1 /(mol/L) at 469 nm. The reciprocity of irradiance and exposure time holds for changes of CQ absorption coefficient, that is, irradiance × exposure time (=radiant exposure) = constant. Both LED and QTH lamps yielded the same curing threshold (the radiant exposure when CQ absorption drops to 1/e) and the same quantum yield conversion under different irradiances. In our dental resin formulation (0.7 wt.% CQ with reducing agents 0.35 wt.% dimethylaminoethyl methacrylate (DMAEMA) and 0.05 wt.% butylated hydroxytoluene (BHT)) the quantum yield was measured as 0.07 ± 0.01 CQ conversion per absorbed photon. © 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction Photo-cured composites are widely used in dental restora- tions due to their many advantages, including the esthetic appearance and the ability to cure in situ. However, limited light transport in the composite and insufficient extent of cure may compromise the physical properties of the composite and reduce its service life. These composites consist of a mixture of resins with photoinitiators and silane-coated, inorganic filler particles. The component that absorbs light and initiates free radical addition polymerization of the resin monomers is the photoinitiator. The number of the photoinitiators should be limited to a concentration that is just sufficient to obtain an optimum photocuring reaction with the highest possible monomer conversion because any excessive unreacted pho- ∗ Corresponding author. Tel.: +1 503 216 2197; fax: +1 503 216 2422. E-mail address: prahl@bme.ogi.edu (S.A. Prahl). toinitiators, products of their photolysis, or any unreacted monomers, may diffuse out from the polymer matrix into the saliva. On the other hand, to avoid leaving unreacted photoini- tiators also requires a sufficient amount of light application. In order to know the required light dose that will completely convert all of the photoinitiators, we need to know the pho- toinitiator quantum yield conversion, which is defined as the ratio of the number of converted photoinitiators to the number of photons absorbed by the initiators: ˚ = number of converted photoinitiator molecules number of absorbed photons . (1) The most commonly used photoinitiator in dental resin formulations is camphorquinone (CQ), a blue light photoinitia- 0109-5641/$ – see front matter © 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2006.06.005