Molar extinction coefficients and the photon absorption efficiency of dental photoinitiators and light curing units

J Dent. 2005 Jul;33(6):525-32. doi: 10.1016/j.jdent.2004.11.013. Epub 2005 Mar 19.


Objectives: The light absorption of dental photoinitiators should correlate with the spectral emission profiles of dental light curing units compared on an equivalent basis. Spectral data of dental photoinitiators and light curing units can be used to define the photon absorption efficiency (PAE) obtained by integrating the product of the absorption and emission spectra in terms of photons. This parameter can be used to identify the best performance for photochemical process with specific photoinitiators.

Methods: The efficiency of two LED and one QTH lamps were tested comparing their performances with the photoinitiators camphorquinone (CQ); phenylpropanedione (PPD); monoacylphosphine oxide (Lucirin TPO); and bisacylphosphine oxide (Irgacure 819). Absorption and emission spectra of the photoinitiators and the LED (Ultrablue I and Ultrablue IS) and QTH (Optilux 401) LCUs were determined in the 360-550nm range.

Results: CQ exhibited an absorption centered in the blue region and, although the maxima of PPD, MAPO, and BAPO were in the UV-A region, their absorption extended to the visible region. Power output maxima of the LCUs were at 467 (Ultrablue I), 454 (Ultrablue IS) and 493nm (Optilux 401), and the total power densities were 170+/-1, 470+/-4 and 444+/-4mW/cm(2), respectively.

Significance: The use of the PAE allows a prediction of the most efficient photoinitiator/LCU systems. For similar photoinitiator concentrations, Lucirin and CQ are most efficiently photoinitiated by the QTH unit, whereas the high-power LED device is more efficient for Irgacure. PPD is photoactivated similarly by both LCUs.

Publication types

  • Comparative Study

MeSH terms

  • Acrylic Resins / radiation effects*
  • Composite Resins / radiation effects*
  • Light*
  • Molar / chemistry
  • Molar / radiation effects*
  • Photons*
  • Polyurethanes / radiation effects*
  • Spectrometry, X-Ray Emission / methods


  • Acrylic Resins
  • Composite Dental Resin
  • Composite Resins
  • Polyurethanes