Photoinitiator type and applicability of exposure reciprocity law in filled and unfilled photoactive resins

J. G. Leprince, M. Hadis, A. C. Shortall, J. L. Ferracane, J. Devaux, G. Leloup, W. M. Palin

Research output: Contribution to journalArticlepeer-review

130 Scopus citations


Objectives: To test the influence of photoinitiator type and filler particle inclusion on the validity of exposure reciprocity law. Materials and methods: 50/50 wt% Bis-GMA/TEGDMA resins were prepared with equimolar concentrations of camphorquinone/DMAEMA (0.20/0.80 mass%) (CQ) or Lucirin-TPO (0.42 mass%), and were used either unfilled or filled to 75 mass%. Specimens were cured with a halogen Swiss Master Light (EMS, Switzerland) using four different curing protocols: 400 mW/cm2 for 45 s as reference protocol (18 J/cm2), 1500 mW/cm2 for 12 s (18 J/cm2), 3000 mW/cm2 for 6 s (18 J/cm2) and 3 s (9 J/cm 2). Degree of conversion (DC) was measured in real time for 70 s by FT-NIRS and temperature rise using a thermocouple. Depth of cure was determined with a penetrometer technique. Results: With respect to DC and depth of cure, exposure reciprocity law did not hold for any tested material, except for the depth of cure of filled CQ-based materials. At similar radiant exposure, DC was significantly higher (p < 0.05) for all unfilled and filled TPO-based materials compared with CQ-based materials. As exposure time was reduced and irradiance increased, TPO-based materials exhibited higher DC whilst an opposite trend was observed for CQ-based materials (p < 0.05). For similar curing regimes, depth of cure of CQ-based materials remained significantly greater than that of TPO-based materials. Adding fillers generally reduced DC, except at higher irradiance for CQ-based materials where a positive effect was observed (p < 0.05). Significance: The validity of exposure reciprocity law was dependent on several factors, among which photoinitiator type and filler content were important. Lucirin-TPO is a highly reactive and efficient photoinitiator, which may allow the potential for a reduction in curing time of TPO-based photoactive materials in thin sections.

Original languageEnglish (US)
Pages (from-to)157-164
Number of pages8
JournalDental Materials
Issue number2
StatePublished - Feb 2011


  • Degree of conversion
  • Dental resin composite
  • Depth of cure
  • Exposure reciprocity law
  • Photoinitiator
  • Polymerization kinetics

ASJC Scopus subject areas

  • General Materials Science
  • General Dentistry
  • Mechanics of Materials


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