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

Dent Mater. 2011 Feb;27(2):157-64. doi: 10.1016/ Epub 2010 Nov 9.


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/cm²). 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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Barium Compounds / chemistry
  • Bisphenol A-Glycidyl Methacrylate / chemistry
  • Bisphenol A-Glycidyl Methacrylate / radiation effects
  • Composite Resins / chemistry*
  • Composite Resins / radiation effects
  • Curing Lights, Dental
  • Dental Materials / chemistry*
  • Dental Materials / radiation effects
  • Humans
  • Materials Testing
  • Methacrylates / chemistry
  • Methacrylates / radiation effects
  • Phosphines / chemistry
  • Phosphines / radiation effects
  • Photochemical Processes
  • Photoinitiators, Dental / chemistry
  • Photoinitiators, Dental / classification*
  • Polyethylene Glycols / chemistry
  • Polyethylene Glycols / radiation effects
  • Polymerization
  • Polymethacrylic Acids / chemistry
  • Polymethacrylic Acids / radiation effects
  • Radiation Dosage
  • Reducing Agents / chemistry
  • Reducing Agents / radiation effects
  • Silanes / chemistry
  • Silicon Dioxide / chemistry
  • Spectrophotometry, Ultraviolet
  • Spectroscopy, Fourier Transform Infrared
  • Surface Properties
  • Temperature
  • Terpenes / chemistry
  • Terpenes / radiation effects
  • Time Factors


  • (2,4,6-trimethylbenzoyl) diphenylphosphine oxide
  • Barium Compounds
  • Composite Resins
  • Dental Materials
  • Methacrylates
  • Phosphines
  • Photoinitiators, Dental
  • Polymethacrylic Acids
  • Reducing Agents
  • Silanes
  • Terpenes
  • barium glass filler
  • triethylene glycol dimethacrylate
  • Polyethylene Glycols
  • Bisphenol A-Glycidyl Methacrylate
  • camphoroquinone
  • Silicon Dioxide
  • 2-(dimethylamino)ethyl methacrylate