Photoinitiator type and applicability of exposure reciprocity law in filled and unfilled photoactive resins.
OBJECTIVE
To test the influence of photoinitiator type and filler particle inclusion on the validity of exposure reciprocity law.


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).


CONCLUSIONS
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.
School of Dentistry and Stomatology, Université catholique de Louvain, Brussels, Belgium.
J G
JG
Leprince
M
M
Hadis
A C
AC
Shortall
J L
JL
Ferracane
J
J
Devaux
G
G
Leloup
W M
WM
Palin
D017609:Barium Compounds / Q000737:chemistry; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D010720:Phosphines / Q000737:chemistry / Q000528:radiation effects; D055668:Photochemical Processes; D058567:Photoinitiators, Dental / Q000737:chemistry / Q000145:classification*; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D019163:Reducing Agents / Q000737:chemistry / Q000528:radiation effects; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013696:Temperature; D013729:Terpenes / Q000737:chemistry / Q000528:radiation effects; D013997:Time Factors
C520678:(2,4,6-trimethylbenzoyl) diphenylphosphine oxide; D017609:Barium Compounds; D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D010720:Phosphines; D058567:Photoinitiators, Dental; D011109:Polymethacrylic Acids; D019163:Reducing Agents; D012821:Silanes; D013729:Terpenes; C102738:barium glass filler; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C048339:camphoroquinone; D012822:Silicon Dioxide; C049840:2-(dimethylamino)ethyl methacrylate