J. LEPRINCE1, J. DEVAUX2, and G. LELOUP1, 1Universite Catholique de Louvain, Bruxelles, Belgium, 2Universite Catholique de Louvain, Louvain-la-Neuve, Belgium |
Objective: To study the influence of illumination parameters on the
kinetic decay of the two types of trapped free radicals present in dental
resins: allylic- and propagating
ones.
Methods: The resin formulation was the following: Bis-GMA (64wt%) and
TEGDMA (36wt%) with camphorquinone and tertiary amine (0,5:0,5wt%). The illumination parameters, i.e.
energy density (ED, mJ/cm2), power density (PD, mW/cm2)
and time (t, s), were modulated with a halogen light (Optilux 501) coupled with
a rheostat as follows:
Curing Mode (t x PD) | ED (mJ/cm2) | 40s x 150mW/cm2 | 6000 | 80s x 150mW/cm2 | 12000 | 20s x 300mW/cm2 | 6000 | 40s x 300mW/cm2 | 12000 | 10s x 600mW/cm2 | 6000 | 20s x 600mW/cm2 | 12000 |
Three
samples per mode were prepared and analysed by Electron Paramagnetic Resonance
for increasing times (5 minutes, 1 to 6 hours, 1 day, 1-2-3 months)
after light irradiation. Means and
standard deviations were calculated and used to draw the graphs.
Results: Trapped-radicals kinetics of decay can be divided in two
different phases. In the first one (0 to 24h), while curves of all modes decrease with the
same slope, different concentrations of radicals are underlined. On one hand, samples cured at higher
EDs exhibit more trapped radicals.
On the other hand, at a same ED, radical concentrations are higher for a
lower PD, thus for a longer irradiation time. In the second phase, all decay curves seem to tend to 0 after about 100
days. As to compare the behaviour of the two radical types, propagating
species decrease quicker than allylic ones during the first few hours.
Conclusion: ED, irradiation time and PD affect differently the trapped
free radicals concentrations, and the two different radical types behave
differently during the first few hours.
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