IADR Abstract Archives
Delayed-curing Stage and Oxygen Inhibition of Polymerization of Dimethacrylate Resin
Objectives: It is known that after light-initiated free-radical polymerization of dimethacrylate monomers the curing continues for some period of time after the curing light emission has stopped (so-called delayed-curing stage, DCS). It is also known that during free radical polymerization presence of oxygen inhibits polymerization reaction. However, less is known of the influence of oxygen inhibition of light initiated polymerization during the DCS. The aim of this study was to investigate possible effect of O2-exposure for polymerization during the DCS.
Methods: Monomer system of BisGMA-TEGDMA (60/40%) with light sensitive initiator-activator (CQ-DMAEMA) system was polymerized by light-initiation (wavelength average 430-480nm) with radiation intensity of 1200mW/mm2 for 20s on the ATR sensor of the fourier-transform-infrared (FTIR) spectrometer. After light curing, the samples were divided into two groups (n=6): DCS stage was allowed to continue in air (O2–exposed group) and by protecting the effect of air to the DCS (O2-protected group). Degree of monomer conversion (DC%) from the sample surface was monitored up to 360min for both groups and surface microhardness (VHN) was measured with 10 repeated measurements of 6 samples (n=6) at 4 time points (ad 6h) of both groups.
Results: After light-curing, the DC% increased from 50% to 65% in the O2-protected group and the slope of the DC%-curve during the DCS was lower indicating polymerization inhibition in the O2-exposed group. Surface microhardness increased from 2.99 (SD 0.64) to 9.10 (SD 1.40) VHN of the O2-protected samples and to 4.80 of the O2-exposed samples. Surface hardness differed significantly between the groups at the time point of 6h (p<0.005, ANOVA).
Conclusions: This study suggested that O2-inhibition of free radical polymerization of dimethacrylate resin occurred after ending the curing light emission. This was associated to the lower surface microhardness of the polymer when the DCS continued under air-exposure.
Methods: Monomer system of BisGMA-TEGDMA (60/40%) with light sensitive initiator-activator (CQ-DMAEMA) system was polymerized by light-initiation (wavelength average 430-480nm) with radiation intensity of 1200mW/mm2 for 20s on the ATR sensor of the fourier-transform-infrared (FTIR) spectrometer. After light curing, the samples were divided into two groups (n=6): DCS stage was allowed to continue in air (O2–exposed group) and by protecting the effect of air to the DCS (O2-protected group). Degree of monomer conversion (DC%) from the sample surface was monitored up to 360min for both groups and surface microhardness (VHN) was measured with 10 repeated measurements of 6 samples (n=6) at 4 time points (ad 6h) of both groups.
Results: After light-curing, the DC% increased from 50% to 65% in the O2-protected group and the slope of the DC%-curve during the DCS was lower indicating polymerization inhibition in the O2-exposed group. Surface microhardness increased from 2.99 (SD 0.64) to 9.10 (SD 1.40) VHN of the O2-protected samples and to 4.80 of the O2-exposed samples. Surface hardness differed significantly between the groups at the time point of 6h (p<0.005, ANOVA).
Conclusions: This study suggested that O2-inhibition of free radical polymerization of dimethacrylate resin occurred after ending the curing light emission. This was associated to the lower surface microhardness of the polymer when the DCS continued under air-exposure.