Untitled

Abstract

The irradiation time of a visible-light-activated composite necessary to achieve full polymerization throughout the material was studied. Curing-time dependence on the thickness of the material was also investigated. To monitor the visible light-activation effect, the free radical concentration was measured as a function of irradiation time. If the composite sample is less than 0.5 mm thick and exposed to light for a time interval recommended by the manufacturer, full radical concentration is indeed created uniformly. This is not the case in thicker samples. Electron paramagnetic resonance (EPR) was used to monitor the concentration of free radicals in the samples. The number of radicals was monitored as a function of irradiation time during which the radicals were generated in samples 0.5, 0.8, 2.0, 3.0 and 5.0 mm thick. An EPR X-band spectro-meter was used to detect the free radical spectra. The number of free radicals per unit mass as a function of irradiation time shows that 60% of the maximum concentration of radicals in a 1 mm sample is reached in 24 s curing time, while in thicker samples it takes hundreds of seconds. On the basis of the experiments, a depth and irradiation time-dependent radical concentration model was developed. This model shows that a 2.0 mm thick sample is cured at the bottom side if irradiated for 60 s. It is proposed that the measure of the degree of polymerization in composite materials should be the polymerization of the bottom layer of the sample which is modelled from the number of free radicals generated in the sample.

The Influence of a Translucent Fiberglass Post on the Polymerization of Dual Cure Resin Cement Analyzed by Electron Paramagnetic Resonance

“…EPR spectroscopy is a highly sensitive and nondestructive technique for identifying and quantifying the paramagnetic species in a sample (free radicals in this case) 13 . EPR has been used to study the behavior of methacrylate radicals in numerous situations, including: irradiation at different wave lengths 14 , required polymerization time as a function of resin composition 15 or sample thickness 16 , resin hardness as a function of the relative number of radicals 17,18 , degree of conversion 19 , translucence 13,[20][21][22] , and molecular structure of the generated radicals 23 . As the signal intensity of the EPR spectrum is proportional to the amount of free radicals in a sample, and considering that the translucency of some fiberglass posts provides the 12,24,25 , this current study evaluated the free radical concentration according to the depth into a simulated root canal to characterize the influence of the translucent fiberglass post on the polymerization of resin cement, and then its influence on cementation.…”

Infrared spectroscopy: a tool for determination of the degree of conversion in dental composites

“…Techniques such as Fourier transform infrared (FTIR) spectroscopy 3 , 13 , 14 , RAMAN 4 , 12 , EPR 15 (electron paramagnetic resonance), NMR 9 (nuclear magnetic resonance), DSC 1 (differential scanning calorimetry) and DTA 6 , 8 (differential thermal analysis) have been used to determine the DC. Among these, FTIR is the most frequently used technique.…”

A Reliable Method of Measuring the Conversion Degrees of Methacrylate Dental Resins

“…Techniques such as Fourier transform infrared spectroscopy (FTIR) [ 3 , 4 , 6 , 11 , 12 ], differential scanning calorimetry (DSC) [ 13 ], electron paramagnetic resonance (EPR) [ 14 ] nuclear magnetic resonance (NMR) [ 15 ], Raman spectroscopy [ 16 , 17 ] and differential thermal analysis (DTA) [ 18 , 19 ], have been used to determine the DC. FTIR spectroscopy is the most frequently used technique but requires certain precautions during sample preparation and testing to obtain an accurate value of DC [ 4 ].…”