EPR in the Characterization of the Shade Effect on Translucence, Remaining Free Radicals, and Polymerization Depth of Commercially Available Resin Composites

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

“…It is concluded that the paramagnetic species in the sample are the "propagating" and "allylic" radicals shown by Fontes et al 23 , which generated during the irradiation of the sample. These radicals are present in the sample even one month after the irradiation because of the vitrification phenomenon, although in much less concentration 13 . The reaction kinetics of dental materials is dependent on the initial concentration of monomers and initiators, as well as the light intensity and depth of cure and temperature 26 .…”

“…When the polymerization degree of the resin cement does not reach satisfactory levels, its mechanical properties are compromised 6,11,12 . The initial concentration of free radicals is crucial to promote better clinical results and is directly connected to the degree of conversion of monomers to polymers 13 , so that the knowledge of the variables that affects the initial amount of free radicals generated is fundamental to de development of more efficient materials and technics.…”

“…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 .…”

“…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.…”

The influence of free-radical concentration on the shear bond strength of dental composites

“…12 This method was successfully employed in a study of the curing time of visible-light-activated composites as a function of the sample thickness as well as in other investigations involving dental composites. [13][14][15][16] The influence of the free-radical concentration in the underneath composite layer on the effectiveness of the bonding between dental composites has not been investigated yet. Therefore, the aim of our study was to clarify the role of the free-radical concentration on the shear bond strength between two layers of composite using the EPR method and simultaneously to verify the polymerisation process by measuring the DC using Raman spectroscopy.…”