Time-Resolved Study of the Photo-Curing Process of Dental Resins with the NMR-MOUSE

Abstract

The photo-curing reaction of dental resins has been examined with unilateral nuclear magnetic resonance (NMR-MOUSE) allowing nondestructive high-resolution measurement of depth profiles as a function of time and space. The NMR signal is sensitive to both the monomer concentration and changes in molecular mobility. Upon irradiation with blue light, it first increases due to molecular mobility enhanced by the reaction heat and then decreases exponentially with the monomer concentration as the polymer signal is lost in the dead time of the instrument upon curing. The space and time dependence of the NMR signal can be described by the photo-polymerization reaction kinetics together with a heuristic approximation of the temperature dependence.

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

“…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 . This supports the analysis in two different days and light intensity in this study.…”

“…The irradiation time, radiation power and distance from the curing device to the irradiated region directly influence the conversion degree and, consequently, the mechanical properties of a cement and in the bond strength of the fiberglass post to the radicular dentin 5,8,21 . Other variables that can influence the amount of generated free radicals and the conversion degree are the post diameter, arrangement of the fibers, composition, translucence degree and the cementation line thickness 12,[25][26][27] . In the present experiment, the power and time were kept constant, 1,500mW/cm 2 and 40s, respectively, as well as the distance from the curing device to the cemented post.…”

Microporosity and polymerization contraction as function of depth in dental resin cements by X‐ray computed microtomography

“…In the photo‐cure polymerization reaction, the rate of conversion of monomers is greater than the verified in the self‐cured (Bruno Luiz Santana Vicentin et al, 2017). This rate reduces with increasing distance from the irradiated surface (Marchi Netto, Steinhaus, Hausnerova, Moeginger, & Blümich, 2013; Bruno Luiz Santana Vicentin et al, 2017) according to the Lambert–Beer Law because of light attenuation (Watts, 2005). Thus, the proximity to the photo‐cure device in the first 0.5 mm promoted faster polymerization reaction, resulting in rapid vitrification of the polymeric matrix, restricting the mobility of macroradicals, thus forming shorter polymer chains with lower molecular weight (Watts, 2005).…”

“…It is important to notice an important behavior of the material: as the microporosity decreases, the volumetric contraction increases (both as function of increasing depth). This is due to the attenuation of light irradiance through the cement mass, resulting in slower rate of polymerization and extended gel‐point at the deepest layers (Marchi Netto et al, 2013; Soares et al, 2017; Vicentin et al, 2017). Therefore, the greater the light intensity in a layer the higher the rate of polymerization (and vitrification), resulting in decreased volumetric contraction and increased microporosity.…”