Free Volume Structure of Acrylic-Type Dental Nanocomposites Tested with Annihilating Positrons

Abstract

Positron annihilation spectroscopy in lifetime measuring mode exploring conventional fast-fast coincidence ORTEC system is employed to characterize free volume structure of commercially available acrylic-type dental restorative composite Charisma® (Heraeus Kulzer GmbH, Germany). The measured lifetime spectra for uncured and light-cured composites are reconstructed from unconstrained x3-term fitting and semi-empirical model exploring x3-x2-coupling decomposition algorithm. The governing channel of positron annihilation in the composites studied is ascribed to mixed positron-Ps trapping, where Ps decaying in the third component is caused entirely by input from free-volume holes in polymer matrix, while the second component is defined by free positron trapping in interfacial free-volume holes between filler nanoparticles and surrounded polymer matrix. Microstructure scenario of the photopolymerization shrinkage includes cross-linking of structural chains in polymer matrix followed by conversion of bound positron-electron (positronium) traps in positron-trapping interfacial free-volume voids in a vicinity of agglomerated filler nanoparticles.

Light-curing effects in acrylic-type dental nanocomposites probed by annihilating positrons: the case of densely monolith ЭCTA-3® restoratives

“…The methodology of the current PAL studies on light-curing photopolymerization effects was identical as in our preliminary research (Shpotyuk et al 2016b(Shpotyuk et al , 2017.…”

“…( Shpotyuk et al 2016bShpotyuk et al , 2017. If Ps-decaying and positron trapping sites are interconnected, so that no changes occur in other channels, we can treat these PAL spectra within the × 3-× 2-CDA (see Shpotyuk et al 2016a).…”

“…In our recent works (see Shpotyuk et al 2016bShpotyuk et al , 2017, this possibility was disclosed for two commercially available dimethacrylate-based DRC, namely, the Charisma ® (Heraeus Kulzer GmbH, Germany) and the Dipol ® (Oksomat-AN Ltd, Ukraine). These DRC belongs to loosely-monolith restoratives, since they are composed of monomer (bisphenol A-diglycidyl dimethacrylate, and triethylene glycol dimethacrylate) modified by multisized glass filler particles (typically, of pyrogenic SiO 2 ) to mediated weight-packing densities approaching 70-78%.…”

Comparative study of free-volume changes in light-cured (dimeth)acrylate-type dental resin composites affected to artificial aging in dry-air and water-immersed mode

“…Recently, we have shown that three-term decomposited PAL spectra with unconstrained fitting parameters treated with × 3-× 2-CDA (coupling decomposition algorithm) methodology (Chakraverty et al 2005;Mitra et al 2006) allow an adequate description of modification processes in the DRC caused by light-curing polymerization and artificial dry aging (Shpotyuk et al 2016(Shpotyuk et al , 2017(Shpotyuk et al , 2020. Current research is intended to compare the microstructure nature of degradation processes in light-cured polymer/filler composites exemplified by commercially available DRC Charisma ® (Heraeus Kulzer GmbH, Germany) affected to one-year aging in dry-air and water-immersed mode.…”

Light-cured dimethacrylate dental restorative composites under a prism of annihilating positrons

“…Such simplification makes it possible to resolve additional components in the generalized x2-term PAL spectrum for modified matrix (with lifetime τ int and intensity I int ), the compensating (τ n , I n ) input in the 1 st channel being found assuming a reasonable condition of full interchannel equilibrium. [33][34][35][36][37] Thereby, the parameterization of transformed Ps-e + traps in the photopolymerized DRC matrix can be performed accepting (τ n , I n ) and (τ int , I int ) as the respective 1 st and 2 nd components of the generalized x2-term PAL spectrum for some hypothetical medium obeying parameterization, with respect to formalization of a simple 2-state positron-trapping model. [4][5][6][7][8] The defectrelated τ int positron lifetime in this model reflects appearing/disappearing traps in dependence on a positive/negative sign of I n and I int intensities.…”