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This research is intended to compare degradation processes in light-cured (dimeth)acrylate-type polymer/filler dental composites affected to aging in dry-air and water-immersed mode. The positron annihilation lifetime (PAL) spectroscopy has been employed to study changes in atomic-deficient structure in these composites under aging. Under light-curing polymerization initiating crosslinking of monomer chains, fragmentation of free-volume holes in resin matrix dominates over enhanced fraction of trapped positrons, since filler–particles assemblies get to be more tightly covered by surrounding polymer causing disappearing of interfacial voids at the filler–polymer surface. Therefore, the PAL spectra-transforming trend in light-cured composites obeys inverse positron-to-Ps trapping conversion. In contrast, the PAL spectra-transforming trend in these restoratives under aging obeys direct Ps-to-positron trapping conversion. After dry-air aging, the observed changes in the density of annihilation sites are ascribed to a strong agglomeration of Ps-decay holes in polymer sub-system accompanied by weaker agglomeration and appearance of positron traps in filler–polymer sub-system. Under the water aging, the agglomeration of Ps-decaying holes in the polymer sub-system is suppressed due to absorbed water molecules, this effect being slightly revealed at lower polymerization. New positron traps are observed at the filler–polymer interfaces in all light-cured composites. The agglomerated Ps-decay holes in a polymer matrix and positron traps inside filler–particles assemblies and filler–polymer interfaces of artificially aged composites cause their progressive microcracking.

Dental caries and its complications remain one of the current problems of pediatric dentistry. Important in its development is a complex of local and general factors that contribute to the insufficient enamel mineralization, which creates conditions for the occurrence of dental caries, that is, caries favorable enamel is formed. Viral infection, which is nowadays extremely common in both adults and children, is one of the important risk factors for dental pathology, as it can lead to a reduction in nonspecific resistance and depletion of the body's defense mechanisms.Objective. Assessment of caries incidence of deciduous teeth in children with Epstein-Barr viral infection.Material and methods. To assess the state of dental hard tissues, 133 children aged 6-9 years (48 children with infectious mononucleosis and 85 practically healthy children) were examined. The prevalence and intensity of decay teeth caries, as well as caries activity were studied.Results. It was found that the prevalence and intensity of temporary tooth decay is significantly higher in children with Epstein-Barr viral infection than in children without evidence of viral infection. The proportion of incisors and canines affected by caries averaged 10.33 ± 1.08% with 89.64 ± 2.76% of temporal molar lesions. And the degree of activity of dental caries revealed in 20,94 ± 2,58% of children with infectious mononucleosis, the II degree of activity - in 50,22 ± 3,24%, the III degree of activity - in 21,23 ± 1,45%, this is true higher than in virtually healthy children (p

Photopolymerization volumetric shrinkage in densely monolith dental restorative composites is characterized at the example of ЭCTA-3® composites, employing positron annihilation lifetime (PAL) spectroscopy within unconstrained × 3-term analysis applied to reconstructed PAL spectra. The governing process in these composites is identified as mixed positron-Ps trapping, where Ps-decaying originates from free-volume holes in polymer matrix, while free positron trapping occurs in interfacial holes between preferential filler nanoparticles and surrounded polymer matrix. Meaningful phenomenological description of this photopolymerization process is developed at the basis of semi-empirical model exploring the × 3- × 2-CDA (coupling decomposition algorithm). Within this approach, it is shown that under light-curing polymerization, strong monolithization of agglomerated filler particles occurs in these nanocomposites caused by photoinduced disappearing of Ps-decaying holes due to cross-linking of structural chains, mainly in “purely” polymer matrix.

The possibility of application of positron annihilation lifetime (PAL) spectroscopy to commercially available dimethacrylate-based dental restorative composites Dipol® (Oksomat-AN Ltd, Ukraine) subjected to photopolymerization due to light curing is analyzed. The governing annihilation process in these composites is identified as mixed positron (e+)-positronium (Ps) trapping, where Ps decaying is caused entirely by input from free-volume holes in polymer matrix superimposed on free e+-trapping contribution from interfacial free-volume holes between filler nanoparticles and surrounded polymer matrix. Photopolymerization shrinkage is revealed through decrease in the average lifetime of annihilating positrons due to opposite changes in Ps-decaying and e+-trapping channels. The growing light-activated polymerization is characteristic of both intensities related to the second and third components in the unconstrained ×3-term decomposed PAL spectra, accompanied by decrease in the corresponding lifetimes. This process resulted in enhanced trapping rate in the defects and depressed fractional free-volume saturation with light curing. Light exposure causes smaller voids in composites owing to free-volume fragmentation in Ps- and e+-trapping sites. The microstructure scenario for these transformations includes photo-induced cross-linking of structural chains in the polymer matrix, followed by conversion of o-Ps traps in interfacial free-volume voids near agglomerated filler nanoparticles. A meaningful description of this process is developed on the basis of the semi-empirical model exploring the ×3– ×2-coupling decomposition algorithm.

The applicability of positron annihilation lifetime (PAL) spectroscopy to identify volumetric changes in nanostructured polymer/filler substances is first verified at the example of commercially available dimethacrylate-based dental restorative composites Charisma® (Heraeus Kulzer GmbH, Germany) affected to light-curing photopolymerization and one-year dry physical ageing. Principal channel governing PAL spectra in these nanocomposites is recognized as mixed positron-Ps trapping, where positronium Ps (i.e. bound positron-electron state) decay occurs in free-volume holes localized preferentially in polymer matrix, while free positron self-annihilation is character for interfacial voids at the surface of filler-particles assemblies in the filler and/or mixed filler-polymer environment. Methodological algorithm for experimental PAL spectra refinement referred to as the x3-x2-CDA (coupling decomposition algorithm) is validated for these nanocomposites, obeying changes in atomic-deficient structure due to direct conversion between positron-trapping and Ps-decaying sites. Straightforward parameterization of the reconstructed PAL spectra allows meaningful identification of free-volume entities responsible for nanostructurization-driven transformations.

Peculiarities of microstructure changes in void subsystem under light-curing polymerization in loosely- and densely-packed polymer/filler nanocomposites are studied using positron annihilation lifetime (PAL) spectroscopy, at the example of commercially available dimethacrylate-based dental restorative composites Dipol® and ЭСТА-3®. Main process governing volumetric shrinkage in these polymer/filler nanocomposites is identified as positron-to-Ps trapping conversion, initiated by fragmentation of Ps-decay holes due to crosslinking of monomer chains. Meaningful description of photopolymerization changes is developed within x3-x2-CDA (coupling decomposition algorithm). In loosely-packed nanocomposites (such as Dipol®), the Ps decay takes place in intrinsic holes of polymer matrix, and free positron trapping occurs in filler sub-system, specifically in the interfacial voids between filler particles themselves and filler particles contacting with surrounding polymer. Under photopolymerization, fragmentation of intrinsic holes in polymer matrix dominates over enhanced trapping of positrons in filler sub-system since filler-particles assemblies get more tightly covered by polymer owing to disappearing of interfacial free-volume voids at their surface. In densely-packed nanocomposites (such as ЭСТА-3®), where positron trapping in interfacial voids at the surface of agglomerated filler particles takes minor role, the polymerization-driven fragmentation of Ps-decay holes causes stress inside monolith filler-particles assemblies, resulting in disappearing of some interparticulate traps (positron-trapping voids between filler particles).

Background Breakthrough resolutions in current biopolymer engineering rely on reliable diagnostics of atomic-deficient spaces over the finest sub-nanometer length scales. One such diagnostic is positron annihilation lifetime spectroscopy, which probes space-time continuum relationships for the interaction between electrons and their antiparticle (positrons) in structural entities like free-volume defects, vacancies, vacancy-like clusters, interfacial voids and pores, etc. Objectives This paper is intended to highlight the possibilities of positron annihilation lifetime spectroscopy as an informative instrumentation tool to parameterize free-volume evolution in light-cured dimethacrylate dental restorative composites exemplified by Charisma® (Heraeus Kulzer GmbH, Hanau, Germany) and Dipol® (Oksomat-AN Ltd, Kyiv, Ukraine). Material and methods The subjects of the study were the commercially available dimethacrylate-type dental restorative composites Charisma® and Dipol®. The analysis used a fast-fast coincidence system of 230 ps resolution based on 2 photomultiplier tubes coupled to BaF2 scintillator detectors and ORTEC® (ORTEC, Oak Ridge, USA) electronics to register lifetime spectra in normal-measurement statistics evolving ~1 million coincidences. Results The annihilation process in both composites is identified as mixed positron-Ps (positronium) trapping, where ortho-Ps decaying is caused entirely by free-volume holes in the polymer matrix, and the 2nd component is defined mainly by interfacial free-volume holes between filler nanoparticles and the surrounding polymer. The most appropriate model-independent estimation of photopolymerization volumetric shrinkage in dental restorative composites can be done using averaged positron annihilation lifetime. Partiallyconstrained x4-term analysis of lifetime spectra is less efficient, giving greater scatter of variance with an additional artifact of fixed shortest lifetime allowing unresolved mixing in the 2nd component. A meaningful phenomenological description of transformations in Ps and positron-trapping sites under light curing, which occurs more efficiently in Charisma® than in Dipol® nanocomposites, can be developed at the basis of a semi-empirical model exploring a x3-x2-coupling decomposition algorithm. Conclusions A deep understanding of void-evolution processes in dimethacrylate dental composites employing positron annihilation lifetime spectroscopy makes it possible to diagnose, characterize and engineer novel biomaterials for advanced use in medical practice.

Positron annihilation lifetime spectroscopy combined with Doppler broadening of annihilation radiation was applied to study free-volume entities in GeS2-Ga2S3glasses affected by Ga additions. It is shown that Ga-related void sub-system plays a decisive role in positron trapping process, while the overall density variation is defined mainly by Ge-related sub-system. These results serve as basis for new characterization route for inner free-volume structure of these glasses.

One of the most important field of interest in respect to hydrogel materials is their capability to water storage. The problem mentioned above plays an important role regarding to diffusion of fluid media containing nanoparticles, what is very useful in biomedical applications, such as artificial polymeric implants, drug delivery systems or tissue engineering. In presented work, dehydration process in hydrogels used in ophthalmology as intraocular lenses was observed. Before measurements studied materials were immersed in deionized water and saline solution to obtain equilibrium swelling state. Studies of the dehydration process were carried out by use of gravimetric analysis, Fourier-Transform Infrared and Positron Annihilation Lifetime Spectroscopy. Obtained results revealed changes in hydrogen bonding structure and free volume holes induced by saline solution ingredients.

Light-curing volumetric shrinkage in dimethacrylate-based dental resin composites Dipol® is examined through comprehensive kinetics research employing nanoindentation measurements and nanoscale atomic-deficient study with lifetime spectroscopy of annihilating positrons. Photopolymerization kinetics determined through nanoindentation testing is shown to be described via single-exponential relaxation function with character time constants reaching respectively 15.0 and 18.7 s for nanohardness and elastic modulus. Atomic-deficient characteristics of composites are extracted from positron lifetime spectra parameterized employing unconstrained x3-term fitting. The tested photopolymerization kinetics can be adequately reflected in time-dependent changes observed in average positron lifetime (with 17.9 s time constant) and fractional free volume of positronium traps (with 18.6 s time constant). This correlation proves that fragmentation of free-volume positronium-trapping sites accompanied by partial positronium-to-positron traps conversion determines the light-curing volumetric shrinkage in the studied composites.

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.