Nanocomposites and nanomaterials

Light-curing effects in acrylic-type dental restorative composites probed by annihilating positrons 
Shpotyuk O.O.1, Ingram A.2, Shpotyuk O.I.3,4, Cebulski J.5, Bezvushko E.V.1
1Danylo Halytsky Lviv National Medical University, 69, Pekarska st., Lviv, Ukraine
2 Opole University of Technology, 75, Ozimska str., Opole, 45370, Poland
3 Vlokh Institute of Physical Optics, 23, Dragomanov str., Lviv, 79005, Ukraine
4Jan Dlugosz University in Czestochowa, 13/15, al. Armii Krajowej, Czestochowa, 42200, Poland
5WMP, University of Rzeszow, 1, Pigonia st., Rzeszow, Poland

Possibilities of annihilating positrons in lifetime measuring mode is analyzed in application to commercially available dimethacrylate-based dental restorative composites, these being Charisma (Heraeus Kulzer GmbH, Germany), Dipol (Oksomat-AN Ltd, Ukraine) and ESTA-3 (Kiev, Ukraine). These composites are based on monomer consisted of bisphenol A-diglycidyl dimethacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA) modified by multisized filler particles (highly dispersive phase of silica glass). The positron annihilation lifetime spectra were treated with different algorithms described in details elsewhere [1,2]. 
In respect to the data parameterized within constraint-free x3-term analysis, the annihilation processes in these nanocomposites are identified as conversion from “purely” positron trapping to positronium (Ps) decaying, where ortho-Ps component is caused entirely by free-volume holes in the polymer matrix, and positron-trapping component is defined preferentially by interfacial free-volume holes between filler particles and surrounding polymer matrix. Most adequate model-independent estimation of polymerization volumetric shrinkage in the studied nanocomposites can be performed in terms of average positron lifetime. Meaningful phenomenological description of photoinduced ortho-Ps transferring in positron-trapping sites, can be developed at the basis of semi-empirical model exploring a so-called x3-x2-coupling decomposition algorithm [2].

1.	Shpotyuk Olha, Ingram Adam, Shpotyuk Oleh. Free volume structure of acrylic-type dental nanocomposites tested with annihilating positrons // Nanoscale Res. Lett.-2016.-11.-P. 528-1-6.
2.	Shpotyuk Olha, Ingram Adam, Shpotyuk Oleh, Bezvushko Elvira. Light-cured dimethacrylate dental restorative composites under a prism of annihilating positrons // Polim. Med.-2017.-47.-91-100.