Shpotyuk Olha, Ingram Adam, Shpotyuk Oleh, Bezvushko Elvira
Department of Pediatric Dentistry, Danylo Halytsky Lviv National Medical University, Ukraine.
Department of Physics, Opole University of Technology, Poland.
Polim Med. 2017 Jul-Dec;47(2):91-100. doi: 10.17219/pim/81450.
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.
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).
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.
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.
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.
当前生物聚合物工程领域的突破性进展依赖于在最精细的亚纳米长度尺度上对原子缺陷空间进行可靠诊断。正电子湮没寿命谱就是这样一种诊断方法，它探究电子与其反粒子（正电子）在诸如自由体积缺陷、空位、类空位团簇、界面空隙和孔隙等结构实体中的相互作用的时空连续关系。
本文旨在突出正电子湮没寿命谱作为一种信息丰富的仪器工具的可能性，以参数化光固化二甲基丙烯酸酯类牙科修复复合材料（以德国哈瑙的贺利氏古莎有限公司的Charisma®和乌克兰基辅的Oksomat-AN有限公司的Dipol®为例）中的自由体积演变。
研究对象为市售的二甲基丙烯酸酯类牙科修复复合材料Charisma®和Dipol®。分析使用了基于耦合到BaF2闪烁体探测器的2个光电倍增管以及ORTEC®（美国橡树岭的ORTEC公司）电子设备的分辨率为230皮秒的快 - 快符合系统，以在正常测量统计中记录寿命谱，累积约100万个符合事件。
两种复合材料中的湮没过程均被确定为正电子 - 电子偶素（Ps）混合俘获，其中邻位 - Ps衰变完全由聚合物基体中的自由体积空穴引起，第二成分主要由填料纳米颗粒与周围聚合物之间的界面自由体积空穴定义。牙科修复复合材料中光聚合体积收缩的最合适的与模型无关的估计可以使用平均正电子湮没寿命来完成。寿命谱的部分约束x4项分析效率较低，方差散射更大，还有固定最短寿命的额外伪像，导致第二成分中存在未解决的混合情况。基于探索x3 - x2耦合分解算法的半经验模型，可以对光固化下Ps和正电子俘获位点的转变进行有意义的唯象描述，这种转变在Charisma®中比在Dipol®纳米复合材料中更有效。
利用正电子湮没寿命谱深入了解二甲基丙烯酸酯类牙科复合材料中的空隙演变过程，有助于诊断、表征和设计新型生物材料，以便在医学实践中得到更广泛应用。
