Influence of blenching agents on the mechanical properties and colour of dental restorative nanocomposite

Purpose: Bleaching agents are commonly used to make the natural dentition look more attractive. Currently, in addition to products from reputable manufacturers, products of not fully known origin are available for purchase. The aim of the study was to investigate whether products of this type have a destructive influence on the mechanical and aesthetic properties of the dental restorative nanocomposite. Design/methodology/approach: Four bleaching agents were used, two recognized brands, and two products were purchased from Chinese websites (their manufacturer is unknown). Two gels and two types of whitening strips were used. One composite nanomaterial was used. Microhardness, diametral tensile strength,, compressive strength and colour measurements were tested. Findings: For some bleaching agents, studies have shown a relatively small effect on mechanical properties and an acceptable effect on colour changes. Regardless of the observed changes, the use of bleaching agents qualified for the experiment should be considered safe for composites. Research limitations/implications: The number of blenching agents used as well as dental composites in this study was limited. In future studies, increasing the number of cycles in the bleaching process should be considered. Practical implications: A popular method of improving the aesthetic properties of teeth is the use of a wide range of blenching agents. Most patients who use teeth whitening procedures are also users of composite fillings. The use of bleaching agents may have a different effect on the mechanical and aesthetic restorative composites. For economic reasons, many people decide to import cheap bleaching agents of unknown or dubious origin via Internet services to perform the bleaching process on their own. In this study, it was investigated whether products of this type have an influence on the mechanical and aesthetic properties of the dental restorative nanocomposite. Originality/value: Until now, no comparison of the safety of the use of bleaching agents of recognized manufacturers and of unknown origin in terms of the effect on composite materials has been presented, despite their high social importance

Composition of Nb-Ta-Ti-Sn-W oxide minerals: indicators of magmatic to hydrothermal evolution of the Cínovec granite intrusion and Sn-W deposit (Czech Republic)

The Cínovec (Zinnwald) Sn-W ore deposit is genetically linked to intrusion of late Variscan, highly fractionated granite which expresses the latest evolutionary stage of a volcano-plutonic system of the Teplice caldera. Whole intrusion is relatively highly fractionated and from bottom ( ~ 1500 m) to top part of cupola-shaped deposit is obviously following succession from biotite (annite) granodiorite-granite-zinnwaldite granite, with the partly greisenized uppermost part at 300–500 m depth (Štemprok 1965, 1971). In 1961−63 the Czechoslovakian Geological Survey (CGS) drilled a 1596 m deep borehole in the Sn-W-mineralized Cínovec granite cupola (Štemprok 1965, Štemprok & Šulcek 1969). All studied rock types include W- and Sn-bearing minerals (wolframite series, scheelite and cassiterite) and disseminated accessory Nb-Ta-Ti-W- Sn minerals (Štemprok & Šulcek 1969, Štemprok 1989, Johan and Johan 1994) which were obtained from the collection of CGS in Prague and studied by BSE and electron microprobe. They crystallized in following succession: rutile + columbite + cassiterite (biotite granodiorite) → rutile + columbite + W-rich ixiolite + cassiterite + scheelite in zinnwaldite granite. Textural relationships of these Nb- Ta-Ti-Sn-W minerals indicate predominantly their magmatic origin and part of them (e.g., cassiterite and columbite) show minor post-magmatic alteration phenomena like distinctly inhomogeneous mixtures of secondary pyrochlore-group minerals (“oxykenopyrochlore” and oxycalciopyrochlore). Nb/Ta and Fe/Mn fractionation trends led to characteristic Mn and Ta enrichment from bottom (biotite granite) to uppermost zinnwaldite granite, especially in columbite-group minerals. While Nb/ Ta fractionation is limitedly applied, effective Fe/ Mn fractionation led to significant Mn – enrichment of late-magmatic phases [columbite-(Mn) and W-rich ixiolite]. Post-magmatic to hydrothermal metasomatic fluids caused partial greisenization of the granites and this stage is represented by latest columbite + scheelite + cassiterite + wolframite assemblage. The last two minerals were objects of extensive mining in the past. Although the hydrothermal system was enriched in F and Li (presence of topaz and zinnwaldite), there are only relatively limited Nb/Ta and Fe/Mn fractionations in post-magmatic columbite. Similarly to primary fractionation, both Nb/Ta and Fe/Mn ones take place and overlap characteristic primary Mn-enrichment. Effective Mn-redistribution is predominantly controlled by crystallization of Mn-dominant wolframite like hübnerite in the hydrothermal stage. Scandium is typical rare element in primary (magmatic) and secondary (hydrothermal) mineral assemblage. While primary Sc-fractionation continues the ongoing Sc-enrichment mostly in columbite to uppermost parts of intrusion, the hydrothermal Sc-redistribution is controlled by crystallization of main ore mineral – wolframite, which consumed a major part of scandium. Main substitution mechanisms in rutile-cassiterite-wolframite-columbite assemblage include following heterovalent substitutions: (i) Ti 3 (Fe,Mn) 2+ −1 (Nb,Ta) −2 , (ii) Ti 2 Fe 3+ −1 (Nb,Ta) −1 , (iii) (Nb,Ta) 4 Fe 2+ −1 W −3 . Moreover, a part of minor cations can enter via: (iv) (Fe,Mn) 2+ 1 W 1 (Fe,Sc) 3+ −1 (Nb,Ta) −1 into wolframite lattice, (v) W 1 (Ti,Sn) 1 (Nb,Ta) −2 , (vi) (Sc,Fe) 3+ 3 (Fe,Mn) 2+ −2 (Nb,Ta) −1 , and (vii) W 2 Sc 3+ 1 (Nb,Ta) −3 into columbite lattice. Calculated Fe 3+ can be introduced into rutile lattice predominantly via mechanism (ii), while via (iv) into wolframite lattice and together with Sc 3+ via (vi) into columbite lattice. The last mechanism results in charge imbalance of A and B positions of columbite lattice entering R 3+ cations to. The distinctly varying calculated Fe 3+ values can refer to changing f O 2 during columbite, rutile, W-rich ixiolite and wolframite crystallization. Therefore, the textural and crystallo-chemical features of studied Nb-Ta-Ti-Sn-W oxide minerals in the Cínovec granite cupola reflect a complex geochemical development of this granite system and ore mineralization from primary magmatic stage, through late-magmatic to subsolidus conditions, and ending in distinct hydrothermally – metasomatic overprint of pre-existing phases

Influence of silver-containing filler on antibacterial properties of experimental resin composites against Enterococcus faecalis

Purpose: The aim of the presented work was to investigate the impact of the S-P introduction into resin-based composites on their effectiveness against Enterococcus faecalis (E. faecalis). Design/methodology/approach: Seven experimental composites based on typical matrix were developed. Six of them contained a filler with antimicrobial properties (silver sodium hydrogen zirconium phosphate, S-P), while the control material contained only common reinforcement fillers. The materials were characterized in terms of the dispersion of the extender in the matrix and then subjected to microbiological tests. The efficiency in the reduction of E. faecalis in the microenvironment was tested. Findings: The composites show a satisfactory distribution of fillers and a high initial reduction of bacteria colonies for the tested strain of E. faecalis. The reduction in bacteria colonies achieved for S-P concentrations from 7% to 13% was similar (median value from 99.8 to 99.9%, when for control material and compound with 1% S-P the number of colonies increased compared to positive control. Research limitations/implications: Laboratory test results may differ from in vivo test performance. In addition, there are many models for conducting laboratory antimicrobial efficacy studies, the results of which are also varied. The cytotoxic tests, long-term investigations and in vivo experiments need to be performed in future experiments. Practical implications: E. faecalis is a Gram-positive bacterium that is commonly detected in persistent endodontic infections and may enter the root canal through the coronal part. Development of composites with antimicrobial properties against this bacterium is as important as obtaining efficacy against cariogenic bacteria. Originality/value: The antimicrobial effectiveness against E. faecalis of experimental composites with submicrometer-sized particles of S-P was not investigated until now

The novel semi-biodegradable interpenetrating polymer networks based on urethane-dimethacrylate and epoxy-polyester components as alternative biomaterials

Purpose: This paper presents the pilot study aimed at the development of new full interpenetrating polymer networks based on urethane-dimethacrylate and biodegradable epoxy-polyester as the proposition of new biomaterials with gradually emerging porosity. Methods: The urethane-dimethacrylate monomer was obtained from 4,4’-methylenebis(phenyl isocyanate) and tetraethylene glycol monomethacrylate. The redox-initiating system was employed for its radical polymerization. The epoxy-polyester was produced by oxidation of the polyester, synthesized from succinic anhydride and allyl glicydyl ether. It was cured in a step-growth process with biogenic, aliphatic amine – spermidine. The mixtures of both monomers with adequate curing agents were room temperature polymerized. The hardened materials were characterized for damping behavior and dynamic modulus, hardness, water sorption, the course of hydrolytic degradation as well as the morphology – before and during the degradation process. Results: The cured materials revealed the nonporous, dense morphology. In the hydrolytic environment, the epoxy-polyester network degraded and the porous urethane-dimethacrylate scaffold remained. The epoxy-polyester appeared to prevent the urethane-dimethacrylate from attaining a high degree of conversion, even if the polymerization rate and the molecular mobility of the latter one are higher than those of the epoxy-polyester. The most homogeneous material with the best physico-mechanical properties was obtained when the urethane-dimethacrylate content was smaller than the epoxy-polyester content, respectively 25 and 50 wt%. Conclusions: The system presented in this work could be useful in tissue engineering, where at the beginning of the tissue regeneration process it would meet the implant mechanical properties and then would deliver its porosity, facilitating the tissue regeneration process