Characterisation of microparticle waste from dental resin-based composites

Clinical applications of resin-based composite (RBC) generate environmental pollution in the form of microparticulate waste. Methods: SEM, particle size and specific surface area analysis, FT-IR and potentiometric titrations were used to characterise microparticles arising from grinding commercial and control RBCs as a function of time, at time of generation and after 12 months ageing in water. The RBCs were tested in two states: (i) direct-placement materials polymerised to simulate routine clinical use and (ii) pre-polymerised CAD/CAM ingots milled using CAD/CAM technology. Results: The maximum specific surface area of the direct-placement commercial RBC was seen after 360 s of agitation and was 1290 m2/kg compared with 1017 m2/kg for the control material. The median diameter of the direct-placement commercial RBC was 6.39 μm at 360 s agitation and 9.55 μm for the control material. FTIR analysis confirmed that microparticles were sufficiently unique to be identified after 12 months ageing and consistent alteration of the outermost surfaces of particles was observed. Protonation-deprotonation behaviour and the pH of zero proton charge (pHzpc) ≈ 5–6 indicated that the particles are negatively charged at neutral pH7. Conclusion: The large surface area of RBC microparticles allows elution of constituent monomers with potential environmental impacts. Characterisation of this waste is key to understanding potential mitigation strategies

Distal Versus Conventional Radial Access for Coronary Angiography and Intervention: The DISCO RADIAL Trial.

BACKGROUND: Currently, transradial access (TRA) is the recommended access for coronary procedures because of increased safety, with radial artery occlusion (RAO) being its most frequent complication, which will increasingly affect patients undergoing multiple procedures during their lifetimes. Recently, distal radial access (DRA) has emerged as a promising alternative access to minimize RAO risk. A large-scale, international, randomized trial comparing RAO with TRA and DRA is lacking. OBJECTIVES: The aim of this study was to assess the superiority of DRA compared with conventional TRA with respect to forearm RAO. METHODS: DISCO RADIAL (Distal vs Conventional Radial Access) was an international, multicenter, randomized controlled trial in which patients with indications for percutaneous coronary procedure using a 6-F Slender sheath were randomized to DRA or TRA with systematic implementation of best practices to reduce RAO. The primary endpoint was the incidence of forearm RAO assessed by vascular ultrasound at discharge. Secondary endpoints include crossover, hemostasis time, and access site-related complications. RESULTS: Overall, 657 patients underwent TRA, and 650 patients underwent DRA. Forearm RAO did not differ between groups (0.91% vs 0.31%; P = 0.29). Patent hemostasis was achieved in 94.4% of TRA patients. Crossover rates were higher with DRA (3.5% vs 7.4%; P = 0.002), and median hemostasis time was shorter (180 vs 153 minutes; P < 0.001). Radial artery spasm occurred more with DRA (2.7% vs 5.4%; P = 0.015). Overall bleeding events and vascular complications did not differ between groups. CONCLUSIONS: With the implementation of a rigorous hemostasis protocol, DRA and TRA have equally low RAO rates. DRA is associated with a higher crossover rate but a shorter hemostasis time

Cadmium and lead:contamination

The presence of cadmium and lead in the environment is greatly sourced and affected by anthropogenic activities. These activities are severe and present global environmental and human health issues. The detection of these elements and the determination of their chemical state thus toxicity has challenged scientists and engineers for many years. Based on the knowledge gained, production is changing and regulations are being put in place to be able to reduce and control the effect of cadmium and lead in the environment

In situ studies of green rust formation using synchrotron-based X-ray scattering : helping to develop a new range of environmental materials.

The natural environment is rich in nanoparticulate mineral phases, such as iron and manganese oxides and oxyhydroxides, with unique chemical properties. Some of these minerals, for example Green Rusts, have the potential to be developed into a new generation of environmental remediation materials which could be utilized to clean up contaminated land. Advances in X-ray technologies at third-generation synchrotron sources (e.g. the Diamond Light Source) have helped to characterise the formation and crystallisation of highly reactive nanoparticles under simulated environmental conditions. In this article, Dr. Imad Ahmed, Dr. Sam Shaw, Ms. Gabriella Kakonyi and Prof. Liane G. Benning, describe how stateof- the-art in situ time-resolved synchrotron-based scattering and diffraction methods are used to determine the mechanisms and kinetics of green rust nanoparticle formation and growth

The environmental impact of dental amalgam and resin-based composite materials

Direct-placement dental restorative materials include dental amalgam, glass ionomer, resin-modified glass ionomer, compomer and resin-based composite (RBC). The choice of restorative material is determined by its ability to restore the structure and/or the aesthetic appearance of the dentition and to impart a net therapeutic value. In this way, the most appropriate material system is chosen to manage each particular clinical situation in the most effective manner. The most commonly used direct-placement materials in everyday modern dentistry are dental amalgam and resin-based composites. To date, concerns about the environmental impact from the use of dental materials has focused on dental amalgam and mercury release. It is now evident that the continued use of dental amalgam is time-limited on the basis of environmental pollution as recommended by the Minamata Treaty. The recommendations include a planned phase-down of use of dental amalgam with an anticipated complete phase-out by 2030. The environmental impact of other restorative dental materials deserves further consideration. This article provides a detailed overview of the environmental issues associated with the use of dental amalgam, the potential environmental issues associated with the alternative resin-based composite restorative materials and to consider recommendations for further research

Behavior of dental composite materials in sterilized and non-sterilized landfill leachate

Treatment of used and unused dental resin based composites resulting from the activities of dental industries and clinics is challenging. Disposal to landfill site is commonly utilized to manage this waste. We investigated the release of monomers from dental composites in landfill leachate and the chemical changes of sterilized and non-sterilized leachate in the existence of dental composites. Solid phase micro-extraction (SPME) coupled with high performance liquid chromatography (HPLC) was used to extract and quantify the released monomers. Chemical characterization of leachate was carried out using pH meter, gas chromatography (GC), ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS). The HPLC results, revealed that Bis-GMA, TEGDMA, UDMA, HEMA and BPA monomers were released from dental composites. According to the results of pH, GC, IC and ICP-MS, the presence of dental composites has no significant effect in the chemistry of leachate except increasing the production of CH4 and CO_2. However, autoclaving increased pH values and decreased calcium concentration in sterilized samples. Furthermore, Mn^concentration increased and Fe^ concentration decreased in non-sterilized samples due to microbial activities

Green rust nanoparticle formation, stability and oxidation, and its role in natural and engineered systems.

Highly reactive green rust (GR) nanoparticles are believed to play an important role in the geochemistry of water saturated sediments (e.g. hydromorphic soils) and engineered systems where zero-valent iron is used for decontaminating polluted sites (e.g. permeable reactive barriers). The presence of structural Fe2+ within GR and its high specific surface area make it an effective reductant for many inorganic (e.g. Cr, U, Se) and organic substances (e.g. tetrachloroethene (TCE)). These reduction processes can lead to breakdown of organic molecules or the formation of insoluble reduced inorganic phases (e.g., UO2(s)), thus reducing the bioavailability of these toxic compounds. Understanding the formation and geochemical stability of GR is key to assessing its potential role in natural sediments and engineered environments. However, characterizing GR is difficult due to the rapid oxidation (seconds - minutes) of structural Fe2+ in the presence of air. Thus, to obtain detailed information about the mechanism and kinetics of GR formation, stabilisation and oxidative breakdown, novel synchrotron-based methods have been developed which combine in situ and time-resolved X-ray diffraction/scattering (XRD/SAXS) analysis with controlled anaerobic chemical synthesis. This system allowed the simultaneous quantification of several chemical parameters in the aqueous solution (i.e., pH, Eh) with detailed analysis of the changes in the solid phase crystal structure. In conjunction with this X-ray Absorption Spectroscopy (XAS) was used to characterise the speciation of trace elements (i.e. U, Zn and Se) associated with GR as it crystallised and/or transformed. The formation of green rust (Fe2+/Fe3+ > 1.2) from solution occurs via a 3 stage process. The first stage is the nucleation and growth of ferric hydroxysulfate (schwertmannite) nanoparticles (~5 nm). With increasing pH the schwertmannite transforms into nanogoethite particles (< 50 nm). This process is catalyzed by adsorbed Fe2+ ions on the surface of schwertmannite which facilitates the transformation reaction. Green rust formation occurs when the surface adsorbed Fe2+ hydrolyses and reacts with the goethite above pH 7. With further increases in pH the GR remains stable up to pH 10. Experiments conducted at lower Fe2+/Fe3+ ratios (0.5-1) show that green rust is formed at pH 7-9, but is metastable with respect to magnetite above pH 7. Oxidation reactions reveal that the green rust breaks down to a mixture of Lepidocrocite (L) and goethite (G) with the L/G ratio and the rate of breakdown increasing with pH. Speciation analysis indicates that U6+ and Se6+ are reduced to U4+ and Se4+/Se0 during GR formation and that during the oxidation process the reduced trace elements are fully or partially reoxidised, yet a significant amount remains sorbed to the FeOOH particles. This study suggests that green rust nanoparticles could be utilised to sequester key inorganic contaminants under a range of natural pH conditions (neutral - alkaline). Also, following oxidation, a significant proportion of some trace elements are retained within the oxidised minerals which could significantly reduce their long-term mobility

Simultaneous detection of monomers associated with resin-based dental composites using SPME and HPLC

As resin-based composites (RBC) replace dental amalgam for environmental reasons, there is a requirement to understand the environmental impact of this alternative dental restorative material. In this study we standardize the simultaneous detection of five monomeric components associated with RBCs using high performance liquid chromatography (HPLC) coupled with solid-phase microextraction (SPME). Factors affecting method performance (detection wavelength, calibration conditions, method sensitivity/accuracy/precision, extraction time/efficiency) are evaluated using standard solutions containing the mixture of TEGDMA, UDMA, Bis-GMA, BPA and HEMA. Detection sensitivity and analytical efficiency of the method is optimized for these compounds using 200 nm detection wavelength, PDMS/DVB fiber and extraction time of 90 min. Analytical accuracy of the HPLC is >95% for all monomers, with precision of 2.3–5.1%. Detection limits under the conditions described are 25 µg/L for HEMA, BPA, UDMA, Bis-GMA, and 100 µg/L for TEGDMA. The extraction time is governed by the largest molecular weight compounds

Formation of green rust sulfate : a combined in situ time-resolved X-ray scattering and electrochemical study.

The mechanism of green rust sulfate (GR-SO4) formation was determined using a novel in situ approach combining time-resolved synchrotron-based wide-angle X-ray scattering (WAXS) with highly controlled chemical synthesis and electrochemical (i.e., Eh and pH) monitoring of the reaction. Using this approach,GR-SO4 was synthesized under strictly anaerobic conditions by coprecipitation from solutions with known FeII/FeIII ratios (i.e., 1.28 and 2) via the controlled increase of pH. The reaction in both systems proceeded via a three-stage precipitation and transformation reaction. During the first stage,schwertmannite (Fe8O8(OH)4.5(SO4)1.75) precipitated directly from solution at pH 2.8−4.5. With increasing pH (>5), Fe2+ ions adsorb to the surface of schwertmannite and catalyze its transformation to goethite (α-FeOOH) during the second stage of the reaction. In the third stage, the hydrolysis of the adsorbed Fe2+ ions on goethite initiates its transformation to GR-SO4 at pH >7. The GR-SO4 then continues to crystallize up to pH ∼8.5. These results suggest that with an FeII/FeIII ratio of ≤2 in the initial solution the structural FeII/FeIII of the GR-SO4 will be close to that of the starting composition