Interaction of rat alveolar macrophages with dental composite dust

Particle and Fibre Toxicology, Nov 2016

Background Dental composites have become the standard filling material to restore teeth, but during the placement of these restorations, high amounts of respirable composite dust (<5 μm) including many nano-sized particles may be released in the breathing zone of the patient and dental operator. Here we tested the respirable fraction of several composite particles for their cytotoxic effect using an alveolar macrophage model system. ​Methods Composite dust was generated following a clinical protocol, and the dust particles were collected under sterile circumstances. Dust was dispersed in fluid, and 5-μm-filtered to enrich the respirable fractions. Quartz DQ12 and corundum were used as positive and negative control, respectively. Four concentrations (22.5 μg/ml, 45 μg/ml, 90 μg/ml and 180 μg/ml) were applied to NR8383 alveolar macrophages. Light and electron microscopy were used for subcellular localization of particles. Culture supernatants were tested for release of lactate dehydrogenase, glucuronidase, TNF-α, and H 2 O 2 . Results Characterization of the suspended particles revealed numerous nano-sized particles but also many high volume particles, most of which could be removed by filtering. Even at the highest concentration (180 μg/ml), cells completely cleared settled particles from the bottom of the culture vessel. Accordingly, a mixture of nano- and micron-scaled particles was observed inside cells where they were confined to phagolysosomes. The filtered particle fractions elicited largely uniform dose-dependent responses, which were elevated compared to the control only at the highest concentration, which equaled a mean cellular dose of 120 pg/cell. A low inflammatory potential was identified due to dose-dependent release of H 2 O 2 and TNF-α. However, compared to the positive control, the released levels of H 2 O 2 and TNF-α were still moderate, but their release profiles depended on the type of composite. Conclusions Alveolar macrophages are able to phagocytize respirable composite dust particle inclusive nanoparticles. Since NR8383 cells tolerate a comparatively high cell burden (60 pg/cell) of each of the five materials with minimal signs of cytotoxicity or inflammation, the toxic potential of respirable composite dust seems to be low. These results are reassuring for dental personnel, but more research is needed to characterize the actual exposure and uptake especially of the pure nano fraction.

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Interaction of rat alveolar macrophages with dental composite dust

Van Landuyt et al. Particle and Fibre Toxicology Interaction of rat alveolar macrophages with dental composite dust K. L. Van Landuyt 0 S. M. Cokic 0 C. Asbach P. Hoet L. Godderis F. X. Reichl B. Van Meerbeek 0 A. Vennemann M. Wiemann 0 KU Leuven BIOMAT, Department of Oral Health Sciences, University of Leuven & Dentistry University Hospitals Leuven , Kapucijnenvoer 7, Leuven 3000 , Belgium Background: Dental composites have become the standard filling material to restore teeth, but during the placement of these restorations, high amounts of respirable composite dust (<5 μm) including many nano-sized particles may be released in the breathing zone of the patient and dental operator. Here we tested the respirable fraction of several composite particles for their cytotoxic effect using an alveolar macrophage model system. Methods: Composite dust was generated following a clinical protocol, and the dust particles were collected under sterile circumstances. Dust was dispersed in fluid, and 5-μm-filtered to enrich the respirable fractions. Quartz DQ12 and corundum were used as positive and negative control, respectively. Four concentrations (22.5 μg/ml, 45 μg/ml, 90 μg/ml and 180 μg/ml) were applied to NR8383 alveolar macrophages. Light and electron microscopy were used for subcellular localization of particles. Culture supernatants were tested for release of lactate dehydrogenase, glucuronidase, TNF-α, and H2O2. Results: Characterization of the suspended particles revealed numerous nano-sized particles but also many high volume particles, most of which could be removed by filtering. Even at the highest concentration (180 μg/ml), cells completely cleared settled particles from the bottom of the culture vessel. Accordingly, a mixture of nano- and micron-scaled particles was observed inside cells where they were confined to phagolysosomes. The filtered particle fractions elicited largely uniform dose-dependent responses, which were elevated compared to the control only at the highest concentration, which equaled a mean cellular dose of 120 pg/cell. A low inflammatory potential was identified due to dose-dependent release of H2O2 and TNF-α. However, compared to the positive control, the released levels of H2O2 and TNF-α were still moderate, but their release profiles depended on the type of composite. Conclusions: Alveolar macrophages are able to phagocytize respirable composite dust particle inclusive nanoparticles. Since NR8383 cells tolerate a comparatively high cell burden (60 pg/cell) of each of the five materials with minimal signs of cytotoxicity or inflammation, the toxic potential of respirable composite dust seems to be low. These results are reassuring for dental personnel, but more research is needed to characterize the actual exposure and uptake especially of the pure nano fraction. Dental composite; Nanoparticle; Biocompatibility; Filler; Dust; Inhalable; Occupational; Dentist; Nano-dust; Resin; NR8383; Alveolar macrophage; Biotest - Background After polymerization, the surface of a composite restoration is usually finished with diamond burs, stones or disks to remove excess material. Once the restoration has a satisfying shape, the composite will be polished using disks and rubber points, wheels and cups. Finishing a composite restoration is by preference performed using water-cooling, but in clinical circumstances this is not always possible (for example when using disks, or due to reduced visibility) [1]. Previous research revealed that composite restorations release high amounts of very fine respirable dust during abrasive procedures in the breathing zone of the patient and dental operator [2]. Exposure measurements in a dental office confirmed that finishing and polishing composite restorations leads to spikes in the concentrations of nanoparticles [3]. Further laboratory assessment showed that composites, irrespective of their classification, mainly released sub-100 nm particles. These particles often consisted of very small pieces of composite with filler particles embedded in resin [4], but single nano-sized filler particles were also observed by transmission electron microscopy [3]. Given the fact that the use of composites in dental practice is still increasing and that composite is one of the most frequently used dental materials, toxicological assessment of composite dust seems warranted. Health concerns have namely been expressed with regard to inhalation of nanoparticles. Not only does their size imply deep and easy penetration into the lungs, their small dimensions also impart different chemical and physical properties to nanoparticles compared to particles of the same material with larger size [5]. In general, for the same mass dose, nanoparticles represent a much larger surface which makes them more reactive. Exposure of animals, Table 1 Manufacturer and composition of the included composites most often rodents, to ambient or laboratory-generated nanoparticles consistently indu (...truncated)


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K. Van Landuyt, S. Cokic, C. Asbach, P. Hoet, L. Godderis, F. Reichl, B. Van Meerbeek, A. Vennemann, M. Wiemann. Interaction of rat alveolar macrophages with dental composite dust, Particle and Fibre Toxicology, 2016, pp. 62, 13, DOI: 10.1186/s12989-016-0174-0