Characterization and toxicity evaluation of air-borne particles released by grinding from two dental resin composites in vitro.

Objective: The project aims to evaluate whether inhalation of particles released upon grinding of dental composites may pose a health hazard to dentists. The main objective of the study was to characterize the dust from polymer-based dental composites ground with different grain sized burs and investigate particle uptake and the potential cytotoxic effects in human bronchial cells.

Methods: Polymerized blocks of two dental composites, Filtek™ Z250 and Filtek™ Z500 from 3M™ ESPE, were ground with super coarse (black) and fine (red) burs inside a glass chamber. Ultrafine airborne dust concentration and particle size distribution was measured real-time during grinding with a scanning mobility particle sizer (SMPS). Filter-collected airborne particles were characterized with dynamic light scattering (DLS) and scanning electron microscopy (SEM). Human bronchial epithelial cells (HBEC-3KT) were exposed to the dusts in dose-effect experiments. Toxicity was measured with lactate dehydrogenase (LDH) assay and cell counting kit-8 (CCK8). Cellular uptake was observed with transmission electron microscopy (TEM).

Results: Airborne ultrafine particles showed that most particles were in the size range 15-35 nm (SMPS). SEM analysis proved that more than 80% of the particles have a minimum Feret diameter less than 1 μm. In solution (DLS), the particles have larger diameters and tend to agglomerate. Cell toxicity (LDH, CCK8) is shown after 48 h and 72 h exposure times and at the highest doses. TEM showed presence of the particles within the cell cytoplasm.

Significance: Prolonged and frequent exposure through inhalation may have negative health implications for dentists.