The effect of water spray on the release of composite nano-dust

To evaluate the collection efficiency of water spray on the release of airborne composite particles during grinding of composite materials.

Composite sticks (L:35 mm × W:5.4 mm × H:1.6 mm) of seven commercial dental composites were ground with a rough diamond bur (grain size 100 μm, speed 200,000 rpm). All experiments were performed in an enclosed 1-m³ chamber with low particulate background (< 1,000 #/cm³), and airborne particles were evaluated based on their electrical mobility. The number size distribution was determined by scanning mobility particle sizer (SMPS). Particles were collected by an electrostatic precipitator (ESP), and were ultramorphologically and chemically analyzed by a transmission electron microscope equipped with energy-dispersive X-ray spectroscopy (TEM-EDS).

SMPS measurements confirmed that both dry and wet grinding generated high concentrations of nanoparticles particles with the highest concentration recorded during the last minute of grinding (1.80 × 10⁶ - 3.29 × 10⁶#/cm³), after which a gradual decline in particle concentration took place. Nevertheless, grinding with water spray resulted in a significant reduction of the number of released particles (5.6 × 10⁵ - 1.37 × 10⁶#/cm³). The smallest particle diameter was recorded during the last minute of grinding followed by a continuous growth for every next measurement. TEM of composite dust revealed a high concentration of particles varying in both size and shape.

Regardless of whether the water cooling spray system was used during bur manipulation of composite materials, predominately nanoparticles were released. However, the particle concentrations were significantly decreased with water spray.

Since water spray might not be sufficient in nanoparticle collection, special care should be taken to prevent inhalation of composite dust.