Assessment of microparticles and monomer elution following clinical operative grinding of resin-based composite restorations

Objectives: To assess and compare the potential environmental pollutant risk of resin-based composite (RBC) after the removal of old restorations and the finishing and polishing of newly placed restorations.

Methods: Two RBCs, one representative of current commercially available materials (CompA) and one custom-made calibration composite (CompB) containing monomers of interest were tested (in duplicates). Standardised discs (0.5g) were uniformly polymerized and split into two groups, G1 and G2. G1 discs were aged for 12 months in artificial saliva at 35°C to simulate the oral environment and then ground following clinical protocols to simulate the removal of an old restoration. G2 discs were ground in the same manner, immediately after polymerisation to reproduce standard clinical finishing/polishing regimes. RBC microparticles were stored in tap water and sampled regularly over 12 months to simulate environmental release through waste water emissions. Eluted monomers triethylene glycol dimethylacrylate (TEGDMA), urethane dimethacrylate (UDMA), bisphenol-A glycidyl methacrylate (Bis-GMA), hydroxyethyl methacrylate (HEMA), bisphenol-A (BPA) were quantified via solid phase micro-extraction coupled with high-performance liquid chromatography.

Results: G1: A consistent trend of eluted monomers was observed over the 12 months period for both RBCs. In general, CompB leached monomers in higher (up to 8x) concentrations compared to CompA. For both composites TEGDMA was released in the highest concentration (550mg/L CompA, 4000mg/L CompB), peaking at 2-3 days.
G2: CompA released up to 6x higher concentrations of monomers than CompB, except for TEGDMA. For CompA UDMA was released in the highest concentration (3300mg/L), while TEGDMA-release dominated for CompB (4500mg/L). CompB peak monomer release was reached within 1 month, while for Comp B for up to 200 days.

Conclusions: Elution of identifiable monomers was quantified from microparticles of both RBCs, that varied in accordance with the specific RBC formulation. Finishing and polishing regimes demonstrated longer-term consistent release of the monomers investigated than for the removal of old restorations.