Dental amalgam receives significant attention in discussions on sources of pollution from dentistry due to its mercury content. However, little consideration is given to resin-based composites (RBCs). Perceived as being inert, and likely reinforced by ‘natural’ appearances and healthy lifestyle marketing connotations, RBCs may pose more of a harm to the environment than we think.
Initial thoughts on environmental impact of RBCs focusses on its constituents. BisGMA is a potentially harmful monomer, releasing Bisphenol A (BPA). At a critical level, this oestrogen-mimicking chemical can produce harmful effects. Release of BPA from RBCs and sealants has been reported, increasing overall individual exposure when combined with day-to-day background exposures. RBCs also contain diluent TEGDMA, which may be the major monomer released from RBCs. Concerns relate to its biocompatibility and potential toxicity.
Release of chemicals is dependent on degree of RBC polymerisation. More polymerisation means less leakage of potentially harmful chemicals. However, the average conversion to a polymerised state is 60-70%, with conversions of as little as 30% at cavity bases. There may be far more leakage of these components into the body and environment than previously thought.
Factory produced RBCs have higher levels of polymerisation, but microparticulate and microplastic waste from CAD-CAM milling of composite blocks is discharged into wastewater and sewage in large volumes. Microplastic pollution is a growing concern, accessing the food chain and being found in edible fish species including cod and haddock. As well as the obvious damaging effects of ingestion of microplastics, their increased surface area leaches increasing levels of monomer into the environment. Removal, finishing and polishing of RBCs in clinics produces part-polymerised microparticulate waste, allowing further release into the environment.
Waste products from manufacturing and unused materials are disposed of in landfill sites. This may allow more leakage of chemicals into the environment. Landfill-produced fluid mixtures react with RBCs, releasing components including BPA. Coastally located landfill sites are high risk areas due to erosion. Deposition of landfill contents into sea and waterways because of erosion could have catastrophic outcomes. Incineration of RBC waste could mitigate this.
Like dental amalgam mercury, RBCs can continue to leach unpolymerised monomers, detectable in saliva and urine months after placement. This provides yet another avenue of pollution into the environment through human excretion. Interred cadavers with RBC restorations may leach unpolymerised monomer into ground soil, whilst those cremated may release breakdown products into the air.
There are clear potential environmental pollution pathways for RBCs. Their negative impact arises from both the leaking of chemical constituents and microparticles/microplastics produced during everyday clinical placement, removal and CAD-CAM fabrication.
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