Sustainability in dentistry: Part 1 - Plastics and biodegradability

By Emeritus Professor Laurence J. Walsh AO

In the first part of this series of articles on sustainability in dentistry, the focus is understanding plastics, especially biodegradable plastics and the issues around recycling of plastics. Later instalments will address other topics within sustainability, including using the life cycle analysis (LCA) to compare different options for equipment and materials and how facility design can enhance sustainability in dental practice.

Understanding this topic links to the newly published (July 2023) updated Australian Dental Council statement of the expected competencies for new graduates from dental education programs of any type, which includes as a core competency the need to “recognise the environmental impacts of health care provision and use resources responsibly, making decisions that support environmentally sustainable healthcare”

Which plastic is what?

Table 1 provides a list of common plastic materials, dividing these into the fossil-based varieties and those that are biologically-based polymers, also known as bioplastics. Note that this term bioplastic does not necessarily mean that a biologically-based plastic will be more sustainable than a fossil-based plastic. Adding to the complexity around this topic is inconsistent labelling regarding the features of various types of plastics, contradictory information regarding their LCA and “greenwashing” where the product labelling is misleading.

There are many single use plastic items used in dental practices. Plastics are also used in the packaging of items, in PPE and in sterilisation pouches (Table 1).

Each of these plastic materials has different properties (physical strength, flexibility, permeability, etc) that reflect its unique chemical structure, specifically what monomer has been used as the building block in the polymer.

An important aspect for any plastic material is how much it will be affected by temperature, since this will dictate whether the particular plastic item will sustain exposure to a washer disinfector cycle or a steam steriliser cycle without melting. Many plastic materials used in dental practice are made from lowfusing thermoplastic materials where the polymer is formed into its final shape using low temperature heat. As a result of this, when exposed to hot water (65°C) or to a steam steriliser cycle (134°C), the material will revert from its shape into an unformed mass of polymer, making it impossible to reuse. This design feature is used deliberately to prevent single use plastic items being reprocessed.

Common plastic materials that are used in dentistry include polypropylene (in surgical masks and respirators), polyethylene and polyethylene terephthalate (PET) in packaging and in containers of various types and polyvinylchloride (PVC) in rigid plastics. The plastics used in packaging and in PPE have the shortest working life, because of single use. As a particular example, during the COVID-19 pandemic, it was estimated that hundreds of millions of facemasks were used, of which around 80% ended up in landfill, with the remainder most likely to have been incinerated as medical waste.

Understanding bioplastics

Abioplastic is typically made from a renewable resource (such as plants), by extracting natural polymers (starch, proteins, natural rubber, etc), or by using monomers from plants as building blocks to create polymers. Depending upon their type, bioplastics can contribute to circular economies by using renewable plant-based non-fossil resources and then having improved end-of-life outcomes through reuse or biodegradation. In each case, an assessment of the entire lifecycle of the bioplastic using the LCA approach is necessary.

The challenges of introducing more bioplastics into dentistry include their greater cost, lower efficiency for manu- facturing than fossil-based plastics, limited recycling opportunities and a lack of composting facilities. There are environmental impacts associated with agricultural production. An inherent challenge with bioplastics is competition with food production when considering agricultural land use.

Bioplastics are attracting considerable interest because they have a lower carbon footprint than fossil-based plastics. Some of them are compatible with