Materials · 6 min read
What are dental retainers made of?
Almost every retainer sold in the UK is made from one of a handful of thermoplastics — and almost no manufacturer publishes what those materials release during years of nightly wear. Here is what they actually are.
If you've finished orthodontic treatment, you've almost certainly been handed a retainer and told to wear it nightly, indefinitely. What you were probably not told is what it's made of. For a device that sits against your teeth and gums for eight hours a night, often for decades, that's a surprising gap — and it's the gap this article exists to close.
The two main types of retainer
Retainers fall broadly into two categories, and the material story is different for each.
Clear (vacuum-formed) retainers
These are the transparent, removable retainers most people picture — the same style as a clear aligner, but worn to hold teeth in place rather than move them. They are almost always made from a thermoplastic, most commonly polyethylene terephthalate glycol (PET-G), or sometimes polypropylene or a polyurethane-based copolymer. The plastic is heated and vacuum-formed over a model of your teeth.
Bonded (fixed) retainers
A bonded retainer is a thin wire fixed to the back of the front teeth with composite resin. The wire is usually stainless steel or a nickel-titanium alloy; the resin that holds it is a BPA-derived composite — the same broad family of materials used in white fillings.
What thermoplastics shed during wear
Plastics are not inert. Under mechanical stress, temperature change and contact with saliva, thermoplastics degrade at the surface and release particles. In the context of a retainer, that means micro- and nanoplastic particles, and in some cases chemical additives, can be released into the mouth and swallowed.
This isn't fringe science. Peer-reviewed studies have measured particle and chemical release from orthodontic thermoplastics under simulated oral conditions, and a 2025 narrative review in Progress in Orthodontics drew the existing literature together, concluding that leaching of microplastics and associated compounds from clinical dental polymers is a real and under-examined exposure pathway.
The retainer is, for most people, the single longest-contact plastic device they will ever put in their body — worn nightly, for years, against soft tissue and in constant contact with saliva. Yet it is one of the least scrutinised.
Why don't manufacturers publish testing data?
Because they aren't required to, and because testing costs money and creates a paper trail. Medical-device regulations focus on biocompatibility — broadly, "does this provoke an adverse biological reaction" — rather than long-term microplastic shedding, which is a newer concern that existing standards weren't written to address. The result is that you can buy a retainer from a high-street practice or an online brand and find no published data anywhere on what it releases during wear.
What to look for
- Ask what polymer your retainer is made from. A brand that knows — and will tell you — is already ahead of most.
- Ask whether the material has been independently tested for microplastic release, not just biocompatibility.
- Ask whether any testing results are published, by batch or lot, rather than simply asserted.
This is the question bio. was built to answer. Our retainers are made from a bio-derived polymer and independently tested, lot by lot, for microplastic particle release, BPA, BPS, BPF and phthalates — with every result published on
The bio. Standard.
Source: Shariff et al. (2025), "Microplastics and nanoplastics in clinical dentistry and orthodontics," Progress in Orthodontics 26(1), Article 49.
