Clear Aligners Shed Microplastics — and the BPA Comes From Somewhere Else

The short answer

Clear aligners are thin thermoplastic shells that sit against your teeth for something like 22 hours a day, get pushed on by every swallow, and are taken in and out several times daily. Plastic under repeated mechanical friction sheds. Researchers have now measured that shedding directly, in more than one lab, with more than one method, and the finding is consistent: aligners release microplastic particles into the fluid around them.

What the research does not show is how much of that reaches you over a real course of treatment, or whether it does anything once it does. The honest summary is that the release is real and small in absolute terms, the particle sizes sit in a range that mostly passes through the gut, and the studies were all short. That is a different sentence from “aligners are dangerous”, and it is worth resisting the pull toward the shorter one.

What the research actually measured

The seven-day saliva study

The foundational experiment came out of the Università Politecnica delle Marche and L’Aquila in 2023. The team took aligners from seven manufacturers — Alleo, FlexiLigner, F22, Invisalign, Lineo, Arc Angel and Ortobel — immersed two of each in artificial saliva for seven days, and stirred them five hours a day to approximate the mechanical friction of teeth. Then they filtered the saliva and put the filters under Raman microspectroscopy to identify the polymer, and scanning electron microscopy to count and size what came off.

Two results matter. The first is chemical: five of the seven aligners were polyethylene terephthalate — PET, the same polymer family as a drinks bottle — while F22 and Invisalign were polyurethane. If you assumed all clear aligners are the same material, they are not, and the brand your orthodontist uses determines which one is in your mouth.

The second is the count. The highest particle release came from Arc Angel and the lowest from Invisalign, and the difference was statistically significant. Particle sizes clustered between 5 and 20 µm across the board with no significant difference between groups, though the researchers did find a highly significant correlation between the size distribution and the manufacturer. In other words, the brands differ in how much they shed and in the shape of what they shed, and the market leader was at the good end of that range.

The chewing-simulation study

A 2025 paper in PLOS ONE approached the same question mechanically rather than chemically. The team loaded three appliances — Essix Ace (0.75 mm thermoformed PET-G), Ghost Aligner (0.75 mm thermoformed polyurethane) and Invisalign (0.5 mm polyurethane blend, additively manufactured) — through 22,500 compression cycles at 50 newtons, a number derived from roughly 1,500 swallows a day across a 15-day aligner interval.

Every tray shed. The interesting part is that the particles were not the same size. Essix Ace produced the largest debris, with major axes of 30–111 µm; Ghost Aligner sat in the middle at 17–81 µm; and Invisalign produced the smallest particles, 12–23 µm. The authors noted that most of the Essix Ace and Ghost Aligner particles exceeded 20 µm, which points toward passing through the gut rather than being taken up by tissue.

Read carefully, that is not an unambiguous win for the low-shedding brand. Fewer, smaller particles and more, larger particles are different trade-offs, and the smaller a particle gets, the more of the body it can reach. Anyone telling you the literature crowns a clear winner has read one of these two studies and not the other.

One more detail from that paper is genuinely actionable: the Ghost Aligner’s mechanical performance degraded sharply after about cycle 16,750 — roughly day 11 of a 15-day interval. Trays wear out on a schedule, and stretching one past its change date is asking a structurally tired piece of plastic to keep working.

What the pooled review found

A 2025 systematic review in Materials gathered 11 studies — four straight in vitro, seven testing material that had been aged in real mouths first — and found the picture above holds up. Particles of 5–20 µm made up more than half of what was detected across all aligners; particles above 20 µm accounted for 30–50%; and particles below 5 µm turned up in only three brands — Alleo at 17%, F22 at 18% and Invisalign at 14%.

The reviewers were also blunt about the limits. Only one of the 11 studies measured microplastic release directly. Most evidence comes from in vitro work that cannot reproduce real-world conditions. Many manufacturers use proprietary materials of undisclosed composition. And nobody has systematically looked at what diet, oral hygiene habits or bruxism do to the numbers — which, given that the mechanism is friction, are probably the three biggest variables there are.

The BPA question, answered properly

This is where most of the internet goes wrong, and it is the single most useful thing on this page.

What the clinical study did

Researchers at the University of Valencia recruited 24 patients about to start aligner treatment and split them into two groups of 12: one treated with Invisalign, one with aligners thermoformed in-office from 0.762 mm Ortolan sheets. They took four saliva samples per patient at different points, froze them at −80 °C, and ran them through mass spectrometry, with a one-week follow-up.

What they found

Saliva BPA rose significantly — but the rise came half an hour after the composite attachments were bonded to the teeth, in both groups. Attachments are the small tooth-coloured bumps of resin composite that give the tray something to push against. They are a dental filling material, and resin composites are a known, well-documented source of transient BPA release.

Within a week, levels were back where they started. And in the Invisalign group, the values recorded after the aligners themselves went in were not significantly different from baseline. The differentiation from the peak and the return to baseline was actually faster in the in-office group.

So the accurate version of “aligners release BPA” is: the glue-on attachments produce a brief BPA spike on the day they are placed, and the tray itself did not measurably raise saliva BPA at all. If BPA specifically is your concern, the appointment to worry about is the bonding visit, not the fourteen months after it. Rinsing thoroughly and drinking water for the rest of that day is a reasonable, proportionate response. Refusing treatment is not.

Worth keeping straight, too: “BPA-free” and “does not shed particles” are unrelated claims. Align states its SmartTrack material is BPA-free, and nothing in the particle research contradicts that. Bisphenol A is a chemical that migrates out of certain polymers; a microplastic is a fragment of the polymer itself. A tray can be entirely free of the first and still produce the second, which is exactly what the studies above describe.

Where 3D-printed aligners fit

Direct 3D printing is displacing thermoforming across the industry, and the Invisalign tray in the 2025 loading study was additively manufactured rather than pressed over a mould. That changes the chemistry, so the older literature does not automatically transfer.

A 2025 systematic review in International Orthodontics screened 524 papers and found nine that examined printed aligners. The results cut both ways. No BPA release was detected from printed aligners in the studies that looked for it, and no estrogenic effects were found. But urethane dimethacrylate leached in every single study that measured monomer release, and compared with thermoformed trays, direct-printed aligners showed higher cytotoxicity in cell assays. The reviewers flagged post-curing — how thoroughly the resin is hardened after printing — as the step that determines whether a printed tray behaves acceptably.

All nine studies were in vitro with a moderate risk of bias, and the authors concluded there is no consensus yet. Printed aligners are not obviously better or worse; they are less studied, and they trade a bisphenol question for a methacrylate one.

Retainers and night guards are the longer exposure

Aligner treatment ends. Retention does not. A course of clear aligners runs somewhere between six and eighteen months for most people, and is then followed by a retainer worn nightly — often indefinitely. A night guard for bruxism is the same arrangement, worn by someone whose defining habit is grinding hard on it.

Nobody has studied this properly, which is a real gap given the arithmetic. Eight hours a night for ten years is more contact time than 22 hours a day for a year, and grinding applies far more force than swallowing. The Essix material in the loading study is the same thermoplastic used for a large share of retainers, and it produced the largest particles of the three tested.

A few practical implications follow from the mechanism rather than from direct evidence, and are worth stating as such:

• A bonded lingual wire retainer involves no full-coverage plastic at all. It is a thin wire cemented behind the front teeth. If you want the lowest-plastic retention option, that is the conversation to have with your orthodontist — it has its own trade-offs around hygiene and breakage, and it does not suit every case.
• A worn, cloudy, scratched retainer is a retainer that has been abrading. Visible surface damage is the mechanism made visible. Replacing one that has gone hazy is not vanity.
• If you grind, treat the guard as a consumable. A night guard chewed to a translucent lip is doing its job by being destroyed, and the material it loses has to go somewhere.

What to actually do

Every lever here acts on friction, heat or time, because those are what the studies varied. In rough order of how much they matter:

• Take the trays out for anything but cool water. This is standard orthodontic advice for staining and decay reasons, and it happens to be the right advice here too. Hot coffee softens the polymer surface; sugary drinks trapped under a tray are a separate problem entirely.
• Do not clean them with toothpaste. Toothpaste is an abrasive — that is its function — and scrubbing a tray with it every morning is a small daily sanding operation on the exact surface the research is measuring. Cool water, a soft brush kept for the purpose, and clear unscented soap or a dedicated aligner cleaner do the job without the grit. Whitening pastes are the worst offenders.
• Never rinse or soak in hot water. It warps thermoplastic and accelerates surface degradation. Both effects work against you.
• Change trays on schedule rather than stretching them. One of the three appliances in the loading study lost mechanical integrity around day 11 of a 15-day interval. Wearing week three of a two-week tray is not thrift.
• Stop chewing on them. Idle clenching, chewing the edges, using chewies more than instructed — all of it is the experimental condition, applied voluntarily.
• Rinse well after the attachment-bonding appointment. That is the visit where the measured BPA spike actually happens, and it resolves within a week.

What is not worth doing

Abandoning orthodontic treatment over this is not a proportionate response to the evidence, and malocclusion has documented consequences that microplastic release from a tray currently does not. Neither is buying a microplastic “detox” supplement — there is no evidence any of them clear particles from the body. Switching brands mid-treatment on the strength of one in vitro ranking is also hard to justify: the differences between brands were real but modest, and continuity of treatment is worth more.

What we still do not know

This is a young literature and it is worth being explicit about its edges, because the gaps are large:

• No one has counted particles in a real mouth over a real treatment. Every figure above comes from artificial saliva, a loading rig, or a one-week clinical follow-up. There is no particles-per-day number, and any page giving you one has made it up.
• No study has measured a health outcome in aligner wearers. The concerns raised — inflammation, oxidative stress, tissue accumulation — come from the broader microplastics literature, not from anyone following aligner patients.
• Swallowing is not the only route. The oral mucosa is thin and highly vascular, and what that means for particles at this size has not been established.
• Retainers and night guards are essentially unstudied despite representing the longest exposure of all.
• Proprietary materials block comparison. Several manufacturers do not disclose composition, so a review can report what came off a tray without being able to say what the tray was.

Related reading: do contact lenses shed microplastics, gel and acrylic nails, microplastics in toothpaste, is BPA-free plastic safe, and how long microplastics stay in your body.