What Clear Aligners Are Made From
For adults asking what clear aligners are made of: the plastics, layering, force decay, change schedules, heat, safety and staining. In laboratory tests aligner plastic loses much of its force within hours, and the evidence on chemical release is still inconclusive.
5.0 from 550+ Google reviews
Open 8am to 8pm, seven days
Free parking at the door
CQC & GDC registered
No referral needed
Clinically reviewed by Dr Ibraheem Ijaz, dentist · GDC 301711
Medical disclaimer: This page is for general information only. It does not replace an examination or treatment by a dentist.
Dr Ibraheem Ijaz, principal dentist at Deepcar Dental Care, reviewed this page. He is a General Dental Practitioner.
What are clear aligners made from?
Thermoformed clear aligners are made from thermoplastic, a plastic that softens with heat and is shaped over a model of the teeth. Materials described in a 2023 review include PETG (polyethylene terephthalate glycol), thermoplastic polyurethane and polypropylene; laboratory analyses also find PET.
Forming changes the plastic: in a 2018 laboratory study, thermoforming raised water absorption in all four materials tested and reduced transparency in two.
How do single-layer and multilayer aligner materials differ?
Single-layer aligners use one plastic; multilayer materials often combine a harder and a softer layer. In a 2023 review, the soft layer gives elastic give for smooth seating and the hard layer strength and durability.
In a 2017 24-hour laboratory test, two single-layer materials gave the highest force and lost it fastest; two double-layer materials released it steadily, at up to four times lower levels.
What is force decay in clear aligners?
Force decay, also called stress relaxation, is the fall in force an aligner exerts while held in the same stretched shape. Each aligner is shaped for the teeth's next planned position, so it presses on them; laboratory tests show that pressure fades fast:
- In a 2017 24-hour laboratory study of four materials, every material lost significant force, most in the first 8 hours; the authors say losses may exceed half the starting force early in wear and may influence planned tooth movement.
- In a 2022 two-week laboratory study of five materials, force fell fastest in the first hours, then levelled off; the two materials holding most kept 39% and 37%, the two holding least under 5%. Its authors call for research on aligners aged in the mouth.
How ligament and bone respond to force is the subject of our page on how teeth move in orthodontic treatment.
Why are aligners changed on a schedule?
Aligners are changed in sequence to carry out planned tooth movements, a 2023 review explains. As general guidance, the routine is 22 hours of daily wear and a new aligner every 2 weeks, as your treatment plan confirms.
Force decay research may bear on that timing. A 2025 laboratory ageing study found forces fell significantly within the first 2 days, and its authors say this work may guide when aligners are changed. In a 2023 laboratory study of PETG strips, force fell to 20% to 24% of its start in the first loading period, then a further 13.5% over 7 days at 12 hours' daily loading, against 8.4% at 23 hours.
Evidence from patients is limited: a 2024 systematic review comparing change intervals across six studies found 7-day, 10-day and 14-day changes moved teeth similarly, apart from some movements favouring 14 days, at very low certainty.
To ask about clear aligners, book online or call 0114 288 2121.
How do heat and moisture affect aligner plastic?
Heat speeds up force decay in aligner plastic, laboratory research shows. In a 2025 study of five materials, stress relaxation rose by 0.7% to 18% at mouth temperature (37 °C) and by 21% to 88% at 55 °C, compared with room temperature (22 °C); two weeks in water did not speed it up.
In a 2026 laboratory study, water lowered the glass transition temperature, where plastic turns from rigid to rubbery, in all four materials tested after a week in salt water at body temperature.
As general guidance, rinse aligners in cool or lukewarm water, never hot. If an aligner no longer fits as it did, show it to the dental team treating you.
Are clear aligners BPA free?
Whether aligners release BPA (bisphenol A) is unsettled: a 2025 umbrella review found it can be neither confirmed nor ruled out. The research includes:
- A 2023 systematic review of six studies found BPA leaching in two and none in four, at low to very low certainty, and called safety questionable pending high-quality patient studies.
- A 2020 systematic review found no hormone-like or cell-damaging effects or detectable BPA in laboratory studies, but one clinical trial found higher saliva BPA after up to 30 days with a thermoplastic retainer than a Hawley retainer; evidence quality was low to medium.
- A 2025 laboratory study found no BPA from four aligners over 72 hours but bisphenol S from one; leachables were generally low, but its authors advise considering cumulative exposure.
Can aligners shed microplastics or cause allergic reactions?
Laboratory studies show aligners can shed microplastics, tiny plastic particles, but what this means for health is unknown. Under simulated friction, seven manufacturers’ aligners shed particles mostly 5 to 20 micrometres across (2023), and release rose significantly from 7 to 14 days (2026). The 2023 authors said this may be a great concern for general health; the 2026 authors said changing after 7 days may help limit release, though its clinical significance is unclear.
Reactions, some serious, have been reported too: a 2017 analysis of ten years of US device reports for one aligner system found 173 reports, including breathing difficulty, throat, tongue or lip swelling, hives and 30 of anaphylaxis. NHS guidance says call 999 if your lips, mouth, throat or tongue suddenly become swollen, you are breathing very fast or struggling to breathe, your throat feels tight or you are struggling to swallow, your skin, tongue or lips turn blue, grey or pale, you suddenly become very confused, drowsy or dizzy, someone faints and cannot be woken up, or a child is limp, floppy or not responding like they normally do.
If you think you may have an allergy, the NHS advises seeing a GP; tell your dentist too.
Why do aligners go cloudy or stain?
Aligners can lose clarity through wear and deposits, and can stain from coloured drinks, research shows:
- Wear: a 2023 review reports microcracks, separated layers, hardened plaque deposits and lost transparency in one brand's aligners used for 2 weeks.
- Drinks: coffee and tea stained aligner materials most in laboratory tests, turmeric most in one study; cola ranged from no significant change to a visible change on one brand's aligners.
A 2025 staining study recommended removing aligners before drinks. Cleaning is covered on our page about cleaning your aligners.
Which aligner system does Deepcar Dental Care use?
Deepcar Dental Care offers clear aligner treatment to adults only. Smartee clear aligners are the system used at the practice.
Frequently asked questions
What is the difference between PETG and polyurethane aligners?
They are different thermoplastics. A 2024 systematic review of 24 studies found polyurethane-based materials harder and stiffer, but more prone to creep and stress relaxation; properties deteriorated with thermoforming and wear in the mouth. The studies were too varied to pool.
Is an aligner's force highest when it is new?
In laboratory tests, yes: force peaks when the plastic is first stretched into shape. As general guidance, mild pressure or soreness is normal while a new aligner settles in over its first few days; if it is stronger than mild or goes on longer, ask the dental team treating you to check.
Can I drink hot drinks with aligners in?
No, as general guidance: take aligners out to eat and to drink anything but water. Heat affects the plastic too: in a 2025 laboratory study of five materials, stress relaxation was higher at mouth temperature (37 °C) than at room temperature (22 °C), and higher still at 55 °C.
Are 3D-printed aligners made from the same materials?
No. Directly printed aligners use light-cured resins, not heated sheets, a 2023 review explains. A 2026 review of retrieval studies, to be read with caution, found their relaxation index rose after use, and a 2025 laboratory study found most leachable compounds in a printed and a shape-memory aligner; levels were generally low, but its authors advise considering cumulative exposure.
Does a thicker aligner push harder?
In laboratory testing, yes. In a 2013 study, appliances made from 0.75 or 0.8 mm sheet always produced significantly more force than those made from 0.4 or 0.5 mm sheet. Force depended on the material, its thickness and how far the appliance was displaced from the tooth.
Book a consultation.
Online in under a minute, or call and speak to a real person.
You can book online or call the practice, open 8am to 8pm, Monday to Sunday. Patients' feedback about the practice is on the practice's reviews page.
Aligner treatment as a whole is covered on our clear aligner therapy page, and our guide to clear aligner treatment sets out the full course.
334 Manchester Road
Deepcar, Sheffield S36 2RH
0114 288 2121
Contact us
Opening hours
Open 8am to 8pm, seven days
Free parking at the door