Orthodontics
Clear aligners: how they work, who they suit and their limits
Clear aligners are almost invisible plastic trays that straighten the teeth little by little. People like them because they are discreet and can be taken out to eat and brush your teeth. But they are not "magic appliances": they have their uses and their limits, and they only work if you wear them. This guide sums up what published reviews of studies say, with each one cited in the text. It is here to inform you; it does not replace an examination. For an overview of all types of appliances, see the guide on dental braces.
How do aligners work?
Treatment starts with an examination and a record of your teeth (an impression or a scan of the mouth). Software then prepares a series of custom-made trays: each one is slightly different from the one before and moves the teeth a little. You change trays roughly every one to two weeks, depending on the treatment plan.
To help the tray "grip" the tooth, small tooth-coloured bumps of resin, called attachments, are often bonded to the teeth. Sometimes the contact surfaces between certain teeth are filed very slightly to make a little room: this is called stripping.
Sometimes the teeth do not end up exactly where the software planned: a new record is then taken and extra trays are made, called refinements.
Which cases do they suit?
Aligners are mainly suited to mild to moderate crowding, small gaps between the teeth and some moderate mismatches between the dental arches. A review of 21 randomised trials (970 participants) found no difference in results between aligners and braces for these simple cases treated without extractions; the quality of the evidence remains low (Baneshi et al., 2024, PubMed). A more recent meta-analysis reaches the same conclusion for cases without extractions (Alhafi et al., 2025, PubMed).
Some movements remain more difficult:
- Cases with extractions: braces give a better result in these cases, thanks to better control of tooth movement (Alhafi et al., 2025, PubMed). With aligners, studies show poorer control of the roots and molars tipping into the extraction space (Abu Arqub et al., 2025, PubMed; Vicioni-Marques et al., 2025, PubMed).
- Rotations, especially of canines and premolars: a review of 12 studies found an average accuracy of about 65%, lower for these teeth (Benedetti et al., 2025, PubMed).
- Intrusion (pushing a tooth up into the bone), widening the arches and correcting a deep bite (upper front teeth that cover the lower ones a lot) are also less reliable (Drohomyretska et al., 2025, PubMed).
In a child whose jaw is too narrow, the problem is often in the bone: it is first treated in another way (see the guide on palatal expansion). The examination, with X-rays if needed, tells you whether aligners are right for your case.
Wearing them: 22 hours out of 24
This is the most important rule. The tray only moves the teeth when it is in your mouth: you wear it about 22 hours a day, and only take it out to eat, to drink anything other than water, and to brush your teeth. Not wearing them enough is their main contraindication: if you know you will often forget them, talk about it openly with the dentist.
A few habits to adopt:
- Brush your teeth before putting the tray back in, so you don't trap food or sugar against your teeth.
- Don't drink sugary drinks, tea or coffee with the tray in: they sit against the teeth and stain them.
- Keep the tray in its case, never in a paper napkin: that is how they get lost.
- Clean it every day as instructed, in cold or lukewarm water (hot water can warp it).
Aligners or braces: what do studies say?
| Aligners | Braces (fixed brackets) | |
|---|---|---|
| Discretion | Almost invisible | Visible (except ceramic or lingual braces) |
| Simple cases without extractions | Similar result | Similar result |
| Cases with extractions | Less control | Better control |
| Gums and hygiene | A little easier | More plaque around the brackets |
| Pain at the start | A little less | A little more |
| Depends on the patient | A lot (22 h/24 wear) | Less (fixed appliance) |
Gums and hygiene
Because you take the tray out to brush your teeth, studies find a little less plaque and gum inflammation than with braces (Llera-Romero et al., 2023, PubMed). However, a review of reviews considers this difference small in practice (Di Spirito et al., 2023, PubMed), and the benefit depends on wearing the trays properly and brushing well (Alhuwaizi et al., 2026, PubMed). Aligners do not replace careful brushing: see the guide on scale and polish.
Pain and comfort
On average, aligners are a little less painful than braces, especially at the start of treatment, and quality of life during treatment is better (Kaur et al., 2026, PubMed). Feeling pressure during the first days of each new tray is normal.
Roots
Any orthodontic treatment can slightly shorten the tips of the roots (resorption). A meta-analysis found slightly less resorption with aligners than with braces, although the clinical importance of this difference has not been established (Darvizeh et al., 2025, PubMed).
How long does aligner treatment take?
It depends on the case. For mild to moderate crowding, the length seems similar to that of braces, based on low-quality evidence (Alhamwi et al., 2024, PubMed). Refinements, if needed, make treatment longer. The dentist gives you an estimate after the examination, but it depends a lot on how well you wear the trays.
After treatment: retention
As after braces, the teeth tend to move back towards their old position. So you need retention: a wire bonded behind the teeth or a tray to wear, often at night. The Cochrane review on retention cannot say that one method is better than another, for lack of solid evidence (Martin et al., 2023, PubMed): the dentist chooses according to your case. Without retention, the result does not last.
Aligners sold directly to patients
Some offers provide aligners remotely, without an examination at the practice. An aligner is still a treatment that moves teeth and bone: cavities, gums and roots must be checked first, and tooth movement must be followed. Treatment without an examination or follow-up can worsen a gum problem or create a bite mismatch. Always ask who is examining you and who is following your treatment.
In practice
- Get examined: the examination tells you whether aligners suit your case.
- Have cavities and gum problems treated before starting.
- Wear the trays 22 hours out of 24 and change them on schedule.
- Brush your teeth before putting them back in; drink only water while wearing them.
- Come to your check-up appointments.
- Wear your retainer as prescribed after treatment.
Frequently asked questions
What is Invisalign?
It is one brand of clear aligners among others; the principle is the same: a series of custom-made trays that move the teeth, worn about 22 hours a day, with an examination and follow-up by the dentist.
Are aligners as effective as braces?
For simple cases without extractions, studies find no difference in results; for cases with extractions or some difficult movements, braces still offer better control.
Do aligners hurt?
You feel pressure during the first days of each new tray; on average, aligners are a little less painful than braces at the start of treatment.
Can you eat with aligners in?
No: you take the tray out to eat and to drink anything other than water, then brush your teeth before putting it back in.
Are aligners suitable for children?
There are aligners for children and teenagers, but many problems in children, such as a jaw that is too narrow, are first treated in another way; the examination is what helps you choose.