Clear aligners: what they do well and where they are weaker

How invisible they really are

Clear trays are discreet, not invisible. At conversational distance they can be noticed, particularly in bright light. Most plans also involve small tooth-coloured composite shapes bonded to the teeth, called attachments, which give the tray purchase for a specific movement. They match the tooth shade but are still visible close up.

We use the popular phrase because that is how people search, but clear aligners is the more accurate term. The distinction is not pedantic: expecting total invisibility leads to disappointment in the first week.

How aligners work

Treatment starts with a scan and planning. A digital plan of the intended movements is produced, and a series of trays is manufactured from it. Each tray moves the teeth by a small increment and the next continues from there.

Trays are worn for almost the entire day and taken out only for eating and cleaning. This is the factor that rests entirely with you: a tray in its case moves nothing. If wear time falls short, the plan and reality diverge, and a new scan and a new series become necessary.

Some plans also involve interproximal reduction, minimal thinning of the enamel between teeth to create space. It is planned in advance and discussed rather than carried out by default.

What they do well

A systematic review of 22 clinical studies concluded that clear aligners are viable for mild to moderate malocclusion in non-growing patients not requiring extractions. The outcome is predictable for levelling, tipping and derotation, except on canines and premolars.

In practice that covers many common adult situations: mild crowding of the front teeth, small spaces, teeth that have drifted after previous orthodontic treatment, and alignment before aesthetic work.

A review of 8 comparative studies reported that aligner treatment was 6.31 months shorter (95% CI −8.37 to −4.24) than treatment with fixed appliances. That advantage applies to cases suitable for both methods, not to every case.

Where they are weaker, from the same evidence

The same review reports limited efficacy for bodily arch expansion, extraction space closure and correction of occlusal contacts, as well as for larger antero-posterior and vertical discrepancies.

The comparative review adds that aligners were less effective than fixed appliances at producing adequate occlusal contacts, at controlling torque, which is the inclination of the root, and at maintaining the result.

These limits do not make the method weak. They mean that choosing between aligners and a fixed appliance is a clinical decision rather than a preference. If a case falls outside the range, the honest answer is a referral, not a compromise on the result.

Retention and relapse: the part that matters most

Teeth do not stay in their new position by themselves. Active treatment is followed by retention with a retainer, whether bonded behind the teeth, removable, or a combination. That is part of the treatment, not an addition to it.

A Cochrane review of 47 randomised trials with 4,377 participants found that the evidence on retention methods is of low to very low certainty and does not support a conclusion that any one approach is superior.

Over long periods the data are sobering. In a study of 31 cases treated with four premolar extractions, mandibular anterior crowding continued to increase between ten and twenty years post-retention, and only 10% of cases had clinically acceptable mandibular alignment at twenty years, with no identifiable predictors of stability. That is why we discuss retention as a long-term commitment rather than a few months after treatment.

What has to be sound before starting

Moving teeth through inflamed gums makes the inflammation worse. Decay is treated first, gum inflammation is brought under control and a professional cleaning is carried out before treatment starts. Where bone has been lost around the teeth, the plan is adjusted to that limitation.

Aligners are not an aesthetic treatment in themselves, but they are often the first step towards one. Once teeth are aligned, a small correction with composite is sometimes enough instead of preparing teeth for veneers. That is the more conservative sequence where a case allows it.

Aligners have no published price, because the number of trays and the complexity differ. The quotation is issued in writing after examination and includes the retainer.