How do clear aligners move teeth?

The biomechanics of aligner treatment

A clear aligner is not a copy of where your teeth are now. Each tray is made to a position slightly ahead of them, so when it is seated it holds particular teeth under light, sustained pressure. That pressure passes through the periodontal ligament to the bone around the root, and over days the bone remodels — resorbing on the side the tooth is being pushed towards and rebuilding behind it. That remodelling is what lets a tooth move at all, and what eventually lets it settle in a new position.

Because bone can only remodel at a certain pace, each stage is planned to deliver a small movement rather than a large one. That is why treatment is a numbered series rather than one or two trays, and why the journey runs assessment and records, a staged plan, the tray series itself, progress reviews at intervals, any extra trays needed to finish, and then retention.

Wear time is the part of the mechanics a patient controls. Most plans ask for roughly 20 to 22 hours a day, with trays out only to eat, to drink anything other than water, and to clean your teeth. Force only acts while the tray is seated, so short wear days do not simply postpone one stage — they let teeth drift back towards where they started and stretch the whole timeline.

Smooth plastic struggles with some movements, particularly rotating a rounded tooth or moving a root rather than tipping a crown. Clinicians answer that with attachments — small tooth-coloured composite shapes bonded to chosen teeth so the tray has something to push against — and with interproximal reduction, where a very small amount of enamel is polished from between teeth to create the space a planned movement needs.

That also sets the limits. Crowding, spacing, and many mild to moderate alignment problems are well within what trays can do. Large bite corrections, substantial rotations of rounded teeth, and moving several roots bodily are where aligners become less predictable and fixed braces keep more control. Suitability is a clinical judgement made from records, not something a photo settles on its own.