Clear aligners move teeth by applying force to the crown. But every tooth movement you’ll ever prescribe — no matter how complex the plan — is one of just six. Learn this vocabulary, and you can read any treatment setup.
Think of these six as the alphabet of orthodontics. Some come easily to an aligner; others take real engineering — attachments, a couple, and a little overcorrection. As we go through them, watch not just what each movement looks like, but how hard it is to deliver.
Tipping
A single force at the crown, and the tooth pivots around its center of resistance — the crown goes one way, the root the other. This is the aligner’s native move: fast, and the most predictable thing you’ll ask for. The catch is control: left unchecked, every movement collapses into tipping.
Bodily movement (translation)
The whole tooth slides together, crown and root, without tilting. To get it you need a couple — a moment‑to‑force ratio around 10:1. That means attachments, and patience: bodily movement is slower, and it’s where cases quietly drift off track.
Rotation
Turning the tooth around its long axis. Flat teeth like incisors rotate fairly well, because the aligner has a surface to push against. Round teeth — canines and premolars — are the real challenge: there’s little to grip. Plan an attachment, and build in overcorrection.
The vertical pair: intrusion & extrusion
Intrusion pushes a tooth deeper into the bone; extrusion draws it out toward the bite. Aligners intrude reasonably well, often just by leaving the neighbours alone. Extrusion is the hardest movement to track — the tray simply tends to lift off. Attachments are essential here, and sometimes buttons and elastics.
Torque
Moving the root while the crown stays put. It demands the strongest couple of all — a high moment‑to‑force ratio. Anterior torque — keeping the incisor roots in the bone as you retract — is one of the most demanding things an aligner does. It needs attachments, staged carefully.
How hard is each one?
When you review a setup, ask it of every tooth: which of the six is this, and how hard will it be?
- Comes easily: tipping, intrusion.
- Needs engineering (attachments, a couple, overcorrection): rotation of round teeth, bodily movement, extrusion, torque.
Key takeaways
Six movements: tipping, bodily, rotation, extrusion, intrusion, and torque. Every plan is built from them. Know which come easy and which need engineering, and you’ll spot the hard movements before they cost you a refinement.
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