We’ve named the movements — now the engine that drives them: the force system. How much force a tooth actually needs, and why an aligner, uniquely, won’t let you dial it in directly.
A force system: force and moment
Every time an aligner loads a tooth, it delivers a force system — not just a force, but a force and a moment together. A push on the crown is the same as a push through the center of resistance plus a turning moment. That pairing — the moment-to-force ratio — decides whether the tooth tips, translates, or torques. So we never just ask how hard; we ask how hard, and with how much moment.
Light, continuous force wins
The periodontal ligament rewards light, continuous force. A light force triggers clean, frontal bone resorption, and the tooth glides. Too much force does the opposite: it crushes the ligament, the blood supply is cut, and movement stalls — the state called hyalinization — with more pain and more risk to the root. More force is not more speed.
How much force? The optimal ranges
Each movement has its own light range — and it scales with how much root you’re moving:
Distance-based, not force-based
Here’s what makes an aligner different. With braces, you choose the wire and dial the force. An aligner is distance-based: you prescribe a target position — each tray about 0.3 mm of movement — and the plastic delivers whatever force that deflection happens to produce. You program the distance; the material decides the force.
Force isn’t steady — it decays
And that force isn’t steady — the material decides how unsteady. A freshly seated tray is deflected the most, so it pushes hardest, often above the optimal range. A single-layer PETG spikes high then fades fast — dropping below useful force before the tray is even changed. A 3-layer material starts gentler and holds far more of its force, staying in the optimal range much longer.
Your force controls
You can’t set the force directly, but you can shape it:
- Smaller steps per stage keep the starting force gentler.
- Attachments spread and redirect it.
- Consistent wear — 22 hours a day — keeps the force in its useful window instead of spiking and dying.
Staging, attachments, and wear are your force controls.
Key takeaways
An aligner delivers a force system — a force and a moment. Teeth want that force light and continuous, scaled to how much root is moving. But an aligner sets distance, not force, and it over-forces when fresh — so your job is to keep it in range, through staging, attachments, and wear.
Shafaf partners with trained dentists across Iraq and the region. Find a Shafaf provider or talk to us about partnering.