Clear aligners look like thin plastic trays. They feel like a snug mouthguard. But they are engineered to do something precise: move teeth through bone in a controlled, predictable sequence.
Most patients understand that aligners straighten teeth. Fewer understand how. If you are considering clear aligners and want to know what is happening inside your mouth during treatment, this guide covers the mechanics in plain language.
The basic principle: controlled force
Teeth are not fixed in the jawbone like posts set in concrete. Each tooth sits in a socket and is attached to the surrounding bone by a thin ligament called the periodontal ligament (PDL). This ligament is about 0.15 to 0.38mm wide and contains blood vessels, nerve fibres, and specialised cells.
When sustained pressure is applied to a tooth, the PDL compresses on the side the tooth is moving toward and stretches on the opposite side. This triggers a biological response:
- On the compression side, cells called osteoclasts break down (resorb) bone to make room for the tooth.
- On the tension side, cells called osteoblasts build new bone to fill the gap the tooth has left behind.
This process is called bone remodelling. It is the same biological mechanism used by traditional braces. Clear aligners and metal braces differ in how they deliver force, not in how teeth respond to it.
How aligners deliver force
Each aligner tray is manufactured to be slightly different from the current position of your teeth. When you place a new tray, it does not fit exactly. It is intentionally off by a small amount, usually 0.2 to 0.3mm per tray.
That misfit creates a force. The rigid plastic of the tray pushes against specific teeth, directing them toward their programmed position. As your teeth move into alignment with the tray over 1 to 2 weeks, the force diminishes. You then switch to the next tray, which introduces a new small misfit and a new set of forces.
This incremental approach means each tray does a tiny amount of the total movement. A full treatment might involve 20 to 50 trays (or more for complex cases), each moving your teeth a fraction of a millimetre closer to the planned result.
Attachments: increasing what aligners can do
Aligners alone can push teeth in straightforward directions. But teeth sometimes need to rotate, tip, or move vertically. These movements require more grip than smooth plastic on smooth enamel can provide.
This is where attachments come in. Attachments are small, tooth-coloured composite bumps bonded to specific teeth. They act as handles that the aligner can push or pull against. Each attachment is shaped and placed to facilitate a specific type of movement.
Common attachment shapes include:
- Rectangular: for bodily movement (moving the entire tooth, root and crown, in the same direction).
- Bevelled or ramped: for rotational movements.
- Vertical ellipsoid: for intrusion (pushing a tooth up into the bone) or extrusion (pulling it down).
Your dentist places attachments at the start of treatment and removes them at the end. They are barely visible and do not damage the tooth surface when removed.
Types of tooth movement
Not all tooth movements are equally straightforward for aligners. Understanding the types helps explain why some treatments take longer or require additional techniques.
Tipping
The crown of the tooth tilts in one direction while the root stays relatively in place. This is the easiest movement for aligners because the force is applied at the crown level, which naturally creates a tipping motion. Closing small gaps and correcting mild crowding often involve tipping.
Bodily movement (translation)
The entire tooth, crown and root, moves in the same direction by the same amount. This is harder because it requires force distributed along the full length of the tooth. Attachments and careful staging of the movement sequence help achieve this.
Rotation
The tooth turns on its vertical axis, like a revolving door. Round teeth (canines and premolars) are harder to rotate because the aligner has less surface area to grip. Attachments are almost always needed for significant rotation.
Intrusion and extrusion
Moving a tooth vertically. Intrusion pushes it deeper into the bone. Extrusion pulls it further out. Both are challenging movements for aligners, and treatment plans often stage these carefully to maximise predictability.
Root torque
Changing the angle of the root within the bone while keeping the crown in place. This is one of the most difficult movements for aligners to achieve predictably, particularly in the front teeth. Complex cases requiring significant torque changes may benefit from a period of wire-based treatment.
Why 22 hours matters
Aligners only work when they are in your mouth. The force they exert needs to be sustained for bone remodelling to proceed at the programmed rate.
Most aligner systems recommend 20 to 22 hours of daily wear. Removing them for meals and oral hygiene typically accounts for 2 to 4 hours per day, which is within the acceptable range.
Wearing aligners for significantly fewer hours slows down or stalls movement. If the teeth do not reach their target position before you switch to the next tray, each subsequent tray fits progressively worse. This is called tracking loss, and it is one of the most common reasons aligner treatment stalls.
Our aligner compliance guide covers practical strategies for hitting your wear-time targets.
How long does the process take?
Treatment length depends on the complexity and distance of the movements required.
- Mild cases (minor crowding or spacing): 3 to 6 months, 10 to 20 trays.
- Moderate cases (moderate crowding, bite correction): 9 to 18 months, 25 to 40 trays.
- Complex cases (significant crowding, rotations, bite issues): 18 to 24+ months, 40+ trays.
At Ivy Dental, clear aligner treatment starts from $6,500. The final cost depends on case complexity and the number of trays required. Visit our aligner cost page for more detail on what affects pricing.
Indicative pricing. Your quote may differ based on clinical assessment.
What aligners cannot do
Clear aligners are effective for a wide range of orthodontic cases, but they have limitations.
Movements that are difficult or unreliable with aligners include:
- Large vertical movements (significant intrusion or extrusion).
- Major root torque changes.
- Correcting severe skeletal discrepancies (where the problem is jaw position, not tooth position).
- Moving teeth when there is no adjacent tooth to anchor against.
For cases where aligners alone may not achieve the desired result, your dentist will discuss alternatives. In some situations, a combination of aligners and other orthodontic techniques may be recommended. See our comparison of aligners vs braces for more on when each approach may be appropriate.
The role of retention
Once your teeth reach their final position, the bone around them needs time to consolidate. Without retention (a retainer worn after treatment), teeth tend to drift back toward their original positions. This is called relapse.
Retainers do not move teeth. They hold them in place while the bone fully remodels around the new position. Most patients wear a retainer full-time for the first few months after treatment, then transition to night-time wear long-term.
Book an aligner consultation at Ivy Dental
If you are considering clear aligners and want to understand whether they are suitable for your teeth, a consultation is the starting point. We see patients at our Everton Park and Nundah practices in Brisbane, 7 days a week. Contact us to book.
Call us on (07) 3266 7120 to book.
