This article covers the following topics:
- The different types of tooth movements in clear aligner treatment; crown tipping, root tipping, torquing, rotation, translation, extrusion, intrusion
- The predictability of tooth movements in clear aligner treatment, including; predictable, moderate and unpredictable/difficult tooth movements
We use these terms to describe the movements of teeth during clear aligner treatment.
Our case parameters describe how much movement we recommend for each of these types of movements.
Crown tipping is the tilting of the crown of a tooth without moving the apex of the root.
Root tipping is tilting the root of the tooth without moving the apex of the crown.
Torquing The definition of torque has evolved from fixed appliances and although there is no wire and bracket, the concept remains the same with clear aligners. In clear aligner therapy, to torque a tooth is to move the tooth buccolingually around the centerpoint, so the crown and root move in opposite directions. It is the twisting force which is traditionally required to adjust the inclination of a crown.
Rotation is turning a tooth about its long axis.
Translation is shifting the tooth along the occlusal plane without changing the orientation of the long axis.
Extrusion is moving a tooth out of the supporting structures.
Intrusion is moving a tooth into the supporting structures.
Predictability of movements
Due to variations between teeth, some are more amenable to certain types of orthodontic tooth movements with clear aligners than others. Here are some rough guidelines to help you choose cases and calibrate expectations.
Clear aligners are particularly-well suited for facial/lingual movements. They excel when there's a broad surface to apply force to, and adjacent retentive surfaces to anchor against.
- Distal/mesial movements - if there is inadequate tooth contact with the aligner with the portion of the clinical crown to "push" the tooth in the desired direction, consider adding an engager for additional surface area
- Most rotations/rotations of lower premolars - ensure there is adequate space to rotate the tooth and consider the position of the tooth root as it is easier to rotate a tooth that is normally inclined. For example, a tooth that is mesially tipped should be uprighted first before attempts to correct its rotation. Conically-shaped teeth, such as mandibular premolars, offer little natural morphology for an aligner to "grip" onto. These teeth commonly require engagers to provide for added morphology.
- Torquing - evaluate the crown morphology, particularly length of the clinical crowns as these are more easily torqued. Short clinical crowns and lack of defined crown morphology (e.g. bulbous shaped crowns) may be assisted with engagers
How does ClearCorrect torque upper and lower anterior teeth?
More challenging movements
These tooth movements require added attention to details such as the crown morphology, position of the tooth root, available space/arch length to perform the movement and can be assisted with engagers and/or auxiliaries such as buttons and elastics.
- Extrusions - most effective with single rooted teeth that have a straight root. Also consider the crown morphology and interproximal areas. Triangular shaped tooth crowns and or interproximal areas that allow for the aligner to engage more of the crown may be extruded without engagers. Short clinical crowns, lack of defined crown morphology and multi-root teeth more commonly require engagers
- Intrusions - consider the morphology and retentiveness of the adjacent anchor teeth. If they do not provide sufficient natural undercut, engagers are often used. ClearCorrect's extended trimline design often provides sufficient retention for intrusion of single rooted teeth without the need for engagers. Intrusion of multi-rooted teeth is extremely rare as this is a very difficult movement and will require engagers on adjacent teeth to assist.
How does ClearCorrect intrude or extrude teeth?