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.
Movement Types
- Crown tipping refers to the angling of a tooth's crown without altering the position of the root's apex.
- Root tipping involves the angling of a tooth's root without shifting the crown's apex.
- Torquing a tooth with clear aligners involves moving the tooth buccolingually around its centerpoint, causing opposite movements of the crown and root. This process utilizes a twisting force aimed at modifying the crown’s inclination, specifically rotating the tooth around its long axis and moving the apical portions with orthodontic devices.
- Rotation involves rotating a tooth around its long axis.
- Translation is the process of moving a tooth along the occlusal plane while maintaining the orientation of its long axis.
- Extrusion is the upward movement of a tooth from its supporting structures.
- Intrusion involves moving a tooth downward into its supporting structures.
- Distalization refers to moving a tooth backward along the occlusal plane away from the midline.
- Mesialization involves advancing a tooth forward along the occlusal plane towards the midline.
- Expansion is the lateral movement of posterior teeth away from the midline.
- Proclination involves tilting the crowns of the anterior teeth forward towards the lips.
- Lingualization is the movement of teeth towards the tongue side of the dental arch.
Predictability of Movements
Due to differences among individual teeth, certain orthodontic movements with clear aligners are more feasible for some teeth than others. Below are general guidelines to aid in case selection and expectation management.
Basic Movements
Clear aligners perform exceptionally well for facial/lingual movements, benefiting from a wide surface area for force application and neighboring retentive surfaces for anchorage.
Moderate Movements
- Distal/Mesial Movements: If the contact between the tooth and the aligner is insufficient on the clinical crown to effectively move the tooth in the required direction, adding an attachment may increase the surface area.
- Rotations: Adequate space and proper positioning of the tooth root are crucial for rotations, especially in teeth with natural inclinations. For instance, a mesially tipped tooth should be uprighted before correcting its rotation. Teeth with conical shapes, like mandibular premolars, often lack natural morphology for secure aligner grip and typically need attachments for better engagement.
- Torquing: Assessing the crown's morphology, particularly the length of clinical crowns, is vital as those with longer crowns can be torqued more easily. Teeth with short clinical crowns or undefined crown shapes may require attachments for effective movement.
Difficult Movements
These movements necessitate close attention to various details such as crown shape, root position, and the available space or arch length for performing the movement, and may benefit from the use of attachments and auxiliaries like buttons and elastics.
- Extrusions: Most effective on single-rooted teeth with straight roots. Consider the crown's shape and the interproximal areas, which might allow the aligner to engage more of the tooth without attachments. Teeth with short crowns, undefined shapes, or multiple roots generally need attachments.
- Intrusions: The morphology and retentiveness of neighboring anchor teeth are critical. Attachments are frequently employed if these teeth do not provide enough natural undercut. Intrusion of multi-rooted teeth is exceedingly challenging and rarely attempted, typically requiring attachments on adjacent teeth for support.