Newsletter 4 – February 2024

Predictability of Clear Aligner Therapy

Clear aligner therapy predictability refers to the ability to accurately forecast and anticipate the expected outcome of orthodontic treatment using aligners.

It refers to the level of certainty and reliability in achieving specific planned movements of teeth to achieve the desired final alignment and bite correction.

The concept of predictability in clear aligner therapy involves several key aspects:


Compliance: This is one of the most important factors in treatment success, therefore, if the aligners are not worn as prescribed, the patient receives little or no result.


Aligner tracking: It is essential to keep a constant check on the movement of teeth during aligner therapy, as sometimes they might not remain in the desired position within the plastic trays. 

This can lead to a gap between the tooth and the plastic, which is referred to as “lag or tracking error”. These errors can occur unexpectedly during the sequence of aligners, causing a loss of tracking and the treatment going off course.

Several factors can contribute to these errors, including diagnosis and treatment planning, intraoral scanning, tolerances in the creation of laboratory printed models, tolerances in the molding of plastic, and limitations of the plastic materials themselves.

Aligner chewies are recommended for patients to help them fit more comfortably and firmly. They not only help maintain proper tracking of the teeth but also increase the forces on the teeth to promote movement. In case of a lag, chewies can help seat the aligner properly on the teeth that are not tracking as intended.


Lack of Space: There are two options to address the lack of space: expanding the dental arches to create more space or reducing tooth mass through procedures such as interproximal reduction (IPR) or extraction.

Significant expansion can displace teeth into less stable positions, due to a change in equilibrium in the facial musculature and an associated risk of bone loss as teeth are forced beyond the confines of the alveolus. Certainly, a certain amount of expansion appears tolerable or, at the very least, retainable. Arch expansion up to 2mm in the molar region and 0.7mm in the canine region can be easily achieved and typically comes with acceptable stability.

Reducing tooth dimensions through interproximal reduction (IPR) to fit them within the arch perimeter is beneficial, however, its scope should be limited. If there is insufficient space for a tooth to move, it won’t be able to do so. Without creating space, the binding collisions or contacts between irregular incisors will prevent movement.

An effective strategy for addressing anterior crowding with clear aligners combines mild expansion and mild interproximal reduction (IPR). Opting for IPR from the beginning may not be justified unless the initial discrepancy is minimal. In such cases, focusing on labial and lateral expansion is more sensible. 

Resolving minor crowding may involve prescribing the creation of visible space, up to 0.2 mm between specified teeth, before cautiously implementing reasonable amounts of IPR for safer and more controlled adjustments. Once space is achieved, corrections of rotations and labiolingual discrepancies become more predictable.

Opting for extractions introduces a distinct set of considerations, including the management of anchorage control, torque, root rotation, tipping, bodily movement, and ensuring the establishment of proper interproximal contacts by the conclusion of the treatment.

To improve predictability, a combination of auxiliary accessories such as elastics, and temporary anchorage devices (TADs) should be considered, along with the size and type of composite attachments.

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