Kravitz et al. reported that the average effectiveness of clear aligners (TA) was 41% with the most predictable movements being lingual movement (47.1%), extrusion (29.6%), mesiodistal crown inclination (26.9%) and rotation of the mandibular canines (29%).
Haouili et al. published an updated set of results in 2020, reporting that movement accuracy had improved slightly (up to 50%), rotations still had poor predictability (46%).
Predictability is considered to be worse in cases considered more difficult, specifically extraction cases, cases with open bite or deep bite greater than 1.5 mm, or when pure root movements (torque and translation movements) were necessary. Multiple finishing phases have been described in approximately 70%-80% of patients treated with AT.
What is the correct amount of overcorrection?
This study was designed to provide clinically useful information on overcorrection that should be included in the initial treatment planning of ATs. The hypothesis was that the same amount of overcorrection to the initial setting for all planned movements investigated, regardless of the magnitude of the prescribed movement or tooth type.
150 patients (80 women and 70 men; mean age 33 years ± 12) were selected with clear aligner therapy according to the inclusion criteria: Class I dental malocclusion, 12 to 20 clear aligners per arch, without use of elastics, auxiliaries, miniscrews, cantilevers or buccal and lingual fixed partial appliances, interproximal enamel reduction (IPR) and no previous history or active periodontal disease at the beginning of orthodontic therapy.
The objective The purpose of this study was to obtain clinical information on the amount of overcorrection that should be included in the initial AT planning to reduce the need for or duration of the finishing phase. The amount of correction performed during the finishing phase was directly proportional to the magnitude of the initially planned movements and varied according to tooth type. During the finishing phase, it was necessary to correct the inclination by an average of 20.5%, the angulation by 14.5%, the rotation by 28.4%, the extrusion by 11.7% and the intrusion by 22%.
Both tilt and rotation appear to be the least accurate and require the most overcorrection in the initial planning phase. The results of this study suggest that rotation is the most difficult type of movement to achieve with aligners, and that overcorrection should Apply to all teeth and not just rounded ones.
Conclusion
In conclusion, overcorrection should be incorporated into the initial digital setup to optimize AT performance. Approximately 20% should be prescribed for difficult movements such as tilting and rotation. In the case of angular movements, the tilt and rotation overcorrection values seem to depend on both the type of tooth and the magnitude of the movement, while the precision of the intrusion is not necessary.
