Are Aligners with attachements really invisible?
14.11.2022Predictability of orthodontic movement with orthodontic Aligners: A retrospective study
The advent of clear aligners came at the turn of the 21st century, despite the principle it is based on originating many decades prior. Clear aligners are thermoplastic orthodontic appliances that can be individually customized to mimic natural tooth movement with the help of CAD/CAM technology – virtual planning and stereolithographic prototyping technology.
Ever since their launch on the orthodontic market, clear aligners have been experiencing a swiftly growing demand among patients. This can be owed to their comfortable wearability, high efficiency, and superior aesthetics, especially when compared to the conventional alternative of fixed appliances.
Despite their shining glory, not many studies have been done to uncover the true potential of these clear aligners. And while they have been widely preferred over braces in treating mild cases, their efficacy to correct complex malocclusions is still shrouded in scepticism. How much do we actually know about orthodontic aligners when it comes to the predictability of movement? This new study strides to answer this blaring question.
This study was conducted by a team from Italy and published in Progress in Orthodontics.
Predictability of orthodontic movement with orthodontic aligners: a retrospective study.
Lombardo L(1), Arreghini A(2), Ramina F(1), Huanca Ghislanzoni LT(3), Siciliani G(1).
Prog Orthod. 2017 Nov 13;18(1):35. doi: 10.1186/s40510-017-0190-0.
What they asked
They conducted this study:
“To evaluate the predictability of F22 aligners (Sweden & Martina, Due Carrare, Italy) in guiding teeth into the positions planned using digital orthodontic setup.”
What they did
They selected sixteen adult Caucasian patients (6 males and 10 females, mean age = 28 years and 7 months) who were treated with F22 aligners. A total of 345 teeth were analysed.
The maximum movement planned for each aligner (treatment staging) was calculated at
- 2° rotation
- 5° vestibulolingual and mesiodistal tip
- 2 mm linear displacement
They did not use any kind of auxiliaries such as intermaxillary elastics, buttons, or chains. They did, however, use F22 system Grip Points (attachments) and also allowed anterior and/or posterior stripping.
The patients were asked to wear the aligners for 22 hours per day, excluding mealtimes and oral hygiene routines. Aligners were replaced every 14 days.
Pe-treatment, ideal post-treatment (as planned on digital setup), and real post-treatment models were analysed using VAM software (Vectra, Canfield Scientific, Fairfield, NJ, USA). This allowed them to identify anatomical reference points, planes and axes on the digital models. These were, in turn, used to calculate the angulation, inclination, and vestibular prominence of each tooth, as well as linear and angular measurements.
Prescribed and real rotation, mesiodistal tip and vestibulolingual tip were calculated for each tooth and subsequently analysed by tooth type. This was done to identify the mean error and accuracy of each type of movement achieved with the aligner.
What they found out
They included this table to illustrate their findings for mean (%) accuracy of tooth movements achieved using F22:
| Tooth | Mean (%) | ||
| Vestibulolingual tip | Mesiodistal tip | Rotation | |
| Upper incisors | 64.5 | 76.7 | 61.5 |
| Upper canines | 54.0 | 78.3 | 62.3 |
| Upper premolars | 69.6 | 70.6 | 54.0 |
| Upper molars | 52.5 | 93.4 | 78 |
| Lower incisors | 86.1 | 87.7 | 67 |
| Lower canines | 66.4 | 86.7 | 54.2 |
| Lower premolars | 90.4 | 96.7 | 82.7 |
| Lower molars | 86.2 | 61.8 | 85.4 |
| Total | 71.2 | 81.5 | 68.1 |
They found that the most accurate movement achieved using F22 was mesiodistal tipping, whose mean accuracy was 82.5% (SD = 77.4). Overall, the accuracy of mesiodistal tipping at lower premolars was 96.7% (SD = 96.9), closely followed y the upper molars and lower incisors.
Some of the least precise movements were found to be vestibulolingual tipping of the upper molars (52.5%, SD = 53.3) and upper canines (54.0%, SD = 57.2%) and rotation of the upper premolars (54.0%, SD = 54.3) and lower canines (54.2%, SD = 73.9).
Interestingly, there was an even more significant reduction in the accuracy of upper canine rotation at rotations greater than 15° (19%, SD = 14.1, P <0.05). However, they could discern that the mean rotation of the upper incisors was significantly more accurate than the mean rotation of the lower premolars.
They demonstrated that among the lower teeth, the canine movement was the least accurate. Ultimately, they concluded that F22 aligners were able to achieve a mean accuracy of 73.6%, considering all the movements in the anterior and posterior teeth.
What we can conclude
There were no significant differences in the accuracy index when they assessed the different tooth movements except for upper incisor rotation, which was significantly lower than that achieved at the lower premolars.
With the extensive research provided by this study, we can conclude that orthodontic aligners on their own (without the use of auxiliaries) are not programmed to achieve movement with 100% predictability. The authors had this to say about the results, “Although tipping movements were efficaciously achieved, especially at the molars and premolars, rotation of the lower canines was an extremely unpredictable movement.”