Predictability of rotational tooth movement with orthodontic aligners comparing software-based and achieved data: A systematic review and meta-analysis of observational studies.

Clear aligners have been widely in use over the last decade owing to their upstanding properties like aesthetics, efficacy in treatment duration, ease of wear, and reliability. Despite their increased demands in the market, there is still a bubbling clinical dispute based on their efficiency in primarily controlling complex orthodontic tooth movements like rotation.

A principal reason why experts are hesitant to fully embrace clear aligners in the treatment of difficult dental malocclusions might have something to do with the force transmission mechanism. In fixed appliance therapy, forces originate from the metal wire and bracket interactions and are then transmitted to tooth structures causing displacement. Contrarily, in aligner systems, the desired outcomes are brought on by a fairly unique mechanism.

Tooth movements in aligners are caused as a result of a predetermined “mismatch” between the tooth and aligner, which also coincides with the desired position of the tooth. The final tooth positions are achieved by sequential aligners worn by the patient for 22 hours a day. Over time, the teeth get progressively repositioned to their final positions.

However, even considering the pioneering efforts of clear aligner systems, there arise many challenging situations especially when they are used to treat severe rotations. Several studies have even indicated that clear aligners cannot provoke rotational movement alone. They demonstrate that auxiliaries such as attachments and elastics are mandatory in clear aligner therapy to achieve predicted results.

While incisors and molars are fairly easy to rotate with the help of plastic aligners, the cylindrical morphology of premolars and canines may command the use of composite attachments or buttons. In these instances, one button is placed on the tooth to be rotated while another button goes on the ‘anchor’ tooth. The goal is to provide rotational correction to the targetted tooth without moving the anchor tooth. But how effective is it?

This study was conducted by a team from Greece and Switzerland. It was published in the Journal of Orthodontics.

Predictability of rotational tooth movement with orthodontic aligners comparing software-based and achieved data: A systematic review and meta-analysis of observational studies.

Koletsi D, Iliadi A, Eliades T

J Orthod. 2021 Sep;48(3):277-287. doi: 10.1177/14653125211027266. Epub 2021 Jun 27.

What they asked

The aim of this study was:

“To review systematically the scientific evidence on the prediction potential of aligner software programs for rotational orthodontic tooth movements with the use of aligners.”

What they did

The authors included studies based on the following inclusion criteria:

• Study design: Clinical (in vivo) studies of this nature: observational designs, retrospective or prospective cohorts, and cross-sectional or case-control studies.
• Participants: Participants undergoing aligner orthodontic treatment. Any type of tooth with a rotational movement plan was considered in the maxillary and/or mandibular arch.
• Index tests: Virtual treatment plan and tooth movement, ClinCheck (Align Technology) for prediction of tooth movement and other prediction software models.

An electronic search was done of 7 databases and also a hand search of the included studies for additional relevant publications. The databases that were included were: PubMed via Medline, Scopus, Cochrane Central Register of Controlled Trials (CENTRAL) and Cochrane Database of Systematic Reviews (CDSR). Unpublished literature was searched within Open Grey, ClinicalTrials.gov (www.clinicaltrials.gov), and the National Research Register (www.controlled-trials.com).

Data selection: They deemed the studies eligible if they included evaluation of rotational tooth movement with any type of aligner, through the comparison of software-based and actually achieved data after patient treatment.

Data extraction and data synthesis: The data extraction process was done independently and in duplicate. Furthermore, the risk of bias assessment was performed using the QUADAS-2 tool (Quality Assessment of Diagnostic Accuracy Studies-2). They also performed meta-regression analytical techniques for the assessment of the effect of the tooth with confidence intervals (CIs) of 95%. The overall quality of the evidence was assessed through Grading of Recommendations Assessment, Development and Evaluation (GRADE).

What they found out

A total of seven studies were included in the final qualitative synthesis. Of the seven studies included in the review, 3 were prospective cohorts while the remaining 4 were retrospective cohorts. Sample sizes for the studies included in the review were in the range of 20– 38 within eligible studies.

The overall results showed a non-accurate prediction of the outcome for the software-based data, irrespective of the use of attachments or interproximal enamel reduction (IPR). Maxillary canines demonstrated the lowest percentage accuracy for rotational tooth movement (three studies: effect size = 47.9%; 95% CI = 27.2-69.5; P < 0.001), although high levels of heterogeneity were identified (I2: 86.9%; P < 0.001).

On the contrary, the highest percentage accuracy for predicted rotational movement was revealed by the mandibular incisors (two studies: effect size = 70.7%; 95% CI = 58.9-82.5; P < 0.001; I2: 0.0%; P = 0.48).

The overall risk of bias was rated as unclear for three of the seven studies and low for the remaining four studies.

What we can conclude

According to the data presented to us through this review on the comparison between software-predicted and actual rotational tooth movement, the percentage accuracy was low for anterior teeth and premolars.

The quality of the existing evidence could not be interpreted as strong enough to say for sure that the rotational movements would be accurately performed by clear aligners. Aligner treatment should be selected carefully especially if tooth rotations are required.