Efficacy of Clear Aligners in controlling orthodontic tooth movement: A systematic review

In the past, many researchers have set forth to evaluate the true effectiveness and accuracy achieved by clear aligners in line with the anticipated orthodontic treatment plan. Leading authors the likes of Djeu and Kassas not long before have conducted clinical studies that have compared the treatment results accomplished by Invisalign® and clear aligner patients with those of conventional fixed braces. The results have been extraordinarily typical. Studies like these and others have uncovered some unfavourable truths about clear aligners.

In fact, a study conducted by Kravitz et al in 2009, working in a similar scope of objective, was able to pursue the narrative that clear aligner systems, in this case, Invisalign®, were only able to achieve 41% of the predicted tooth movement!

So, what does this mean? Are the expectations we bestow on these up-and-coming clear aligner systems too high? Should we stick to the traditional method of fixed orthodontic therapy for a straighter smile? A well-celebrated study led by Gabriele Rossini might just be the clarification we need.

This study was conducted by a team from Italy and published by Angle Orthodontics.

Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review.

Rossini G(1), Parrini S(1), Castroflorio T(2), Deregibus A(3), Debernardi CL(4).

Angle Orthod. 2015 Sep;85(5):881-9. doi: 10.2319/061614-436.1. Epub 2014 Nov 20.

What they asked

The authors conducted this study with the objective:

“To assess the scientific evidence related to the efficacy of clear aligner treatment (CAT) in controlling orthodontic tooth movement.”

What they did

They organized a systemic search in the medical literature produced between the years 2000 and 2014 with the intention to identify all peer-reviewed articles relevant to the review’s objective. They made use of a specific search strategy and respective inclusion and exclusion categories to retrieve lists of potential articles to be included in the study.

The databases they searched from included:

• PubMed
• PubMed Central
• National Library of Medicine’s Medicine
• Embase
• Cochrane Central Register of Controlled Clinical Trials
• Web of Knowledge
• Scopus
• Google Scholar
• LILACs

They also made sure to conduct a manual search in order to identify additional articles in the medical library of Turin University, in the authors’ personal libraries, and in the references of selected articles. International patents, abstracts, and presentations from international orthodontic meetings were also evaluated.

What they found out

For the study, they selected eleven relevant articles out of which two were randomized clinical trials, five prospective non-randomized trials, and four retrospective non-randomized trials. The risk of bias was assessed to be moderate for six of these studies whereas it remained unclear for the others.

The amount of mean intrusion reported was 0.72 mm. It was found that extrusion was the most difficult movement to control with only 30% accuracy, followed by rotation.

The highest predictability (88%) was found to be the upper molar distalization, especially when a bodily movement of at least 1.5 mm was prescribed. A decrease of the Little’s Index (mandibular arch: 5 mm; maxillary arch: 4 mm) was also observed in aligning arches.

What we can conclude

We learn through this study that clear aligner therapy can align and level the arches – no shocker there. However, while CAT is effective in controlling posterior buccolingual inclination, it is not as effective in preventing anterior buccolingual inclination. It was also revealed that it is not effective in controlling the rotation of rounded teeth. Fortunately, CAT proved to be highly effective in controlling upper molar bodily movements of about 1.5 mm.

Finally, this review, while giving us some good insight into the treatment efficacy of clear aligners, should be approached with caution, considering the number, quality and heterogeneity of the studies.