July 29, 2019

Does Clear Aligner Treatment result in less root resorption?

We all know that fixed appliance treatment is associated with some root resorption. However, we have limited information on the effects of clear aligner treatment on root resorption.  This new systematic review hoped to provide us with an answer.

Root resorption is one of the harms from fixed appliance treatment.  Investigators have done many studies to identify the risk factors and the amount of resorption with fixed appliances. However, we know little about the incidence and severity of root resorption with clear aligner treatment.  This problem was investigated in this new systematic review.  Orthodontics and Craniofacial Research published the paper. A team from China did the study.

Root resorption in orthodontic treatment with clear aligners: a systematic review and meta-analysis

Fang et al

Orthodontics and Craniofacial Research Online.  doi: 10.1111/ocr.12332

What did they ask?

They set out to ask:

“Does clear aligner therapy reduce the incidence and severity of external root resorption (ERR) in orthodontic patients”?

What did they do?

They did a standard systematic review with a hand search, identification of papers, data extraction and assessment of bias.  They did not set out the PICO clearly, and I have worked out that this was:

Participants: Orthodontic patients

Intervention: Clear aligner treatment

Control: Fixed appliance treatment

Outcome: Root resorption measured from panoramic radiographs or CBCT images.

They did electronic and manual searches of the literature. They extracted the data and used the Cochrane Risk of Bias tool for RCTs and the ROBINS-I tool for non-randomised studies.  Finally, they carried out a meta-analysis with RevMan 5.

What did they find?

They found 11 studies that were suitable for qualitative analysis and three studies that they could use in a meta-analysis.  Four were cohort studies, one was a case-control genetic study, and the remaining six were before and after studies of clear aligner therapy patients.  Their risk of bias assessment suggested that six were at moderate risk, and the remaining five were at serious risk of bias.

When they looked at the amount of external root resorption in a meta-analysis, they found that there was decreased external root resorption with clear aligner therapy (SMD= -0.65 (95% CI -0.74, -0.55). They also did a subgroup analysis of the individual incisors, and this showed significantly less root resorption with aligners than with fixed appliances.  They took most of this data from one study by Eissa et al. I will come back to this later.

Their overall conclusion was

“Clear aligner therapy might not prevent ERR during orthodontic treatment, but both the incidence and the severity could be lower compared with fixed appliance treatment”.

They also made the “more research is needed” conclusion.

What did I think?

This review attempted to answer a clinically relevant question.  The authors came to a surprisingly firm conclusion. I am concerned that such a definite conclusion could be used to promote aligner therapy by aligner companies.  As a result, I have looked at this systematic review very carefully.  Unfortunately, I felt that there were several important issues that the referees of the journal must have overlooked. These were:

  • The systematic review did not contain any RCTs.  The absence of this type of study means that the review is not going to give us useful levels of evidence.
  • All the included papers were of severe and moderate risk of bias.  As a result, any conclusions from the review must be treated with a great deal of caution.
  • They placed a great deal of emphasis on the study by Eissa et al. This was a pilot study of 33 patients whose records had been retrospectively collected. We need to be very cautious about using data from such small studies.

As a result, I feel that we need to be very cautious about the findings of this paper.

I have tried to be positive about this paper, but unfortunately, these flaws are significant. I cannot help wondering if the journals are publishing too many systematic reviews that are not adding to our knowledge.  I have posted about this before.

Perhaps a journal editor could comment?

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Have your say!

  1. Are these studies really comparing like for like treatments?. For example, aligners tend to be used for fairly minor corrections whereas they are not generally used to correct more severe Class 2 div 1 or 2 div 2 malocclusions where significant bodily movement and intrusion of teeth might be required often resulting in more significant ERR?

    • Bingo! That’s my question as well. Aligner therapy tends to Ben more non extraction cases, whereas fixed appliances could have a 50/50 ratio ex extractions vs. non-extractions. Cannot reach conclusions if you are comparing different treatment types.

    • Same, I’d be interested to see if the length of treatment was similar, as we know longer treatments have a higher risk of root resorption.

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