August 20, 2018

Is periodontal health better with aligners than fixed appliances?

We know that periodontal health is influenced by fixed appliances. But is it better with aligners?

It is logical to assume that as aligners can be removed it should be easier for our patients to maintain good oral hygiene than with fixed appliances. As a result, periodontal health should be better with aligners than with fixed appliances.  However, research has shown that this potential benefit is not always clear. This new systematic review is, therefore, timely and relevant to clinical practice.

A team from China did this review. The Journal of the American Dental Association published it.

Periodontal health during orthodontic treatment with clear aligners and fixed appliances

Qian Jiang, et al

JADA 2018:149(8):712-720

It is not possible for many people to read this paper because it is not open access.

They did this study to compare periodontal health in patients treated with clear aligners or fixed appliances.

What did they do?

They did a systematic review and followed the standard steps for this form of research.  The PICO was

Participants:Patients having orthodontic treatment

Intervention:Clear aligners

Control:Fixed appliances

Outcomes:  Periodontal health.

They included RCTs and cohort studies.

They did standard electronic searches. Two independent authors assessed the articles and extracted the data.

They evaluated bias with the Cochrane Risk of Bias tool for the RCTs. They also used the Newcastle-Ottowa Tool for the cohort studies. Finally, they applied the GRADE system to assess the overall quality of the evidence.

What did they find?

They identified 9 studies for inclusion in their review and divided them into 2 trials and 7 cohort studies.  This included data on 427 patients. 190 used clear aligners and 237 were fitted with fixed appliances. The investigators used the plaque index (PI) in 8 studies, 6 studies reported on the Gingival Index (GI) and 7 studies recorded the Probing Depth (PD).

When they looked at the risk of bias, the RCTs were of medium quality, 1 cohort study was high and they rated the remaining studies as medium. The most common reason for bias was lack of blinding.

I decided to have a close look at the cohort studies because it was not clear whether they were prospective or retrospective. This is important because the inherent bias in retrospective studies may influence the overall quality of the findings of the review.

I was surprised to find that three of the cohort studies did not appear to evaluate the effect of aligners, they studied removable and functional appliances.  However, I could only access the abstracts of these papers. Here is a link to the full paper of the third of these studies.  This was surprising and I would have thought that the JADA referees would have identified this problem.

Unfortunately, I wonder if the cohort study data is flawed. As a result, I have only considered the data derived from the two RCTs.  This showed that the use of aligners resulted in a difference in Plaque Index -1.79 (95% CI= -2.13, 1.45).  This data was derived from just over 30 patients in each group. This small sample size and wide confidence intervals means that there is a high level of uncertainty in the data.

What did I think?

When I first started reading this paper I thought that it had potential. However, I was disappointed to find that the authors appeared to include data on removable and functional appliances. I was not sure why they did this?   I have checked this several times and I also attempted to email the contact author for the study, but the emails bounced.

As a result, I have had to exclude a large amount of data from this review.  I can only conclude that we do not know if removable aligners result in better oral hygiene than fixed appliances.

This also reminds me that we should not simply accept the findings of systematic reviews. It is necessary to have a look at the basic data and the papers reviewed by the authors.

You may ask why I have posted about this paper?  I decided to do this because their conclusion is likely to be used in claims on the advantages of aligners.  However, this study appears to have a major methodological problem and I feel that the conclusions cannot be supported by the data.

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Have your say!

  1. Very nice article Dr. O’ Brien.

    As a specialty trainee in my last year I find myself ever so frequently wondering about the most efficient way for the average orthodontist to critically review any claim made by a firm or a scientific piece of evidence on a regular basis, given the fact that many orthodontists are most of the time lacking of knowledge of statistics and/or scientific methodology (myself included). Free-time is also a rare commodity.

    The plain answer is to educate ourselves. Point. As we all have established though through similar articles such as yours, there is a tendency to accept, bit by bit, a quasi unerroneous nature of systematic reviews, opinions of “key influencers”, claims of firms and their representatives. It is also a reality, that many of us do/will eventually succumb to “patient pressure” regarding this or that system.

    To cut it short, how can we maintain a high scientific standard while at the same time remaining financially and “socially” relevant? This seems to me as a zero-sum problem, at least in most cases.

    PS: I understand that my lack of experience is a potential shortcoming in my way of seeing things, but as a dentist which has already worked in 2 EU countries and prepares himself for the third one, I think that this is a real problem which will only get more significant in the coming years. The technology which is rapidly gaining ground clinically is largely unknown or at best contested.

  2. Thanks Prof O’Brien. Yes the claim for the aligners to be better than fixed appliances from periodontal health would have been used, without substantial evidence.

  3. Sorry to go off slightly off topic but just seen this:

    Lots of users say a vibrating device helps with comfort on change of aligner days. eg I find chewing helps pain control by overriding the pain signal. This study seems to say there is no difference?? I would have thought even the placebo effect of such a device to distract would help. Strange no effect then. Did they measure only initial pain levels, what about length of pain? I dont understand the wilcoxon test being used. If a person used a pain relief device or not would be irrelevant in a wilcoxon scale.
    A person using the device would not know the pain of someone not using the device, so the baseline is not consistent? This study sounds flawed. Also if they stuck to the change schedule for aligners, how could there be a difference? I thought the vibrating device allowed people to change to the next aligner more quickly?
    Sorry for the ramble.

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