June 19, 2017

Which is better Invisalign or Fixed Appliances: Part 2: Does this new systematic review help?

Which is better Invisalign or Fixed Appliances: Part 2: Does this new systematic review help?

This is the second of two posts on the effectiveness of Invisalign and Fixed Appliances. Last week I looked at a retrospective study and this week I will look at a new systematic review.

A lot of people read this post and generated a number of comments in the blog comments section and on other forms of social media. In my post last week, I pointed out that the study was retrospective and this meant that we needed to be cautious about the conclusions because of the potential for bias. Nevertheless, I still felt that the study provided us with some useful information. Just as I finished this post, I came across this new systematic review. I would like to discuss whether this helps us further.

Efficiency, effectiveness and treatment stability of clear aligners: A systematic review and meta-analysis

M Zheng et al DOI: 10.1111/ocr.12177

Orthodontics and Craniofacial research: Advance publication.

A team from Wenzhou, China did this study. They had the following aims:

“To identify and review the literature on efficiency (treatment time), effectiveness (occlusal indices) and long term stability of treatment with clear aligners”.

 What did they do?

They did a standard systematic review with the following steps:

Electronic and hand search of the literature up to October 2014

Two independent authors reviewed the abstracts to select a final sample of relevant papers.

The two authors extracted data and assessed risk of bias.

The PICO was:

Participants:    Orthodontic patients

Interventions: Clear aligners

Comparator:    Fixed appliances

Outcomes:      Treatment duration, occlusal index scores and stability of treatment

They excluded investigations with no comparison group, editorials and case reports. I was not clear on whether they excluded retrospective studies.

What did they find?

After the selection process, they included four studies. Three of these were prospective cohorts and one was a randomised trial. They rated the cohorts as evidence level 2b and the trial as 1B. As a result, they felt that any conclusions they drew were only supported by limited evidence..

When they looked at treatment time they concluded that treatment duration in the fixed appliance patients was significantly longer than with Invisalign. I was not sure about this conclusion because the mean difference was 0.5 with a 95% Confidence interval of -1.29 to 0.26. We can see that this range includes zero. This means that the difference is not statistically significant. When I looked at the amount of heterogeneity this was 88% which is considered to be high and I had to conclude that the findings were not very robust.

When they looked at chair time, appointments etc, they found one study and this concluded that treatment with conventional brackets required 4 more visits, 1 more emergency attendance, 7 minutes more emergency chair time and 93 minutes greater chair time.

Only one study looked at treatment outcomes. This used the ABO objective grading system. They concluded that Invisalign treatment was 13 OGS points more than fixed appliances. Invisalign did not treat malocclusions as well as fixed appliances.

Finally, only one study evaluated stability. This showed that there were greater post-retention changes in the Invisalign patients.

They concluded that

  • Aligner therapy has advantages in a reduced treatment and chair time
  • There is insufficient evidence of any difference in treatment effectiveness and stability.

 What did I think?

When I critically looked at this review, it was clear that they included studies that did not provide a high level of evidence. The studies were rather small and were cohorts. As a result, there is a high degree of uncertainty in the results. However, this is the best evidence that they could find.

 A possible summary of what I may know about Invisalign vs Fixed Appliances?

When we combine this systematic review and the retrospective paper from last week. I think that the current state of knowledge appears to be:

  • There is no evidence of any differences in the effectiveness of Invisalign and Fixed Appliances.
  • Treatment duration with aligners may be shorter than with Fixed Appliances.

Nevertheless, we need to be really cautious about these findings as the only evidence that we may have is a retrospective study and a limited systematic review.

We had a lot of comments on last weeks post. I think that it was important that several people suggested that these studies did not add value because the treatment was not delivered by practitioners who had a high aligner case load (experts) who worked in a private practice setting. As a result, the studies had operator bias. I tend to agree with this suggestion.

If we are to investigate aligner treatment we need to carry out studies in private practice settings. While there have been some orthodontic studies carried out in this setting in the UK, I am not aware of these being done in other countries. It is time that we moved orthodontic research into the “real world” settings. While this is complex, it will address many concerns that clinicians have about studies carried out in Dental Schools.

We also need to be cautious that our current knowledge is not dominated by the case reports that are shown at conferences. These are frequently miracle cases treated by the orthodontic Key Opinion Leaders. I would like to see more routine treatments and even cases that did not “work out”.

Overall conclusion

However, as things stand we have an absence of evidence about aligner treatment. This does not mean that it does not work, we just do not have the evidence that it does or does not work. We just have clinical experience. Surely with the all the funds generated by the aligner companies we could organise a trial in the private practice setting, if we want…

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Have your say!

  1. Thanks Kevin for your succinct review. Corroborates my thinking that there is not much in peer reviewed literature that is currently relevant, unbiased and definitive re aligner mechanics in terms of treatment outcomes. I would like to add that there have been and currently are significant attempts to address this deficiency. I kind of hold my breathe as I am not sure how many of these attempts will pass the KOB blog test. Re your last sentence, as far as Invisalign goes, Align Technology do have an annual global University research award Program, providing over 300K in 2016 (and 1 of the recipients is comparing fixed and aligner outcome). I think this is a spectacular program for supporting ortho grad education in terms of research proposal, design and execution, for helping out with department funding, and for Align Tech PR. Nevertheless, I wonder if the study we all want to see was funded by aligner companies, whether we would dismiss it due to perceived bias? Would we dismiss or question a study into effectiveness and efficiency of fixed appliances sponsored by a bracket manufacturer, or if it was conducted in the practice of a KOL? And at the risk of being labelled a heretic, what is / are the equivalent definitive research evidence that shows us that fixed appliances work? ,,,No, I’m serious! ,..(maybe too familiar w Richmond, Shaw, O’Brien)… wouldn’t we would need to produce at least that same level of existing evidence that we have for fixed appliances, using an agreed measurable definition of “work”?

  2. Dr O’Brien,
    I do appreciate your efforts in dissecting the orthodontic literature/ research from a methodological perspective .And without sounding pessimistic I would be surprised if we ever can establish conclusive results in any scientific endeavor . For this would be paradoxical to the notion of the ever questioning mind that the scientific process t
    attempts to encourage .
    Now to the question at hand aligners versus fixed appliances . Firstly ,we need to recognize that they are two different orthodontic force delivery mechanisms . So this begs the question which of the two systems is better at delivering predictable/ controlled force systems i.e. more reliable forces .
    Secondly, fixed appliance therapy is generally practiced with little effort on planning , A reactive approach . Whereas ,there is an element of proactive planning with aligner therapy .So this begs the question whether
    Proactive planning impact the care cycle .
    Thirdly, when the final goals in treatment are different i.e. The finishing line then any study investigating the effectiveness of these therapies is in vain . You may argue that a s
    this may controlled for by better design ,
    Sample size etc …And then after all these investigations a clinician is confronted with the question how do I best serve the patients wants and balance them with their needs ?
    This brings me to my last point . In every profession there is a normal distribution of skill sets . Some doctors are just better than others . A harsh reality often clouded in a world of doublethink.
    Our profession is blessed with both the Aligner as well as the Fixed appliance expert and I can assure you each of them can perform at the highest of levels .(although I must confess I have a personal bias in terms of who would perform better! ).
    And we cannot forget that patient care has many facets to it . Diagnosis , Prognosis
    Communication etc . And each of these attributes requires special skills that impact the quality of care .
    And finally ,orthodontic care cannot take the face of an industrial model . For each patient
    Is different ( i.e. The input ) so to expect a consistent outcome may be an excerise in orbital habituation .
    So what really matters beyond all these devices that we chase , these appliances of mass destruction that we have accumulated in our arsenal is really establishing a culture of Patient First !

  3. I think this comparing apples to oranges. Both are a good treatment choices and a treating clinician is in a better position to decide which appliance system to work with. It’s just another tool in your toolbox, that’s all it is!!

    • Yes, this is true and as we do not know which is the best method of treatment we have to base our choice on clinical experience and patients wishes.

  4. I did not note any mention if there were any differences in case complexity at the start of treatment. . It would be a fair assumption that most practioners would be biased towards selecting more complex cases for fixed appliance therapy.

    • While we do not really know if there is a difference in complexity, I suppose that we do know that there was not much difference in the dent-alveolar features of the malocclusion and to a degree this may reflect skeletal issues and therefore complexity. However, this is a long shot!

  5. I would question those results which I base on just my clinical experience.

  6. Thank you again. Most of these types of studies evaluate treatment time. I feel a more important metric is the number of appointments it takes to complete an orthodontic case. In a private practice setting, each appointment has an associated cost to the patient and the orthodontist.

    I feel efficiency is best measured by this metric. I realize patients and parents are most “tuned into” treatment time and it seems us orthodontists are also; however, in a very efficient practice, the number of appointments it takes to complete a case, can make a significant impact in patient time and the financial bottom-line of the practice.

    It would be interesting to see studies measuring this metric. The difficulty of measuring this would be the different skill levels of the orthodontist. One would think that a skilled orthodontist would be more efficient than a resident, but we don’t know that. Another difficulty is that orthodontic studies measure averages and deviations. If one orthodontist was super-efficient, that data point would lie outside the norm. While this may not be significant for the study, to that one orthodontist, it is highly significant.

    I just wanted to give a perspective from an everyday orthodontist in a private practice setting. I certainly don’t claim to be a orthodontic researcher and I’m sure that are many factors that I have not considered.

    Thank you again for your contribution to orthodontists everywhere.

    • Great comment and you have made good points. I agree totally that when we have no differences in the morphological features of malocclusion then patient factors are very important. In fact all studies should measure patient factors.

  7. Dear friend, this is a very interesting topic. I have been working as a specialist orthodontist since 1992. I started using Invisalign since 2003. I still use fixed appliances as well. Although Invisalign is a very “sexy” approach to use on adults (since most of the wouldn’t accept fixed appliance treatment), I need to comment that in the VAST majority of cases (and I am a platinum user), at least one refinement is required. Occasionally, a second refinement is also necessary. I seriously doubt that the authors of the studies you mention, considered the refinements when they assessed treatment duration. Also, on the chairside time issue: I often need to custom fit aligners, especially in complicated adult cases. If this happens, the time required is BY FAR more than if I were to treat these patients with conventional ceramic appliances. There is wide room for improvement in the Invisalign approach. Admittedly, they Invisalign people work hard on it.

    • Could you elaborate why refinements are required?
      Aren’t teeth supposed to be in the exact position if they fitted into every aligner?
      What is a usual length of treatment without and with refinements?

  8. To Dr Tom Nasiopoulos. I am not an user of Invisalign but I am curious to know what do you mean by “custom fit aligners”. What do you exactly do? Thank You.

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