November 18, 2019

Is clear aligner therapy effective?

The use of clear orthodontic aligners is one of the most exciting developments in orthodontics.  But are they effective?  This new systematic review provides us with some up to date information.

Clear aligner therapy has revolutionised orthodontic treatment.  This has led to an increase in adults having this form of treatment. Recently, there have been further developments into the use of aligners for teenage treatment, mandibular advancement and do it yourself orthodontics.  It has been suggested that one disadvantage of this treatment is a lack of efficiency in treating certain malocclusions. A team from Alberta, Canada looked at this in a new systematic review. Orthodontics and Craniofacial Research published this study.


Lindsay Robertson et al

Orthodontics and Craniofacial Research: Advance access: DOI:

What did they ask?

They did this study to ask two related questions:

“What is the contemporary knowledge on the predictability of clear aligner therapy”?


“What are the outcomes of clear aligner therapy compared to fixed appliances”?

Importantly, they acknowledged that there have been many improvements in clear aligner therapy. As a result, they only included contemporary literature between 2014-19.

What did they do?

The PICO was:

Participants: Orthodontic patients having clear aligner therapy.

Intervention: Any form of clear aligner therapy

Comparison: Fixed orthodontic treatment

Outcome:   Percentage of achieved results compared to predicted results. The secondary outcome was a comparison of clear aligners and fixed appliance treatment.

They wanted to include RCTs, prospective cohorts and retrospective cohort studies. The papers needed to be published between 2014-2019.

They did a standard electronic and hand search and filtered the papers to identify the studies.  They assessed the risk of bias with the Cochrane Risk of Bias tool for any trials and the ROBINS-I tool for observational studies. Finally, they used the GRADE approach to evaluate the overall quality of evidence.

What did they find?

They identified 7 papers for inclusion in the systematic review.  One was an RCT the remainders were retrospective cohorts. Six of the studies investigated the treatment of mild to moderate malocclusion. Five used Invisalign.  The studies reported a total of 254 patients. Five looked at the predictability of tooth movement and two compared clear aligners to fixed appliances.

One study had a high risk of bias and six had moderate risk.  They could not carry out a meta-analysis because of marked heterogeneity between the studies. As a result, they did a narrative review. I thought that these were the main points:


  • Rotation of teeth tended to be incomplete
  • There was a degree of under torque by about 15%
  • Mesio-distal tipping movements were the most predictable.

Comparison with fixed appliances

  • There were minimal differences in the amount of incisor proclination.

Their overall conclusions were:

  • Most tooth movements may not be predictable with clear aligner therapy except for minor horizontal tooth movement.
  • Clear aligners may produce clinically acceptable outcomes when compared to fixed appliances, for minor bucco-lingual inclination of upper and lower incisors.
  • Additional refinements are likely to be needed in almost every case.
What did I think?

I thought that this review was ambitious. The most important fact that I learnt was that there has still not been much research into clear aligner therapy. For example,  they only found two trials, and they had to rely on retrospective studies to provide additional information.

As I have previously discussed, the problem with retrospective studies is the high risk of selection bias.  The authors pointed out that this was a problem with their review. Importantly, this resulted in a reduction of the overall strength of evidence or confidence in their findings.

I cannot help feeling that there is a need for trials into the effectiveness of clear aligner treatment. Surprisingly, this popular treatment has so little evidence underpinning its effectiveness. This may be because this treatment is directed at mild malocclusions and clinical experience suggests that it “works” to the satisfaction of patients and operators. As a result, there is no need to carry out trials.  However, there is a risk in the use of clear aligners on children with potentially more severe problems.

Final summary

In many ways, this review reinforced the clinical perception of clear aligner therapy. It is not straightforward, and refinements are needed to achieve the predicted results.

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Have your say!

  1. Great! As we all thought about aligners

  2. It may not have the strength that we would like, but the conclusions are what we experience.

    Well, most of us. I know of an orthodontist who has stated that he can do treatments non extraction with Invisalign, or needs 4 premolars extracted with fixed.

    He also suggested Invisalign for a very severe, skeletally based, Class II with a very deep bite and 18 months of treatment , or a Herbst and fixed.

    It’s all in the marketing. Evidence just gets in the way of magic

  3. Firstly ,as regards invisalign.Many proficient clinicians are finishing ,not just simple BUT very complex cases to a ,very ,high standard .I do not include myself in that category but I know who is ,in order to learn from.
    Refinements are a normal part of the treatment course and are to be expected.Similar to detailing and finishing.
    Thanks for another excellent post.

    • Does “a very high standard” include a “seated condylar position” when the teeth are in maximum intercuspation? My experience tells me that Invisalign has no way to control for this, and if it happens you were just lucky.

      • Yes it does include a seated condylar position as verified by tomos and CBCT.
        I am as lucky with invisalign as I am with psl braces.LOL.
        I do appreciate your comments as we all strive to move forward.

  4. I agree that research is required. I have been offering aligner tx to all of my patients for several years and I am confident that I achieve the same board quality results that I achieve with fixed appliances. I have worked at it since 2001, pushing the envelope. You can’t just take a scan and take what the tech gives you, just like with fixed appliances, you have to know how to use the aligners to get what you want. Some malocclusions are more efficiently treated with fixed appliances but I routinely treat patients that were told they can’t do Invisalign, many times with fewer visits and shorter treatment times. The limiting factor is patient cooperation. PS, love the Blog Kevin, keep up the good work.

  5. While, I don’t dispute the results, I do find the presentation odd. I would have thought that the need for refinement was well understood, given that even invisalign does not claim the clincheck simulation will occur 100%. Is this trailing behind the clincheck after first phase of treatmwnt the 15% torque discrepancy, or relative to ideal outcome, or relative to conventional techniques?

    Many practitioners have been overcorrecting or using other techniques to account for where it is lacking for many years. I would never place a bracket and wire and expect to never have to modify the mechanics at any point throughout treatment. Why would aligners be any different? One could look at it from the other point of view and ask, if it does not work, then why have refinements? Clearly it does, for many tooth movements.

    I find the mesio-distal tipping most unusual as I think uprighting of multi rooted teeth is where aligners struggle most. Perhaps they are not looking at molar teeth in the study, unfortunately, I don’t have access at the moment.

    Given that patient acceptance, satisfaction with treatment, reduced caries risk, reduced emergency appointments are all benefits of aligners, should we not accept their shortcomings as well as their benefits? I find it unusual, given all the controversy in orthodontics at the moment, that we are still stuck ,dividing into teams, comparing apples and oranges, rather than treating all appliances as tools with pros and cons. We can then selext what tool will best apply a force to the periodontium with in each particular set of circumstances.

    It is just unfortunate that companies like invisalign don’t make their clinchecks and scans open for anonymous analysis to see what does work in the real world. Big data is here and digital orthodontics are best placed to take advantage, if only they would.

  6. It is astounding to me that clinicians are still surprised to learn that the refinement, or additional aligner series process is required today (and in perpetuity as long as patient variability and cumulative engineering error exist in the universe) in order to achieve our treatment goal in most moderate to complex cases. As Andrew and James have pointed out above, it is an aligner finishing procedure necessary because it always will be as long as we treat 5 year-olds, 90 year -olds, pregnant patients, less compliant patients…..etc. Really and truly – do you actually expect as scientists and clinicians that a single digital tooth moving plan can ever be 1 fit for all? Never as long as biology exists! Do clinicians using fixed appliances never need to bend a wire or rebond a tooth? Almost never. Why? Because there is error in that system, slop in brackets, patient variability. How much under- torquing do you get with a “full size” wire? Likely same or more however; the measurement capability is minimal or non existent, as unless you are comparing to a digital bracket system where the goal is actually known, as it is with computer programmed aligner systems, you can never compare these things. Or you may choose to pretend otherwise, and you gather meaningless results. Or you may choose to attempt to evaluate the equivalent of a 7 year old cell phone with a current version (2014 papers I assume are evaluating outcomes form cases treated as early as 2012). So please lets stop the ignorant deceit of evaluating a system that actually provides digital measuring capability against systems that allow none.
    It also astounds me that we are still using the term “predictability” to assess efficacy and accuracy of such systems. (Apologies, Prof Boyd and VV likely used it in the first paper 19 years ago but have learned since then). Arguably computer programmed aligners are the most predictable orthodontic appliance system available. Please think about the terms we are applying. Additionally, hear my plea! Please provide us the study design/s of the paper/s that definitively show that fixed appliances are “predictable” or more accurately “effective” as Kevin describes. (…My thoughts drift to Shaw/ Richmond / O’Brien days with less than staggering outcomes using objective measures in fixed cases). We may then simulate that/ these designs with computer programmed aligners. Much of my clinical day is spent retreating patients previously treated with fixed appliance systems, with features including poor extraction space closure, periodontal defects, decalcified enamel, retained rotations, cross bites, A-P under treatment, loss of anchorage cases, relapse and also planning complex treatments for previously rejected patients including extraction, impactions, other. Treating any orthodontic patient is complex and I believe that it is not only the appliance system mechanical properties but the patient characteristics as well as the skill and determination of the clinician that combine in order to achieve the best possible outcome for every patient , no matter what appliance is selected.
    If we are not prepared diagnose, treatment plan, communicate; be competent in the use of our chosen appliance, to bend a wire, rebond a tooth, reprogram a digital appliance, communicate, evaluate.. we will simply not obtain outcomes consist with treatment goals no matter what we choose to use. Finally, thanks to all evaluating computer programmed aligner systems. No one said it was easy.

    • Excellent summary !!
      “Be not the first to try the new nor the last to discard the old “.
      As always there is a happy medium re use of braces and aligners.Depends on retraining ability and mindset.
      Patients often will not proceed with any tmnt.if it has to be braces and not aligners.We would be well advised ,I think,to listen to the marketplace .

  7. One more awesome blog … cant say clear aligners can only correct minor malocclusion issues. Have come across many cases of invisalign where complex malaocclusion issues have been treated… it is not of surprise when u point out that there are more trials needed… its limiting factor in countries like india is the cost, nd patient co operation… but once again have to mention wonderful write up…

  8. It confirms the outcomes of the initial research on aligners (JADR Supplement ion the IADR Washington meeting 2000)… lots of US dental schools brought abstracts to IADR that year… and the overall “summary” of the work was as you have reported.
    However, I cannot recall any of those abstracts being formally published. Interpret that as you wish
    just saying

  9. I don’t think there is much doubt that you can get good results with aligners, I don’t personally use them much and not in cases involving over 10 aligners but I have seen great cases utilising lots of aligners and extns, especially now with attachments being used most of the time. Thus saying I see fewer adults who are bothered about having a metal brace than I used to so, a bit like ceramic brackets, I find I don’t have the need to sell aligners since I can just put a metal brace on.
    There are really 2 main advantages/disadvantages with aligners (I’ll suspend judgement on whether they are quicker or slower, since not really sure). One is that anyone can do them, even the patient without seeing a dentist/orthodontist and the other is the cost. Either of these could be an advantage or a disadvantage depending on your point of view.

  10. “Surprisingly, this popular treatment has so little evidence underpinning its effectiveness.”

    The following case presentations (hopefully the site will open) are not a substitute for a quality control study but does illustrate the capability of proficient clinicians utilizing a clear aligner system. And yes additional aligners are almost always required to achieve a good result.

  11. Refinement is not a limitation of aligner treatment, it is absolutely no different to repositioning a bracket during treatment, adding additional torque into an archwire or gable bend, or indeed adding a reverse curve to aid overbite correction. If brackets were positioned perfectly we should achieve ideal
    Outcomes….. Every time right…… clear aligner treatment is a skill that unfortunately teaching institutions and research has not kept upto speed with.

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