June 20, 2022

A trial suggests that Clear Aligner Treatment is a shorter duration than braces.

At last, we are seeing more research papers on the effectiveness of Invisalign. This new trial looks at the duration of treatment with aligners and patients’ quality of life. The findings do not agree with the conclusions of another report on the treatment duration of Invisalign treatment. It is worth a close look.

While aligners have been around for many years, we still do not know much about their effectiveness. This deficiency is particularly true regarding their effect on oral health-related quality of life. These outcome measures are becoming increasingly important as dental research moves towards outcomes relevant to patients. This work is essential because it provides information on the effects of our appliances during and after treatment.

What did they ask?

They did the trial to find:

“What is the impact of clear aligners on patients’ Oral Health Related Quality of Life (OHRQoL) and the duration of orthodontic treatment compared to fixed appliance treatment”?

What did they do?

The team carried out a single centre two arm parallel group RCT with a 1:1 allocation. The PICO was:


44 adult orthodontic patients with Class I molars and mild malocclusions (2-6mm crowding). They treated the patients without extractions.


Clear aligner treatment. Follow-up appointments every two weeks.


022 MBT fixed appliances. The patients attended every three weeks to have their appliances adjusted.


Oral Health Quality of Life using the Oral Health Impact Profile (OHIP-14). They collected this data at the start of treatment, then after 1 week, 1 month, 3 months and 6 months and post-treatment. The secondary outcome was the duration of orthodontic treatment in months.

One experienced operator did all the treatment.

They used an ITT approach in which all patients were analysed, regardless of the outcome. They analysed the OHIP data with multiple regression. The treatment duration between the interventions was analysed with t-tests.

The team used pre-prepared randomisation. They concealed the allocation with sealed envelopes. This was done by a researcher who was not involved in the trial. As a result, it was impossible to blind the operator or the patient to treatment allocation.

What did they find?

All the patients completed the study. This meant they had two groups of 22 participants who received treatment with fixed appliances or aligners. There were no differences in the mean ages, gender or discrepancy index data between the two groups at the start of treatment.

There were no differences in the OHIP-14 scores at the start or end of treatment. However, during the early stages of treatment, the oral health quality of life for the fixed appliance group was significantly lower for the fixed appliance group. This was reinforced by the regression.

Treatment duration was 15.73 (SD=2.45) for the fixed appliance group and 11.55 (SD=2.0) for the aligner group. This was a difference of 4.1 months (95% CI=2.8-5.5). This was statistically and clinically significant.

Their overall conclusions were:

“The Oral Health Quality of Life of patients treated with Clear Aligners was higher than those treated with fixed appliances throughout the course of treatment.”

“OHRQoL was improved by orthodontic treatment regardless of the treatment method.”

“Clear aligners reduced treatment time by 26% compared to fixed appliances”.

What did I think?

This was an interesting small trial. Firstly, let’s have a look at the good points. The groups were similar at the start of treatment. The randomisation was pre-prepared, and the allocation was concealed. Notably, the team followed the patients to the end of their treatment.

When I looked for components of the trial that were not ideal. There were several that we need to consider when we interpret this paper. Firstly, I was unsure whether any of the differences in OHRQoL were clinically significant. Furthermore, I was unclear on why they chose a slight difference in OHIP14 scores when they did the power calculation.

I was more concerned that the patients were seen at different time intervals. This was 3 weeks for the fixed appliance group and 2 weeks for the aligners. I was also unclear on why the aligner patients attended for aligner changes. As a result, I cannot discount that the difference in treatment times may have been influenced by the treatment interval.

I also could not find any information on how the operators judged that treatment had been completed. Furthermore, there was no data on the final occlusal result at the end of treatment. Both these omissions could influence the duration of treatment.

Finally, strictly speaking, the lack of blinding puts the trial at risk of bias. Again, however, this is like all orthodontic trials.

Final comments?

I have thought hard about this trial. But, first, we must consider why another study suggested that fixed appliances were faster than aligners. This may be due to the methodology and other issues. However, we are now seeing more investigations into the effectiveness of aligners. This means that soon we can do meaningful systematic reviews. This will allow us then to make recommendations to our patients.

Related Posts

Have your say!

  1. A major factor in treatment time is how often the aligners are changed. Two week changes versus one week will obviously take twice as long. Also, I have to wonder why the aligner patients were seen every three weeks unless this was a part of the study to assess tracking. We see patients in 12 to 16 weeks with aligners. It’s one of the benefits of aligners. I agree, it’s good to see some research on aligner treatment. Also, I am thankful for this blog, I appreciate your efforts Dr. O’Brien.

  2. First, the authors should be applauded for reporting data from the comprehensive treatment, not just part of it. To check patients every two- or three weeks during treatment is not a reflection of what happens in most clinical practices. The advantage of shorter appointment interval times may be the better capability to enforce compliance and OH positively. On the downside, I suggest that authors must be more cautious with their conclusions. The abstract states, “Patients treated with clear aligners reported higher OHRQoL and shorter treatment duration as compared to those treated with fixed appliances.” We must remember that busy clinicians will likely only read the title and the abstract’s conclusions. Clarity should have been provided that the same was of Class I cases with mild crowding. It cannot be extrapolated to any malocclusion case. Also, we should provide in the conclusion sections the magnitude of the differences to adequately explain those stated differences.

  3. The debate is over ,regarding the potential of aligners to produce results comparable with braces.
    They only valid question remaining is comparing treatment times between aligners and braces for complex cases.
    I think we may be close to the last few flogs of this dead horse!LOL
    On another note;it is good to see Invisalign “knock offs”or “me too “products from other companies.This is a similar pricing system as illustrated by “Big Pharma.”This will serve our profession well in terms of controlling our overheads.

  4. Maybe I missed this: when is treatment finished? Did the authors check the end occlusion and made an intergroup comparison? If not: we have no idea whether the end result of the 2 groups is at a comparable level.

    • Hi Frank, yes you are correct. I missed this paragraph in my blog post and I have added it. There was no real assessment of the end point or overall treatment result. This must have influenced the duration of treatment.

  5. “The cases were assessed separately by two of the research supervisors … to decide the end of treatment”: I could not find any quantitative evaluation of the cases at the end of treatment. The Discrepancy Index (DI) was measured at the start, but it is not reported for the end. How do we know that all cases were treated to the same standards? Detailed finishing requires time.

    • yes you are correct. I missed this paragraph in my blog post and I have added it. There was no real assessment of the end point or overall treatment result. This must have influenced the duration of treatment.

  6. Thanks Kevin. Agree, without an equivalent outcome end point, difficult to form a conclusion when comparing treatment duration. Would have loved to see an ABO / PAR assessment of occlusion at end point as well as other treatment outcome measures- (should still be able to perform this -blinded I hope) ; and also as yourself and other colleagues mentioned, the intervals of monitoring being equivalent. Seeing the patients more often may have biased the hygiene findings. Regarding the wider question of treatment duration, I am not convinced that we may ever be able to have a sufficiently scientific, clinically useful conclusion. We would require, I feel, not only equivalent start points – difficult enough – , defined end points (not just for the digital aligners but the analogue treatment), and the same frequency of monitoring. Additionally, the real confounding variable being the movement programming. Aligner activated tooth movement may be staged in many ways. There is no (external) evidence that the default staging provided in our initial plan is the most efficient in terms of outcome nor treatment duration; we do know that the activation is within physiologic limits for the majority of patients. So in order to obtain a blanket conclusion as to treatment duration of computer programmed aligners versus fixed appliances, the largest variables are likely again to be the clinician (controlled above) and the aligner companies’ clinical protocols. As staging protocols differ for different types of malocclusion, they may differ between companies and are able to be altered by the clinician, this variability directly effects treatment duration, as it impacts number of aligners to be worn. Theoretically, ignoring other variables, duration could be clinically significantly shorter duration than with fixed appliances due to the ability to avoid round tripping, waiting for large wires to run elastics or waiting to level and align before commencing translations. This seems appealing, especially when we receive programs with enticingly small number so for aligners, representing shorter treatment duration. However in my experience, I am learning that not all tooth movements are ideally staged simultaneously (just as with fixed appliances) and my outcomes may be improved by considering the biomechanics behind what we are presented with. The good news is that we can measure and assess and improve with digitally programmed mechanics, not so easy for non-digital fixed appliance systems. In the end, its the osteoblasts and clasts that dictate the velocity of physiologically safe orthodontic tooth movement, we may optimize duration with improved knowledge of aligner biomechanics but ultimate respect goes to the cells. VV speaks for Align Technology 🙂

    • In addition to my comment above, would be remiss not to mention that as we treat more complex malocclusions with computer programmed aligners, this invariably involves 1 or even 2 Additional Aligner Series – refinements to finish with the goal of same or better occlusal result than obtained with fixed appliances. Even mild malocclusion and simple alignment may involve 1 refinement in my experience. To be objective, this additional time involved, including manufacturing and shipping should be integrated into future studies attempting to answer the comparison in treatment duration. The information I currently give to my patients, based only on anecdotal evidence from my 25 years with aligners, is that for mild to moderate malocclusion, treatment duration is same or slightly less that with fixed appliances,; for more complex malocclusions, impacted canines, Class II / III distalization , extraction, treatment duration is the same or slightly longer with aligners – also depending on how well patients comply with either wearing aligners or avoiding broken brackets! Isn’t ortho fun:)

      • Congratulations to you for 25 years of experience with clear aligners 🙂
        I think you should be JJ Sheridan (VV) who made the first minor tooth movement with essix plates.

        Clear aligner treatment:
        Expand the arches
        Do an Interproximal stripping much then the anatomical limits
        Do not notice the biolocical concepts
        Ohh yes, shorter treatment duration

Leave a Reply

Your email address will not be published. Required fields are marked *