An excellent practice-based research paper on the effectiveness of Invisalign.
There has been limited high-quality research into the effectiveness of Invisalign. A specialist orthodontist did this new prospective study. It provides us with some clinically meaningful information and I thought that it was great.
A few weeks ago, I posted about a study done in a private practice setting. I felt that this was an important step. This is because investigators should do trials in the setting that an intervention is most frequently used. As a result, it was good to see another study done in a practice setting. This Virginia based team did this study to find out the accuracy of Invisalign in moving teeth.
The AJO-DDO published the paper.
Nada Haouili, Neal D. Kravitz, Nikhilesh R. Vaid, Donald J. Ferguson, and Laith Makkia
AJO Online advanced access: https://doi.org/10.1016/j.ajodo.2019.12.015
I was also pleased to see that this paper was open access and the AJO has started an advanced access section, so we do not have to wait for papers once they are accepted.
What did they ask?
They did the study to:
“provide an update on the accuracy of Invisalign with new technology”.
In their introduction, they pointed out that since 2008 Invisalign have made several improvements. The most notable have been introducing the SmartForce features and the SmartTrack material. Furthermore, they have replaced impressions with scans.
What did they do?
They did a prospective cohort study of 38 patients with a mean age of 36 years. He treated 29 the patients with Invisalign Full and 9 had Invisalign Teen treatment.
The mean number of aligners for each arch was 21 maxillary and 20 mandibular. The average time between the start and final scans was 8.5 months.
One specialist orthodontist treated all the patients. Importantly, he overengineered the tooth movements when he felt that this was necessary for good treatment results. He also asked the patients to honestly record their compliance with the 22 hours per day wearing advice.
The inclusion criteria for the patients were that they had completed treatment with scans, and their compliance was good. He excluded six patients because 3 of them did not complete in time, and 3 had errors in their scans.
They evaluated the tooth movement superimposing the individual teeth from the initial ClinCheck model over the final ClinCheck model. They measured the M-D crown tip, B-L crown tip, intrusion extrusion and rotation. Finally, they calculated the per cent accuracy of the tooth movement. This was the primary outcome of the study.
Finally, they randomly selected half of the sample and evaluated the ABO cast evaluation system scores.
What did they find?
They found that the mean accuracy of Invisalign for all tooth movement was 50%. The most accurate movement was bucco-lingual crown tip of the upper incisors (56%), and the least accurate was the mesial rotation of the lower first molars (28%).
When they looked at the ABO scores, they found that 74% were allocated as passing. The average length of treatment was 8.5 months.
Importantly, they pointed out that the ClinCheck is a graphic depiction of force systems; it is not necessarily the decided final tooth position. As a result, if the tooth movements are over-engineered, it does not mean that the treatment is only 50% effective.
Their overall conclusions were:
- The mean effectiveness of Invisalign was 50%
- The per cent accuracy may underestimate the products overall accuracy.
- Invisalign appliances are improving but they still struggle with specific types of tooth movement.
What did I think?
This was another excellent study done by a specialist practitioner, and I want to compliment the authors. We need more of this type of research.
Their findings were fascinating and clinically relevant. I found that one of the most interesting points was that Dr Kravitz “over-engineered” the tooth movements to compensate for any mechanical inefficiencies in the system. This will have contributed to the low level of effectiveness of Invisalign of 50%. As an experienced orthodontist, I can see that this is necessary, even though I have never done an Invisalign treatment.
It was also important to see that the overall quality of the treatment was high, as most of the cases were ABO “passes”. Nevertheless, the mean duration of treatment of only 8.5 months suggests that these cases are likely to be mild.
However, this does bring out an important question. A highly experienced orthodontist did the treatment. I wonder if those who are not so experienced, for example, general dental practitioners, provide their treatment with the same level of expertise and care with respect to over-engineering? This will have implications for the treatment that they provide. In many ways, this is similar to issues with the effects of specialist training and experience when operators use fixed appliances.
The way forward?
Finally, in 2005 David Turpin suggested that clinical trials were needed to evaluate the effectiveness of Invisalign. I am disappointed that there are so few trials that compare Invisalign with fixed appliances.
Ironically, the best research into Invisalign seems to be studies like this one. It is clear that this study is a step in the right direction. It would be great to see a trial of Invisalign and fixed appliances in a practice setting. I hope that someone can do this soon, perhaps with funding from Invisalign? Or is this a “dead question” because so many people are entirely confident that it just works?
Emeritus Professor of Orthodontics, University of Manchester, UK.