Does Invisalign reduce overbites?
It is good to see that the journals are publishing more research on clear aligner treatment. This is long overdue. While dedicated researchers have made good progress, most of this has been retrospective case comparisons. This new paper takes us one step further in our evidence. This is a prospective cohort analysis of the use of Invisalign in reducing overbites. I thought that this was an interesting paper, but I have come to slightly different conclusions from the study team.
A team from the USA, South Africa and India did this study. The Angle Orthodontist published the paper.
Neal D. Kravitz; Ismaeel Hansa; Nikhilesh R. Vaid; Mazyar Moshiri; Samar M. Adel
Angle Orthodontist: Advance On line: DOI: 10.2319/050223-320.1
This was a well-known team of investigators with expertise in Invisalign. Mazyar Moshiri is a Faculty member of Align Technology and well known KOL.
The journal did not publish any conflicts of interest.
What did they ask?
In their introduction, the team covered the development of Invisalign very clearly, and they drew attention to improvements directed towards increasing the effectiveness of Invisalign in correcting overbites. They pointed out that previous studies had only looked at adults. As a result, they did this study to;
“Compare the accuracy of mandibular incisor intrusion with Invisalign in adults and adolescents”.
What did they do?
They did a prospective clinical cohort study of 58 patients. Who were consecutively enrolled between January and April 2021? The PICO for the study was
The participants were orthodontic patients treated with Invisalign who had an overbite of 4mm or greater with good compliance and complete initial and final scans.
They defined an adolescent as 11-19 years old. They treated these patients with Invisalign Teen. An adult was over 20 years old and treated with Invisalign full.
The primary outcome was the amount of incisor intrusion. They calculated the predicted tooth movement by superimposing the initial and final ClinCheck models. They also calculated the actual tooth movement by superimposing the Initial ClinCheck and digital models from the first refinement scans. This enabled them to calculate the amount of mandibular incisor intrusion.
The team used simple univariate statistics to compare the adult and adolescent groups.
What did they find?
All the patients completed the treatment.
These were the main findings for tooth movement.
The accuracy of the prediction for mandibular incisor intrusion was 63.5% for the adolescent and 45.3% for the adult patients. This difference was statistically significant.
When they looked at the amount of incisor intrusion per tooth, it was 1.7mm for the adolescent and 0.9mm for the adult group (p=0.001).
The teams conclusion was
“Mandibular incisor intrusion with Invisalign is significantly more accurate in adolescents than in adults”.
What did I think?
This was an interesting study using a prospective cohort study. It indeed represented some progress with research into Invisalign. It was also great to see some practice based research done in the “real world”. While this was good, I did have some issues with the methods used that we need to consider when we interpret the findings.
I have written about Invisalign studies before. One criticism of measuring the difference between final tooth position and ClinCheck prediction has been made. This is based on the suggestion that the final ClinCheck is not an actual predicted final position of the teeth but represents a force system. This means that the prediction accuracy against the ClinCheck is not of value.
As a result, I feel that the actual tooth movements are the most critical data. The authors suggest that this is greater for adolescents than adults. I wonder if this is simply due to the relative difficulties of achieving this movement in different age groups.
This data also suggests that Invisalign does not really intrude the teeth to a meaningful degree. I may be an old-fashioned orthodontist, but I am sure I got more than this with fixed appliances.
I do have some concerns about the method of superimposition. The team did this using a geographical best-fit method. This is based on superimposing sequential “casts” on the teeth. As a result, this method is subject to some errors as the teeth are not stable structures. For example, I am not sure we can assume that there is no extrusion of the buccal segments as part of overbite reduction.
Finally, it is about time that someone did a trial comparing Invisalign and fixed appliances. I note from the open payments website that Align Technology spent $17 million on key opinion leaders in 2022. Surely, some of this money could be used to fund a clinical trial..
Emeritus Professor of Orthodontics, University of Manchester, UK.
Surely the clinically significant measurement would be ‘change in overbite’? This would be much easier to measure than ‘intrusion’ and more clinically relevant. I also think that taking a minimum of 4mm as the start point is not an especially deep overbite.
I’ve found overbite reduction to be pretty poor with aligners, and often struggle to get enough space for a bonded retainer. I wouldn’t usually choose it as my first choice appliance if overbite reduction was a goal
The degree of intrusion for both groups is frankly of little use and would have very little clinical impact in a large proportion of clinical cases. I find myself less enamoured of aligners as the days go by!
Hi Kevin,
completely agree with your analysis of the superimposition method. In fact is very likely that some extrusion happens on premolars and molars that act as posterior anchorage units. By superimposing on this area it’s only possible to talk of a “relative intrusion”, relative to the superimposition method that has been selected.
It’s for sure encouraging to see some research done on aligners but a more objective and stable reference plane should be selected =)
This study was quite flawed, and it is unfortunate that this appeared to pass the scrutiny of both Editor and Reviewers alike. Aside from the obvious limitation of comparing initial and final ClinChecks (neither of which actually represent tooth movement), the authors superimposed on digital models using a best fit analysis.
This is certainly not a stable landmark to measure tooth movement. The mean age of the adolescent group was 15.1 years, and thus is it likely that there was the typical and expected vertical ramus growth with compensatory eruption of the buccal segments that helped level the curve of Spee. As can be evinced by observing multiple cephalometric superimpositions, COS leveling in adolescents involves a significant amount of eruption of posterior teeth vs. incisor intrusion.
Why was the ClinCheck data not corroborated with cephalometric superimpositions? That is the Gold Standard to measure tooth movement. Now, with regards to the achieved results, what was the final overbite in both groups? Isn’t that the outcome of interest? This could have been a very useful study, but instead, it ended up being an exercise in futility.
And, last but not least, is it not customary and expected for authors with Conflicts of Interest, to declare those at the end of the publication? That is conspicuous by it’s absence.
I don’t think I would be using aligners for OB reduction! As I understood, OB reduction is achieved mainly by “overeruption” of the separated buccal segments with minimal incisor intrusion. Intruding the incisors significantly can lead to more apical root resorption which we don’t want. Interesting paper though.
In assessing a “deep” overbite it is necessary to evaluate facial esthetics, upper lip length, inclination of upper and lower incisors, cephalometric vertical measurement as well as skeletal measurements and classification in order to determine what treatment will produce the best overall result for the patient. I agree with Danny and would look to mainly erupt the bicuspids using an anterior bite plate and vertical elastics. What treatment to use on the upper incisors can be determined by using all of the above. There is so much more helpful information available now
than 50 to 100 years ago.
Referencing teeth intrusion against extruding other teeth is a lame methodology because all of the reference markers are moving!! Only a static non-moving marker can be a valid type of reference.
VV provides sponsored lectures for Align Technology
1. The authors measured only linear “absolute” intrusion and not any “relative” intrusion (tipping / proclination). Absolute intrusion is a less highly expressed movement with any mechanical appliance system. (That’s why we had to develop reverse curve wires, TAD mechanics, intrusion arches). So when you believe that you may be more effective with fixed appliances, are you thinking in terms of overbite correction (largely obtained via proclination due to the undesirable labial force application- perfect for labial tip but not ideal for absolute intrusion) and posterior extrusion (due to equal and opposite laws) ; or in terms of the ability to express absolute intrusion only?
2. If we read the paper, the clinicians prescribed “reverse curve mechanics” combined with Invisalign “deep bite features” such as bite ramps and attachments of various design. They prescribed extrusion of premolars and first molars, so unless we use Bjork type implants, or keep a posterior segment unprogrammed (understanding teeth still move), then it is most difficult to obtain an accurate quantitative measurement as we cant differentiate anterior from posterior movement, especially with “best fit” methodology even via ceph (“growing patients”) or software program. ..(as Geoffrey Wexler and other have noted)
3. It would be interesting and prudent to repeat this study using default programming to verify that the modified mechanics requested are beneficial to efficacy of overbite reduction and symbiotic with other programming defaults. If however one of the aims is simply to determine the difference between the degree of expression of adolescents and adult patients, then as long as this same modified protocol was applied to both cohorts, which it was, then the conclusion that expression of programmed movement is significantly greater in adolescents, as found in this sample has validity. There is more than 1 reason we prefer to treat adolescent patients!
4. Given that the average treatment time at T1 was 5.5 months (extrapolating from data provided of average 22 lower aligners and weekly change), these measurements of absolute intrusion (to be differentiated from decrease in overbite) are positive and likely again similar to what we would express with fixed appliances after 5.5 months of solely absolute intrusion (not overbite reduction, which will typically be greater as it adds posterior extrusion, and proclination). This is not a treatment outcome – any clinician treating moderate to severe malocclusion using Invisalign ( or fixed appliances) will typically use a series of finishing / additional aligners and have a treatment time greater than 6 months.
5. You mentioned that all patients “all patients completed treatment”. Actually the way I read it, 58 of the initial 66 enrolled patients made up the final sample- and we are unaware of the completion of treatment being at T1 (mean 5.5 months) – that would be unusual for any “deep bite” patient.
PS. For any faculty bloggers, you may be interested in the 2024 Align Technology Annual University Research Program, submission now due! (The links are different in different regions so didnt list – )
Kevin off the subject. I recommend the movie “Pain Hustlers” for you.
Thanks, I will watch it. I wonder if this is similar to the “pankillers” series on Netflix?