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.