Is Class II correction possible with Invisalign?
Surprisingly, there have been very few studies into clear aligners. This new paper suggests that Invisalign is not effective for Class II correction. But is the evidence strong, and is this a holistic evaluation?
Clear aligners are a well-established orthodontic treatment. I have posted several times about the effectiveness of this intervention. Importantly, there have been few studies of large samples of treated cases. In summary, the general message from these studies is that aligners are not as effective as fixed appliances. Furthermore, operators may not readily achieve the predicted outcomes. This new paper looked at the effectiveness of Invisalign in correcting Class II malocclusion.
A team from St Louis did the study. The AJO published the paper.
What did they ask?
They asked this question:
“Can Class II malocclusion be corrected with Invisalign after completion of treatment with the initial set of clear aligners”?
What did they do?
They did a retrospective study with the following stages:
- They obtained the records of 80 Invisalign treated patients treated by a specialist with extensive experience with clear aligners (top 1% provider).
- Next, they divided the group into 40 with Class I and 40 with Class II malocclusion (end on and full step molar relationships).
- They collected data at pre-treatment (T1), undertook a ClinCheck prediction of the outcome (T2A) and post-treatment (T2B).
- The outcomes were the ABO MGS scores for each stage.
- They then calculated the change in score and the percentage of treatment accuracy.
I could not find much detail on the treatment process, particularly treatment protocols and use of Class II elastics in the paper. These protocols are an essential point, and I shall return to this later.
What did they find?
They produced a large amount of data, and I have extracted what I think is the most critical information.
- Only 47% of Class I and 0% of the Class II cases would pass the ABO score assessment.
- The mean start ABO score for the Class I group was 35.2, and treatment reduced this to 27.5.
- The mean start ABO score for the Class II group was 55.98, and treatment reduced this to 48.7.
- The AP change was a mean of 1.25% in the Class I and 6.8% in the Class II group.
- When they looked at the percentage accuracy of the tooth movement compared to the ClinCheck for the ABO scores, this was 21.9 % for the Class I and 17.7% for the Class II groups.
Their conclusions were:
- Invisalign significantly improved both Class I and Class II malocclusions.
- There were no improvements in Class II AP relationship for Class II problems when using elastics.
- The ClinCheck predicted an ABO quality occlusion for the entire sample. However, the operator did not achieve this for any of the Class II treatments.
What did I think?
I have never done an aligner case. This treatment was not suitable for my caseload of children with craniofacial and severe medical problems. As a result, I have tried to approach this from a purely scientific point of view. So forgive me if I have misinterpreted the paper. Padhraig also contributed to the clinical comments below.
I was not sure what to make of this study. My first concerns were that it was retrospective. As a result, it must have considerable selection bias. The authors did not provide any information on how they attempted to reduce this. We, therefore, must treat the findings with a degree of caution because we do not know the direction of bias.
I was also a little confused that they analysed the records after seven months. I would not be consistently able to correct a substantial Class II relationship in an adult patient with fixed appliances in this time. Furthermore, we do not know the elastic protocol. We do not know if all the Class II patients wore Class II elastics. The mechanism of Class II correction used and the approach to the use of attachments to facilitate distal movement of the upper buccal segments is also not entirely clear. Nevertheless, it is a surprise that there was no Class II correction in this group.
It was also interesting to see that none of the Clas II cases achieved an ABO pass score. This finding is particularly relevant when we consider that the orthodontist was a top 1% provider. I wonder if this reinforces the possibility that Invisalign is a compromise treatment? Or am I missing something, as I have never done an aligner case?
Equally, I wonder if this study represents a mid-treatment progress evaluation? We know that the changes predicted on the ClinCheck are often not achieved and that the ClinCheck might better represent a force delivery system rather than being an entirely realistic representation to tooth movement. Equally, Class II correction in adults is time-consuming. It is therefore likely that many of these cases will undergo considerable further refinement before completion. It would be very interesting to evaluate the predictability of Class II correction over the entire course of treatment. I, therefore, hope that the authors re-evaluate these cases after treatment.
Perhaps it may be more appropriate to conclude that ClinCheck software poorly predicts Class II correction with Invisalign (at least for the protocol used in this study) and more efficient approaches to Class II correction do exist?
I think that there will be a lot of discussion about this paper. Let’s have a heated debate.
Emeritus Professor of Orthodontics, University of Manchester, UK.