Invisalign doesn’t control labial incisor movement?

Clear aligner therapy is very popular and has a strong following amongst orthodontists, dentists and their patients.  Its use has revolutionised the delivery of orthodontic care.  However, recent studies have suggested that the planned tooth movements are not always achieved with Invisalign. 

I have posted about the studies that have reported this problem for closing extraction spaces, torque control, overbite reduction and reducing overjets.

This new study looks at the effects of Invisalign on controlling labial incisor movement when reducing overbites.

A team from Adelaide and Bendigo, Australia did the study. The AJO-DDO published the paper.

This paper is open-access, allowing everyone to read it.

What did they ask?

They did this study to ask this question.

“How closely are the achieved labiolingual movements of incisors compared with the planned in patients treated with Invisalign”?

What did they do?

This team has not several studies using the same methodology. Their source of patients was the Australasian Aligner Research Database. This contains the treatment records of more than 17,000 patients who had been treated with Invisalign by 17 operators.

The inclusion criteria for this study were

• Patients aged 18 years or older
• Two arch non-extraction treatment with Invisalign
• Started treatment on or after January 2013 with SmartTrack material
• Completed the initial aligner treatment before the end of July 2023
• Digital scans were available at the start and end of treatment.

The team utilised digital models to calculate tooth movements. any discrepancies between the planned and actual tooth movements.  They divided the patients into 3 groups according to the values for planned overbite correction. These were (i) 2-4mm, (ii) 4-6mm (III) > 6mm overbite correction.

They calculated the mean labial movement of the constructed root apices for the overbite correction groups.

This enabled them to calculate any discrepancies between the planned and actual tooth movements.

What did they find?

They included data on 232 patients. 62.75% were female.  The team produced a large amount of information and I am going to cover what I thought were the main outcomes.

There was a moderately strong correlation between the amount of planned overbite correction and the number of aligners.

There were no clinically or statistically significant differences between the predicted and achieved arch depths.

However, there were clinically and statistically significant differences between the predicted and achieved angular changes in the maxillary and mandibular incisors. These ranged from -10.83 ( 95% CI -14.42 to -7.24) with a percentage accuracy of prediction of 57% to -2.38 95% CI= -4.22 to -0.52) predicted accuracy 90.3%.

The authors also stated that for all depths of overbite correction the clinically achieved incisor positions had more labial root torque than planned.

Their overall conclusion was that. 

“Central incisor apices moved more labially than planned with a corresponding potential increased risk of alveolar bony dehiscence”.

What did I think?

I have commented on studies conducted by this team using the extensive database before. The most significant criticism is that this is a retrospective sample and carries a risk of selection bias. Nevertheless, this is the largest collection of aligner patient records, making it useful. It is certainly the best source of data on the effectiveness of Invisalign.

There has also been some criticism of the methods used in this and other studies. In effect, it is argued that the ClinCheck represents a force system and we cannot use it to measure the effectiveness of treatment. Following this criticism, I asked the study team for their comments, and they stated 

“We also look at the types of orthodontic tooth movement that occur – ie torque, translation, controlled and uncontrolled tipping. The findings from our studies indicate that when torque, translation, or controlled tipping are prescribed, most cases result in uncontrolled tipping. We cannot see how this finding can be dismissed by those who claim that ClinCheck predictions represent a force system. We eagerly await research of impeccable quality that will supersede our less-than-ideal attempts and encourage all who have doubts and concerns to produce research themselves that addresses their concerns.

I agree with this sentiment.

What about the results?

After reviewing the results of this study, it is evident that they align with findings from this research team and others. We can conclude that Invisalign treatment is associated with uncontrolled tooth tipping. This supports the prevailing consensus that it is appropriate for mild to moderate malocclusions.

Importantly, the authors also suggested that the importance of the findings of this study lies in potential harm, with root apices potentially being pushed outside the average alveolar housing, rather than inadequacies of the appliance. 

I would also like to see similar studies on Invisalign First treatment. It would be interesting to see if this is characterised by tipping problems.  This would be similar to the old-fashioned removable appliance treatment that was the mainstay of UK orthodontics in the 1970s. 

We may not like it, but as research is being published, I wonder if aligners are beginning to have a whiff of the “emperor’s new clothes”.

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