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.
Maurice J. Meade, Tony Weir, and Haylea L. Blundell
AJO-DDO advance access. Doi https://doi.org/10.1016/j.ajodo.2025.03.010
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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Several related and disrelated things struck me when I read this blog post.
The first is that here we are once again with research showing that Invisalign does not achieve what it and its KOPs claim that it achieves. Even more telling is the researcher’s refutation of the claim that all obstacles might be overcome by considering it a “force system”. This is refuted by the unpredictable nature of what results secondary to some movements.
This unpredictable nature is not just that only 30% to 50% of movements are expressed, as Invisalign and the KOLs would have us believe. Were that the happy truth, we need only overcompensate by programming in two or threefold the movements that are desired. Instead, what appears to happen, as we have previously seen with Invisalign transverse corrections, is that some desired movements are never fully accurately achieved and that other movements are unwanted and sometimes undesirable completely. As an example, the researcher’s statement “Central incisor apices moved more labially than planned with a corresponding potential increased risk of alveolar bony dehiscence”.
Second is that, after all of this time, so much so that Invisalign’s patents have expired, it now seems clear why there is a dearth of research sponsored by Invisalign showing its efficacy. Quite to the contrary, in the past few years, nearly every valid scientific article seems more a critique of Invisalign’s efficacy and final results achieved. Is it just a coincidence that Invisalign did not use all of that time to publish research when we consider that now when independent research does come out, it is not complimentary?
I am left pondering the current treatment Invisalign recommends, their new palatal expansion appliance. It is worth noting that the only evidence in support of Invisalign’s palatal expansion appliance efficacy comes from their KOLs, their in-house experts. Not a single respected peer-reviewed journal would publish their research. The most that they managed to push their way into was a protocol article, with no research support. This seems insufficient support.
Given that all we have is the Invisalign KOLs stated support, it seems worth remembering that in the pyramid of evidence, expert opinion occupies the lowest rung. It is the lowest quality of evidence. Yet here we are, all these many years later and the greatest evidence that they have to support their expansion appliance, and so many of their other claims, is the expert opinion of their KOLs. The lowest quality level of evidence seems all too often all that they have. Indeed, is the emperor parading through the online streets without livery?
More, at this point, if we accept what Invisalign claims, despite the lack of valid research support, is it time that we admit that the blame might fall on ourselves? They have fooled us so many times in the past, at what point is it our responsibility not to believe their claims until proven? Personally, I cannot imagine even trying Invisalign’s expansion appliance on patients until there is a valid RCT showing that it is at least as effective as classic Hyrax. If it does not achieve this, the claim might be that its expansion appliances constitute harm.
Third, still considering that expert opinion seems all that Invisalign has left to support their expansion appliance and many claims, it seems impossible not to notice that even evidence to support their expert opinion is lacking. IMO, too many KOL claims of successful treatment of difficult cases are presented without full pre and post-treatment records. Too often, the last time point records shared have glaring inadequacies. Is this is why the phrase “The patient was happy” is often used as their final arbiter of treatment excellence?
We do also have to remember, that none of us, KOLs included, wants anyone to see 10% of our cases. The other side of that is that, when we see a KOL case, we are looking at the top 10% to 5% of what they can produce. If that is not ideal, IMO, we need to be very suspicious of what they are claiming and what they are selling. TIGER-FAT (That Is a Good End Result – For Aligner Treatment) is not a sufficient quality bar to judge outcomes by. Either something is good and acceptable or it is not. IMO, the treatment modality, braces, aligners, or paperclips, should not change our judgment of the end result.
Disclosure: I personally do clear aligner treatment. I just believe that we need to accept the limitations of the modality and what research tells us. We also have to be honest with ourselves and our patients as to what we can and cannot achieve with CAT.
Dr. Kazmierski, I agree with every sentence of your review.
I congratulate you for these sincere comments.👏
Especially the new generation of orthodontists have given a lot of meaning to this Clear Aligner treatment mechanics. They have made various comments that go beyond their purpose, such as “the end of orthodontic biomechanics and the beginning of a new era in orthodontic treatments”.
Orthodontic science, which has a foundation of about 125 years, will continue to remind them the truth that tooth movement is an inflammatory reaction with a biological basis in every incomplete treatment they make.
Well said, sir.
Since orthodontics is a discipline grounded in biomechanics, it is with regret that I must state: for the past 100 years, since the concept of the Center of Resistance (CRes) was introduced by Fish, not a single serious reevaluation of the physics behind the profession has taken place. True, Burstone offered one interpretation, based on the idea that the CRes maintains a fixed location: approximately mid-root in single-rooted teeth, or in the furcation area in multi-rooted ones.
However, if we return to what Fish wrote in 1917, we find that he claimed the position of this point depends on the restraint intensity acting on the tooth, and on the location of this restraint. It is universally acknowledged that the CRes in a tooth with periodontal breakdown and gingival recession is more apical than in a healthy tooth. So why has no one considered the artificial restraint imposed by fixed orthodontic appliances?
Indeed, fixed appliances, brackets, and relatively stiff metal wires form a coronal restraining system, mechanically bonded to the tooth, and thus become a functional part of it. This artificial restraint is located coronal to the natural restraint (located in the root), and because it is often much stronger then the natural one, it shifts the CRes toward the bracket, but only when a moment by a couple, is generated inside the slot, producing significant friction between the archwire and the bracket slot. In such cases, the CRes of the tooth, which normally shifts apically due to apical periodontitis or bone loss, can move coronally due to the strong mechanical restraint applied by the appliance.
This concept was published in the Journal of Indian Orthodontic Society, in an article titled:
“Treatment Efficacy and the Center of Resistance Location”
by Brezniak, Krausz, and Protter, on January 2025.
The paper explores how only fixed appliances can shift the CRes by altering the restraint profile, thereby enabling movement of the tooth in all directions. In contrast, removable appliances in general, and clear aligners in particular, can only produce tipping, not couples. There is no appliance in existence, fixed or removable, that can produce true translation, because such movement requires exact knowledge of the CRes, and since it is a variable, not a fixed point, due to the dynamic nature of the alveolar bone and periodontal ligament (PDL), translation through a single force vector is not physically achievable.
This issue was also addressed in AJO-DO (February 2025 issue, pages 135–141), which discussed how orthodontic appliances cannot induce translation without controlling or relocating the CRes and much more.
We hope these publications will help pave the way for a biomechanical paradigm shift in orthodontics, just as Dr. Robert Kazmiersky advocated in his blog, calling for a return to physical principles and a reassessment of long-standing but unexamined assumptions in our field.
“We also have to be honest with ourselves and our patients as to what we can and cannot achieve with CAT.”
This is ethically correct: informing patients of the advantages and disadvantages of appropriate treatments and recommending the best treatment for a particular case. This is very common in medicine. For example, I have seen orthopedic surgeons discuss various approaches for knee injuries, typically giving approximate percentage improvements for each approach.
Everyone is aware that clear aligner orthodontic therapy is very popular worldwide. It is not going away, nor should it. However, we must be mindful that for most adults, the decision between CAT and fixed is between treatment and no treatment.
Lastly, since I have a lot of free time (LOL), I decided to write to Dr. Mitra Derakhshan, the chief clinical officer and executive vice president of Align Technologies. I attached the AJO-DO paper even though I think she is aware of it!
Dear Dr. Derakhshan,
Please read and evaluate the attached study, which was recently published. Is this study consistent with your findings? If so, is your engineering team developing a solution for this problem?
Thank you.
Sincerely,
Barry Winnick, DDS
“Recent studies have suggested that the planned tooth movements are not always achieved with Invisalign.”
I’m curious if clinical evidence exists demonstrating planned tooth movements are always achieved, with any product. Is that a standard that should be expected of any product, or perhaps, as worded, demonstrates a potential inherent bias. If so, have you considered a randomized peer review process prior to posting?
Thank you and all the commentors for your contribution to our profession and its knowledge base.
“Recent studies have suggested that the planned tooth movements are not always achieved with Invisalign.”
That IS what the science shows – what we found. The interpretation of that statement becomes problematic. Science can investigate claims – eg those made by a company that a certain product or feature produces certain results or demonstrates superiority to an alternative treatment. Such claims have been made by Align for the efficacy of the MA appliance, the efficacy of Power Ridges (that they are 500% better than no Power Ridges), for the superiority of SmartTrack over Ex30 material, to name just a few. If the claimant does not provide evidence, as rightly they should, it is up to others to use the only tool we have (no, not opinion, science, with all its flaws).
We present our findings. We welcome others providing their evidence, their science, even if it conflicts with ours. Personally, I simply want to know if I give my patient an appliance, with a certain “prescription” what will happen to the teeth. Then I can plan to adjust things. All we are doing is cataloguing the findings and presenting them. We are not saying any other appliances are better or worse, only what the aligner product is doing vis-a-vis the claims made. In this particular case the finding of a potentially damaging outcome – moving the apices of teeth potentially outside the bony housing in a large sample that seems linked to overbite correction seemed concerning enough to report upon. Similar concerns have been raised with other appliances in the past. The problem is that people want to take an emotional view to interpretation of the results. This is not helpful. We should be scientists, in the interests of our patients, not advocates in defense of our opinions.