October 10, 2022

Does non-extraction Invisalign treatment reduces bone support?

New research on aligners seems to be coming out every week. This paper looked at the association between non-extraction Invisalign treatment and alveolar bone support. The authors may have come to a dramatic conclusion. But was this justified?

We seem to be seeing increasing papers on clear aligner treatment. This is a good development, as these studies are long overdue. As a result, this paper was timely and it worth careful examination.


Association between nonextraction clear aligner therapy and alveolar bone dehiscences and fenestrations in adults with mild-to-moderate crowding.

Diaa Ossama Allahham, Elli Anna Kotsailidi,  Abdul Basir Barmak, Paul Emile Rossouw,  Tarek El-Bialy,  and Dimitrios Michelogiannakis

AJO-DDO advanced access. https://doi.org/10.1016/j.ajodo.2021.08.022

What did they ask?

They did this study to:

“Assess the association between non-extraction aligner therapy and the presence of alveolar bone dehiscences and alveolar bone fenestrations in adults with mild-to-moderate crowding immediately after treatment”.

What did they do?

The team did a retrospective study of a convenience sample of cases from a private orthodontic practice. They followed these steps to select the patients.

  • Screening treatment records from January 2012 to November 2019.
  • They looked for patients treated non-extraction with Invisalign by an experienced orthodontist (Dr. El-Bialy).
  • He resolved the crowding using expansion and IPR.
  • All the patients had to be greater than 18 years old with a mild sk2 or class I relationship. In addition, they had mild to moderate crowding (<7.5mm).
  • Importantly, they had good quality CBCT images before and immediately after treatment.

An experienced investigator assessed the images for alveolar bone dehiscences (ABDs) and alveolar bone fenestrations (ABDs).

The team also measured dental expansion and used a limited cephalometric analysis to evaluate tooth movements.

They did not record or provide any information on the quality or duration of treatment or whether any magic adjuncts were used, for example, vibration or special ultrasound. This is relevant because the operator promotes AEVO, and he may have used this for these cases.

What did they find?

They provided a large amount of data. Unfortunately,  I do not have the space to go into all this here. However, I thought that these were the most important findings.

  • They obtained data on 22 patients with 1923 root surfaces.
  • Before treatment, they found 859 ABDs and 194 ABFs.
  • After treatment, they detected 1068 ABDs and 282 ABFs.
  • Most of these defects were found on the buccal surfaces of the teeth.
  • Most ABDs (66%) were in the buccal segments, and 63% of the ABFs were in the anterior segments.
  • The regression analysis showed that the presence of ABDs was influenced by the patient’s age and pre-treatment ANB.

Their overall conclusion was:

“Immediate posttreatment CBCT showed that nonextraction CAT is associated with increased ABDs and ABFs in adults with mild-to-moderate crowding”.

What did I think?

It was great to see another study looking at clear aligners’ effects. There has been a lot of interest in this paper on social media. While on initial reading, it may be easy to conclude that non-extraction CAT causes alveolar bone support problems. However, we cannot make this conclusion from this paper. There are two main reasons for this. Firstly, the authors have only measured association. We must remember that association is not causation. As a result, we can only conclude that there may be an association.

However, there is further uncertainty because of the study design. This is because there is no comparison group. This paper would be far more valuable if the non-extraction CAT was compared to non-extraction fixed appliance treatment or even no treatment. We would have much more helpful information on bone support problems if the authors did this.

The authors also mentioned that there is a risk that the CBCT may overestimate the presence of ABDs/ABFs. Furthermore, they collected the data immediately after orthodontic treatment. As a result, they did not consider that remineralisation may occur.

I was also somewhat concerned that the operator took CBCT images at the start and end of treatment. In many countries, this would be unethical and unnecessary radiation exposure. Indeed, the Canadian guidelines state.”

“Dental X-ray examinations should only be performed after a clinical examination of the patient has determined an expected health benefit to the patient”.

I really cannot see any indication for the end of treatment CBCT. This should have been another major concern to the referees of this paper.

Final comments

On cursory reading of this paper, it is easy to come to an incorrect conclusion about the effect of CAT on bone support. But unfortunately, when I consider the flaws in this study, my conclusion is that the findings are interesting, but they should not influence practice.


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Have your say!

  1. Hi Kevin –
    It’s not the appliance system that causes reduced bone support, it’s the operator. Aligners don’t treat patients, clinicians do. It is up to those using these systems to apply the tools available- and there are numerous: side by side radiographs and intra-oral photos, superimposition and numeric tooth movement tables to assess the amount of proclination or expansion programmed – as well as other movements that may contribute to dehiscence such as uncontrolled tip in retraction – and now conebeam integration with ClinCheck Pro software (this was likely not available at the time of the interesting retrospective study).
    Thank-you for asking the same question of fixed appliances. Proclination is arguably more difficult to control in crowded cases treated with continuous wire mechanics, even with cinched wires due to force system being labial to the center of resistance of the tooth, whereas aligner geometry may prevent (a degree of )spontaneous proclination – this must be programmed (or ignored and default space creation accepted). Additionally I wonder if the ability to maintain a high standard of oral Hygiene with various appliance systems is a significant variable? No doubt with CBCT integration into 3D software programs – fixed or aligner – we will enhance our knowledge in the area of periodontal response to all orthodontic mechanotherapy. ..Cant help thinking of the saying that radiographs cause root resorption and now CBCT causes ABD’s!
    VV speaks for Align Technology

  2. Hello Kevin,
    It is an excellent study. Regarding losing alveolar bone, I have a question: did anybody encounter a case where the anterior part of the root moved anteriorly due to severe tipping out of the alveolar bone following aligners or other, for example, conventional orthodontic treatment (whether such treatment still exists)? Unfortunately, I cannot attach the pre and post-treatment CT pictures. I would like to know if there is a study or data about the future of teeth that lost the whole anterior part of the bone.

  3. Not even worth the paper it’s written on. CBCT is worthless for evaluating exact bone levels. The voxel size of even the best machines is several times larger than bone cells. Additionally, they do not take into account the stage of mineralization that the remodeling bone may be in when they gathered their post-op data. This would further complicate their already futile attempts at seeing what they are trying to see.

  4. Thank you for your review Kevin.

    First of all, there is no published data to show that cone beam radiographs can reliably identify the presence or shape of actual bone dehiscences or fenestrations. Another major problem is that the average slice thickness (based on the usual voxel size in these radiographs) of 0.3 to 0.4 mm could easily miss a thin layer of bone. Histologic studies have long established that bone may be as thin as 0.1 mm on the buccal root surface and still have an intact layer of bone. There have also not been any studies to determine if periodontal disease progression is influenced by the presence or absence of thin buccal plate as long as there is an intact connective tissue periodontal ligament and epithelial attachment. Most importantly, as you point out, taking the radiographs right after orthodontic tooth movement when the bone is undergone remodeling would not detect partially calcified thin bone that was present.

    A few years ago we had a recently graduated dental radiologist come to our institution. When this radiologist read the post treatment cone beam radiographs taken on our patients (including fixed and Invisalign extraction and non-extraction cases) they were shocked at what they saw was “numerous fenestrations and dehiscence being created in a generalized manner “ when radiographs were taken shortly after the completion of orthodontic treatment.
    In the periodontal literature, several recent studies have reported that the osseous form of the remaining bone after progression of active periodontal disease cannot be accurately characterized by a cone beam radiograph, especially in areas where the bone is thin.

    My mentor, Dr. Sheldon Baumrind, always reminded me me not to use a measurement tool that you did not know exactly what it was actually measuring.

    One final point is that recent studies have reported that the radiation dose from our present cone unit called the I- CAT Flex can be set to have less radiation dose than the average pano and lateral ceph. So we have been taking these radiographs as a replacement for our previously used post treatment radiographs since they provide additional information such as airway characteristics and the possibility for three dimensional superimpositions with correctly mounted intraoral scans.

    So this study raises more questions than it answers!
    Robert Boyd
    Professor Emeritus

  5. Reading your analyses is like a breath of fresh air; thank you for doing what you’re doing, Dr. Obrien! Your points on the CBCT radiation were especially interesting. Here in the U.S., the dental field x-rays patients to a massive degree & likens all radiographs to the “same amount of radiation you get on a plan ride.” I’ve even heard this said about cone beams.

  6. In interesting study. When I was in practice, I was always concerned about some colleagues basically treating almost everything non extraction, basically expanding and proclining everything to get the “broad American smile”. That definitely doesn’t suite everybody!. My fear was always perio problems later in life. It doesn’t matter how you do it, ether invisalign or conventional fixed appliances. The consequences are the same.

  7. The methodology of routine CBCT prior to and after treatment is unethical. This opinion piece brings attention to the article and fame to the author. Personally, wherever possible, I do not refer to articles with unethical methodology and I would recommend that should become our collective practice.

    Our primary duty is to work for the health of each patient. Unnecessarily exposing patients to radiation is unacceptable.

    Discussing the merits or otherwise lends credence to the paper and should be avoided.
    . Patients trust us to care for them, to diagnose well but to avoid harm. Kevin’s highlighting the dangerous methodology is commendable and that the peer reviewers let this through.

    It raises the question as to whether the article should be withdrawn.

    • I understand you also extend your comment about unethical practice to the reviewing board of the journal ??

      • Dear Maria
        Almost all reviewers should be aware CBCT is not appropriate for routine examination (some reviewers may not be dentists). https://pubmed.ncbi.nlm.nih.gov/22668710/ These are current recommendations by radiology experts and one of the authors confirmed to me that the substance is still valid. Earlier comments on dosage are fanciful and 3D imaging done at such low doses is unlikely to be useful diagnostically. Should we be praising Mengele’s embryo research? My view is simple, the failure to protect patients from risk is unethical, it should not be published especially in a peer reviewed journal.

  8. Very eye opening work, well done! the link between thin/non-existent buccal bone and gingival recession has been highlighted by many clinicians (Richman C. Is gingival recession a consequence of an orthodontic tooth size and/or tooth position discrepancy? “A paradigm shift”. Compend Contin Educ Dent 2011;32: 62–9.), Those who don’t like the findings have a simple explanation, treating everything non-extraction and selling this idea to the patient that we do non-extraction using clear aligners and therefore we are the best!

    The poor patient obviously wouldn’t know about the risk and things are OK for a while, and then gingival recesion starts to appear a few years later, and obviously the clinician BS the patient that he/she got the gingival recession because of the aggressive brushing!!!

    I hope the authors do another CBCT study on the same cohort after 2-3 years and see the extent of the damage to the periodontium.

  9. Totally agree with so many of the points above and in particular the ethics of this paper. IMHO, it should not have been accepted for publication (in addition to the lack of comparison group) when unnecessarily subjecting patients to additional x-rays. Yes, it may be lower dose than a post-Tx OPG and Ceph but you don’t need them either, it’s just to satisfy our curiosity or a hangover from older training and should be stopped as routine practice and only when indicated. This paper could have been done with a clinical outcome of recession and monitored over a longer time with a comparison group without any additional radiographs and it would then also be more clinically meaningful.

  10. Hi Kevin, thank you for your interest in our work and for addressing this very important topic. As the corresponding author of this study I agree with many of the points. This is a retrospective study suggesting an association (rather than cause) between non-extraction clear aligner therapy in adults with crowded dentitions on the presence of alveolar bone dehiscences and fenestrations. In addition, as the post mentions (and has been indicated in the discussion of the paper) CBCT might over-estimate the presence of these defects. Nonetheless, we used some recommended cut-off points in the determination of the defects to minimize that as much as possible. Although there is no control group, we do believe that in this type of study the baseline (before treatment) has served as a control for the post-treatment results. An important limitation is that post-treatment CBCTs (and related measurements) were conducted immediately post-treatment. Bone remodelling could occur 6-12 months in retention so it will be interesting to see the long-term impact on bone support. The practice where the study was conducted takes CBCT instead of a pan and a lateral and/or frontal ceph for orthodontic records. Radiographs are also obtained post-treatment to better evaluate the treatment results. I am aware that it is currently difficult to reach a consensus whether a CBCT is a valuable alternative to pan/cephs but definitely I think it would be unfair to consider it unethical especialy with the reduction of radiation exposure with newer CBCT machines. I perceive CBCT can provide valuable information regarding orthodontic treatment outcomes in regards to several variables such as root resorption, bone volumes, skeletal changes, and changes in airway dimensions. Within the limitations though it is important to note that with the growth of clear aligners in clinical orthodontics it is important to obtain evidence-based information (rather than merely expert opinions) regarding the treatment effects of clear aligners on variables other than just the alignment of teeth (such as airway volume, alveolar bone support). It is our hope that this will be a study towards that direction. Hope to meet you soon in the future. Best wishes, Dimitris

    • Thanks for your comments. Yes, I agree with you and this study is a step in the right direction and the findings were interesting.

      I see that you feel that it was justified to take the radiographs post treatment. I know that this is a controversial area and practice varies between countries. Nevertheles, most radiographic guideline suggest that this should not be done, as it does not benefit the patient. I am going to address this in a future blog post that will generate some discussion.

      • Thank you Kevin, I am looking forward to the future blog post as it will be an interesting discussion. I personally do not obtain CBCTs routinely but accept that this is the preference of several practitioners. In addition, clinical studies based on CBCT information are becoming an important part of recent orthodontic literature. Just a quick search of indexed literature shows that there are multiple CBCT studies on clear aligner therapy conducted throughout the world (and published in multiple diverse peer reviewed and leading journals): https://pubmed.ncbi.nlm.nih.gov/?term=clear%20aligners%20CBCT. I think it is extreme to want all of these “withdrawn” from scientific literature. Moreover, it will be interesting to see how the integration will work with CBCT and Invisalign clinchecks and the implications on future treatment outcomes.

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