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.
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.
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.
Emeritus Professor of Orthodontics, University of Manchester, UK.