Going solo with Invisalign?
Happy New Year to all our readers. Padhraig has written the first post of the year. This is on the need to change from aligners to fixed appliances, in order to finish treatment.
Aligner therapy continues to gain traction among the dental and orthodontic community. Aligner treatment now accounts for 10% or more of the caseload of orthodontists in the United Kingdom. Their popularity primarily relates to pleasing aesthetics, patient experiences and good tolerance (at least among compliant patients). However, numerous studies have shown that the predictability of tooth movement is limited. For example, severe rotations and deep overbite correction remain challenging. As such, some do not see aligners as a standalone solution, and most orthodontists offer both fixed appliances and aligners.
Moreover, it is not uncommon for fixed appliances to either precede or follow aligner therapy as a ‘hybrid’ approach to achieve optimal outcomes and enhance efficiency. There is, however, little information regarding the requirement to transition to fixed appliances during Invisalign treatment. Therefore, the authors attempted to study this in this paper published in the American Journal of Orthodontics and Dentofacial Orthopedics.
American Journal of Orthodontics and Dentofacial Orthopedics, 18th December 2022.
Neal D Kravitz, Dalloul B, Zaid YA, Shah C, Vaid NR.
What did they do?
They conducted a retrospective study evaluating 500 patients who had commenced treatment with either Invisalign Full or Invisalign Teen.
Participants were 14 or older, with an average age of 33.6 years. Those commencing treatment with sectional fixed appliances, requiring extractions, surgical exposure or restorative work during treatment were excluded.
Invisalign Full or Invisalign Teen.
The need for fixed appliances to detail the outcome with Invisalign, number of refinements and treatment duration
What did they find?
Overall, 1 in 6 patients (17.2%) required a hybrid approach with fixed appliances to detail the outcome. An average of 2.5 refinement scans were needed in each case. Interestingly, only 6% completed treatment without a refinement stage. This group required an average of 22 aligners. Conversely, 41% required 3 or more refinements overall. The overall mean number of aligners was 64, and the average length of Invisalign treatment was 22.8 months, which exceeded the projected treatment length by 5 months.
For those requiring a hybrid approach, the average number of aligners was 81, and the mean duration of the fixed appliance phase was 7 months. More refinement scans did correspond with a higher likelihood of the need for fixed appliances.
What did I think?
I liked this study because it provided us with new and helpful information. It gives us ‘fly on the wall’ insight into how aligners are used by one world-leading orthodontist. As clinicians, we know that many patients are aware of and are knowledgeable about aligners before seeing us. Equally, experiences among adults using aligners tend to be positive. However, as Peter Greco suggested in a recent article in the AJO-DO, ‘Ideal treatment objectives should be approached without bias toward the appliance used to meet those objectives’. The frequency with which fixed appliances were used as an adjunct to aligners in this study supports the idea that ‘going solo’ risks unnecessary compromise in many patients.
From a methodological perspective, the study was limited, being retrospective and confined to just one practitioner’s office. There is, therefore, a question mark around external validity. There is also an increased risk of selection bias, whereby the researchers may have been tempted to select those performing better. Notwithstanding, as the study was directed at identifying patients who may have fared less well, I think this risk is relatively low. Moreover, given the provider’s experience, the relatively high frequency of transition to fixed appliances (17%) and near routine requirement for refinement are interesting. In particular, the practitioner is experienced and, therefore, likely to have carefully selected patients and planned cases (thus minimising the likelihood of refinement). However, this is likely to be balanced by his high standards and a low tolerance for imperfection prompting the decision to either undergo further refinement or to transition to fixed appliances.
Finally, it would be helpful to understand the specific reasons for additional refinements or the need for fixed appliances. As such, a more granular evaluation of these cases may help assist our treatment planning. This information may, in turn, also be helpful in better informing our consent processes.
What can we conclude?
Aligners are a tool. Fixed appliances are another. Both offer advantages. But both subordinate to trained clinicians. Some (like me) are more comfortable using fixed appliances in most scenarios and particularly to optimise finishing. However, if this study proves anything, it may be that the ability to use both approaches well is becoming increasingly indispensable.
Professor of Orthodontics, Trinity College Dublin, The University of Dublin, Ireland