Is clear aligner therapy effective?
The use of clear orthodontic aligners is one of the most exciting developments in orthodontics. But are they effective? This new systematic review provides us with some up to date information.
Clear aligner therapy has revolutionised orthodontic treatment. This has led to an increase in adults having this form of treatment. Recently, there have been further developments into the use of aligners for teenage treatment, mandibular advancement and do it yourself orthodontics. It has been suggested that one disadvantage of this treatment is a lack of efficiency in treating certain malocclusions. A team from Alberta, Canada looked at this in a new systematic review. Orthodontics and Craniofacial Research published this study.
What did they ask?
They did this study to ask two related questions:
“What is the contemporary knowledge on the predictability of clear aligner therapy”?
“What are the outcomes of clear aligner therapy compared to fixed appliances”?
Importantly, they acknowledged that there have been many improvements in clear aligner therapy. As a result, they only included contemporary literature between 2014-19.
What did they do?
The PICO was:
Participants: Orthodontic patients having clear aligner therapy.
Intervention: Any form of clear aligner therapy
Comparison: Fixed orthodontic treatment
Outcome: Percentage of achieved results compared to predicted results. The secondary outcome was a comparison of clear aligners and fixed appliance treatment.
They wanted to include RCTs, prospective cohorts and retrospective cohort studies. The papers needed to be published between 2014-2019.
They did a standard electronic and hand search and filtered the papers to identify the studies. They assessed the risk of bias with the Cochrane Risk of Bias tool for any trials and the ROBINS-I tool for observational studies. Finally, they used the GRADE approach to evaluate the overall quality of evidence.
What did they find?
They identified 7 papers for inclusion in the systematic review. One was an RCT the remainders were retrospective cohorts. Six of the studies investigated the treatment of mild to moderate malocclusion. Five used Invisalign. The studies reported a total of 254 patients. Five looked at the predictability of tooth movement and two compared clear aligners to fixed appliances.
One study had a high risk of bias and six had moderate risk. They could not carry out a meta-analysis because of marked heterogeneity between the studies. As a result, they did a narrative review. I thought that these were the main points:
- Rotation of teeth tended to be incomplete
- There was a degree of under torque by about 15%
- Mesio-distal tipping movements were the most predictable.
Comparison with fixed appliances
- There were minimal differences in the amount of incisor proclination.
Their overall conclusions were:
- Most tooth movements may not be predictable with clear aligner therapy except for minor horizontal tooth movement.
- Clear aligners may produce clinically acceptable outcomes when compared to fixed appliances, for minor bucco-lingual inclination of upper and lower incisors.
- Additional refinements are likely to be needed in almost every case.
What did I think?
I thought that this review was ambitious. The most important fact that I learnt was that there has still not been much research into clear aligner therapy. For example, they only found two trials, and they had to rely on retrospective studies to provide additional information.
As I have previously discussed, the problem with retrospective studies is the high risk of selection bias. The authors pointed out that this was a problem with their review. Importantly, this resulted in a reduction of the overall strength of evidence or confidence in their findings.
I cannot help feeling that there is a need for trials into the effectiveness of clear aligner treatment. Surprisingly, this popular treatment has so little evidence underpinning its effectiveness. This may be because this treatment is directed at mild malocclusions and clinical experience suggests that it “works” to the satisfaction of patients and operators. As a result, there is no need to carry out trials. However, there is a risk in the use of clear aligners on children with potentially more severe problems.
In many ways, this review reinforced the clinical perception of clear aligner therapy. It is not straightforward, and refinements are needed to achieve the predicted results.
Emeritus Professor of Orthodontics, University of Manchester, UK.