Braces are faster than Invisalign? An RCT
We need more research into clear aligner treatment. Some would suggest that this research is overdue, as this form of treatment is still to be scientifically evaluated. I was, therefore, pleased to see this new trial that compared the effectiveness of Invisalign and fixed braces.
Most research into clear aligners has been observational. There are very few clinical trials that have looked at this form of care. When we look back, it appears that clear aligners were widely adopted by dentists and orthodontists with little evidence of their effectiveness. The main drivers for this uptake were advertising, case reports, and key opinion leaders. In general terms, aligners are suitable for treating mild to moderate malocclusions. Although, skilled operators are using them for more complex care. This new RCT provides us with very useful information.
A team from Texas wrote this paper. The Angle Orthodontist published it.
Eric Lin et al. Angle Orthodontist: Online: DOI: 10.2319/032921-246.1
What did they ask?
They did the study to:
“Compare patients treated with traditional braces to patients treated with Invisalign”.
What did they do?
They did a randomised trial. The PICO was
Participants: Orthodontic patients with Class I molar and canine relationship, non-extraction treatment, mandibular crowding of 4 mm or less with no missing teeth.
Intervention: Invisalign treatment with SmartForce attachments.
Comparator: Fixed appliance treatment.
Outcome: ABO-Objective Grading System scores. Secondary outcome: Duration of treatment.
The authors carried out a sample size calculation that showed they needed to enroll 31 patients per group for sufficient power. They used pre-prepared randomisation. However, I could not find any information on allocation concealment.
One operator treated all the patients using standard protocols. The participants changed their aligners every two weeks. They collected data at the start and end of treatment and after 6 months of retention.
They recorded data from the cephalograms blind. Unfortunately, it was not clear whether they blinded the study model data collection.
What did they find?
They enrolled 40 patients into each intervention group. At the end of treatment, they analysed data for 31 braces and 32 Invisalign patients. It was relevant to see that 1 brace and 4 Invisalign patients did not complete their treatment. Other patients were excluded because of the absence of records. This is important, and I shall return to this later.
At the start of treatment, the mean age of the Invisalign patients was 26.7 years, and the braces patients were 25.9 years old.
The median DI scores for the Invisalign and braces groups at the start of treatment were 4.5 and 7.0, respectively. This was statistically significant, but this was a small difference.
At the end of treatment, there were no differences between the groups for the overall OGS scores. The median scores were 12.0 and 17.00 for the braces and Invisalign groups. This was not statistically significant.
Similarly, after 6 months of retention, there were no differences between the groups.
When they looked at treatment duration. This was 1.7 years for the Invisalign and 1.3 years for the braces group. So again, this was clinically and statistically significant.
Their overall conclusions were:
“There were no differences in the occlusal results of treatment between the two treatments”.
“Invisalign patients took 4.8 months longer to complete treatment than the braces patients”.
What did I think?
I felt that this was an ambitious trial to carry out. The good points were that the randomisation and sample size calculation was clear and logical. Importantly, all the patients were treated by the same experienced operator. This removed any operator effect. However, it does reduce the generality of the findings.
I was concerned with the lack of information on the concealment of the treatment allocation and the apparent lack of blinding of occlusal index scoring. Unfortunately, this means that the trial is at high risk of bias. We need to consider whether this had an effect. In this respect, I thought it was interesting to see that there were differences in the DI at the start of treatment. Again, this may reflect possible bias.
Finally, we need to consider that 4 of the Invisalign and 1 of the brace patients did not complete their treatment. This is important because in a trial we are measuring the effect of an intervention. This means that the outcome should be analysed regardless of whether the treatment is complete. This is called an Intention to Treat analysis. I wonder if this had been done whether this would have influenced the results?
The most important take-home message is that the standard of treatment for mild malocclusions with braces and Invisalign is high. Nevertheless, the duration of treatment with Invisalign was much longer than with braces. Perhaps, this is the price to pay by our patients for having relatively invisible appliances? However, we do need to take the high risk of bias into consideration when we interpret these findings.
Emeritus Professor of Orthodontics, University of Manchester, UK.