Can patients wear their aligner for only 12 hours a day? 

This is my final post of the year, and it examines a really interesting study on different wear-time protocols in aligner treatment.

As with all removable appliances, cooperation can be a challenge during aligner treatment. It is crucial that patients wear their aligners for 22 hours each day. Nevertheless, it remains uncertain whether shorter periods of wear are effective and improve patient cooperation. This question was explored in this very interesting randomised controlled trial. 

A team from Baru, Brazil, did the study. The European Journal of Orthodontics published the paper. 

What did they ask?

They did this study to:

“Evaluate whether a 12-hour daily wear protocol can achieve clinically comparable outcomes to the 22-hour standard protocol in Class I patients with mild crowding”. 

What did they do?

The team conducted a single-centre randomised clinical trial with two parallel groups and a 1:1 allocation ratio.

The PICO was:

Participants

Male and female orthodontic patients aged between 18 and 60 years presenting with Class 1 malocclusion, a complete permanent dentition, good general health, and a maximum Little’s Irregularity Index (LLI) of 2 mm.

Interventions:

They treated the patients with Invisalign orthodontic aligners made of SmartTrack material and enrolled in a Comprehensive Protocol. 

Group 1 included 25 patients, who were asked to wear their aligners for 22 hours a day.

Group 2, again, included 25 patients. They were asked to wear their aligners for 12 hours a day.

It is important to note that the intervention is a request asking patients to wear their aligners for a set period of time. We do not know the actual wear time. Nevertheless, this is a perfectly reasonable design as it reflects “real-world” clinical practice.

Outcomes

The primary outcome was the Little’s Irregularity Index.

The secondary outcomes were various dental measures such as intercanine distance, overjet, and overbite.

The team collected data at the start of treatment and at the end of the 10th aligner treatment. This corresponded to approximately 140 days of treatment.

All the aligners were fitted with compliance indicators. However, the study team preferred to collect compliance data by asking the patients to record the number of hours they wore their appliances.

Statistics

They conducted a thorough sample size calculation to determine the number of participants required. They powered the study to detect a 1.25 mm difference in the Littles Irregularity Index. This indicated that the required sample was 11 participants. However, to enhance statistical robustness, they recruited 25 participants per group.

They performed block randomisation before the study. They ensured allocation concealment by using sealed envelopes. A separate, independent operator from the clinical team generated the randomisation sequence and assigned participants.

They analysed the dat with an Intention-to-Treat Analysis. As with most orthodontic studies, it was not possible to blind the operator and the patient to the allocation of their treatment. However, the final scans and measurements were performed blinded.

They carried out a fairly simple statistical analysis using inter-group comparisons of the variables with an independent t-test.

What did they find?

50 participants took part in the study, and none were lost to follow-up. As a result, all the patients were included in the analysis.  There were no differences between the groups at baseline.

At the end of treatment, both groups demonstrated a statistically significant improvement in the maxillary and mandibular Little’s Index. However, there was a greater correction (0.84mm) in the 22-hour group for the mandible (p=0.017) than for the 12 hour group.. The mean difference between the interventions was 0.84 mm. I have calculated the 95% CI as -1.5327 to -0.1473.

When I looked at the tables, I spotted some problems and raised these with the authors. They kindly got back to me to confirm that the data columns were transposed in the advanced access PDF. The authors have raised this with the journal, and they are addressing the problem. They also sent me the corrected data tables.

I have compiled this data into a table to present the LLI values at the end of the 10 aligner treatment stage. These are means with standard deviations in brackets.

	12 hour		22 hour
	Pre-treatment	Post-treatment	Pre-treatment	Post-treatment
Maxillary LLI	5.3 (2.2)	3.11 (1.76)	4.47 (1.54)	2.48 (1.26))
Mandibular LLI	4.43 (1.81)	2.71 (1.35)	4.32 (2.6)	1.87 (1.07)

They reported no harms in the study. I could not find any data on the number of hours of wear recorded by the participants. 

Their most important conclusion was that, 

“For the sample of patients included in this study and with outcomes assessed after the first 10 aligners (140 days), the 12-hour daily wear protocol produced clinically adequate alignment in the maxilla in cases of very mild crowding. However, correction of mandibular anterior irregularity was significantly more efficient with the traditional 22-hour protocol”.

What did I think?

This was another good randomised trial into the effectiveness of clear aligners. As I have previously stated, studies of this nature are long overdue. In this respect, this study provided us with helpful information. 

The authors came to some clear conclusions. It was good to see that they compared values at the end of the treatment period rather than simply looking at treatment change. This is a far more valid way of analysing orthodontic data because it gives us a comparison at the end of the observation period.

Regular readers of my blog will now know that I am going to discuss the effect size and whether this was clinically significant. I know I have been writing about this for some time, but in studies of this nature, it is essential to consider. The only significant difference in alignment at the end of the study period was in 0.86 mm for the mandible.This is not clinically significant. As a result, we must bear this in mind when considering the conclusions of this study.

I cannot help feeling that there is no real difference between the two types of interventions, and it is perfectly feasible for patients to wear their aligners for the reduced 12 hours of daily wear. While this may be a bold conclusion, we also need to consider that this is only relevant to a group of patients with very mild malocclusions, as shown by their start-of-treatment Little’s index scores, which were in the region of 5 mm.

Concerns and confusion?

Another factor we need to consider is the length of follow-up. It was only for 140 days. As a result, we must consider these overall treatment results interim. It would be invaluable to see a follow-up paper outlining the end-of-treatment results for this group of patients.