Is oral hygiene influenced by Invisalign or self ligating brackets?

We are all concerned about the oral hygiene of our patients, but is it influenced by our choice of orthodontic appliances?  This new trial sheds some light on this problem.

Some people have suggested that the choice of appliance may influence the ability of our patients to maintain their oral hygiene.  This may be particularly relevant to removable appliances as they can be removed to make tooth brushing easier.  As a result, claims are being made that aligner treatment reduces oral hygiene/periodontal problems. This was the subject of this trial.

A team from Connecticut did this study. The AJO-DDO published the paper in February.

Which orthodontic appliance is best for oral hygiene? A randomized clinical trial

Aditya Chhibber et al

Am J Orthod Dentofacial Orthop 2018;153:175-83

https://doi.org/10.1016/j.ajodo.2017.10.009

They did the study to answer this question

“Is there an effect of clear aligners, self ligating brackets and conventional brackets on oral hygiene”?

What did they do?

They did a three arm randomised trial with a 1:1:1 allocation. The PICO was

Participants: Patients having orthodontic treatment in the permanent dentition.

Intervention:  Invisalign

Comparator: Self ligating brackets or conventional brackets

Outcome: Periodontal measurements. The primary outcome was Plaque Index (PI), The secondary outcomes were the gingival index (GI) and papillary bleeding index (PBI).

They collected this data from the maxillary second premolars before treatment (T0), after 9 months (T2) and after 18 months (T3).

They did a sample size calculation and pre-prepared a block randomisation. When a patient consented to take part in the trial, the investigators phoned or texted a person who let them know the treatment allocation. Therefore, the investigators were independent of allocation etc.

It was not possible to blind the treating orthodontist to the intervention. Importantly,  the person recording the periodontal measures was not done blinded. This is important and I shall return to this later.

They did a complex intention to treat statistical analysis which took confounders into account.

What did they find?

They entered 71 patients into the study. Unfortunately, they did not always allocate the correct intervention to the patients. Consequently, they lost 10 patients from the study. This loss was unbalanced and resulted in 5 of the patients in the self ligating group not receiving self ligating brackets.

They found that there were differences in all the outcome measures between the brackets and Invisalign after 9 months. However, after 18 months there were no differences.  They showed this in these nice graphs.

Overall, they concluded that there was no significant difference in the oral hygiene level between clear aligners, self-ligated brackets and conventional brackets after 18 months of orthodontic treatment.

What did I think?

This was an ambitious and difficult study. I think that the authors did a good job and the results are interesting. They also clearly outlined the limitations of their study and did not make extreme claims about their findings.

We now need to consider whether this study provides us with high quality clinical information. As usual, I will start this discussion with the good points of the trial. Firstly, they carried out most aspects of the trial such as randomisation, enrolment and allocation well. They did an appropriate ITT statistical analysis.

I then looked for issues that may influence bias. The most relevant was that they did not blind the examiners to the treatment allocation when they recorded the outcome measures. This is important, because the examiners may have internal bias towards an intervention and may measure the outcomes differently accordingly. However, it is also difficult to see how they could blind the plaque recordings as this was a clinical measurement and the examiner was bound to see the bracket/aligners.

Another important factor was that the participants knew that their oral hygiene was being monitored because they were in a trial. This is a common issue in trials and is called the Hawthorne effect. I am not as concerned about this because we monitor the oral hygiene of all our  patients.  As a result, the Hawthorne effect may not have a large influence.

Finally, I am not clear about the reasons for 10 of the participants not receiving the correct treatment allocation. This could be a simple error. Alternatively, the operator may not have been in equipoise and they decided to prescribe their own choice of treatment rather than the treatment allocated by the randomisation. This could result in bias.

Summary

I have thought about these factors and I feel that there were problems with blinding and treatment allocation. These introduce uncertainty into the results. As a result, we should bear this in mind when we interpret this study.

I was surprised to see that the oral hygiene measures were not better for Invisalign. However, the authors pointed out that their finding was similar to other studies. This does suggest that aligner treatment does not make it easier to practice good oral hygiene.

As with many studies I cannot help feeling that “the person wearing or adjusting the appliance has a greater effect than the appliance”.