August 09, 2021

Invisalign does not influence speech more than brackets.

One of the potential drawbacks of aligners is that they may interfere with speech. However, this new trial shows that this is not the case.

We know that all orthodontic appliances interfere with speech production to some degree.  It could be suggested that aligners because they cover the teeth may cause more problems than fixed appliances.  This problem may be a disadvantage of aligners. Unfortunately, there has been limited research done on this problem. Therefore, It was great to see this new RCT.


A team from Londrina, Brazil, did this study. The Angle Orthodontist published it.  As usual, it is open access, so we can all read it.

Effects of orthodontic treatment with aligners and fixed appliances on speech: A randomised clinical trial.

Paulo Melo et al, Angle Orthodontist. DOI: 10.2319/110620-917.1

What did they ask?

They did the study to;

“Evaluate speech production in patients undergoing orthodontic treatment with aligners or fixed appliances”.

What did they do?

They did a two-arm parallel-sided randomised controlled trial. The PICO was

Participants:  Orthodontic patients aged 13-35 years old, with Class I malocclusion, moderate crowding, treated non-extraction.

Intervention: Invisalign aligners. The patients changed the aligners every ten days.

Control: Fixed appliances.

Outcome: The primary outcome was a speech evaluation done by a speech therapist.  The secondary outcome was a self-assessment of their speech.

They did a sample size calculation based on a previous study looking at speech in patients wearing removable appliances.  This calculation showed that they needed to recruit 18 patients per group.  They used pre-prepared randomisation and concealed the allocation in sealed envelopes.  The speech assessment was done blind.

They collected the data at baseline, immediately after they fitted the appliances and then at 3, 30 and 180 days.

What did they find?

Forty patients took part in the study.  Importantly, they all completed the study period.

There were no differences in the groups at baseline.

The aligner patients had a significant change in their speech compared to fixed appliance patients at the insertion of their appliances and three days later.  However, at 30 days, there were no differences between the groups.  They found that the phoneme /ch/was responsible for the change.  Interestingly, the patients reported similar data from their self-assessment for both appliances.

The authors suggested that this occurred because of interference of the aligners with speech production. However, after a short time, the patients adapted because of the thin, well-adapted aligners.

Their overall conclusion was

“Changes in speech production occurred at the start of aligner treatment. Patients reported changes for both appliances. We should inform our patients of these changes in speech production with aligners”.

What did I think?

I thought that this was a good small study that looked at a relevant question to our patients.  The authors did the study well and used standard trial methodology.  Importantly, they analysed the data blind.

I was also impressed that they managed to carry out a trial of aligners v fixed appliances.  I have always thought this would be difficult because patients may not want to be randomised to fixed appliances.

We need to consider whether the results are helpful to us.  Firstly, there were considerable differences between the groups in terms of alteration up to three days. For example, at three days, only 1 of fixed appliance patients had a significant alteration. In contrast, this was reported for 12 of the aligner patients.  I think that this is an important finding.

This study provides us with useful evidence-based information that we can give to our aligner patients.




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Have your say!

  1. Humans adapt! Same as people wearing dentures for the first time adapt after a while. Speech impairment improves remarkably quickly.

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