April 12, 2021

Patient experiences with Invisalign Mandibular Advancement (ITMA) vs Twin Block

Invisalign Teen Mandibular Advancement (ITMA) is a new functional appliance. There is little evidence of its effectiveness. However, this new study does provide us with information on patient perceptions of this appliance compared to the Twin Block.

I have posted about ITMA treatment before. In effect, these appliances are aligners with small blocks that posture the mandible forwards.  I thought it was exciting to see this study that looks at how our patients feel about this new treatment.

It is a common clinical experience supported by research that patients feel uncomfortable with the relatively large blocks of the Twin Block appliance’s active component.  We also know that this discomfort diminishes with time.  Nevertheless, compliance with the Twin Block is not always good. It is, therefore, logical to attempt to improve the patient experience. The advertising material on ITMA claims that they have replaced bulky appliances.  Invisalign Clinical Salespeople (KOLs) have suggested high levels of patient comfort and satisfaction with this appliance.

A team from Manitoba, Canada, did this new study. The Angle Orthodontist published the paper.

Investigation and comparison of patient experiences with removable functional appliances:

Tyrone Zybutz et al., Angle Orthodontist. DOI: 10.2319/050520-393.1

What did they ask?

They did the study to:

“Compare patients experiences with the Invisalign Teen with Mandibular Advancement (ITMA) and Twin Block (TB) appliances”.

What did they do?

They did a cross-sectional questionnaire survey of patients who were wearing either the ITMA or TB. They collected the data after 2 months of treatment. The patients were asked to remember their experiences at the start of treatment.

The questionnaire that they used was developed to measure patient’s perceptions of functional appliances. The developers of this questionnaire, based it on a measure that I used to compare Herbst and Twin Block appliances. You can see a copy of their questionnaire in this paper.

The graduate clinic at Manitoba and two private offices treated the patients. They asked patients to take part if they were between 8 and 17 years old and they were being treated for at least 2 months with the ITMA or TB.

What did they find?

They obtained data on 68 patients. This included 45 patients treated with the ITMA (18 boys, 27 girls, mean age 13.6) and 23 TB patients (13 boys and 10 girls, mean age 10.6 years). The two groups were statistically different in terms of age. I will return to this later.

They presented the data for the statistically significant responses only.  This was a little confusing, so I hope to extract the relevant data in this bullet list.

The Twin Block was worse than ITMA for:

  • Being visually intimidating (21% v 9%)
  • More noticeable (69% v 25%)
  • Appliance insertion (21% v 4%)
  • Embarrassment (14% v 0%)
  • Extra appointments for breakages (50% v 22%)

After several months the ITMA was worse for:

Soreness of lips and cheeks

There were no fundamental differences between the treatment for facial change, treatment experience, or time to acclimatise.

They concluded:

“Although there were some differences between the appliances, the patient’s experiences were comparable.”

“Most patients in both groups reported high levels of satisfaction with their appliances”.

What did I think?

This was a good attempt at obtaining information on patient’s perceptions of their treatment.  It was good to see a study that was not simply reporting orthodontist measurements that are not relevant to patients.

I thought that the findings were interesting and clinically relevant. However, we need to evaluate several areas in the study that were not ideal.  These were:

  • There was an age difference in the treatment groups. The Twin Block group was older, and this may have influenced their responses. As a result, we must conclude that the groups were not entirely comparable. The authors draw attention to this in their discussion.
  • The patients were asked to recall their first experiences with the appliances. This means that the study may suffer from recall bias.
  • The questionnaire may have limited validity. However, it has been used in other studies, and the findings appear logical.

What we, as readers, need to do now is to consider whether these issues concern us so much that we do not accept the findings.  In this respect, the difference in ages of the groups is the most important problem.  As a result, I feel that the findings are interesting, but there is a large amount of uncertainty in the conclusions.

Final comment

I know that I am a stuck record, but an RCT would be really useful in which participants are allocated to treatment with an ITMA or a TB. This would answer the question.  Perhaps, Invisalign could pay for this with the fees they pay to a couple of their KOLs

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Have your say!

  1. I am not sure how ,practically,relevant this study is to a private practice setting in N.America,generally.I just could not see a clinician having much success convincing a patient to wear such a bulky appliance as the twin block.

  2. Two years ago there was a comment on another KOB review (Align Technology Responds to My Post About Invisalign Mandibular Advancement):

    “To date, over 17,000 teenagers have used Invisalign with the mandibular advancement feature. As we continue to add more data to this IDE study (and from the 17,000 treatments in progress), we hope that we will be able to present this to you in a future blog.”

    At 17,000 patients, Align company have a lot of data. They know from the additional aligner scans how well it’s working and those numbers should iron out a lot of the regular variables, so even if it’s not a legit RCT they should be able to show whether it’s a go-er or not. I think it’s a great idea, but I’m interested to see if it works.

    Guys, we’re 2 years on.
    What’s the jackanory?

    Stephen Murray
    Swords Ortho

  3. Hi Kevin,

    I value the effort you put into this blog. As a pediatric dentist, I find your assessments helpful for articles I might not otherwise read from the source. Could you please consider a post on Invisalign First? I’m not sure if that’s possible given how new this branch of Invisalign seems.


    • Hi Heather, thanks for the nice comments. Yes, I have a post about Invisalign first in the pipeline. Hopefully, I will get this done in the next couple of months.

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