February 03, 2020

Do orthodontic patients co-operate with functional appliance treatment?

We all know that functional appliance treatment needs high levels of co-operation.  But how much co-operation do we get?  This new study may add to our knowledge of orthodontic co-operation.

Several investigators have measured the degree of co-operation with functional appliance treatment.  I have posted about this before. These studies have shown that we get less than we hope. Interestingly, the amount of co-operation does not influence the outcome of treatment. While the results of these previous studies were interesting.  It is necessary for studies of this type to be repeated. I was, therefore, pleased to see this new study. A team from Finland did the research. The EJO published the paper.


Treatment compliance of adolescent orthodontic patients with headgear activator and twin-block appliance assessed prospectively using microelectronic wear-time documentation.

Heidi Arponen et al

EJO Advance access: DOI:10.1093/ejo/cjaa001

The authors have also put this up on Research Gate here.

What did they ask?

They did this prospective mixed-methods study to answer this question;

“How much compliance do we get when we use a headgear activator or a Twin Block appliance”?

 They also asked:

“What are adolescents treatment experiences with the headgear activator and the Twin Block”?

What did they do?

They did a randomised controlled trial. The PICO was


Adolescent patients with a Class II skeletal or dental Class II malocclusion who had not completed their growth.


Twin Block appliance. They asked the patients to wear this appliance 18 hours per day.


Van Beek headgear activator. They asked the patients to wear this 12 hours per day.


  • Duration of appliance wear. They measured this using the Theramon timer embedded in the appliances. 
  • They also collected data on the patients’ experience of wearing their appliances using a specially constructed questionnaire.
  • Finally, they carried out qualitative semi-structured interviews of the patients.

Two experienced orthodontists diagnosed and identified the patients. They also carried out the treatment. The first follow up appointment was one month after fitting the appliances. They then saw the patients every three months.  The operators did not let the patients know about the timers.

They did not provide any details of sequence generation or concealment of allocation.  However, they did a sample calculation, but it was not clear what data they used in this calculation.

What did they find?

Fifty-two participants entered the study. They randomly allocated them into the two intervention groups of 26.  At the end of the 23 month study period, they had data for ten headgear activator patients (38% of the original sample) and 20 of the Twin Block patients (76% of the original group).  Seventeen of the patient dropped out. They stated that ten timers did not work and eight patients discontinued treatment.

Furthermore, I think that they did not use the data for five patients because they were still in treatment.   I, also, found it difficult to interpret this data because the CONSORT flow chart was not sufficiently detailed. However, the bottom line was that they used data on 30 patients.  As a result, they lost 38% of the data from the study. 

There were no marked differences between the groups at the start of the study.

I found it challenging to interpret the data that they presented because they provided data both for the combined sample and for each group. I felt that the combined data was not too useful. As a result, I have concentrated on the data for each intervention.

There was no difference in the treatment duration of the two appliances. Still, I could not find the data for this outcome by the appliances.

The patients who had the headgear activator appliance were more likely to interrupt treatment.

There was little difference in wear time of the appliance during the course of treatment. When they looked at the wear time between 7 and 23 months, they found that the participants wore the headgear activator for a mean of 5.0 hours (42% of the prescribed time). Similarly, they wore their  Twin Blocks for 7.5 hours (41% of the specified time). Unfortunately, they did not provide information on the standard deviation and 95% confidence intervals of this data.

Finally, I could not find any information on the clinical effects of the treatment for each type of appliance.  However, they presented combined data for the whole sample. This showed that the overjet decreased by a mean of 4mm and overbite by a mean of 2mm.  Again,  I could not find any information on the distribution of the data). 

The qualitative data showed that the most common concern of the patients was with tissue irritation with the headgear activator and speech with the Twin Block.

Their overall conclusion was;

“Adolescent patients wear their removable functional appliances much less than advised”.

What did I think?

When I saw the title and subject of this study, I was interested. I thought that this paper had the potential to be clinically useful. Furthermore, it was somewhat unusual as it was not a standard “cephalometric festival”.   Unfortunately, I found that the paper was not easy to understand and assess. This is simply because this paper was not written according to the CONSORT guidelines.  

 Nevertheless, I have tried to identify clinically relevant information from this study. However, we have to consider this in light of the high drop out rate, the unclear dental outcomes and the lack of concealment in the treatment allocation. It is essential to recognise that all these issues increase the risk of bias in the paper.  We also need to consider the effect size, and this is large.  As a result, this paper does add some evidence that our patients do not wear functional appliances as well as we would hope.  Unfortunately, the strength of the evidence from this paper is not high.  Again, I am sorry to be so critical, but we need to interpret the literature carefully.



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Have your say!

  1. I am getting a little tired of responding to studies by clinicians who do not understand first principles of patient management.A good clinician does not ask patients, he/she instructs them and follows up weekly to ensure instructions are strictly followed. Any recalcitrant patients can be weeded out in the first 3 weeks, less than 1% of Twin Blocks.
    With Twin Blocks this approach results in happy patients wearing the appliance 24 hours per day, including eating and sport, with many complaining about decreasing wear after the active phase; no dropouts, no breakages and great predictable results.
    The H/G activator is more challenging but the same approach results in 95% of patients wearing the appliance out of habit during sleeping; night attire on, headgear on.
    I have no RCT to confirm this but many years of practice, including children and grandchildren confirming this approach and over 30 years of PG students changing their initial scepticism

    • I often think that the most success in treatment is acheived when encouragement and lack of confrontation are used.I find this produces happier pts.and staff and a stressless clinician.
      To this end ,I use almost no appliances (excluding braces /aligners)except ,maybe ,4 RPE.s per year and12 crossbow appliances ,a year,in extreme class 2 cases.
      I am always confused by the perceived need to use awkward ,bulky appliances,like the twin block.I tried them 30 yrs ago and feel they have been superceded many yrs.ago .
      Just my view as I dont want to run my office like a drill seargent .
      Just my views,as always in ortho.,no right or wrong.

  2. Hello,
    Thank you for the post and for detailing your analysis.
    I wonder about the “functional” aspect of the headgear appliance. Which function is used to treat the patient?
    I rarely use twin blocks as well, maybe because I find them very difficult to set in order to be useful, to put the mandible forward enough and not too much…

  3. Hello Kevin, firstly I want to thank you for your interesting study analysis and questions.

    My protocol for functionals is start for the first 2 weeks as a ffa (fixed functional appliance) to get the biology started. After 2 weeks unfix it and then my experience in 100% of the cases when the patient stops wearing it ; and they all try it; they will be very uncomfortable and comfort returns when they wear the appliance. That way I get close to 100% compliance and my correction rarely take more than 9 months after which they graduate to a maintainer.
    This has been my experience. Perhaps fuel for a study?

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