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Is overjet reduction influenced by the duration of functional appliance wear?

By on February 6, 2017 in Recent posts with 13 Comments
Is overjet reduction influenced by the duration of functional appliance wear?

Is overjet reduction influenced by the duration of functional appliance wear?

We all think that the effectiveness of removable functional appliances is influenced by the amount of time that our patients wear their appliances. This post is about a new study that answers this question.

Overjet reduction in relation to wear time with the van Beek activator combined with a microsensor

Ali S.A. Al-Kurwi,, Annemieke Bos, Reinder B. Kuitert

AJO-DDO 151, Issue 2, 277–283

When intra oral timing devices were developed I thought that they would be useful in research projects. As a result, it was great to find this interesting paper in the American Journal of Orthodontics.

A team from Amsterdam, the Netherlands did this very interesting research project.

What did they do?

They did the study to find if there was an association between overjet change, duration of wear and length of functional appliance treatment.

This was a prospective cohort study of 28 adolescent patients who had overjets of at least 6 mm. The residents in the Department treated the patients with a van Beek activator. This is a headgear/activator combination method of treatment.

They fitted a TheraMon timing device to record the duration of functional appliance wear. They told the patients and the parents that they were measuring their cooperation.

The TheraMon sensor is a small device which is embedded in the removable appliance. The sensor works by  recording  the time that its surrounding temperature is more than 35°C. This corresponds to the wear time of the appliance. The orthodontist reads the data using a special readout station.

They used standard van Beek activators with headgear, and asked the patients to wear their appliances for at least 12 hours a day.

They evaluated the progress of treatment for the first three appointments which covered a period between 3.6 months and 9.3 months. At each appointment they measured the overjet with a ruler and the duration of appliance wear with the Theramon.

They calculated the amount of overjet reduction as percentage change between recordings.


What did they find?

I have put the relevant data in this table below.

Percentage reduction in Overjet (median)

Time period< 8 hours wear>8 hours wearP
T1-T06.2512.50.32
T2-T110.525.40.004
T3-T211.220.000.05
T3-T127.250.000.004

It was interesting to see that the patients wore their appliances between 0.49 and 11.03 hours per day.

They also found an association between wear time and percentage reduction in overjet.  For example, wear times of eight hours or more was associated with greater overjet reduction. Importantly, the patients who wore their appliance more than eight hours a day achieved an overjet reduction of 50% compared to 20% when they wore it less than eight hours.

I thought it was also interesting to see that patients with a daily where time of 11 hours or more a day had overjet reductions of 6.5 mm. Those who only wore their appliance for 1.8 hours or less had overjet reductions of only 1.0mm

What did I think?

This was very interesting observational study.  I thought that there were several important findings..

Firstly, the patients did not wear their appliances for the length of time that the operators asked them  (at least 12 hours per day). In effect, they did not do what the orthodontists asked! However, if they wore the appliance for more than eight hours a day they still achieved satisfactory overjet reduction.

It was also interesting to find that even though the patients knew they were being monitored none of them achieved the target time of 12 hours a day.

As usual, I would like to consider the effects of this paper on clinical practice. Importantly, it provides interesting information on the time that we ask our patients to wear their functional appliance.  For example, I ask my Twin Block patients to wear their appliances for 24 hours a day, apart from when they were eating. I wonder if this study shows that we only need to ask our patients to wear their appliances for 12 hours a day? This would mean that they would not have to wear their Twin Blocks when they are at school.  This may boost our success rates.

This also showed that if when the patients wore the appliance for less than eight hours, the appliance did not work. This makes me think that if a patient is wearing the appliance for less than eight hours, according to the timing device, then we should consider another treatment.

In summary, I thought this was a really interesting study that answered fundamental clinical questions. These findings would persuade me to start using timers for my removable functional appliances.

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There Are 13 Comments

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  1. Hero Breuning says:

    Hello Kevin, The 12 hours wear of the van Beek activator was the main reason to describe this kind of functional appliance. But the appliance should be used in combination with a high pull headgear. This is different from other functional appliances. Secondly, the van beek activator is closed; nos breathing is obligatory. Finally the construcion bite is made in an open mouth position (+6 mm vertical opening) the patients have to stretch their muscles. So the results for this type of activator or a twin block can be different because of the differences between the functional appliances.

  2. Alaa elhusiny says:

    The most interesting part is that part regarding Thermon
    Finally our patient can,t lie as we will have an excellent evidence ,
    But i wonder if the patient knows the secret and put the device in worm water and dceives us ?

  3. vicki vlaskalic says:

    Thx Kevin and Happy New Year – Rooster and all!
    I’m thinking that the addition of the headgear to the functional appliance in the study (van Beek) adds to the overjet reduction, as opposed to a functional based on mandibular advancement alone (Twin Block), even given the maxillary force component resulting from mandible posturing. Also the effect on incisor angulation is likely different between the 2 designs. If so, maybe you should stick to your 24 hour (that’s tough!) requirement until determined? Sounds like an interesting study..VV

  4. JS says:

    Yes . . . but the timers don’t work!

    • I’ve been using Theramon on a routine basis for over 5 years now and in my opinion they work quite good, provided you don’t damage the chip ( when reducing the bite block of a twin block, for example, or when the patient submerges the appliance in warm water) In my opinion the chip doesn’t really motivate non-cooperative patients, but at least it puts an end to endless dicussions with patients and parents

  5. Kevin Boyd, MSc, DDS says:

    Given what the authors reveal in the opening paragraphs about the known ‘headgear’ Tx effects of the van Beek activator are, specifically mentioned: ‘restraint of maxillary forward growth, limited limited retrusion of the maxillary incisors, distal displacement of the maxillary molars, etc., it would be interesting to know what the pre-/post-Tx mandibular AND maxillary positions (relative to ant. cranial base) were for these teenage study patients. McNamara (Angle Orthodon. 1981) revealed that the majority of class II skeletal children in his trial were, of course significantly mandibular retrusive, but also ‘not’ maxillary protrusive; in fact, the majority his study patients were either pre-Tx maxillary ‘neutral’, and many were actually maxillary retrusive. It would also be interesting to know if any of these patients were assessed with validated screening tools (e.g., Chervin’s PSQ, etc.) for possible pre-Tx sleep and airway health problems (e.g., SDB/OSA, etc.).

    Given what is now clearly understood, and supported in the peer-reviewed literature, about how maxillo-mandibular retrusive phenotypes in early childhood and beyond, can be associated with existing airway health problems, or can be predictive of risk for future negative sleep and airway health consequences, it seems it would be difficult to ethically defend a prospective research protocol that proposes to: 1. delay mandibular advancing treatment until adolescence; 2. intervene on a test cohort of kids with a potentially maxillary retruding regimen that might impede maximizing posterior pharyngeal airway dimensions; and 3. withold potentially airway health-enhancing treatment (i.e., mandibular advancing/non-maxillary retractive interventions) from an age-matched, etc. control cohort who might in some cases, otherwise receive health benefits from appropriately applied protractive/non-retractive intervention.

  6. dt says:

    I have often used a simple scheme which I have found more realistic than a blanket insistence on 24 hour wear. It seems to work (although I’ve never verified it with timers) and I put it to patients like this: wear the brace 24 hours a day – you’ll do brilliantly; wear it 18 hours a day – you’ll still do quite well but it may take longer (so you could perhaps leave it out at school or at nights if you wanted, but not both!); 12 hours wear a day is the absolute minimum to make useful progress (“the brace must be in more than it is out if it is going to win”); wearing it just at nights or less is not even worth trying.

  7. Dr Danny Radnzic says:

    Does anybody actually still use the Van Beek activator plus headgear when the Twin Block is now available? Surely a lot easier to wear? A study using Twin Block could give different results.

  8. Andrei says:

    Hello Dr. O’Brien. I’m relatively new to the practice of orthodontics and i have a question if i may. I’ve noticed that you don’t encourage wearing the Twin Block appliance during meal time.. is it a great discomfort that doesn’t justify the benefits? I’ve read Dr. Clark’s book on Twin Block therapy and he states that wearing the appliance during meal time helps us to correct the malocclusion through the power exerted by the masticatory muscles and helps the patient with the retention of the appliance by strenghtening the anterior oral seal. What is the approach that you recommend for a succesfull Twin Block therapy? Thank you!

    • Kevin:
      I think Dr Proffit mentioned that a device needs to be in the mouth for at least 8hrs to have a clinical effect in his 2005 Contemporary Orthodontics textbook. It might have been mentioned even earlier than that.
      It’s interesting and perhaps not surprising that no clinical effects were found with respect to tooth movement with application of a vibrational signal using Accelodent for only 20mins per day.
      I advocate a biomimetic protocol that harnesses the circadian rhythm, which means a removable device could be worn in the late afternoon/evening when the premolars erupt (Proffit WR, Frazier-Bowers SA. Mechanism and control of tooth eruption: overview and clinical implications. Orthod Craniofac Res. 2009;12(2):59-66) and at nighttime to capture the growth hormone peak during stage 3 of the sleep cycle. We have successfully used this protocol in adults also.
      The headgear effect with Twin-blocks has been reported previously e.g. Singh GD, Hodge MR. Bimaxillary morphometry of patients with class II division 1 malocclusion treated with twin block appliances. Angle Orthod. 2002;72(5):402-409.

  9. Antonio Belmonte De Cristofaro says:

    Hi Kevin can’t wait to’ se you in florence in may

  10. Ali Al-Kurwi says:

    Dear dr. O’brien’s, Thanks For this review of my study. I will continue this study in the coming years by other soort activators and also with the twin block. My regards Ali Al-Kurwi

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