November 24, 2014

Removable functional appliances do not change skeletal pattern to a clinically meaningful amount

Functional appliances do not influence skeletal pattern…

This post is on functional appliances, which is an area that I have covered several times.

A few postings ago I mentioned that the journals are publishing more and more systematic reviews. I also made the point in a previous post, that we need to critically read these reviews because they are of variable quality, despite being published in the refereed literature. We have recently published a Cochrane review into Class II treatment and I was, therefore, very interested in this new review that was published in the EJO.  This is, unfortunately,  behind the EJO paywall, which restricts the availability of useful clinical information.

 Treatment effect of removable functional appliances in patients with Class II malocclusion: A systematic review and meta-analysis.

Vasilis Koretsis et al

EJO 2014, 1-7. Advanced access

DOI: 10.1093/ejo/cju071

 What did they want to do?

The authors aimed to assess the effects of removable functional appliances in treated vs untreated patients using outcomes from radiographs. Bearing in mind my comments about radiographs and research, I did start reading this paper with a degree of trepidation, as I feared that I was entering a morass of cephalometrics. However, I was pleasantly surprised and I thought that this was an interesting and relevant review.

When I started reading I did become concerned because they did not confine the review to RCTs and included prospective non-randomised controlled clinical trials. As a result, we need to bear in mind that this is not as high a level of evidence as a Cochrane review, which only includes randomised studies. However, reviews of this nature do have a place, as long as we remember this shortcoming and interpret them accordingly.

 What did they do?

They outlined their methods in a very clear way. It was good to see that they carried out a quality assessment of the literature that they included. They did this by assessing the RCTs with the Cochrane risk of bias tool and the CCTs with a similar instrument. They finally used the GRADE methodology to evaluate the overall strength of evidence from the review.

 What did they find?u

They included 17 studies and these were divided up into 7 RCTs and 10 CCTs. They carried out a series of planned meta-analyses. These were clearly set out.

They concluded that when the effects of removable functional appliances were compared to no treatment, the following differences occurred


95% CI(0.23-0.35)(0.15-0.27)(-0.006-0.16)

They also found that the Twin block was the most effective appliance, when compared to others.

The strength of evidence according to GRADE varied from moderate for SNA change to very low for ANB change.

They finally concluded that the skeletal effects of RFAs are minimal and of negligible importance. Most of the change was dental.

 What did I think?

I thought that this was an interesting review that came to good sensible conclusions. I was a little concerned about the inclusion of CCTs, particularly when there was an adequate number of RCTs to draw some conclusions. However, they did report this in sufficient detail for the critical reader to interpret the evidence that they presented.

I did disagree with one of their conclusions when they stated that “more research is needed”. I cannot help thinking think that we have enough research from trials and systematic reviews to conclude that


I actually think that it is time to move on…….I now wonder whether it is necessary to carry out any more studies on the cephalometric effects of removable functional appliances. This review systematically covers a large amount of the published literature and it pretty much says it all….

Can we say the same for fixed functional appliances? I have seen no reason to say otherwise…

Does this finding help us in practice, when we see a patient with a Class II malocclusion. If the skeletal discrepancy is mild to moderate then I would be fairly certain that if I used a functional appliance I could obtain a good result from a combination of dental movements and some favourable growth.  But what if the skeletal discrepancy is severe?  I think that I would treat with a functional, but I would warn the patient and parent that they will still have a skeletal problem and this may need surgical correction in the future.  Does anyone one to contribute to this discussion on this dilemma?
Koretsi, V., Zymperdikas, V., Papageorgiou, S., & Papadopoulos, M. (2014). Treatment effects of removable functional appliances in patients with Class II malocclusion: a systematic review and meta-analysis The European Journal of Orthodontics DOI: 10.1093/ejo/cju071

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Have your say!

  1. Thank you, once again. It is my recollection that years ago, Ron Roth suggested the same.

    • Yes, I think that this is correct. It is certainly my experience that when I have lectured on functional appliances in the USA several delegates have pointed out to me that all a Twin Block does is to correct the overjet by tipping teeth. These results should also be achieved by fixed appliances and standard Class II mechanics. A comparison of Twin Blocks and upper and lower fixed appliances would be interesting.

  2. So, do you think that we have to rethink about using functional appliances -once they are not “functional” anymore?

    • Thanks, this is a good point. But these appliances are still good at correcting overjets etc and to do this they use ‘functional’ forces. So I think that the name still stands.

  3. Dear Kevin,

    Are you suggesting on your Blog that we stop treating patients with sagittal discrepancies with functional appliances as this is the impression you give with your ‘sound bite’ conclusion? As you know there are some clinicians that do suggest this is ‘the way to go’.

    They advocate that, rather than treating them in their early teens, we should wait until the patients are in late teenage or early twenties, and then set them up for orthognathic surgery.


    • Thanks for the useful comment. I have added a further conclusion at the end of the original post. I think that this helps?

      Best wishes: Kevin

  4. Hello Dr. O’Brien, what about the results showed by Dr. Lorenzo Franchi, which concluded that the use of removable functional appliances allowed a gain of 3mm in the mandibular length and this “extra” growth was kept in the long term when postretention period was assessed when compared to controls? Nice blog!

    • Thanks for the nice comment. The Franchi review included retrospective comparison of case series. These types of studies are recognised as having bias towards the positive effects of treatment. As a result, I felt that this review and other Cochrane reviews were of a higher quality than the Franchi review. I have outlined the problems of systeamtic reviews that include poor quality papers in an earlier blog and the Franchi review is a good example of a review that did not adopt high quality inclusion criteria.

      • Dear Professor O’Brien,
        Do you not agree that ‘case selection’ is a pillar for any success in treating with functional appliances? If yes, how could you possibly incorporate ‘true’ randomisation to obtain good quality RCT?

  5. Are functional appliances any more good than class II elastics? If we can’t answer that question with a big yes, then I think it is much easier to spare a child several months of unnecessary treatment and spare his parents some money and start immediately with fixed appliances! What do you think? .

  6. Kevin if you have a severe skeletal discrepancy why suggesting the use of a functional appliance and then, if it does not work, propose surgery. Don’t You think that the dental compensations might compromise the effectiveness of Surgery. Is the overjet correction a good enough criteria of success?
    Contratulations for your blog.

    • Hi Renato, you are right. Bearing in mind this evidence, which is now strong, I agree with you. I think that I am going to follow up this blog next week with a post on “how we should treat Class Ii problems”. I will incorporate your great comment.

      Thanks for your kind words on the blog, it is becoming very popular and is now almost part of my job!

      Best wishes Kevin

  7. Dear Kevin and Shwan; To partially address the concept of fixed functionals and Shwan question about elastics, there are two articles by Nelson (AJODO 2000;118:142-9 and AJODO 2007;132:499-503) where they compare a Herbst with the Begg appliance and elastics. Initially the Herbst seemed fantastic with a skeletal contribution of 51% to overjet correction compared with only 4% in Begg. What was wonderful with these authors is they reviewed the patients again ~7 years later and found that many of the changes reverted and the outcome long term was similar regardless. The same ‘mortgage on growth’ effect that Lysle Johnston stated and the UNC, Florida and UK trials found. Other trials and reviews tend to use historical controls which are not a valid comparison group. Then the other issues come into play as Kevin has discussed in previous Blogs; trauma risk, psychological benefit, quality of life, etc. I discuss with patients and their families what they are prepared to cooperate with and what suits their goals – I use many appliances including headgear (if they state they are willing to wear it), Twin Blocks, Herbst, Forsus, elastics, etc. based upon the patients goals and willingness to cooperate and also the dreaded… extractions, there I said it! There are some differing effects with each appliance in the vertical plane which also sways my discussion with a patient. To discuss Kevin’s point about the severe cases, if a functional approach is indicated then I tend to recommend the Herbst purely to reduce the lack of compliance issue (~25-30%) with removable appliances as pointed out in many of the Twin Block and other removable studies but again informing the family that a full correction is unlikely and they will achieve an improvement rather than a more comprehensive/ideal outcome. Thanks again Kevin for a fantastic topic!

  8. Morphometrics(Ceph/model/gauges &indices) as the only tool to measure orthodontic outcomes, and thus form body of ‘evidence’ shows only the ‘tip of iceberg’.
    As suggested/implied in your recent article(co-authored with Aliki Tsichlaki:AJODO:Sept.2014) we need to address the ‘outcomes’ with more parameters of function, patient perspectives, risks and benefits, stability and well-being. They are not easy to measure, of course. Conclusions drawn by measuring biology with mathematics are good for publication, but practical applications limited.

    • Yes, I agree totally. It appears that cephs etc are telling us very little about functional applicants and IT would be far better if we had some research that gave us information on the way that patients felt about our Class II treatment.

  9. If the result is all or mostly all dental-alveolar
    Do we not have to ask, what about the periodontal impact of moving lower incisors beyond their boney housing. Tipping lower incisors 5, 10 or more degrees forward cannot be good for long term periodontal health or at least that is what our perio colleagues tell us.

    • In many mild to moderate skeletal class III cases, upper incisors are well proclined and lowers greatly retroclined, by Nature’s compensatory adaptation. They are usually stable and not prone to diseases. It appears that the concept of ‘straight, upright and standards’ are marketing strategy of straight wire prescription people. Teeth are ‘pawns’ in the hierarchy of systems(bone, soft tissues & teeth) of masticatory apparatus.
      Similarly, a bit of retroclination of upper incisors & proclination of lowers may be in balance to optimise for skeletal discrepancy.

  10. Dr. O’Brien, there is a way to measure how functional appliances are affecting our patients. We can measure their physiologic response with Heart Rate Variability. There are over 14,000 articles on HRV and it’s relation and indication of physiologic response. There is actually dental software to measure what happens when we introduce these retractive functional appliances in our patient’s.

    As far as Herbst appliances are concerned, I have found nothing to show me other an internal headgear affect occurring. Some articles that I have come across are:

    “Soft tissue effects of Twin Block and Herbst appliances in patients with Class II division 1 mandibular retrognathy” (European Journal of Orthodontics 1 of 11 © The Author 2011. Published by Oxford University Press on behalf of the European Orthodontic Society. doi:10.1093/ejo/cjq187) – shows flattening of facial features.

    Three-dimensional treatment outcomes in Class II patients treated with the Herbst appliance: A pilot study
    (Megan LeCornu, Lucia H.S. Cevidanes, Hongtu Zhu, Chih-Da Wu, Brent Larson, Tung Nguyen Received May 2013)- shows maxillary retraction and restraint.

    “A comparison of the skeletal, dental, and soft tissue effects caused by herbst and mandibular protraction appliances in the treatment of mandibular Class II malocclusions.”
    (Alves PF, Oliveira AG. World J Orthod. 2008 Spring;9(1):e1-19.) -showsinclination of mandibular incisors, and retrusion of upper lip)

  11. Removable functional appliances do not change skeletal pattern to a clinically meaningful amount.
    Functional appliances do not influence skeletal pattern…

    The subject of this discussion deserves more attention than brief blogs to evaluate a question that has been the subject of animated discussion for more than a century, with opinions often based more on sentiment than on logical analysis.

    My background of 50 years experience and clinical research in functional therapy leads me to a different conclusion compared to Kevin O’Brien. I have published results that call into question the statement:

    “We cannot grow mandibles or restrict maxillary growth to correct skeletal discrepancies with removable functional appliances to a clinically meaningful degree”.

    My original research in 1985 evaluated the results of the Twin Block Traction technique, which combined functional mandibular advancement with extra oral traction, so it examined both aspects of the maxillary and mandibular growth response.

    I defended a thesis in 2010 for the degree of Doctor of Dental Science at Dundee University. The title was “New Horizons in Orthodontics & Dentofacial Orthopaedics; Aspects of Twin Block Therapy”. This was based on 33 years clinical research and development of Twin Blocks and functional therapy.

    The thesis includes a statistical analysis of the first 76 patients treated consecutively by the Twin Block Traction technique between 1979 and 1982 using the two best published series of controls available at that time. This study was completed before we had access to computers as we know them today. A ‘computer literate’ friend designed a programme on a main frame computer to complete the statistical analysis. Many years later the results were verified by the department of statistics at Dundee University. This study was state of the art in statistical analysis at that time, before the advent of today’s ‘evidence based’ culture and RCT’s.

    The thesis includes comparative studies of groups of patients treated by five experts in Twin Block therapy. Comparison of results before and after treatment show highly significant angular and linear changes. The author’s study was extended to 148 consecutively treated patients and reported a failure to complete treatment of 6.8%. Ten patients failed to complete treatment over a period of 11 years. The study confirmed that patient cooperation is excellent when Twin Block appliances are designed to be aesthetic and comfortable.

    More recently cephalometric analysis has been overtaken by more sophisticated investigative techniques. We now have the facility to study changes in three dimensions and can evaluate the holistic effects of functional therapy. We cannot afford to base our philosophy on the limitations of past technology. Technological advances have improved our knowledge and understanding of the growth mechanisms and response to treatment. We can now investigate factors influencing growth and development at cellular and molecular levels and genomic studies open new horizons for the future.

    The third edition of my book “Twin Block Therapy: Applications in Dentofacial Orthopedics” has just been published by Jaypee Medical Publishers. Chapters on “Growth Response to Twin Block Treatment” and “The Flat Earth Concept of Facial Growth” include results from statistical studies. These chapters refer to scientific research beyond the scope of cephalometric analysis.

    The third edition has 200 additional pages (559pages) compared to the second edition with new chapters:

    • Fixed Twin Blocks: This is the longest chapter in the book. It introduces a new design and protocol to integrate fixed and functional therapy using the forces of occlusion to correct the malocclusion. I have completed 15 years clinical testing of fixed Twin Blocks and show results up to 9 years post treatment.

    • Pitfalls and Contra-indications for Functional Therapy: is illustrated with appropriate case reports.

    • New Horizons in Orthodontics: This chapter is extended to introduce
    TransForce Lingual Appliances for sagittal and transverse arch development. This technique represents a revolution in interceptive treatment from mixed dentition to adult therapy. Case reports illustrate 15 years of innovation and clinical research in arch development. I used arch development techniques in my practice for 33 years after attending courses on Bioprogressive technique. I taught the Wilson Modular system for 15 years and this motivated me to develop pre-activated appliances for arch development. Long term results of arch development are shown in this chapter.

    • Fixed Functional Appliances: Illustrated case reports of the new range of fixed functional appliances integrated with fixed appliances.

    • Treatment of Sleep Apnea Using Mandibular Repositioning Appliances: This reviews a comprehensive range of appliances, starting with the original sleep apnea appliance, Pierre Robin’s monobloc (1902), through to the present day, introducing “Breathe Easy Twin Blocks”

    • The Flat Earth Concept of Facial Growth is relevant to the present discussion.

    • Art and Science in Orthodontics: This summarises and puts into perspective our present state of knowledge of the complex subjects of fixed and functional therapy.

    I was interested in the blog with a comment that Ron Roth made many years ago because I witnessed this in person when I attended the first course he gave in the U.K. This was in Manchester and his opening statement was:

    “ I don’t use functional appliances because I don’t believe they work. All that happens is that you posture the mandible forward with your functional appliance, but when you leave the appliance out the condyle just goes back in the fossa and you have relapse”.

    It was understandable that Ron Roth would advocate straight wire appliances in preference to functional therapy, as he and many of his contemporaries had little or no experience of functional appliances, which were usually only worn at night when they trained in orthodontics.

    My hand went up and this was my response:

    “This is Europe and we have used functional appliances since the beginning of the 20th century and we know that they work, otherwise we would not continue to use them”.

    We now have irrefutable evidence from scientific research proving that the condyle is relocated in the glenoid fossa after Twin Block therapy.

    We can also demonstrate significant changes in mandibular length as a result of full time functional therapy. However it is esoteric to suggest that we can evaluate the results of functional therapy simply by measuring the mid sagittal axis of the mandible. Distal growth of the condyle and bony remodelling in the glenoid fossa, are additional factors that contribute to improving the facial profile.

    More importantly, two dimensional studies do not take into account the complex bilateral structure of the mandible and the implications for improving the airway, as confirmed by recent three dimensional research. Arch development and mandibular advancement are significant factors to influence tongue position by interceptive treatment.

    Criticism of functional therapy is usually based on lack of experience of the techniques in question. My thesis is available in digital format on request from my website . The third edition of my book is the best source of updated information on Twin Blocks. In addition my e-book “Advances in Functional Therapy and Dentofacial Orthopedics” gives a broader perspective of functional therapy, and is available to order from my website.

    I hope Kevin and others will take the opportunity to study my results as we are getting closer to resolving these thorny questions as our investigative techniques improve.

    One last thought: Lee Graber investigated the effects of fitting a functional appliance. Within 5 minutes the temperature of the fingers increases. How do we explain this? It may be partly an adrenaline response to fitting an appliance in the mouth. However it may equally be related to the immediate increase in the airway, which is now confirmed in 3 dimensional scans. As we posture the mandible forward we move the tongue forward and increase the airway.
    Recent research in Japan detected changes in the brain in response to contact of inclined planes after fitting Twin Blocks.

    Twin Blocks produce dramatic facial changes within two or three months of starting treatment as a result of muscle adaptation in the early stages of treatment. We cannot confine our perspective on functional therapy to measuring the mid sagittal length of the mandible.

    Face the Facts

    Functional Fixed
    Appliances Appliances
    Create Correct
    Esthetic Faces Teeth

    Yours sincerely,

    William Clark

    • Hi Bill, thanks for the comments they are very useful and interesting. My comment was based on the current state of the evidence for the growth modifying effects of functional appliances. This evidence was derived from the published scientific literature and I am afraid that this did not include the sources that you have quoted in your reply. I am sure if you published your research in the academic journals, it would make a contribution to the evidence.

    • It was indeed a pleasure to hear about Twin block for the inventor of Twin Block William Clarke sir. As a student of Orthodontics & Dentofacial Orthopaedics it is a very common question which is asked to us that “does functional appliance work” . Following Kevin sirs blog has helped me a lot to learn about evidence based Orthodontics. After reading the related articles of the systematic review and now when i heard William Clarks sir my believe in functional appliance has just raised a step ahead. Thank you sir for your guidance.

  12. Dear Kevin, I must congratulate you on generating a lively debate on this subject. I agree with you that Functional appliances, like fixed appliances, achieve little dentoskeletal change. However it surprises me that most of the debate is centered on horizontal mandibula change when it appears that much of the contrast in facial development is in the vertical plane and dictated by the maxilla.

    It is obvious that mandibula form is changed to a major extent whenever the Vth, IXth or XI nerve is damaged and lesser changes are constantly associated with open mouth postures, weak muscle tone and frequently with bizarre tongue postures. You know of my interest in the influence of oral posture and it would seem logical to attempt to change oral posture so that the tongue rests against the palate with the lips sealed and the teeth in or near contact.

    Unfortunately this is difficult to achieve or measure (many dentists think impossible) however I know of no evidence to suggest that adverse oral Posture (as distinct from Function) is not the prime cause of adverse skeletal form and most malocclusion. Are we entitled to ignore aspects which we can not measure?

    As you may know I have concentrated on this aspect of treatment for a long time and now feel fairly confident about changing oral posture using Orthotropics, however its success depends highly on patient compliance. This means of course that significant research findings are hard to obtain and in my view the only way of discovering the truth is by prospective clinical comparisons.

    I have frequently suggested these in the past but so far have found no University, or individual willing to compare their results with those achieved by orthotropics. Just a small group of ten or twenty cases selected in advance would quickly expose the relative effectiveness of different techniques.

    I would be most interested in a debate on this subject based on science and logic and think that you are one of the few people with the academic and clinical knowledge necessary to do this. Best wishes John.

  13. Dear professor O’Brien. Would you suggest that the same issue applies also to appliances such as the forsus?

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