October 28, 2019

What is better, The Twin Block or the Frankel 2: A RCT

When I was a specialist trainee our first choice functional appliance was the Frankel 2. We hated them because they were difficult to use and always seemed to be breaking.  So, we switched to the Twin Block because most other orthodontists in the UK were using this appliance. Since then I have always used the Twin Block to treat Class II malocclusion. This decision was not evidence-based and it is interesting to now see a new trial that compares the Twin Block and the Frankel. The results are very interesting and not what I expected.

A team from Cork, Ireland did this study. The Angle Orthodontist published it. As usual from the Angle is it open access.

Frankel 2 appliance versus the Modified Twin Block appliance for Phase 1 treatment of Class II division 1 malocclusion in children and adolescents: A randomized clinical trial.

Ciara Campbell et al. Angle orthodontist: Advance access.

DOI: 10.2319/042419-290.1

What did they ask?

They did the trial to answer the following primary question:

“Is there a difference in Phase I treatment duration between the Frankel 2 and the Twin Block appliance”?

What did they do?

They did a single centre randomised clinical trial with two parallel groups. The PICO was:

Participants:   Orthodontic patients aged 11-14 years old with an overjet of at least 8mm.

Intervention:  Frankel 2 appliance

Comparator:  Twin Block appliance

Outcome:        Primary outcome was treatment duration. Secondary outcomes were PAR scores and several quality of life measures.

They used a standardised design for both appliances. They asked the participants to wear the appliances full time.  Data were collected at the start of treatment and when the operator felt that a Class I incisal relationship had been obtained.

They did a sample size calculation based upon treatment duration. They did pre-prepared block randomisation with an allocation ratio of 1:1, this was concealed using sealed envelopes. Neither the operators or the patients were blinded to the allocation. However, the data was recorded and analysed blind.

They carried out the relevant multivariate analysis. This enabled them to take the effect of any confounders, such as gender, start malocclusion etc. into account. I thought that it was good to see that they did an Intention to Treat analysis. This meant that all participants were included regardless of the outcome or whether they completed treatment.

What did they find?

60 participants entered the trial. They allocated 30 to each group. At the end of the trial period, 20 of the Frankel group and 22 of the TB group completed the trial.

There were no differences in the groups at the start of treatment.  At the end of the functional appliance treatment, there were no differences in the drop out rates or the final overjet. They did not detect any harms.

When they compared the effects of treatment.  The mean treatment duration was 376 days (SD=101) for the Frankel group and 340 days (SD=102) for the TB group.  This was not statistically significant.

When they looked at breakages, the mean number were 4 for the Frankel and 5 for the TB. Again this was not statistically different.

Finally, there were no differences in the PAR scores or any of the quality of life measures.

In effect, the two appliances performed the same.

Their overall conclusion was:

“Phase I treatment duration, number of appliance breakages, occlusal outcome and patient and patient perspectives were similar for the FR2 and the TB appliances”.

What did I think?

I thought that this was a well-done and reported trial that answered a clinically relevant question. The trial methodology was sound in all aspects. Importantly, the sample size was large. Furthermore, they analysed all the data with an intention to treat analysis (ITT)

My only concern was with the drop out rate. Even though they did an ITT, I cannot help wondering if the results would have been different had all the patients completed the study. However, this was a “real world” study and not all our patients complete treatment. Importantly, the dropout rate that they reported was similar to other studies. As a result, I can conclude that this study has considerable validity.

The results of this study make me wonder about my decision to switch from the FR2 to the Twin Block. My main reason was that I was concerned with the breakages of the FR2. This research does suggest that this was not an evidence-based decision.

However, I soon became keen on the Twin Block because of its clinical simplicity. In effect, my preferences governed my treatment decisions.

What do our patients think?

Finally, we need to consider our patient’s preferences. I thought that it was interesting that there were no differences in oral health quality of life between the appliances. However, this questionnaire was not specific to the discomfort and hassle of the two appliances. I would have liked to see the investigators obtain data on this aspect of treatment. It would undoubtedly have given us useful information that may influence our decision on which appliance is preferred by our patients. But, overall, this was an exciting and clinically relevant study.

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Have your say!

  1. another way to look at its “a functional is a functional, is a functional” – they all do the same thing with the same outcome and none is better then the other

    • I’m presuming someone who understands stats better than I do is happy with that sample size. If I did 30 cases with one appliance or another I world probably form a clinical preference even if study didn’t demonstrate similar effectiveness. Or clinical prejudice depending on your point of view.

      Are the breakages as easy to deal with for both appliances, and the cost of fabricating and repairing similar? I think they’d come into the decision of you were doing then regularly.

      From the patient perspective, I think speech is an important factor to investigate… Though here it probably expressed in the drop out rate.

      Lastly, the thing that gives me most grief in class ll correction is lower incisor proclination. Sure you can get an overjet reduced but I’d like class l canines and molars too, so I’d like to see that reported in class ll correction papers.

      Swords Orthodontics

    • Exactly Ross. Should we also evaluate which colour is more effective? It’s time to move on and to research something that matters. Perhaps the most effective way to correct a Class II with a single phase of treatment, as this is the most cost effective method with the shortest duration.

      They all move teeth, don’t grow mandibles and have nothing to do with function.

      A better question might be, why do a phase one treatment when it is not cost effective for the patient? We know that incisor and psychological trauma are barely reasons. Perhaps practice financial considerations are the prime reason?

    • Very true
      There would be variety of patients to whom either of the appliances would not be tolerable.

  2. First of all you have illustrated an FRIII and having been in the orthodontic “game” for 40 plus and following my patients in a small town environment (i.e. they tend to not be all that transient )… the FRII cases are much more stable. It’s my opinion that frankels are the only functional appliance that actually have a direct effect on muscle hence the name ‘Functional Regulator” as Frankel himself preferred to call it. Certainly there is no argument that Twin Blocks are much easier to wear, however there is no direct stimulation of the O-B complex or as Gaber pointed out years ago “pull on the periosteum” Sadly this appliance has fallen out of favour ,as compliance issues have forced us into the era of non-compliance . Hell I don’t think most labs even know how to make these properly

    Having said all that ,it would seem that the profession has turned to non compliance appliances to “get the job done” …. like the mixed dentition use of the Jasper Vektor Force, and for later Tx appliances like The MARA and the Herbst(everything old is new again.

    Dr. Rob Bond

  3. “a functional may be a functional” but, one of the great benefits of the FRII is using it in the early mixed dentition 8-10 yrs) to manage large OJ’s that may be vulnerable to trauma or teasing. With an exfoliating primary dentition the cribbed CTB does much less well. This is not essential for all patients but for some it is a useful and effective early intervention.

  4. In my experience (which I know counts for nothing on the evidence hierarchy), the advantage of the TB is the ability to put in a maxillary expansion screw and perform independent arch expansion which is often required in class II correction. I have always liked the idea of Frankel appliances (being a class II div 2 myself with over-controlling muscles) but prefer the design of the TB.

  5. In der Studie sieht man Bilder der verwendeten Geräte also auch den standardisierten Fränkel II.

    Das ist ein Gerät das aussieht wie ein Fränkel II aber ohne das nötige Verständnis konstruiert und angewendet wird. Da wird Fränkel mit dem Verständnis vom Monoblock angewendet.

    Nicht das Gerät sondern die dadurch angeregten tonischen Muster bewirken morphologische Veränderungen. Das erfordert einen abstrakten Denkschritt und nur wer dazu in der Lage ist soll mit Funktionsreglern arbeiten. (Prof. Fränkel).

    Fränkel hat alles dem Mundschluss untergeordnet, die Biss Sperrung ist viel zu groß und macht den Lippenschluss nahezu unmöglich.
    Die Kieferrelation muss muskulär gehalten werden. Bei einer Klasse II darf der Unterkiefer maximal eine halbe Prämolarenbreite nach vorne orientiert werden um die Muskulatur nicht zu überfordern. Der Unterkiefer wird nicht mechanisch abgestützt, sondern die Drähte oder der Kunststoff liegen mit geringem Abstand an Schmerzrezeptoren um ihn vorne zu halten. Das ist ein bewusstes Trainieren und muss tagsüber langsam aufgebaut werden. Erst wenn der Unterkiefer in der gewünschten Position gehalten werden kann darf das Gerät nachts getragen werden. Man muss den Intellektuellen Gehalt des Geräts verstehen um es richtig konstruieren und anwenden zu können. Dann ist es auch nicht Reparatur anfällig.

    Das Studienergebnis mit richtig konstruiertem und angewandten Fränkel II würde jedenfalls anders aussehen.

    Ich bin Zahntechnikermeister für Funktionskieferorthopädische Geräte (ich stelle ausschließlich modifizierte Funktionsregler her.)

    In the study one sees pictures of the used devices thus also the standardized Fränkel II.

    This is a device that looks like a Fränkel II but is constructed and used without the necessary understanding. There Fränkel is used with the understanding of the monoblock.

    Not the device but the tonic patterns stimulated by it cause morphological changes. This requires an abstract thinking step and only those who are able to do so should work with function controllers. (Prof. Fränkel).

    Fränkel has subordinated everything to the mouth closure, the bite closure is much too large and makes the lip closure almost impossible.
    The jaw relationship must be kept muscular. In class II, the lower jaw may be oriented forwards by a maximum of half a premolar width in order not to overstrain the muscles. The lower jaw is not mechanically supported, but the wires or the plastic lie at a small distance from pain receptors to hold it in front. This is a conscious training and has to be built up slowly during the day. Only when the lower jaw can be held in the desired position may the device be worn at night. You have to understand the intellectual content of the device in order to construct and use it correctly. Then it is not susceptible to repair.

    The study result with correctly constructed and applied Fränkel II would certainly look different.

  6. Hi; thank you for the open source study, actually the simple way of simplifying the study was amazing ,the study design; the study critics it all went perfect, thank you all

  7. How is your preference not influenced by findings from Toth and McNamara’s 1999 study on treatment effects between Twin Block and Frankel II?

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