November 27, 2023

Herbst or Twin Block? Swings and Roundabouts.

I wrote about this interesting trial in the early days of the long, hot UK summer. My post was based on the second of several papers derived from this study. This new paper reports the cephalometric analysis of the data.

The first paper was about the study’s qualitative findings, and the second was concerned with treatment failure, complications, and patients’ perceptions of their treatment. In my blog, I stated that the authors had mentioned that they were preparing a paper on cephalometrics. I have plucked up my courage and looked at this cephalometric paper.

A team based in London, UK, and Dublin Ireland did this study. The EJO published the paper.

The skeletal and dental effects of Hanks Herbst versus twin block appliances for class II correction in growing patients: a randomised clinical trial.

Moaiyad M. Pacha, Padhraig S. Fleming, Muftah Shagmani, Ama Johal

EJO advanced access: DOI:

I would like to declare a conflict on this post. I know members of this team and I have worked with them on previous research.

The paper is not open access, so you need to be a member of the EOS to read or see if you can get it through a library that pays a fee to Oxford University Press.

What did they ask?

“What are the skeletal and occlusal effects associated with the Twin Block (TB) and Hanks Herbst (HH) functional appliances”?

What did they do?

They did a parallel group 3 armed randomised controlled trial with a 1:1 allocation ratio. The study was done in one Dental School site. The PICO was.


Orthodontic patients aged 10-14  with Class II Division 1 incisal relationship and an overjet greater than 7mm.


Standard modified Twin Block appliance. The clinician asked the patients to wear their appliances full time apart from meals and sports.


Hanks Herbst fixed functional appliance. With bands on the first molars, lingual and palatal arches (or RME). The operator cemented the appliance with glass ionomer cement.


The primary outcomes were the anteroposterior skeletal and dentoalveolar change at the end of the 12-month functional appliance phase of treatment. They derived these from the Pancherz analysis.

They did a sample size that was based on the duration of treatment. This was the subject of a previous paper.

What did they find?

I will confine my discussion of the results to cephalometrics only, as other outcomes are reported elsewhere.

We used the Pancherz analysis during our Herbst V Twin Block study 2003. I have never had the intelligence to get excited about cephalometric data.  As a result,  I still shudder at my memory of trying to interpret this data in our trial.  Seeing that the current team has done an excellent job in this report was great. Importantly, they have not done a cephalometric tablefest. I have not really looked at the tables because they include the relevant data in the text. These are the main findings;

  • There were no differences between the groups at the start of treatment.
  • The HH reduced the overjet by 6.9mm and the TB by 5.1mm. The difference of almost 2 mm was statistically significant.
  • The HH was more effective than the TB in correcting the molar relationship by 1.8mm.
  • The HH caused more mandibular molar and lower incisor forward movement by 1.8 and 2mm, respectively.
  • There was a similar change in skeletal discrepancy in the HH. This was 2.9mm, and the TB was 3.4mm.
  • The regression analysis revealed that treatment with TB was a predictor for increased overjet at the end of treatment.

In short, the HH appears more effective at reducing the overjet but also proclines the lower incisor, similar to the difference between overjets. A great example of swings and roundabouts.

What did I think?

I have previously posted about this study and pointed out that it is an excellent trial. This is the third paper from this study. As a result, it is a little tricky to identify all the outcomes the team reports. Nevertheless, this study does report some clinically relevant findings.

The most important of these is that there was no clinical difference for most of the skeletal and dental effects of the appliances. Nevertheless, we must consider that the Herbst appliance causes greater proclination of the lower incisors. We should bear this in mind when we plan our treatment and compensate for this effect in the fixed appliance phase.

We published a study comparing the Herbst and Twin block many years ago and reported on the effects of treatment at the end of treatment. We found that there were no differences in cephalometric measures. This suggests that any differences at the end of the functional phase are washed out or changed by the second phase of treatment. I am interested to see if this occurs with the present study when the authors publish the final paper(s) on this trial.

Final comments

I need to consider whether the results of this study would have influenced my clinical practice. I would continue to prefer the Twin Block over the Herbst because of the ease of use and my personal preferences.

I understand that other papers on this trial are due to be published. When they are all available, I will write a summary blog post of the findings that are particularly relevant to clinical decisions (or I may ask the authors to do this).

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Have your say!

  1. why don’t we all agree to use Lysle Johnson’s pitchfork analysis in ceph based research?
    rather then selecting an analysis that may prove what we want to prove – agreeing one common ceph analysis would make comparisons so much easier

    • I agree, and this would be a good step forwards. But will we be able to get a bunch of orthodontists to agree on an analysis. I am not sure that we could!

  2. Sorry…This part I don’t get;

    “ There was a similar change in skeletal discrepancy in the HH. This was 2.9mm, and the TB was 3.4mm.”

    Are we talking Witt’s here?

    So the TB shows slightly more correction? Or the opposite?

    • Its not the same as Wits, The Pancherz analysis measures distances to a line drawn perpendicular to the occlusal plane, The best way to think about this is to consider that the relationship of the skeletal bases for both appliances did not change much more than we would expect for normal growth and any differences between them were negligible… The TB resulted in mildly greater change,

  3. Ross:

    Cephalometric parameters from Steiner to Sassouni don’t exist in true 3D space – please see and

    p.s. Our 40th class reunion was a blast, literally, courtesy of Storm Babet 🙂

  4. Classic cephalometrics is incapable of measuring an A-P correction of a Class II. The advice of a noted clinician seems worthwhile: 1. Don’t believe what you see in the mouth, 2. Use a reference, and 3. Don’t try to do the impossible. It is clear that the mandible can move. Unless a stable reference is used, such as a seated condylar position both pre and post treatment, the validity of a correction should be questioned. The evidence of functional stability should be included in the evaluation of a long term result.

  5. The Pancherz system measures changes parallel to the occlusal plane so the changes in skeletal discrepancy is very close to changes seen in the Wits appraisal, although in Pancherz system the mandibular reference point is sometime Pg instead of the B-point.
    The side effects of mandibular incisor proclination is well known and also the fact that they relapse towards their pretreatment position when the appliance is removed. This is why you should continue treatment until the patients reach an incisor end to end position.
    Removable functional appliances as the Twin block or e.g. headgear activators works fine in most cases as long as the patients really wears them, cooperation……..

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