Herbst or Twin Block appliance; which is best?

Orthodontic researchers have extensively studied Class II malocclusion. As a result, our knowledge base on this condition is fairly extensive. Nevertheless, one unresolved question concerns the relative effectiveness of fixed versus removable functional appliances. This paper adds to our knowledge in this area.

This is the final report on an innovative study first published in the summer of 2023. I have posted about these two papers before. They focused on treatment outcomes at the end of the functional phase. The first paper examined the patient’s perception of their treatment. The second reported on dental and skeletal effects. This new paper provides useful information from the end of treatment. 

A team in London, in south-east England, conducted this study. The Angle Orthodontist published the paper. 

I have a conflict to declare. I know this study team well.

What did they ask? 

They did this study to. 

“Compare the effectiveness to the completion of active treatment of undergoing an initial phase of fixed or removable functional appliances, followed by comprehensive fixed appliance therapy.” 

What did they do? 

They did a parallel-group, two-arm randomised controlled trial with a 1:1 allocation ratio. 

Recruitment began in February 2017 and concluded in 2019. The study was conducted in the orthodontic department of Queen Mary University of London, UK. One operator treated all patients.

The PICO was

Participants

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

Interventions

Standard modified Twin Block appliance. The clinician asked patients to wear their appliances full time except during meals and sports.

Comparison

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.

Outcomes

The primary outcome was the time taken to reduce the overjet to less than 4 mm. Secondary outcomes included skeletal or dental changes, occlusal index scores, treatment duration and failure, and health-related quality of life. 

Records were collected at the start of treatment (T0), at the end of functional appliance treatment (T1), and at T2 following removal of fixed appliances. The clinician defined the final endpoint as normal occlusion and alignment with adequate intercuspation. I was a little confused by this, as I was unsure how it related to the primary outcome of overjet less than 4 mm.

They analysed the cephalograms with the Pancherz analysis. They also analysed the study models with the Peer Assessment Rating. Finally, they used several quality-of-life questionnaires. 

One operator treated all patients with appointment intervals of 6-8 weeks. They removed the appliance when the overjet had reduced and appeared stable. They classified a patient as non-co-operative if the overjet had not reduced by 10% in 6 months, or if they had not achieved a normal overjet after 12 months.

The study statistician carried out both univariate and multivariate analyses. They also conducted a sample size calculation. This suggested that they needed to enrol 40 patients into each intervention group.

The randomisation was pre-prepared, and they concealed the allocation in sealed envelopes.

What did they find?

According to earlier reports on this study, 80 participants were enrolled. When they reviewed the completion rate in the Twin Block group, they reported that 2 participants did not reduce their overjet after 6 months due to poor compliance. 13 other participants failed to achieve the desired overjet reduction. This resulted in a total of 15 failures (37.5%).

When they looked at similar data for the Herbst group, no dropouts were reported, but treatment was stopped in 7 participants (17.5%) because of poor oral hygiene, frequent breakages, and/or other complications. 

The mean duration of treatment, from the end of the functional phase to completion of the fixed appliance, was 28 months for the Herbst group and 26.9 months for the Twin Block group. I reviewed the previous reports on this study, which showed that the duration of Herbst treatment was 8.8 months and, for the Twin Block, 10.3 months. These are long treatment times. 

When they examined skeletal and dental changes using cephalometric measurements, they found no clinically significant differences at the end of fixed-appliance treatment. Similarly, the Peer Assessment Rating scores did not differ. The mean end-of-treatment PAR score was 4.1 for the Twin Block group and 4.6 for the Herbst group. Oral health quality of life scores did not differ, except that Twin Block patients reported more embarrassment than the Herbst group. 

The skeletal, dental and occlusal outcome measurements were almost identical to those that we reported in our large trial into similar appliances.

Their final conclusion was 

” Both the Twin Block and the Herbst appliances were effective in correcting the Class II division I malocclusion, with long-term skeletal and occlusal outcomes largely comparable. However, the Herbst appliances achieve greater short-term improvements and are associated with fewer compliance issues and less reported embarrassment. This may suggest improved overall acceptability”.

What did I think? 

I have posted about this study twice before. I think it is an excellent study that provides us with a great deal of information about our choice of functional appliances. The results should be considered alongside the other two papers, which, interestingly, showed few differences between the appliances. It is rather unusual for a functional appliance study to report outcomes at the end of treatment. In this respect, this study adds considerably to the literature. 

While the two sets of appliances showed no meaningful differences in overall outcomes, one interesting point is the discontinuation rate. This was difficult to determine from the data in the paper because the authors did not provide a CONSORT flow diagram. However, they reported overall discontinuation rates that were generally similar to those in other studies. Some may expect these rates to be rather high. However, this is a real-world study and provides us with fairly strong data. It is also similar to the discontinuation rates we reported in our Herbst versus Twin Block study published many years ago. 

When we consider the differences in discontinuation rates, the Herbst appliance clearly has lower discontinuation. It is also interesting to note that patients felt more embarrassed with the Twin Block than with the Herbst appliance. This could explain the differences in cooperation. 

Final comment 

This is a really interesting study that was well carried out and reported. It provides a large amount of information that we should find useful when consenting patients for treatment. When I was a practising orthodontist, I always preferred the Twin Block appliance over the Herbst appliance because I felt it had fewer complications. It is interesting to see that these findings are still borne out. However, we need to accept a higher discontinuation rate with the removable appliance compared with the fixed appliance. This study provides very useful information for our patients. 

Overall summary

When I combine the findings from the three papers. I think that these are the main conclusions of this research

In Phase I, the Herbst appliance reduced overjets more quickly than the Twin Block. However, it had a greater dentoalveolar effect, as shown by flared lower incisors. Herbst treatment was 1.5 months faster. Nevertheless, there were more emergency visits.

At the conclusion of all treatment, there were minimal differences in treatment effects and quality-of-life measures. Importantly, the Twin Block had a higher discontinuation rate. Our patients may find the Herbst appliance more acceptable than the Twin Block.