Do the Herbst and Twin Block influence the condyle and glenoid fossa? A great RCT!

There has been considerable high-quality research into the effects of functional appliances, particularly the Twin Block, for the treatment of Class II malocclusion. This suggests that most of the changes are dento-alveolar, with only a small amount of skeletal change. Most of these studies have employed 2D images. However, the advent of 3D imaging has enabled us to make detailed measurements of the condyles and glenoid fossa. This development has opened up new avenues of 3D research.

In a previous blog post, I examined a trial of the Herst and X-Bow appliances. This revealed that there were no differences between these appliances in the fossa and condyle. This new study employed similar methods to assess the effects of the Twin Block and the Herbst appliance.

A team from Rio, Brazil did this research. The EJO published the paper.

I have an interest to declare, as I have worked on research projects with Klaus Batista. He also translated my blog.

What did they ask?

They did this study to find out

“If there was any difference between the Herbst and Twin Block  in treating Class II malocclusions on the condyle and the glenoid fossa”.

What did they do?

They did a parallel group randomised controlled trial with a 1:1 allocation.

The PICO was

Participants

Orthodontic patients with Class II Division 1 malocclusion with an overjet of greater than 6mm and CVM between CS3 and CS4.  

Intervention 1

Standard Twin Block appliance worn full-time apart from eating and sports.

Intervention 2

Herbst appliance cemented to premolars and molars.

Outcome

Glenoid fossa and condyle measurements derived from CBCT images.

They treated the patients for 12 months followed by a period of fixed appliance treatment.  They collected data at the start of treatment (T0) and after 12 months (T1).

The CBCT images were full-head images. They then used an accepted method of measuring change at the condyles and glenoid fossa. They performed a clear sample size calculation, which suggested a sample size of 12 participants. 

Randomisation and concealment were clearly described. It was not possible to blind the operator and patient to the allocation, but they analysed the data blindly.

The data was analysed using univariate statistics. Ideally, I would have liked to see a regression analysis here, but the low sample size may have precluded this form of analysis.

What did they find?

They enrolled 30 participants into the study. There were 15 in each intervention group. At the end of the study, they analysed data from 12 participants in each group. The dropouts were mostly lost to follow up.

I have decided to concentrate on the most important data. They found that the Twin Block group showed posterior growth in both the right and left (CO) of 1.3mm.  For the GF, the changes were 0.8mm and 0.4mm for the right and left, respectively.  

There were similar changes for the Herbst patients. The CO changes were 1.4mm and 1.7mm and for the GF they were 0.1mm for both right and left sides.

There were minimal differences between the two appliances. These were not statistically or clinically significant.

Their conclusion was

“The effects of the appliances on the condyle and glenoid fossa were minor, and there was no difference between the appliances”.

What did I think?

This was a well-conducted small trial. The team followed sound trial methodology and executed the trial effectively. As far as I could determine, the data collection and superimposition methods were appropriate and adhered to established practices.

It is also important to note that the results are similar to the recent study on the Herbst and X-Bow. These emphasise that we do not achieve significant skeletal changes with these fixed functional appliances. Most of the treatment effects are likely due to dentoalveolar change. It would be interesting if both teams published dentoalveolar data.

The authors wrote a good section on the limitations of their study. They felt that their study was quite small, and the results should be approached with caution. I agree with them, but since the effect sizes were small, the chance of statistical error is also low. They also noted that the study measured the effects of growth and treatment because there was no untreated control group. However, it would be unethical to include such a group.

I also have concerns about the use of full-head CBCT imaging on two occasions. As regular readers know, I moan about unnecessary radiation exposure frequently.

In summary, this was a good small study that adds to our knowledge about the effects of functional appliances.

Key points 

• Research Focus on Functional Appliances for Class II Malocclusion: The study investigates the effects of the Twin Block and Herbst appliances, primarily on dento-alveolar structures, using advanced 3D imaging to assess condyle and glenoid fossa changes.
• Methodology of the Trial: A randomized controlled trial with parallel groups was conducted, involving CBCT imaging before and after 12 months of treatment to measure skeletal changes in patients with Class II division 1 malocclusion.
• Main Findings of the Study: Both appliances resulted in similar minor changes in condyle and glenoid fossa measurements, with no statistically or clinically significant differences, indicating limited skeletal effects.
• Study Limitations and Ethical Considerations: The study has two notable limitations: a small sample size and the absence of a control group. Furthermore, the use of full-head CBCT imaging raises concerns about unnecessary radiation exposure.
• Implications and Conclusions: The study concludes that functional appliances mainly induce dentoalveolar changes rather than skeletal modifications, contributing valuable evidence to orthodontic treatment approaches.

Can you help me do something good?

Your response to my plea for donations to support our walk raising funds for Maggie’s Cancer Support Centres has been fantastic. I set a target of £5,000, and readers of this blog have donated £2700 in a week. I would really like to hit our target. If you haven’t donated and feel you can help us, please read on and make a donation for our walk.

I am raising funds for Maggie’s Cancer Support Centres. I will be walking 22 miles across the U.K. moors in memory of my dear friend Dr Betsy Bennett. Sadly, she passed away from leukaemia at only 61. I want to honour her by using the power of this blog to raise a substantial amount. If everyone who reads this blog donates £5.00, we will raise an amazing amount! The donation button is at the bottom of this section.

Betsy was a psychologist. We collaborated in Pittsburgh and North Carolina. Her kindness and personality touched everyone she met. She introduced me to research on patient and psychological outcomes, which changed my research direction. I’m so grateful to have known her. 

What is Maggies?

Maggies is a fantastic charity. There are 24 centres in the UK, welcoming 100+ visitors into each centre every day. I volunteer at the Manchester Centre.

The centres offer free practical and emotional support to anyone whose lives are affected by cancer. They depend entirely on charitable donations and concentrate on issues such as financial worries, housing, stress management, treatment side effects, and family support. They provide this support through one-on-one sessions or group discussions. 

It would be wonderful to provide them with substantial support to help them sustain their incredible work.