October 17, 2022

Does treatment timing influence Twin Block treatment? An RCT.

The Twin Block is probably the orthodontic appliance studied the most using RCT methods. As a result, we know a lot about the effects of Twin Blocks. This new study looks at treatment timing and provides further information on Twin Block treatment.

We have an increasing body of evidence on the Twin Block appliance. I have posted about this several times before. These are the main points of the previous research on this form of Class II treatment.

The Twin Block is an effective appliance for correcting Class II occlusion.

Patients do not need to wear this appliance full-time.

The effects of early and later treatment are similar.

The treatment changes are mostly dentoalveolar.

The intervals between appointments do not influence the treatment result.

When considering treatment timing, current clinical practice suggests we should treat in the pubertal growth period. Unfortunately, few high-level studies have looked at this question.

This new paper looked at the effect of treatment timing on the effects of Twin Block treatment. A team primarily based in Manchester, North of England, did this study. The Journal of Orthodontics published the paper.

What did they ask?

They wanted to answer this question;

“Does delaying Twin Block treatment affect skeletal and dental change and psychological disadvantage”.

What did they do?

They did a multicentre two-arm parallel-sided randomised trial with a 1:1 allocation ratio. The PICO was

Participants: Class II patients with an overjet greater than 7mm.

Intervention: Immediate treatment.

Comparator: Later or delayed treatment for 18 months.

Outcomes: Skeletal change, overjet, oral health-related quality of life, and treatment process.

It is essential to point out that they used different criteria for entering boys and girls into the trial. The boys were within one month of 11- and 12.5-years-old. The girls were within one month of their 12 to 13.5 years old.

They carried out a limited cephalometric analysis. One operator measured the overjet from the study models. The team also measured oral health quality of life with the OASIS measure and the Oral Health Quality of Life (short form).

They collected the data at the start of the trial when they registered the patient (DC1), 18 months after registration (DC2), and three years after registration (DC3).

They did two sample size calculations that showed they needed to enroll 75 participants. The randomisation was pre-prepared, and they used remote concealment. The data were collected blind. Finally, they did an intention to treat analysis with appropriate multivariate analysis.

Randomisation was very important in this study. They used a fascinating and ethical method of looking at treatment timing. In the clinical departments that took part in the study, there was an 18-month waiting list for treatment. So, they randomly allocated the patients to receive treatment without going on the waiting list. This meant they had two groups. One had immediate treatment, and the other had delayed treatment.

What did they find?

They randomised 41 participants to the immediate treatment (IT) group and 34 to the later treatment group (LTG). One patient dropped out of each group. The co-operation rate was very high.

There were no differences between the groups at the start of treatment.

The CVM stages suggested that most patients were still in the growth spurt.

The LTG treatment was 3 months shorter than the ITG treatment.

In the first stage of the study, the ITG participants were the only ones receiving treatment. The treatment group had a

  • 1.6 degree reduction in ANB (95% CI=0.89=2.29)
  • Greater upper incisor retroclination by 3.2 degrees.
  • Mean OJ reduction of 4.9mm with a 0.2mm increase in the LTG group. This reflected a 5.1mm reduction in overjet.
  • There were no real clinically significant differences in skeletal measurements.

In the second stage of the study, when the LTG had treatment. Again, they did not find any major clinically significant differences. For example, the mean overjet reduction for the ITG was 4.6mm compared to 4.9mm for the ITG.

At the start of TB treatment, there was a difference in the ages of the groups. The girls were 11.8 years old in the ITG and 12.1 years old in the LTG. The boys were 12.8 years old in the ITG and 13.11 years old in the LTG.

Their overall conclusion was

“Patients had similar clinical and psychological outcomes irrespective of when they started their treatment”.

What did I think?

Firstly, I will declare a conflict. I have had the pleasure of being part of the team that trained most of this group in clinical and scientific methodology. As a result, it is great to see them doing research work of this nature. Nevertheless, if we can put my personal biases aside. I think that this is an excellently carried out and written up study. The methodology is solid and clear.

I particularly liked the limited cephalometric analysis and use of oral health quality-of-life measures. The findings are robust.

I was a little confused that despite the randomisation, more participants were in the immediate treatment group. I cannot see how this has occurred. Perhaps one of the study team can provide a comment on this?

We must consider whether this leads to bias in the study and influences our interpretation of the results. I am not sure that it does, as I cannot see any evidence of a failure of randomisation?

One important feature of the study that the authors pointed out was the developmental stages of the groups.  They measured this with the CVM technique.  They found that most participants were in the CVM 2 or 3 stages, with no real variation between the groups. As a result, this may explain the limited differences in the effects of delaying treatment.

Final comments

As with all studies, we need to consider the clinical implications of their findings. Firstly, the results suggest there is no harm in delaying treatment because of waiting list pressures. Secondly, and perhaps more importantly, the treatment age does not appear to influence the outcome of Twin Block treatment. This is a similar finding to other studies. I wonder if we can now conclude that because the Twin Block simply moves teeth, and we are not hoping to change the skeletal pattern then the age of treatment does not matter?


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Have your say!

  1. It would be interesting to know how many patients have had an incisor trauma before starting having a 7 mm ovj.

  2. From someone who uses the Twin Block often…thank you for presenting this study.

  3. i think there’s a typo in this sentence “The boys were within one month of 11- and 12.5-years-old. The girls were within one month of their 12 to 13.5 years old.”
    it should be the other way round, right? girls 11 to 12.5, boys 12 to 13.5?

  4. There is ample evidence that CVM is an unreliable tool for skeletal growth, for Class II in particular. Plus it irradiates the Thyroid. Use thyroid shields and hand/wrist for growth assessment.

  5. I would welcome any comment that could explain why this blog focusses on twin block therapy so much ?
    It is bulky ,requires a lot of compliance ,is removable (?compliance)and has significant lab costs.
    There are many ways of achieving the smae goals with less cost,less reliance on compliance and less stress for all parties.
    Just asking ???

    • Thanks for the question. I think that the main reason that many of our posts are about the Twin Block, is that we tend to discuss RCTs of treatments. This then reflects the comparatively high proportion of TB RCTs that are done. If trials are done on other appliances there is no doubt that we would post about them. Best wishes Kevin

  6. I use the Twin Block Appliance very often, patients accept it reasonably well, cooperation seems to be good.
    But we all know that patients have their own ideas about cooperation and wearing time.
    I would like to see a study that also includes optimal wearing time of appliances.

  7. dear Dr kevin
    this journal is not pubmed indexed
    only the abstract and citation
    more over the title of the journal is very misleading and people can qoute this as a reason to start twin lock therapy from any age group
    if you look details into the article the average age is 11 to 12 years with gender variation and that’s the right time due to early pubertal maturity due to the food and hormonal influence
    your own study also support this the diet and early maturity in gender and its variation in different culture
    so many established studies accurately tell its best to start twin lock therapy for that instance any mandibular advancement with any appliance is best just before or beginning of second growth spurt which can be predicted by CVMI index ie…cvmi 3 or 4.
    my only point is title and the content
    are misleading thank you

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