What is best? En Masse or two-step retraction?
When I was doing specialist training, we used to close space by retracting canines and then the incisors. Then we changed to en masse retraction with no evidence. But we now have a new trial! Let’s have a look at it.
When we extract teeth as part of orthodontic treatment, we have decisions to make on the best method of space closure. Currently, we do this by either retracting the canines and then the incisors (two-step) or by retracting the canines and incisors in one go (En Masse). I have always wondered which is the best method. Interestingly, there has been limited research on this very clinically relevant question. As a result, I was keen to read and review this new study. A team from Sao Paulo and St Louis did this trial. The Angle Orthodontist published the paper, and it is open access.
Patricia Pigato Schneider et al
Angle Orthodontist: Online DOI: 10.2319/051518-363.1
In their literature review, they pointed out that there has been limited research into this question. The studies that have been done are restricted to the upper teeth or have confounders, for example, the use of anchorage reinforcement.
What did they ask?
As a result, they did this study to answer the following question.
“Are there any differences in anterior retraction and posterior anchorage control between Two Stage Retraction (TSR) and En Masse retraction (EM)”?
What did they do?
They did a randomised trial. The PICO was:
Participants: Orthodontic patients older than 18 years with bimaxillary protrusion requiring the extraction of four first premolars.
Intervention: En Masse retraction (EM)
Control: Two-stage retraction (TSR)
Outcome: Cephalometric measurements from radiographs taken before extractions (T1) and after all spaces were closed (T2).
I think that it worth looking closely at their mechanics. They treated all the patients with Ovation 022 brackets and bands on the first and second molars. They did levelling and alignment until they could fit 020 round SS wires. Then they did the extractions and started space closure 7-14 days after the extractions.
For the EM group, they tied all the anterior teeth together and retracted the teeth as a single block on 017X025 SS wires using Ni-Ti springs to soldered hooks on the archwires.
In the TSR group, they retracted the canines on 020 wire with omega loops wired to the molars. They retracted the canines with Ni-Ti spring. They then tied the canines to the posterior block of teeth and retracted the remaining anterior teeth in one block on 017×025 SS using Ni-Ti springs.
Unfortunately, I could not see any information on their method of randomisation and allocation concealment. Surprisingly, they did not report a sample size calculation. I will come back to this later.
They then did a complex cephalometric analysis and measured tooth movements relative to a vertical reference line. I do not have the space to go through this in detail.
The person who did the ceph analysis was blinded to the allocation.
What did they find?
48 participants started and completed the study. They provided a large amount of cephalometric data on the movement of the teeth. As you know, I am not a fan of cephalometric research, and I found it very difficult to interpret the tables. If you are interested, you can easily have a look at the paper.
In summary, they found no statistically significant differences in the incisor and molar movements between the two techniques. When I looked at the effect sizes, these were all in the order of 0.01 to 0.7 mm. They did not report the 95% confidence intervals.
They concluded that both methods of space closure were effective and there were no differences in the type and amount of tooth movement. Importantly, they did not find an increased loss of anchorage with either technique.
What did I think?
When I first saw this paper, I was very interested to see that a team had done an overdue piece of research. I really wanted to like the article. However, there are several significant issues with their reporting. These are the lack of information on randomisation sequence generation and allocation concealment. This means that we do not know if the operators could break the randomisation. As a result, the study is at high risk of bias.
Furthermore, they did not report a sample size calculation. This means that we do not know if the study has sufficient power to detect a difference between the treatments. When we consider that this study did not detect a difference, this is particularly relevant. The referees of this paper could have addressed these basic issues.
As a result of these issues, I am not sure what to make of these results. It is very easy to be critical of research methods, and yet, I want to find something from this trial. My only conclusion is that there does not appear to be any difference between En Masse and Two Stage Retraction. However, we need to be very cautious about the results of this trial. If I still worked in clinical practice I would continue with En Masse Retraction, as I think that it is neat and tidy and seems to work in my hands.
Can we have a discussion about this study? But please don’t start about extractions, retraction and airway…
Emeritus Professor of Orthodontics, University of Manchester, UK.