January 14, 2019

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.

Cephalometric analysisComparison of anterior retraction and anchorage control between en masse retraction and two-step retraction: A randomised prospective clinical trial

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…

 

 

 

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Have your say!

  1. Avatar

    Thank you for your critical appraisal of this study. I would agree re: the risk of bias, and lack of a power analysis. To provide some additional perspective, this is the third paper comparing the two modalities and reporting no clinically or statistically significant differences.
    One important factor to consider, is that traditionally, 2-step retraction (Tweed technique) used closing loop arch wires to retract the incisors after canine retraction. All these papers (for ease of comparison) used sliding mechanics for all stage of space closure.

    Based on the trends observed in these 3 papers (and anecdotal experience using the two), I would agree with the findings in the context of the specific mechanics employed.

    With 2-step retraction, you are taxing the same group of posterior teeth twice as opposed to once with En Masse retraction. It is however important to retract the canine enough to allow incisor alignment, in order to prevent round-tripping/anchorage loss etc.

    There might be some differences between sliding and friction-less mechanics with either En Masse or 2-Step retraction, which would be worth studying.

    • Avatar

      Excellent analysis, you are absolutely right. Sliding mechanics will never give a rest to the posterior unit. Anchorage loss will be the same. Having practiced the Tweed Philosophy for 35 years, I am convinced that our approach is much better at controlling anchorage and root paralleling.

  2. Avatar

    Oh dear, my heart sank when you mentioned cephalometrics. Surely this is actually really easy to measure blinded from study models? I’d be more interested in the time taken to close space and the overall treatment time. You could probably better measure anchorage loss by overjet or canine relationship, which is much more clinically relevant.

    Personally, I choose between two-step and en-masse depending on canine relationship and anchorage requirements, and I don’t think this study will change my clinical practice

  3. Avatar

    An issue that needs to be addressed with regard to retraction is extraction space opening after treatment. Retracting canines first may increase stability of space closure by giving more time for canine/premolar contact before debanding and better root paralleling.

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    I have not done the trials, but from my clinical experience I feel very strongly that the two step process if Class 2 elastics are used starting at the time of space closure of the anterior than there is a significant clinical difference. However if no class 2 elastics are used after canine retraction compared to in Mass, then there probably are no clinical differences. The point being if you want almost absolute Anchorage, then do canine retraction and start Class 2 elastics during space closure of the anterior teeth. You also have to do the canine retraction on a stopped archwire.

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    Besides its weaknesses the study corroborates the results of Xu et al., AJODO 2010, who found that en-masse retraction preserved anchorage slightly better than two-stage retraction, although the differences were not statistically significant. Unfortunately such results do not change the clinical practice of most orthodontists, who seem to know better. How can those colleagues justify the longer treatment duration, higher treatment cost and the appearance of an unsightly space between the cuspid and the lateral incisor, if there obviously is no measureable advantage for the patient?

  6. Avatar

    I think it’s interesting that when the engineers at Align came up with what they called their G6 first bicuspid extraction case force system, they opted for a two stage space closure; the incisors only start to retract once a third of the extraction space is utilised by the distal movement of the canine. It’s a pity they don’t publish their rationale for this decision but I’m assuming that the sensors on their metal teeth models led them to the conclusion that 2 stage retraction was less taxing on the posterior anchorage.

    • Avatar

      Hi Morris; Perhaps they create the space to encase the tooth in plastic more for better control over root parallelism as there is no bracket in place? Don’t know that it would necessarily be an anchorage issue.

  7. Avatar

    I trained on 018 but now I am on 022. In addition I do a lot of lingual. Ironically the lingual system I use works enmasse very well. As a result I now do it on the labial and wonder why sliding mechanics is taught. I feel like I do my work twice! Like you said neat and tidy if your arch wire is the right size, but you must be set up properly in my mind. I see arch form dumping if the wire is too small, especially niti.

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    I did not see any reference to a comparison of the time it took to obtain complete retraction of the anterior teeth in both methodologies. I would think that this would also be of importance.

  9. Avatar

    Hi Kevin:

    Why the censorship? Isn’t the health of the upper airway a criterion for orthodontic success? Or are you saying that the cosmetic outcome alone is sufficient? I, for one, am deeply interested in the impact (if any) on the upper airway from retractive orthodontics. These types of studies help us understand the behavior of the craniofacial complex and may help us with predictive modeling as a basis for treatment planning by formulating algorithms that can be encoded as artificial intelligence to help the orthodontist present risks, benefits and alternatives to their patients.

    • Avatar

      Hi, Thanks for the comment. I just wanted to keep the discussion focussed on the aims of the paper and not get sidetracked into other areas.

  10. Avatar

    I think rate of space closure is extremely important. Teeth move by tipping and and then uprighting on a stiff wire. If we do not allow for uprighting then binding occurs which eventually results in anchor loss whatever the method of space closure. Obviously other parameters like friction plays an important role, so welll aligned arches before retraction helps too . Good Orthodontics is all about patience

  11. Avatar

    What is “retractive orthodontics”? There is no such term. The data is very clear….extractions do not adversely affect the airway and certainly don’t cause sleep apnea. Time to accept facts and move on. In the meantime, four on the floor it is.

  12. Avatar

    If they did the aligning before the extractions – and we don’t really know how much aligning was needed – does that set the survey up for some round tripping?

    Stephen Murray
    Swords Orthodontics

  13. Avatar

    When retracting in 2 phases, we have a lighter force for the posterior teeth, but with a longer duration and when we retraction en masse, we have a heavier force, but with a shorter duration. Do you think this can influence the loss of anchorage?

  14. Avatar

    Just as an aside, for En Masse retraction with sliding mechanics in an 022 slot, the wire should preferably be at least 19×25 SS to prevent the afore-mentioned effects of dumping, rolling the molars lingually etc. Also helps to make sure the arches are fully leveled so the SS wire can slide freely.

  15. Avatar

    Bands,Tweed,stopped archwires ,2 stage retraction,slot size discussion, 4 on the floor !
    Deja vu,all over again!
    I really wonder why we are still discussing issues and using techniques that I studied ,as a resident ,over 30 yrs ago–most other dental and medical specialities have totally transformed over that time eg.the ubiquitous use of implants.
    My practice techniques have undergone such a transformative change and without discussing clinical improvements,daily practice stress and work flow are so,so much easier.Why cant we let go of the old and embrace the new??
    Dont even want to start about headgear!LOL

  16. Avatar

    Exactly. Stability, facial balance, periodontal and occlusal harmony are no longer worth discussing since they are “old” and “outdated” concepts. Instead, Digital vs. Analog and Share of Chair would be so much more germane.

    Just because something is “New” doesn’t mean it is “Better”. It is because of this witless “embrace” of the “New”, without consideration for the outcome, that our specialty is besieged by charlatans and predatory companies.

    Unless humans have undergone a drastic genetic mutation in the last 60 years, it would behoove some of us to learn history, lest we are doomed to repeat it. Now that would be Deja Vu.

    • Avatar

      None of the issues mentioned eg .stability were mentioned as outdated ,just the means of acheiving them .Not sure what the “share of chair “is about.?I think this is an attempt at sarcasm but my question is still the same.Why are folks using tmnt.modalities that have not changed in 30 yrs.(actually more like 40 )?Attempts at sarcasm rarely lead to productive debate !!

  17. Avatar

    That’s a silly argument. Just because something hasn’t changed in 40 years doesn’t mean

    A. It doesn’t work.
    or
    B. There is something better.

    As an example, the design of the nail has not changed in decades. Stethoscopes are still used in medicine.
    If the assertion is that “there are new means of achieving the same”, what “modalities” might those be and how do we know they are “better”?
    Inquiring minds want to know.

    • Avatar

      By silly ,I think you mean fallacious.I do take your point but in the specific sense.Generally,as this discussion shows,we ,as a profession have a significant number of folks who are clinging to the life boat of oudated tmnt.modalities .Not all of us need our blanket to get us to sleep!
      Be not the first to adopt the new nor the last to discard the old {plagiarised}.
      I suspect we operate in distant worlds and I suspect,we are both happy where we are.After over 40 yrs.in our wonderful profession ,I am perfectly aware that there is plenty of room for us both to function well.
      I suspect that you may be practising in an academic envoirenment but could be wrong?

  18. Avatar

    By silly, I mean frivolous. This discussion shows nothing of that sort, I’m afraid.
    Unless I’m mistaken, this was a comparison of two methods of space closure.
    What exactly is it that you allude to as being “out-dated” ?
    Is space closure outdated? Are extractions? If so, it seems like some of us don’t even need to sleep!

    As an aside, I’m not in an academic environment.

    And I’m still at a loss for whatever it is you claim to be the “newer, better alternative.” These vague generalizations don’t convey the point. Perhaps being a bit more specific might help?

  19. Avatar

    We agree to differ !
    Thanks for the discussion.

  20. Avatar

    Dear Dr. O’Brien,

    I agree that this is an overdue research, like many other dilemmas in Orhtodontics. We think it is easy to know which one is better by just comparing and trying to simulate similar conditions, BUT it is not.
    I have nothing to add after so many useful comments, but I see this paper like comparing apples to oranges. If we want to draw a conclusion about the superiority or similarity of those 2 techniques, we have to apply each concept as it is initially described, and therefore showing the advantages or disadvantages of each one.
    1- According to the two-step retraction (TSR) proponents, I can site here the Tweed-Merrifield philosophy, extraction is done before bonding and the retraction of the canines starts at the day of bonding, and way before complete leveling and alignment. And this is the major advantage of this technique; especially when we have crowding and deep curve of Spee. The anterior and posterior anchorage units will go through many round-trip movements…
    The authors here aligned and leveled until the 020 SS wire, and later extracted the 1st bicuspids and later started the retraction of the canines, burning one of the main goals of the TSR. Therefore, the comparison is not legitimate anymore.

    2- The retraction of the canines was done with a 020 SS, meanwhile the recommended wire size for TSR, is usually smaller and this might include some bias due to higher friction.

    3- The coil spring to retract the canines was hooked on the 1st molars, and not on the 2nd molars making the anchorage units not similar to the other group, and not conform with the initial TSR technique.

    4- The TSR counts on the intermittent forces and not on continuous forces.

    5- I was hoping to see what happened at the extraction sites after space closure, in term of root parallelism.

    6- For the retraction of the incisors alone, the authors went back to a smaller archwire (.017x.025 SS), burning one more time another main advantage of the Two-Step Retraction: retraction of the incisors with .020x.025 SS wire, controlling the torque of those incisors, and creating differential moments with the posterior second order bends…and then the anchorage cannot be the same. Or at least should be tested.

    This is like comparing manual vs automatic gear cars, to see which one is faster: we cannot drive both cars the same way or with the same driver, and draw a conclusion.
    Best Regards

  21. Avatar

    You are welcome. Although I still don’t know what I’m disagreeing with. Cheers.

  22. Avatar

    As was mentioned before it is important to retract the canine enough inorder to attain rx objectves.
    Burning anchorage will be necessary in some cases.

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