January 22, 2018

What is faster for space closure?  Ni-Ti springs or powerchain?

Those of us who still diagnose malocclusion and extract teeth will want to know which is the best method of force application for sliding mechanic space closure.  This systematic review gives us the answer.

Several trials have been done to help answer this question. This team of authors from Scotland and Australia did this systematic review to pool the results of these trials.


H. Mohammed et al

Orthod Craniofac Res. 2017;1–8. DOI: 10.1111/ocr.12210

They wanted to answer the following question;

“How effective are Ni Ti coil springs and elastomeric chains in orthodontic space closure”?

What did they do?

They carried out a standard systematic review. The PICO was

Population: Orthodontic patients of any age treated with conventional ligation fixed appliances and requiring space closure secondary to premolar extraction.

Intervention: Orthodontic space closure with NiTi springs

Comparison: Orthodontic space closure with elastomeric power chain

Outcome: Primary outcome was the rate of space closure.

They only included human randomised trials and excluded all other study designs.  They did a standard electronic search with no language limitations and assessed bias using the Cochrane Risk of Bias Tool.

What did they find?

They obtained a final sample of 4 RCTs to include in the review.  Two of these used a split mouth design and two were parallel group trials.  All trials reported the rate of space closure per month.

When they looked at risk of bias, one study was low risk, one had unclear risk and the remaining two had high risk of bias. I have interpreted this as suggesting that the evidence that we can obtain from this review is of moderate strength.

When they included the data in a meta analysis they found that space closure with Ni Ti springs was faster than with elastomeric chain by 0.2 mm/month (95% CI 0.12-0.28).

What did I think?

This was a nicely carried out systematic review that showed a statistically significant difference between the two methods of force application. When we interpret this data we need to consider several important factors.

Firstly, the strength of evidence was moderate. However, most orthodontic systematic reviews report this level of bias.  We also need to consider that the risk of harm with either intervention is low. As a result, I am not too concerned about this level of bias.

Then, we need to consider whether the difference is clinically significant.  The difference of 0.2mm/month is small. I have calculated that if we wanted to completely close a first upper premolar space with Ni Ti we would save one month.  I am not sure that I would regard this as clinically significant.

However, we still need to consider the different properties of the two methods.  I find it easier to use Ni Ti springs as they do not always need adjusting at every appointment.  Importantly, I do not like power chain because it accumulates plaque that tends to flick off into my face when I remove the chains. This means that I favour coil springs.  There is  a difference in cost but I accept that with the advantages of Ni Ti.

My final point, is that none of the papers included any information on the way that the patients felt about the interventions.  For example, did they find it easier to clean their teeth with either of the methods of force application?  These are also important questions and it would be great if they could be included in future studies.


I feel that the results of this review reinforce my current practice. I will continue to use Ni Ti springs the next time that I need to close space following the “amputation of premolars”…

Related Posts

Have your say!

  1. Avatar

    Different makes of elastic chain are quite different some lose their pull very quickly

  2. Avatar

    Thank You. This investigation has been done before, maybe not so well, with similar findings, I believe. These days I use latex elastics and ask the patient to change them for me three times a day. I think this beats both NiTi springs as well as polyurethane chain and it’s much less costly. Are there studies on this?

  3. Avatar

    Dear prof. How can you adjust the length of the closing coil spring during retraction? Do you use it 50% of the extraction space, more or less?

  4. Avatar

    “Those of us who still diagnose malocclusion”……..In some circles this is being referred to as the “new normal”. Certainly not a good fit for any health care area attempting to maintain (or, regain) the image of a “learned calling”.
    At any rate, within a clinical setting comparing power-chain to springs for “directional” space closure, I found the combined use of closed coil nitinol-type springs + class 2 (or, class 3) elastics very effective. Using power-chain only was not as satisfying as closed coil nitinol. For opening spaces stainless steel open-coil springs (.009X.030) were clinically just as good as nitinol. Having seen a publication which sited open-coil nitinol as a better choice, I did not find that to be the case clinically.

  5. Avatar

    Dear Kevin, I am a little embarrassed to realize that you consider closing the extraction space before cuspid retraction! The best way to close the space and to adjust the cuspid root parallele to the Bicuspid is to retract first the cuspid. Then a closing loop distal to the lateral to control the retraction of the incisor with Tork controle and Tip forward of lateral incisors . With this protocole we controle the root parallelism with no lost posterior anchorage. This is nessacery for long term stability.
    The second point is to treat a class II and finish in Molar Class II relationship… On the case that illustrate your blog, you have no overset and class I cuspid occlusion! So for me the problem is not how fast we close the extraction space But how you diagnose and decide.
    All my best
    Dr Andre J HORN

    • Avatar

      Dr Horn, I believe there are several studies that show no difference in anchorage loss comparing canine first vs “en masse” retraction. The MBT treatment philosophy/approach uses en masse retraction and has multiple textbooks documenting successful outcomes using this approach.

      • Avatar

        Hello, John. My understanding is the same – “no difference in anchorage loss comparing canine first vs “en masse” retraction”. However, mechanically as well anatomically I see a substantial number of variables which would contribute to individual”predictable” outcomes.

  6. Avatar

    I would like to know what the outcome will be between the above and the use of 16×22 steel or elgeloy
    closing loops ala Wick Alexander?
    Andre Delport

  7. Avatar

    Some of us look at the data…AND then make claims.
    Just sayin 😉

  8. Avatar

    I think Kevin makes a strong point at the end of his review: the feelings of the patient are the most important issue especially if there is only one month’s treatment at stake.
    I have had two courses of orthodontics as an adult and the memory is still fresh.
    I was taken by surprise at how important seemingly trivial details can be to patient comfort. Here are three examples –
    1. The stems between the loops of an elastic chain can be very sharp unless the chain has been carefully trimmed back to the last loop.
    2. Coils and ligatures can have a very sharp wire at the end. It might be small but discomfort can be out of all proportion to the size.
    3. Upper canine bracket traction hooks occasionally have discs at the end and the tiny edge of the disc can easily cause an ulcer in the oral mucosa opposite.
    As a clinician, I have noticed that treatment reaches a more satisfactory conclusion if the patient is comfortable with the appliance, so in my opinion, comfort for the patient is more important than an extra 0.2mm of closure each month.

Leave a Reply

Your email address will not be published. Required fields are marked *