July 03, 2022

What is best? Ni-Ti springs or power chain for space closure?

This post is about a recent paper reporting patients’ viewpoints on Ni-Ti coil springs and power chain when closing space. This is an important clinical question that is very relevant to our patients.

In a previous post, I outlined a systematic review that looked at the rate of space closure for Ni-Ti springs and power chain. This review concluded that Ni-Ti springs closed spaces faster than power chain by 0.2mm/month. However, I pointed out that while this difference was statistically significant, it was not clinically meaningful. I also suggested that it would be valuable if trials included patient-relevant outcomes. As a result, they would have value to our patients.

As a result, I thought it was great to see a recent trial that looked at patient outcomes and the rate of space closure.

A team from Jordan did this trial. The Angle Orthodontist published the paper, so it is open access.

Comparing patient-centered outcomes and efficiency of space closure between nickel-titanium closed-coil springs and elastomeric power chains during orthodontic treatment: A two-center, randomized clinical trial

Serene A. Badran et al. Angle Orthodontist: Online: DOI: 10.2319/120721-906

 

What did they ask?

They did this study to ask;

“What is the patient reported pain, discomfort, ease of eating, plaque accumulation and rate of tooth movement for Ni-Ti springs and elastic chain when closing extraction space”?

What did they do?

To answer these questions, they did a split-mouth randomised controlled trial with an allocation ratio of 1:1 between the two interventions.

The PICO was

Participants:

Orthodontic patients having fixed appliance treatment and extractions of upper first premolars.

Intervention: 

Ni-Ti coil spring

Control:

Elastomeric power chain.

Outcomes:

Primary outcomes were patient-reported pain, discomfort and ease of cleaning. Secondary outcomes were plaque scores and rate of space closure.

The clinicians fitted all patients with 0.022 MBT brackets. When they were in 19×22 ss wires, they started space closure.

The team collected the following data at the start of space closure (T0), 6 weeks (T1) and 12 weeks (T2).

  • The distance from the canine tip to the mesiobuccal cusp of the first molar. They did this with vernier calipers.
  • Plaque Index scores.
  • The patient’s perception of the amount of pain and discomfort using a visual analogue scale.

A blinded examiner recorded all the measurements.

The team used prepared randomisation. They concealed the allocation in sealed envelopes. The randomisation allocated the space closing intervention to either the right or the left side.

When they analysed the data, they used simple multivariate analysis.

What did they find?

There were no differences between the groups at the start of the study. The mean age of the patients was 17.5 years old. 73% of them were female.

I thought that these were the most important findings.

  • There were no differences between the groups for pain scores, onset and duration of pain.
  • However, the coil spring was significantly more uncomfortable than the power chain and more challenging to keep clean.
  • There were no differences in plaque scores.
  • The mean space between the canine and molar at the end of the 3 months for the power chain group was 16.69mm (SD=2.07), and for the coil spring patients, it was 16.16mm (SD=2.17). This was a mean difference of 0.54mm (95% CI= 0.93-0.16). The rate of space closure for the coil spring was statistically faster. But note the effect size was small.
What did I think?

As with many other recent studies, this small trial may add to our knowledge. However, we must consider several important issues that may influence our confidence in the findings.

The first is that it was a split mouth design. This means that we must look for possible cross-over effects. I am not 100% confident that the impact of the different mechanics does not cross over to the other side of the mouth. Notably, the patients’ pain may also be influenced by crossing over.

We also have to consider whether the present sample size calculation and analysis method are relevant for split mouth studies. This has been recently reviewed in this paper. This suggests that the approach carried out in this paper was not ideal.

We also need to look at the effect size. This was only 0.05mm/month and is not clinically significant.

What can we conclude?

My feeling is that this was an interesting study. However, some methodological issues reduce our confidence in the findings. It appears that there are no clinically significant differences in the rate of space closure. However, the patients felt that coils springs were more uncomfortable than the power chain.

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Have your say!

  1. My experience is opposite to this study.My patients had faster space closure with less pain using Niti coils. Also the hygiene was better with coils.

  2. I feel that the studies posted to date miss a critical point in terms of efficiency. Specifically, what is the difference when the intervals between appointments is 10-12 weeks? What is the difference when we see our patients on a 12 week interval during space closure between niti coil springs and elastic chain? Does the decay rate of elastic chain preclude extended periods of time during treatment when the only thing happening is cuspid retraction?

  3. My experience supports these very findings.

    So, I use latex elastics, refreshed by the patient once a day to close extracrion spaces.
    This works way better than anything else I know.

    Prof Kevin or anyone; Can you find any supporting evidence on this?

    From Geoff Wexler. Don’t forget to tune into Melbourne Invisible Braces congress next month.
    World class speakers. Book at http://www.aslo.com.au

  4. An observation on space closure and chain vs coil, assuming a .0195 X.025 steel wire in place. Both the coil and chain will close the extraction space but there is more to consider. If the goal with space closure is to close the space with anterior and posterior torque control then the forces applied to that wire should contribute to the process . The major limiting factor in speed of “controlled space closure” is the biologic process being brought into play that allows for this event to take place. Too much force and anterior tipping and warping of the arch wire can occur. To the best of my knowledge we currently have to means to precisely control coil forces over long periods of time.and given that reality, undesirable movements can occur. The beauty of using chain or chain modules for closure in that the forces are degrading and thereby self limiting. and should Johnny miss an appointment that limiting factor is very beneficial. It is also beneficial by allowing a well formed arch wire in accurately placed brackets to do its thing in a controlled manner when supervised by the treating orthodontist,

  5. I agree with Alfred’s comment that the potential efficiency lies in reducing appointments and not necessarily in faster movement. I wrote about the concept of altering appointment intervals to suit the mechanics used in 2010 (Effective and efficient orthodontic tooth movement, Proceedings of the 37th Moyers Symposium, Vol 48, Craniofacial Growth Series, Chapter 2, pages 33-34) and also in 2013 (Evidence-Based Clinical Orthodontics, Chapter 5, page 51). We should adjust our appointment intervals based upon what we expect of the period of activation – e.g. allow a NiTi wire to work over 8-12 weeks rather than 5-6 weeks, allow a NiTi spring to work over similar longer time frames rather than continuing with monthly recalls as trained at University whereas detailing bends do not remain as active for as long and so can use shorter intervals.

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