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
Orthodontic patients having fixed appliance treatment and extractions of upper first premolars.
Ni-Ti coil spring
Elastomeric power chain.
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.
Emeritus Professor of Orthodontics, University of Manchester, UK.