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”…
Emeritus Professor of Orthodontics, University of Manchester, UK.