Feeling the heat during initial alignment?
This post is about a new trial that looked at the effectiveness of thermal Nickel Titanium archwires. This is the first post by Professor Padhraig Fleming and he has done a great summary. I have to up my game!
Nickel-titanium wires have been the mainstay of initial aligning archwires for more than 3 decades. Interestingly, alterations to bracket design have been accompanied by a frenzied market and feverish adoption. Nevertheless, many believe that improvements in wire properties have had a more telling effect on the rate of tooth movement. However, there has been relatively little research to confirm a clear benefit of NiTi wires or indeed newer generation thermal NiTi wires over alternatives.
A team from Baghdad did this study. The European Journal of Orthodontics published it. The authors aimed to compare the relative effectiveness of heat-activated and superelastic NiTi without thermal behaviour in terms of initial alignment of the lower anterior teeth.
Authors: Sarah A. Nabbat and Yassir A. Yassir
Eur J Orthod. 2020; 1-9. doi:10.1093/ejo/cjz102
What did they do?
They conducted a two-group parallel randomised controlled trial with a 1:1 allocation as follows:
Orthodontic patients with a mandibular Little’s irregularity index of 3-6mm
Heat-activated NiTi wires (0.014- and 0.016- inch): TruFlexTM Thermal Nickel-Titanium, Ortho Technology, USA
Superelastic NiTi wires (0.014- and 0.016- inch): TruFlexTM Nickel-Titanium, Ortho Technology, USA
Initial alignment measured with Little’s irregularity index at 8 weeks
Pain experience (week 1) and root resorption at 8 weeks, assessed with peri-apical radiographs of the lower anterior region.
They used a sealed envelope system to conceal group allocation, and both investigators and data analysts were blinded to the groups. Then they placed A 0.014” NiTi wire for 4 weeks followed by a 0.016” NiTi with wires engaged using elastomerics. The degree of wire engagement (full or partial) was not clear. They reviewed the participants at 4 and 8 weeks, with alginate impressions taken at both visits. The irregularity was assessed using Vernier calipers.
What did they find?
They analysed data from thirty-one participants. There were 16 in the superelastic NiTi group and 15 in the heat-activated group.
Importantly, they did not find any significant difference in arch alignment. The difference between the groups at 8 weeks was only 0.05mm. This was clearly neither clinically nor statistically significant (P= 0.809). They also found that wires did not affect pain experience or root resorption.
What did I think?
This is yet another study assessing the utility of marketed products in speeding up treatment. I continue to feel that many of these adjuncts have preoccupied us as researchers a little more than they should. We may be ignoring far more important aspects that influence treatment duration and outcome. In particular, human factors; specifically, us as the clinician. I wonder if our training, understanding and clinical perceptions influence both our results and efficiency to a far greater extent than any wire, bracket or adjunct.
I thought that they did the study well. They reported in line with accepted guidelines. While they did a sample size calculation, I can’t help thinking that the sample size is very small and the standard deviations are considerable. Nevertheless, the between-groups difference is tiny and does, therefore, suggest that there is no meaningful difference relating to the rate of tooth movement with thermally-active wire behaviour. I struggled to see the merit of taking repeated periapical radiographs at such short time intervals (8 weeks). This led me to doubt that firm conclusions can be made in this respect at such an early stage in treatment.
From a clinical perspective, I would not usually make a fixed decision about progressing from 0.014-inch to 0.016-inch NiTi at 4 weeks (and would typically leave initial aligning wires in place for a more extended period than this). Instead, I tend to review the degree of engagement and slot alignment before making decisions to progress. I am sure that many of us have our own protocols in this respect. As a result, we need to consider whether these results are relevant to our own practices,
What can we conclude?
Based on a relatively small sample, the use of thermal NiTi wires does not appear to accelerate the rate of initial orthodontic alignment. While the search to prove the existence of a magic bullet to accelerate orthodontic treatment will continue, I can’t help feeling that the answer continues to lie within.
Professor of Orthodontics, Queen Mary University of London, UK