June 10, 2024

A new, really good clinical trial of aligning archwires. The wire doesn’t matter.

The choice of archwire is important when we plan initial alignment. A recent Cochrane review, while informative, left a gap in our understanding of the most efficient archwire width. This new trial aims to fill that gap in our knowledge of aligning archwires.

My first trial looked at the effectiveness of different types of aligning archwires. We did not really know how to do trials and had to use a book to help us with the methods. It was a real surprise that we managed to finish this study.  It is nice to see that authors still quote this paper. But it was full of bias and mistakes! Perhaps I should revisit it. But let’s move to this new much better trial

A team from Iran and Canada did this study. The AJO-DDO published the paper.

What did they ask?

They wanted to find out

“The alignment efficacy of different sizes of superelastic NI-Ti wires at 4, 8 and 12 weeks after placing appliances”.

What did they do?

They did a single-centre randomised double-blind 3-arm parallel clinical trial.

The PICO was


Orthodontic patients treated non-extraction in the lower arch, all permanent teeth were present and it was possible to bond and engage all the teeth.


Three types of superelastic Ni-Ti wire with diameters of 012,014 and 016 inches used in 022 Roth Brackets.  The clinician decided whether to fully or partially engage the wires into the brackets using elastomeric ligatures. The wires were retied every 4 weeks.


The primary outcome was Little’s Irregularity index at 4, 8 and 12 weeks. One operator recorded this from sequential study casts using a vernier calliper. The secondary outcomes were permanent wire distortion.

They did a sample calculation before the study started. This was clear and based on data derived from a pilot study. This revealed that they need at least 28 participants in each intervention group.

They developed a pre-determined randomisation, concealment was done using sealed envelopes and the allocation was done by a research assistant remote from the study.

The participants and outcome assessor were blinded. It was not possible to blind the operator.

Finally, the team analysed the data with the relevant regression analyses.

What did they find?

They enrolled 90 participants in each group. 3 of these were lost to follow up and they used a per-protocol analysis.

There were no differences between the groups at the start of the study. They presented their data clearly. I have decided that the important data is at the end of the study period, which was 12 weeks after placing the appliances. I also calculated the 95% CI, so that we estimate our confidence in the data. These are the Little’s Index values at the start and end of the study. This is a simple way of looking at trial data. If there are no differences between the intervention groups at the start, then any differences at the end are due to the intervention.

012 NiTi (29)014 NiTi (31)016 NiTi (30)
T010.93 (9.3-12.4)11.06 (9.6-12.4)11.10 (9.4-12.96)
T31.92 (1.26-2.57)2.38 (1.6-3.0)3.08 (2.05-41)

The regression analysis showed that time had a significant effect on Little’s Index scores. Importantly, the archwire group or interaction between the wire and time was significant.

When they looked at wire deformation. 18 wires in the 012, 7 in the 014 and 2 wires in the 016 were deformed and needed replacing.

Their overall conclusion was

“There was no difference between 012, 014 and 016 superelastic archwires in resolving crowding”.  Because of wire deformations, 014 and 016 wires demonstrated better performance than the 012”.

What did I think?

This clinical trial was well-executed and produced clinically relevant findings. The paper was well-written and I appreciated the clarity of the presentation. The authors were concise, avoided over-analyzing the data, and kept their conclusions simple, which was refreshing.

I will start by addressing the limitations mentioned in the text. The authors provided a thorough discussion of these limitations and highlighted that the wires were retied every 4 weeks, which may not reflect current practice. However, I am not overly concerned about this because a 4-week interval may actually represent ideal practice.

I was concerned that they did not blind the operator to the archwires. I know that this is not possible in clinical treatment. However, it is a risk of bias, and we need to bear this in mind when we consider the results.

I found no other limitations with this study.

Clinical relevance?

The findings are clinically relevant. They suggest placing 016 wires at the first visit and simply retiring them over the next 12 weeks, reducing the number of wire changes.

I have just looked back at Padhraig’s top ten tips about alignment. If you look at point 6, you will see that this study supports his clinical supervisor’s recommendation of starting in 016 NiTi. Perhaps it is time for more simple, straightforward studies like this one.

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Have your say!

  1. I think that one weakness of this study is that it only looked at solid NiTi wires. Sebastian did a randomized controlled prospective study of initial alignment wires* and found that multistranded NiTi wires were significantly more effective than single stranded NiTi wires at initial alignment, and provided approximately 3x the alignment at each of the 3 timepoints (4, 8, and 12 weeks). It doesn’t surprise me that .012 and .014 Niti took on permanent deformations, and in my experience, multistranding more or less eliminates permanent deformations. Including multistranded NiTi wires would likely have shown a significant difference in effectiveness.

    *Sebastian, Biju, Alignment efficiency of superelastic coaxial nickel-titanium vs. superelastic single-stranded nickel-titanium in relieving mandibular anterior crowding-A randomized controlled prospective study, Angle Orthodontist, Vol. 82, No. 4, 2012

  2. It is always lovely to read your blog.
    In my opinion, the results of this, though well conducted trial, will not have changed my clinical practice. For the alignment stage, I will always choose the biggest round NiTi wire that could fit within the slots of the brackets with a reasonable deflection.
    I will always have in my stock 012, 014, and 016 NiTi wires, and choose according to the case. Yet it is interesting to know that 012 wires are more prone to deflection. I think this is more related to the manufacturer than it is to the dimension of the wire itself. I had seen this with the 014 wires, and I also had fractures in some of the initial wires.

  3. I always used 0.014 NiTi wires for initial alignment using slightly stretched elastomeric rings to hold the wire into the brackets to minimise patient discomfort.It worked well. A very interesting study though.

  4. I wonder if ‘time’ is a variable we should think about more often?
    Alas, I can only point to a clinical case, but the patient gave me pause.
    A female patient in her late teens began upper arch alignment, with a view to surgical correction of a Class 2 dental base discrepancy.
    The appliance was placed (by me) and the patient disappeared and was uncontactable for twelve months.
    When she reappeared, arch alignment was quite simply perfect.
    Of course, in the normal way, I would have been far more energetic – arch wire changes, re-ties and everything I could think of.
    And yet, alignment needed only one wire (I think it would have been and 012 solid ni-ti), one tie-in… and time.

  5. This study has some limitations that need to be addressed. 012 is quite useless as an aligning arch wire, given the fact that it’s force/unit deflection tends to be sub-clinical, thus necessitating larger diameter aligning arches. The authors did not study 018 Niti, which is a very commonly used aligning arch (although perhaps not the first wire). Additionally, the end-point that was chosen was not a clinically relevant one. In practice, the largest round Niti should also align the 2nd molars enough to allow transition to a rectangular Niti. The 2nd molars were not even engaged, or assessed in this study. 014 or 016 Niti wires lack the terminal stiffness to align the 7s enough to permit transitioning to a rectangular Niti. If the 7s are not included, the alignment efficiency data is incomplete at best, or erroneous at worst. While the deformation data is interesting, it is quite spurious since that may have more to do with the mm of wire-deflection in the in-out and vertical planes – a factor that will vary across patients.

  6. Great post dr O’brien. Thank you
    It would be great if some researcher published about the effectiveness of the various brands of prefabricated NITI super elastic arches.

  7. Did they relate the index to the amount of wire deflection?
    A single mandibular incisor rotated and displaced lingually can have the same index as three or more teeth with mild horizontal contact discrepancy, yet a response to the wire gauge will differ greatly

  8. Was there any consideration to pain with the different wires?

  9. I have treated cases from other countries that I see 3-4 times in a year using multistrand wildcat wire.
    All show significant correction and some have perfect alignment.
    It would have been nice to see some of these cases with no reties to compare correction at the -2 week period.
    I also echo the sentiment of pain level in heavier wires and question effect on bone level and root resorption.

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