October 10, 2016

What is best for space closure? NiTi or stainless steel springs…

What is best for space closure?  NiTi or stainless steel springs…

This week’s post is about orthodontic space closure and I’m going to discuss a recent paper about a  trial of two types of space closing spring. I felt that this was an interesting clinical question

Most operators will extract teeth, when required, as part of orthodontic treatment. We all know that good space closure requires skill and careful anchorage management. We also would like this phase of treatment to be short.
manchesterSeveral of my close colleagues based in the Republic of Mancunia (Manchester),  North of England, did this trial. They published it in the Journal of Orthodontics.




Nickel titanium springs versus stainless steel springs: A randomized clinical trial of two methods of space closure

Noraina Norman, Helen Worthington & Stephen Laceback Chadwick

Journal of Orthodontics, 43:3, 176-185, DOI: 10.1080/14653125.2015.1122260

In the introduction, they outlined the findings of seven clinical trials that have looked at space closure and summarised these in a very nice table that showed that the mean rate of space closure varied from 0.35 – 1.85 mm per month. I also spotted that the rates of space closure in 5 of these trials were very similar or greater than that  quoted in the much publicised trial on AcceleDent that I have previously discussed.

They also pointed out that NiTi coil springs are felt to be the most effective method of force application for space closure, when sliding mechanics are used.

They decided to carry out this trial to find out if there were any differences in the rate of space closure between NiTi (expensive) and stainless steel springs (much cheaper).

What did they do?

They carried out a two centre parallel group randomised controlled trial. The PICO was;

Population: patients aged between 12 to 35 years old who had pre-molars extracted as part of their treatment.

Intervention: stainless steel coil springs

Control: NiTi  springs

Outcome: rate of space closure measured on study casts

They randomly allocated the patients to have space closure with stainless steel or NiTi coil springs.

Randomisation, concealment and blinding were good.

They took study casts at the start and end of space closure. A blinded examiner used a digital calliper to  measure the distance between the cusp of the canine and the mesio-buccal groove of the first permanent molar.

They used a relevant multivariate statistical analysis.

What did they find?

They enrolled 40 patients in the trial. They allocated 19 (10 boys, 9 girls)  to the NiTi springs and 21 (9 boys, 12 goals) to the stainless steel coil springs. The average age of both groups at the start of treatment was 16 years. Unfortunately, they did not include all the participants who started the study in the data analysis because of time constraints.

The average rate of space closure for the NiTi springs was 0.58 (0.24) mm/4 weeks and for the stainless steel springs this was 0.85 (0.36) mm/4 weeks. The regression analysis revealed that there was no significant differences between the interventions.

What did I think?

This well carried out small study showed us that the lower cost interventions was as effective as the more expensive option. This was an interesting finding.  While some may feel that this is not a “positive” finding. I think that if we consider that the NiTi springs were four times more expensive than stainless steel, this is a useful finding.

Another important point about the study was that they ran it in a “real-world” setting and the results are relevant to the average orthodontic patient.

I also thought that this was another study that showed the wires, brackets, springs and other magical things did not influence the rate of tooth movement. This makes me wonder whether the skill of the operator and the care that is taken during treatment may be the greatest influence on speed of treatment and outcome?

I was a little concerned that they did not follow up all the patients. It appeared that this was because of time constraints of the study period. I assume that as this was a Master’s thesis it needed to be submitted on time! I’m not sure if this could have influenced the results.  Nevertheless, the authors showed that there was an equal number of these patients in each group.

The authors investigated a common clinical problem. We need more studies like this and I would like to congratulate the authors (even though they work with me).

Ultimately this study shows that expensive is not always better. This is true for a lot of life experiences…

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Have your say!

  1. I wonder how either metal spring compares with elastic chain.

  2. Kevin,
    Very interesting. When NiTi springs first came out, the manufacturers claimed, amongst other things, that they were less prone to mechanical damage/over activation and provided a fairly constant force. In general, I found this to be true and felt the extra cost to be justified. Obviously not.
    By the way, being a Manchester study, were the SS springs hand wound?

  3. Hello Kevin!
    I thank you for the wonderful work that you do on our behalf, for increasing our base of legitimate knowledge, and for facilitating learning more about orthodontics.
    You do not need to apologize for the inadvertent advert. Weird things happen. In fact, I would not object if ads appeared (as long as they were not related to orthodontics).
    I think that it could be a source of well deserved revenue to support your hard and dedicated pursuit of orthodontic truth and wisdom.
    Best regards,
    Scott Arbit

  4. Good results depend on the orthodontist’s skills and are not between the compagnies hands….
    The technology,the brackets…will never liberate us from our personal discipline and responsibility…!
    We are not “appliance sellers”…!
    Good orthodontists do good treatments ….expensive appliances do nothing!!

  5. Stephen “laceback” Chadwick ?! ?

  6. Thank you for including our paper. You are correct this was Noraina’s MSc project, it was very difficult getting it finished in time for her submission and follow up was difficult as she went back to Malaysia before some of the Manchester cases finished. However, I am delighted we got it published because it does have something useful to say. Many excellent well constructed RCTs come up with the conclusion the two clinical approaches under investigation are both equally effective. This is very satisfying for the scientist and statistician who like a good score draw but a lot of clinicians would prefer a clear winner in order for them to be able to know which technique to adopt. Cost effectiveness might be a useful way of measuring difference and also a way of manufacturers being held to account for claims of success for their latest expensive product.

    • Hi Steve, yes it does have something to say and you are correct about cost-effectiveness. Now lacebarks are another matter!

  7. Kevin
    Thank You. Good.
    How were the roots Niti group?
    To assess the movement of the canine when submitted to force applied at which point? height insertion? If the force is out of the center of resistence, it creates canine’s crown tip-back, and the steel spring is not constant force, there will be canine’s root tip-back. The resulting is retract the canine with a translation movement. Niti Spring can not promote the time to movement of root, and retract canine’s crown more than root.

  8. I wonder, if the study could be repeated on contra-lateral quadrants as controls, to be more objective to eliminate individual differences, Upper/lower and left/right(chewing habits) differences ?

    • This would be a split mouth study. These have problems with the relevant sample size calculations. In addition, there is a high risk that the effects of treatment on one side of the mouth are influenced by the treatment on the other. As a result, we should try and avoid split mouth studies in orthodontics. But, if the sample size is sufficiently large then individual variation and its effects are minimised.

  9. Hi Kevin,

    I would like to point out that excluding 10/40 patients is quite a large number of patients.

    There are two key issues here:

    – There is loss of power/precision which will be reflected in a wider confidence interval. If the authors came up to a sample size of 40 at the design stage, reducing the sample size after could mean that the trial was inconclusive? Or, if the lost patients represent patients with longer space closure times then the variability of the remaining sample will be smaller and hence the precision and reported confidence interval can be artificially narrower compared to the situation without losses to follow up.

    – The exclusion of patients can potentially bias the results and this would depend on the missingness mechanism. If the losses are a random sample of the remaining in the trial patients then the most likely effect is loss of power. However, if for some reason (unobserved values associated with treatment and/or outcome) the lost patients have different baseline characteristics across groups we may get post randomization bias which in fact can potentially destroy the implemented randomization. Thus we may end up comparing 15:15 patients who are not similar enough since the randomization somehow was “subverted”.

    – In the presence of missing data, having balanced treatment groups after losses is less important than the reason the losses occurred (missingness mechanism) as explained in the comments above and in more detail in the link below:


    Best wishes,


    • Hi Nick, thanks for the comments, yes, they lost a lot of patients and this leads to uncertainty in the data and conclusions. I agree with you that this trial is at high risk of bias and it is a shame that they did not include all the patients

  10. I have a better idea! Why not discontinue extracting (amputating) all these bicuspids so that, instead of creating spaces, we can enlarge (develop) the maxilla to its full size, thereby assisting facial growth in the right direction (forwards and downwards instead of backwards and upwards), allowing the mandible to be enlarged and moved forwards, increasing the nasal, oral and pharyngeal airway as well as tongue space and leaving the patient with the number of teeth they were intended to have.

    I think that would be a much better idea.

    • One question does remain – Did the patients in both groups survive? As we know 100 percent of all patients who have premolars extracted will die. A revolutionary idea would be to expand the maxilla and the mandible indefinitely (stimulate the non-existing mandibular suture) and add a premolar per quadrant. The body reacts differently to those. This way the face grows forward, the tongue grows backward and we bring Zinjanthropus back. We must not let scientific evidence get in the way of our feelings. If only we use these appliances magical things are possible. Unicorns, Ligers living in harmony with multiple premolars.

    • Hi Noel, great idea, how are we going to do this?

  11. I am delighted Dr Ulfr agrees with my suggestion about expanding the dental arches, however his sarcastic comments about Paranthropus (the correct name for Zinjanthropus) are unworthy and 4 million years too late. Clearly he has misunderstood the intended objective – normal arch development to the genetic potential of that individual.

    In fact I think he is missing the point completely. We are all aware that there is a dearth of robust evidence for orthodontic treatment of any sort. What little there is is years out of date and most of the more recent work comprises reviews of old studies. Defending out of date treatment systems with out of date science is unhelpful and fails to convince. Henry Tizard (the father of modern radar) said that a scientist must always be prepared for the fact that his/her science may one day be shown to be wrong. Further than that he said:

    “I hold, in particular, that no true scientist can be an atheist. The more his knowledge grows the more apparent is the depth
    of his ignorance.”

    As Barry Raphael points out so well in another blog, malocclusion is the result of and a compensation for a background structural and/or soft tissue anomaly. Not to address the cause(s) of a malocclusion is illogical; one does not need science to see that.

    • Hi Noel, it is a while since you made a comment on the blog. It would be great if you could provide us with one piece of evidence that shows that we can address the cause of malocclusion which is likely to be genetic?

      • Kevin
        You know as well as I do that there is virtually NO robust scientific evidence for either mainstream or ‘alternative’ orthodontics. Every Cochrane review on orthodontics I have seen qualifies its results with “this study is not suitable as a basis for clinical decision making” and “high quality studies are urgently required” or some such phrase.
        There is a wealth of evidence elsewhere; I recall your saying recently that “we should base our treatments on the evidence when it is there but when it is absent we need to accept that we have to base our decisions on clinical experience and other sources”.
        You asked me a few days ago “how are we going to do this?” referring to the suggestions I had made for “a better way of doing orthodontics”. The answer is so huge that I cannot cover it in a blog, but we could start by a) viewing extractions as a last resort not a first line of attack, and b) discontinuing this crazy process of carrying out retraction of the maxillary teeth (and by default the maxilla) at the precise age when the patient’s craniofacial growth is going in the opposite direction! Makes no sense and is a perfect recipe for relapse. c) remembering what we were all taught at dental school about who wins the contest of muscle vs bone.
        No need to go looking for relevant science to quote to me; all we need here is a little common sense.

        I will not be responding to Fenris Ulfr’s nonsensical reply; I distrust pseudonyms on the internet, especially when they come from a character in a dark-side comic strip about Teutonic mythology whose logo is a death’s head skull and a variant swastika!

        • Dear Noel, thanks for the comments. Firstly, I suggest that you read the orthodontic literature, there are a surprisingly high number of studies that provide us with evidence about orthodontic treatment.

          I did not know about the pseudonym, I will not accept any more emails from people who are being anonymous.

          • Good decision on pseudonyms, but how about a response to my comments a) b) and c)?

          • Sorry I thought that I had covered this when I suggested that you read the literature. In answer to your questions a) I am pretty sure that the reduction in extractions that is reported in many suurveys is a result of orthodontists wanting to avoid extractions. B) similarly the increased use of functional appliances and fixed functionals avoids the use of restriction mechanics c) I am not sure what you mean here?

            Finally, I think that you need to spend sometime reading the contemporary orthodontic literature and discover more about how orthodontics is delivered now. I cannot help thinking that your views represent a criticism of orthodontics that was done 30 years ago.

  12. Hello Kevin
    I think that measuring space closure from the tip of the canine to the mesiobuccal groove of the molar doesn’t allow us to know the movement of the canine’s root. Heavier forces generate more tipping of the canine. The tipping of teeth moves the crowns more rapidly, giving the impression that the spaces are closing quickly. However, at the end of the space closure, the movement of the roots requires more treatment time. The lack of information about the tipping of canines may be a bias of the study.

    • Thanks for the comments. I see what you mean and this may be an issue with the study. However, the mechanics were the same for both groups and so I wonder if the amount of tipping will be the same?

  13. We must indeed address the cause of malocclusion…normal arch development does that. If only the arches can be “fully developed” to their genetic potential – but they can! A new procedure called Geno-expansion ® gently stimulates the hemi-maxillae and the hemi-mandible to slide away from each other thus creating room for teeth, tongue, tonsils, feet etc. In some cases, there is adequate space for a second or third tongue. This in conjunction with Premolarogenesis® will allow us to meet the genetic potential of our hominid ancestors who had four premolars per quadrant. I totally agree that we must discard the evidence when it does not support our hypotheses…of what use is data if it doesn’t support what we do?
    I agree with Dr. Stimson that premolar extraction is a brutal and medieval travesty akin to amputation. Do we remove limbs when we are trying to enhance function? No. After all, esthetics, function, stability, periodontal and TMJ health are not everything. Who is to say that Bimax. protrusion, lip incompetence, drooling, loss of attached gingiva, uncoupled incisors etc. are undesirable? One has to do a better job of explaining to patients why their appearance has worsened substantially – once they understand our concept of Atavistic© Orthodontics, they will leap on board like our primate ancestors. If malocclusion is a modern development, would harkening back to better times not surely resolve malocclusion by removing the cause? In the famous words of James Hetfield (father of down-picking) “ It’s all fun and games till someone loses an eye… then it’s just fun you can’t see.”

  14. In reply to your comments dated Oct 21st, It is clear to me that although some surveys and studies may indicate a ‘reluctance’ to employ extraction/retraction mechanics, we are a long way from a satisfactory state of affairs. In my (non-dental) voluntary work I encounter literally hundreds of children and young people every year, and I am staggered by the number of orthodontic braces I see with just those features. So whatever the teaching is today, it seems it does not always work!
    You are right, the movement to reduce or limit orthodontic extractions in the UK began some 30 years ago and I was part of it! But again, we have a long way to go before such things are the general exception as opposed to the general rule.
    My point c) which I had not made clear enough apparently, was referring to well-known phenomenon that when when muscle and bone come into conflict, muscle will usually win i.e. form follows function. This principle, which so often missed in modern orthodontics, is the fundamental basis for systems such as Myobrace and Orthotropics and which many believe should precede the mechanistic process of fixed braces rather than being (temporarily) overwhelmed by their use, relapse being the final result.
    By the way, I have a pile of studies and reports that indicate the potential for facial damage by mainstream orthodontics. Do you know of any that criticise the non-establishment approach in the same terms?

  15. what ısthe name of study you saıd ın here:’
    I also thought that this was another study that showed the wires, brackets, springs and other magical things did not influence the rate of tooth movement. This makes me wonder whether the skill of the operator and the care that is taken during treatment may be the greatest influence on speed of treatment and outcome?’

    • Thanks. I agree with you, it is likely that the operator could have a greater effect than the wires etc. This needs to be taken into account when evaluating these studies

  16. Exact effects rely upon the orthodontist’s talents and are not among the business’s hands….

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