July 27, 2015

Self ligation: more nails in the coffin?

Self ligation: More nails in the Coffin or “oh no: he is going on about self ligation again”!

Those of you who follow the blog closely will have noticed that I have not posted for a while as I’ve been on holiday. I am now back after a good break  and I have returned to write about our “old friend” self ligation. This is because two papers have recently been published in the free to access journal, the Angle Orthodontist. This also follows on from this post, which created a fair amount of controversy.

A multicentre randomised controlled trial to compare the self ligating bracket with a conventional brackets in the UK population:

Part one treatment efficiency DOI: 10.2319/112414837.1

Part two pain. DOI: 10.2319/112414-838.1

Lian O’Dywer; Simon J. Littlewood; Shahla Rahman; R. James Spencer; Sophy K. Barber; Joanne S. Russell.

The North of England

Angle Orthodontist epub ahead of print:

These two papers reported the same study; One was concerned with treatment efficiency and the other with pain perception. My initial feeling is that it is a shame that this data was not presented as one paper covering the two outcomes. This is because the current presentation leads to repetition in the text. As a result, I will combine my description of the two papers in one blog post.

What did they ask?

The authors carried out a randomised trial that aimed to determine whether using self ligating bracket system increased the efficiency of treatment and reduced patient pain. Those of you who are familiar with self ligation will know that these are some of the claims made to promote this type of orthodontic appliance.

The study was a randomised trial that was carried out in the North of England. As an aside, this is the best part of England (I live there), even though some people think that it is a little bleak up North.

They randomly allocated 138 patients to receive treatment either with a Smart Clip (self ligating) or Victory (conventional. All patients were treated by two specialty trainee operators who were closely supervised. They followed the manufacturers wire sequence.

Randomisation concealment and blinding were good.

The sample size was developed using data on the primary outcome of treatment efficiency. Importantly, they did not carry out an additional sample size calculation for pain perception; I will return to this later. They collected data on the number of appointments, treatment duration, bond failures and pain using a questionnaire. The statistical analysis was appropriate, however, I wondered if they should have carried out multivariate analysis on the treatment efficiency data.

What did they find?

As with most randomised trials of self ligation, they found no difference between self ligating and conventional brackets. This table contains the data for efficiency and pain. I have not included bond failure, because its not very interesting.

Appliance typeMaterial costTimeNumber of appointmentsIndirect costOverall cost

What did I think?

I thought that this was an interesting study that was well carried out and reported. However, I do have some concerns. These were:

  1. The group who were allocated self ligating brackets were on average one year older that the conventional bracket group.
  2. They used to questionnaire to measure pain that had not been validated
  3. They powered the study on treatment efficiency data only. Unfortunately, they did not carry out a similar power calculation for pain. This means that they had sufficient power to detect a difference in treatment efficiency but not for pain.

The authors also raised these issues in their discussion, which I thought was very balanced.

This means that we, as readers, need to consider whether these issues have influenced the results. My feeling is that we can be more confident about the findings for efficiency than we can for pain. Nevertheless, this study does add information that suggests, again, there are no or minimal advantages to the use of self ligating brackets..

I think it is very interesting to look back on the development and promotion of these systems, including the introduction of new treatment paradigms that fitted the theory behind the bracket. We also know that this was followed by claims being made for their advantages both in the advertising literature and by Key Opinion Leaders. We now know that several years following all the excitement that was generated by these claims, several trials have been published that now show the claims were “overoptimistic”.

I also find it interesting that, as far as I know, none of the key opinion leaders have accepted these findings and stated that they were “over keen” on the product.

Finally we need to consider if harm has been caused. At present, there is no real evidence of harm to patients. however, only time will tell with the potential for relapse following the adoption of an extraction policy.

It is also clear to me that self-ligation treatment was promoted and provided at additional costs to patients and their parents. We, therefore, must consider if patients and parents have been the victims of the over promotion of self ligation.  This, again, is for you to decide.

Would any of the Key Opinion Leaders or those who still promote self-ligation on their websites like to comment? It is easy just click on the comments below!


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