February 15, 2016

Self-ligating orthodontic brackets expand arches?

Self ligating brackets expand dental arches?

It is a while since I came across a study of self-ligating brackets. This paper was recently published in the European Journal of Orthodontics and outlined a study that concluded a passive self ligating system produced a widening of dental arches.  This may be useful in expanding dental arch parameters and reducing the need for extractions.

Three-dimensional digital cast analysis of the effects produced by a passive self-ligating system

Linebarger MB et al

EJO 2016, 1-6, DOI: 10.1093/ejo/cjv089

This paper was by a team based in Michigan, USA and Florence, Italy.

In the introduction the authors outlined that one of the claimed advantages of self-ligating brackets was that it is possible to achieve large gains in arch perimeter without the use of rapid maxillary expansion. Furthermore, the use of these brackets may expand both the dental arch and supporting tissues. Thus decreasing the need for extractions and increasing stability.  They drew attention to the fact that there have been few studies looking at the effects of Damon brackets on transverse maxillary width and they decided to evaluate this using digital study casts.

They, therefore, decided to evaluate maxillary and mandibular arch changes induced by passive self-ligating brackets by measuring dental casts.

What did they do?

This was a retrospective study of the patients from one orthodontist who used Damon 3MX brackets to treat a sample of 25 patients.

The inclusion criteria for this study was the following

  • Patients full permanent dentition (apart from 3rd molars)
  • Treated non-extraction
  • Angle Class I molars

Exclusion criteria were

  • Patients debonded early because of poor compliance
  • Incomplete records

These records were compared to a control sample of 25 sets of patients records obtained from a growth study. These records were selected at T1 and T2, approximately two years later.

All models were converted to digital format by scanning and they made the following measurements

  • Transverse arch widths
  • Arch perimeter
  • Arch depth
  • Angular inclination of crowns

What did they find?

There were no differences between the starting form of the arches between the treatment and the untreated control group. However, after treatment the mandibular and maxillary dental arches were expanded by a range of 2.0-2.2mm.  There were also changes in the torque of the teeth.

In their discussion, they suggested that treatment with self-ligating brackets has the potential for producing a modest widening of the arches.

What did I think?

At first I thought that this was potentially an interesting study, but when I looked at it closely I was not so sure because the study was retrospective and they only included successfully treated cases. This meant that the study must have had selection bias.

But more importantly, it appears that they had simply taken a sample of orthodontic patients who had been expanded and compared them to a group of untreated people who had not been treated?  The only conclusion was that the orthodontic  treatment with expanded wires resulted in expansion!  You could easily repeat the study with conventional brackets with expanded wires and reach the same conclusion…..

As a result, I cannot see how this study can help answer any question on the effects of self-ligating brackets and many of these have been answered by high quality trials.  However, this paper was published in the refereed literature and I still wonder if I have missed something?




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Have your say!

  1. Again Kevin, you are wright on your conclusions! This study should not be accepted by the reviewers ( and the head of the Department)
    Torque correction can be used for arch form restauration! That will expand the arches at the occlusal level, without bringing the roots out of the alveolar bone. So that should be used for a selected group of patients! There is no relation with self ligating brackets

  2. Thank you for posting this study. Like you noted, I don’t think there is any doubt that expanded arch wires will indeed expand. I don’t have access to the full text, but it doesn’t seem like there was any evaluation of pre & post Tx degree of incisor protrusion/proclination and depth of overbite.
    The other outcome measures of interest would be esthetics (as it pertains to incisor inclination, buccal corridors, lip competence, and facial balance), stability of the expansion (especially the inter-canine width) and the pre and post-expansion evaluation of the alveolar support (dehiscence/fenestrations etc.) Hard to draw meaningful conclusions about any of these measures from this study.

  3. I agree with your conclusion for this study, orthodontic treatment with expanded arches results in expansion. It has nothing to do with self ligation.

  4. Hello Dr. Kevin.
    You said in text that expand of archs results in less need for extractions and increasing stability. The less need of extration is well clear to me, but expansion gives a real improvement in stability? The thooths out the bony bases don’t tend to loose stability and increase relapse? Thanks for all excelent information.

  5. I agree with you, I feel the control group should have consisted of patients treated with conventional non-self ligating brackets

  6. “Modest” gains (2mm) I feel is certainly possible with any bracket system, speaking anecdotally, from my own treated cases comparing before and after models of patients I have treated that have almost identical malocclusions, allocated randomly either Damon or conventional twinning brackets. Therefore I have to agree, there should have been a group included in the study that had conventional brackets to make it more relevant. It is 1pm per side, very little, after all. The torque difference is also significant as many crossbites can be corrected with changing the buccal segment torque together with disclusion.

  7. “Modest” gains (2mm) I feel is certianly possible with any bracket system, speaking anecdotally, from my own treated cases comparing before and after modles of patients I have treated that have almost identical malocclusions, allocated randomly either Damon or conventional twinwing brackets. Therefore I have to agree, there shouldhave been a group included in the study that had conventional brackets to make it more relevant. It is 1mm per side, very little after all. The torque difference is also significant as many crossbites can be corrwected with changing the buccal segment torque together with disclusion.

  8. Chances are that the reviewers were linient during the reviewing process and ignorant of the basic rules of a good research design. This articles adds to the piles of bias articles that were published about Damon System.

  9. Hi Kevin,
    I think your description of “high quality trials” needs to be revised. The 3 groups were seen at different intervals and the protocol for PSL wire sequencing was not followed. Furthermore, anti-PSL bias is rampant in “peer-reviewed” literature where PSL articles aren’t allowed into publication due to editor bias. Time, not vendor opinion, will validate the results when honest clinicians look at the data.
    What we see depends mainly on what we look for.
    – John Lubbock

  10. Did David Bearne ever publish his study on Self Ligating treatment Vs conventional where the idea was to do the Self Ligation in a Damonista style with Damon typical wire sequence and mechanics as opposed to a previous control study where the treatment plan was confirmed before the brackets were randomly chosen?

    As regards this study, 2mm of arch expansion probably won’t sort out the amount of crowding that you see in literature and lectures supporting Self Ligation as something special, never mind the claims that it sorts out crowding and avoids extractions to correct canine relations.

    In the interests of full disclosure – I do use Damon 3MX brackets, and enjoy doing so, but don’t attempt many of the Damon brocure style treatments or mechanics. I found my debond rate lowered, and I like the vertical slot and the choice of drop in hooks, if I have to retract a canine, I can hook a space closer spring in to the vertical slot and am happy for it to slide back without rotating much.

    Speaking of arches – can you blog on arch form some day?

  11. Thank you for the useful post. I’m a big fan of your work and blog.

    I agree with Dr. Ulfr, one important effect of interest is the pre and post-expansion evaluation of alveolar support (fenestration and dehiscence). There is an apparently well conducted randomized clinical trial evaluating the alveolar support with CBCT. (Orthod Craniofac Res. 2011;14:222-33 http://onlinelibrary.wiley.com/doi/10.1111/j.1601-6343.2011.01527.x/abstract). On the measure of effect there are two main problems. First they only report the volumetric size of buccal bone plate of the second premolar; it would be useful for all posterior teeth and linear measurements would be more clear (at least for me). The second problem is that it was made in 2004-2009 (enrollment started in December 2004 and was completed by November 2009), at that time CBCT had higher than current error, which did not allow evaluating small bone changes. It would be very useful to repeat this same design with current scanners (although the error of the method still would not be ideal for these measurements). It seems very strange that have not been repeated this type of study. Perhaps the high cost could be an explanation.


  12. Wasn’t this what Angle proposed through his “E” arch- Expand the arches, alveolar bone will grow ? As you have pointed out this would have happenned with any other “system” as well. Unless the inclusion criteria included only ‘contracted arches’ as indicated by standard arch width analyses- expansion may not be the best treatment option. Expanding without ability to retain is another aspect.

  13. A wonderful critical appraisal of the article sir. Self ligating brackets still remains a controversial research topic. Such research articles may misguide the clinician into treating patients with non extraction modality.

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