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.
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?
Emeritus Professor of Orthodontics, University of Manchester, UK.