What are the effects of arch distalisation with elastics or TADS?
In this post, Martyn Cobourne reviews a new paper on the effects of different distalisation techniques using lingual appliances. While we do not usually review retrospective studies, this paper is a step in the right direction towards understanding the effects of this treatment.
An international team conducted the study. The American Journal of Orthodontics and Dentofacial Orthopedics published their paper.
What did they do?
They investigated orthodontic treatment in three groups of consecutively treated adult patients with class II malocclusion (characterised by at least a ½-cusp class II canine and molar relationship on one or both sides). All patients were treated without extractions using fixed lingual appliances.
These were divided into 3 groups consisting of:
- Class II correction achieved with full-time class II elastics (n=34); or with maxillary total arch distalisation (MTAD) using (buccal and palatal) inter-radicular mini-screws and intra-arch traction supported by either
- Nocturnal (n=24) or
- Full-time class II elastics (n=21).
The mean ages of the groups ranged from 30 to 37 years. The MTAD group (prescribed full-time class II elastics) had a more severe class II malocclusion than the other groups. The study team evaluated patients with cephalometric radiographs taken before and after treatment, using a Pancherz-type analysis.
What did they find?
Their primary outcome measures were cephalometric.
In essence, class II elastics achieved class II correction predominantly through mesialisation of the mandibular dentition (=1.8mm) and mandibular incisor advancement (+1.6mm).
MTAD (not unsurprisingly) produced more distalisation in the maxillary arch (-3.1mm), with increasing mesialisation of the mandibular arch (+1.8mm) depending on the frequency of class II elastic wear.
The largest overall changes were observed with MTAD and full-time Class II elastics. Furthermore, MTAD linked to intrusion of maxillary dentition and a clockwise rotation of the occlusal plane, both aiding sagittal correction.
There was no difference in treatment time between the groups.
Their final conclusion was
“In nonsurgical adult Class II correction, elastics primarily act on the mandibular dentition, whereas MTAD produces greater maxillary distalization and may reduce dependence on patient compliance”.
What did we think?
This interesting study provides insight into treating Class II malocclusion in adults. The use of consecutively treated patients mitigates some limitations of the retrospective design. For example, the original sample was (n=94). They excluded 15 due to inadequate visibility of structures on their radiographs. This left a final sample of (n=79).
Furthermore, there was likely heterogeneity in the samples with respect to class II malocclusion (certainly, there appears to have been variation in severity and differences in the number of class II division 1 and 2 cases within groups).
There was also other heterogeneity, including variable numbers of patients in the different groups who had maxillary third molars extracted during treatment and patients treated in multiple clinical environments.
Importantly, there was no formal power analysis. Instead, the authors conducted a post hoc sensitivity analysis. One other point – did every single consecutively treated patient in this sample wear their elastics as prescribed?
Some final thoughts.
This paper provides us with interesting data that may be clinically useful. However, we need to consider the study’s retrospective nature. This introduces fundamental flaws: selection bias, potential heterogeneity between groups, and outcomes limited to cephalometrics. Nevertheless, data for this form of treatment remain limited, and this article represents one of the first investigations.
The next step in evaluating this treatment is for clinicians using innovative, high-quality treatment strategies to apply the highest standards of research methodology when they have a genuine interest in investigating the effects of these treatments. I realise this requires a lot of advance organisation, but it would have been nice. It could also have provided more insight into patients’ experiences, rather than just cephalometric data.
That said, it’s still important data and an interesting read.
