TADS are effective in reinforcing anchorage: A new trial
This post is about a new trial that gives us useful information on temporary anchorage devices in reinforcing anchorage. I thought that the findings were interesting and clinically relevant.
Anchorage control is critical to achieving orthodontic goals. Temporary Anchorage Devices (TADs) have revolutionised anchorage control. Recent trials and systematic reviews have illustrated that they are effective. I feel that this new trial adds to our information on this relatively new orthodontic technique. A team from Malmo, Sweden did this study. The American Journal of Orthodontics published it. I thought that it was great that this was an open access paper.
Anchorage reinforcement with miniscrews and molar blocks in adolescents: A randomised controlled trial
Niels Ganzer, Ingalill Feldmann, and Lars Bondemark: Am J Orthod Dentofacial Orthop 2018;154:758-67
This is the main report on this trial. I have posted about their other paper looking at cost-effectiveness before.
What did they ask?
They asked the following question:
“Do TADs deliver better anchorage capacity than blocks of molar teeth”?
They looked at this by doing a trial. The PICO was
Participants: Orthodontic patients aged 11-19 years who needed treatment with extractions of maxillary first premolars and anchorage reinforcement. They defined this as approx 75% retraction of anterior teeth during space closure.
Intervention: Temporary Anchorage Device with space closure using Ni-Ti springs at 150g force.
Control: Molar block formed from tying the upper second molar to the second premolar. Space closure was done with active tie-backs using 150g force.
Outcome: Loss of anchorage during levelling and alignment and during space closure.
This was a clinically relevant trial design. It is worth me pointing out that the two interventions used different methods of applying force during space closure. I shall return to this later.
They did a good sample size calculation, sealed envelope randomisation and allocation concealment.
The data was collected from scanned study casts taken at the start of treatment (T1), at the end of levelling and alignment (T2) and after space closure (T3). The sequential scans were superimposed on the palate. They then measured molar tooth movement, rotations, tip and torque.
What did they find?
80 participants took part in the trial. 7 dropped out in the TADs group, and 2 of the molar block patients did not complete the study.
I will only review the data on loss of anchorage. I have put this into this table.
|Treatment phase||TADs||Molar block||Difference (95% CI)||P|
|Levelling and alignment||1.2||1.4||0.1 (-0.2, 0.5)||0.49|
|Space closure||0.2||2.4||2.2 (1.7-2.8)||0.001|
They also reported that there were no differences in the treatment time between the groups. The alignment and levelling phase took 10.5 months for the TAD group and 9.3 months for the molar blocks. Whereas, the space closure took 8.9 months for TADs and 9.0 months for the molar block group.
“Miniscrews provided increased anchorage capacity over molar blocks. This was mostly during the space closure phase of treatment”.
What did I think?
They did a nice trial with a sufficient number of patients, and they answered a clinically relevant question. Their methods were excellent, and the study was carried out well with only a few dropouts. As usual, there are several matters that we need to consider when we interpret the results. Firstly, there was an unequal number of dropouts, with more participants leaving the trial in the TADs group. Most of these differences were due to loss to follow up from poor impressions and discontinuing treatment. Nevertheless, they did an intention to treat analysis that may reduce any bias due to completion rate differences.
I was a little concerned to see that they used NiTi springs for the TADs group and active ligatures for the molar block patients. They pointed out that these interventions generated the same level of force. Importantly, we know that active ligatures suffer from greater “force fade” than NiTi springs. However, other trials have shown no differences in space closure rate between these two methods. The authors have also used treatment mechanics that they would typically use. Nevertheless, we must assume that there may be a difference in tooth movement between the two interventions. As a result, you need to decide whether this influences your interpretation of the study.
My feeling is that this is another study that illustrates the effectiveness of TADs and reinforces the finding that we get about 2mm anchorage reinforcement with this treatment method. But I wished that they had used NiTi springs for both groups.
Emeritus Professor of Orthodontics, University of Manchester, UK.