January 29, 2018

How many Temporary Anchorage Devices fail?

Temporary Anchorage Devices (TADs) have revolutionised orthodontic treatment mechanics. But how many of these fail? This systematic review gives us useful information.

The TAD is a relatively recent introduction to orthodontic treatment. It is clear that this simple form of treatment has changed orthodontics. For example, a systematic reviews of RCTs have shown that, on average, we gain about 1.7mm of additional anchorage over other forms of anchorage reinforcement. This new systematic review provides us with great information on the failure rates of these useful devices.

Fahad Alharbi, Mohammed Almuzian and David Bearn

EJO Advanced access: doi:10.1093/ejo/cjx093

A team from Dundee, Scotland did this study. They have a nice bridge in Dundee. The European Journal of Orthodontics published the paper.

They did this study to answer this question

“What is the failure rate of mini screw TADS”?

What did they do?

They did a nice simple systematic review. The PICO was

Participants: People having orthodontic treatment that involved the insertion of a mini-screw.

Intervention: Miniscrews to reinforce anchorage.

Outcome: Primary outcome was failure in terms of mobility, infection leading to loss of the miniscrew. They also looked for factors associated with screw failure.

They did a standard electronic search and looked for randomised clinical trials and prospective cohort studies published until July 2017. When they obtained the papers they evaluated bias in the trials with the Cochrane tool and the prospective cohort studies with the Newcastle-Ottowa scale.

What did they find?

They identified a final sample of 46 papers. Sixteen of these were RCTs and 30 were prospective cohort studies. University based researchers had done 78%  of the studies. They obtained data on 3250 miniscrews.

When they looked at risk of bias only 2 of the RCTs were of low risk. This was mostly a result of lack of blinding and inadequate allocation concealment. They felt that the prospective cohort studies were of medium quality.

The failure rate of the TADS ranged from 0-48%. The pooled failure rate was 13.5% (95% CI= 11.5-15.9). Importantly, they looked for any effects of the study design on the outcome by only evaluating the RCTs. They found that the failure rate in the RCTs was 13.3% (95% CI= 9.7-18).

Finally, they looked for any possible predictors of failure rate in terms of screw characteristics, patient age and jaw of insertion. They did not find anything.

What did I think?

I have previously mentioned that there are possibly too many orthodontic systematic reviews of varying quality. I was, therefore, pleased to see this nicely done simple review that answered a relevant clinical question. The authors pointed out in their conclusions that there was a problem with risk of bias in the studies. I feel that this is a common problem with orthodontic research and it has an influence on the finding of trials. As a result, we need to carefully interpret the findings of this review. I have done this and I took into account the following:

  • They did the review well
  • Bias was present and clearly reported
  • The authors analysed the results for the trials and the prospective studies.
  • The outcome was clearly reported
  • The intervention was of low risk and cost.

My overall conclusion was that the level of evidence from this systematic review was moderate to low.

If I was to use this information for my patients, I would use the 95% confidence interval from the RCTs. As a result, I would let them know that the average failure rate of TADS is between 10 and 18 percent with some confidence.


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Have your say!

  1. Dear Dr. O’Brien,

    as a long time reader of your blog and a passionate TAD user I was excited to read about new results but I am surprised by what I read here.
    Like many other orthodontists I place almost all of my maxillary TADs in the palate (the M4 position advocated by Winsauer, actually).
    In my experience and – to my memory – according to literature, there is a significant difference in surcvival rates between palatal and interradicular insertion.
    I must confess that I have not yet checked each item of this review’s primary literature but I would presume that they included investigations focused on interradicular TAD placement only.
    It could have been so much more interresting and useful had they included TADs in the anterior hard palate.
    Just felt compelled to put my 2ct in on this.

    Kind regards

  2. Hello Brian, the problem with these miniscrew failure study is, that the indication, the implantprocedure, the loading, oral hygiene maintenance will have effect on the stability. If the orthodontist knows the limits and indications and the proper way to place the miniscrews, the failure rate will be much lower. When we use the miniscrews in the University setting a failure rate of less then 5% is achievable

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