April 29, 2024

CAD/Cam retainers again, does this one do better?

A few weeks ago, I posted about the poor performance of a CAD/CAM retainer. Here is a new study on the same retainer, with more encouraging results.

An increasing number of papers report the results of randomised trials of different types of retainers. We are, therefore, starting to gain much more knowledge about the effectiveness of retention regimes. When we consider the new publications, we need to remember that not all trials agree. This is why we need to see systematic reviews combining evidence from several trials.  This new paper looked at CAD/CAM and a conventional bonded retainer. It was another addition to our knowledge.

A multi-national team did this study. The EJO published their paper.

This is an open-access paper, so you don’t need to be a member of the EOS to read it.

What did they ask?

They did this study to answer this question;

“How effective are CAD/CAM versus conventional multistrand fixed retainers in terms of post-treatment stability, failure rate, patient satisfaction and cost minimisation”?

What did they do?

The team did a two-centre, two-arm parallel RCT with a 1:1 allocation ratio.  The PICO was;


Orthodontic patients attending two postgraduate clinics at Aarhus University and the University of Oslo who completed fixed appliance orthodontic treatment.


CAD/CAM fixed retainers made from 014×014 Nitinol (Memotain). These were custom cut from a nitinol sheet and made with a silicone transfer key for clinical positioning.


Conventional fixed retainers were made from 0.0215 six-stranded stainless steel by the same dental technician at each centre. A silicone transfer key was used for positioning.


The primary outcome was stability after the treatment. Secondary outcomes were retainer failures, patient satisfaction, and cost minimisation for all the retention phase of treatment.

The team collected data 1,3,6, 12, and 24 months after the retainers were placed. One operator fitted all the retainers in each centre.

They also gave the patients a maxillary removable vacuum-formed retainer.

Randomization was pre-prepared, and the allocation was concealed by sealed envelopes. The data was recorded blinded to the allocation.

Finally, the statistical analysis was the relevant univariate and multivariate analysis to take any cofounders into account.

What did they find?

At the start of the study, they randomised 181 patients. 90 were in the CAD/CAM group and 91 in the conventional group. After 12 months, 153 attended for review. 81 in the CAD/CAM and 72 in the conventional groups.

At the start of the study, there were no differences between the groups.

These were the main findings after 24 months.

In the CAD/CAM group, the LII was 1.1mm (95% CI, 0.8-1.3), and in the conventional group, it was 1.3mm (95% CI, 1.1-1.6).

For the CAD/CAM group, 34% of the mandibular and 38% of the maxillary arch retainers failed.  Similarly, in the conventional group, the failure rates were 42% and 40% for the mandibular and maxillary arches, respectively.  There were no differences in survival between the two groups.

There were no differences between the groups in terms of patient satisfaction.

When they looked at the cost of the retainers they found that the total cost of the conventional retainers was €327 and the CAD/CAM retainers cost €290. The conventional retainers were approximately 10% more expensive than the CAD/CAM.

Their overall conclusion was

“After 24 months, there were no significant differences in the effectiveness of the CAD/CAM and conventional retainers, although the CAD/CAM retainers were slightly cheaper”.

What did I think?

This was another very well-done study on a clinically relevant question. The trial was clearly reported.  It is great to see such good research being done in this area.

The research showed that retainers are successful in retaining alignment. However, any differences were not clinically significant.  I also thought that it was interesting that there were no differences in the outcomes that are relevant to our patients. Again, this emphasises that we should not confine our outcomes to those that are only relevant to orthodontists.

However, the failure rates were very high. This tends to agree with other studies that report rates that are much higher than our own clinical experiences.  It is interesting to see that the Memotain performed better than in the study I discussed a couple of weeks ago.  

Nevertheless, the high failure rates in trials are a mystery to me. While it is easy to think that this is due to inexperienced operators placing retainers in training programmes, this was not the case in this study, where an experienced operator placed all the retainers for each centre.  

I cannot think of any other reasons for these findings. As a result, I have asked Simon Littlewood who is the world’s retention expert to write a blog post to see if he can explain the current state of retainer research to us.  He has kindly agreed and I will publish this as soon as Simon can write it.

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Have your say!

  1. if you abrade the enamel surface with a diamond bit (not air abrasion) you increase the composite enamel bond strength by more than 60%
    in our practice audits of fixed retainer failure it is around 16-18%

    we find that emanuel preparation and careful
    bonding technique is essencial in long term retention of bonded retainers

    IMHO the best retainer regime is “dual retention” bonded and VFR

  2. Kevin, thanks for another interesting informative article.
    Mostly I just want to use this space to say to anyone reading this who has not contributed to support this blog that you should be ashamed of yourself!!! Kevin’s work is a great benefit to all of us and to the profession and we should all be eager to support his efforts. So, don’t put it off, he has made it really easy, do it today. (I was hoping to put a lyric from a classic rock song to support my post, but I drew a blank, please feel free to help out in this department.)

  3. Thank you for this post.

    I don’t get the pricing. 327 Euro for a set of conventional retainers? That sounds a lot.
    I have thinking of trying Memotain, but haven’t made the switch yet because of the big price difference. In southern Sweden I pay 55 euro per conventional retainer (Penta one).

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