April 08, 2024

A CAD/CAM Nitinol bonded retainer has a high failure rate

Maintaining orthodontic correction is a significant challenge. Despite extensive research, no retention method seems to be superior to any other. Currently, there are two main types of retainers: removable and fixed bonded retainers. The primary benefit of a bonded retainer is reducing the need for patient cooperation. However, the downside of these retainers is that they can become detached or may deform and move the teeth.

Recently, there has been a new development in retainers – the introduction of CAD/CAM nitinol retainers. One is Memotain, which claims to have a precise fit and ultra-thin design. While some trials have suggested that these retainers are effective, none have reported on their use in the upper arch. A UK based team has done a new study to evaluate the effectiveness of Memotain and OrthoFlex tech retainers in both arches.

A team from Yorkshire, in the far North of England, did this study. The Journal of Orthodontics published the paper.

retainer disappointment

CAD/CAM nitinol bonded retainer versus a chairside rectangular-chain bonded retainer: A multicentre randomised controlled trial

Adam C Jowett, Simon J Littlewood  Harmeet K Dhaliwal  and Jianhua Wu , Trevor M HodgeJournal of Orthodontics 2023, Vol. 50(1) 55–68 https://doi.org/10.1177/1465312522111893

I would like to declare a conflict of interest as I know the members of this research team well. 

What did they ask?

They did this study to:

“Compare stability, failure rates and patient satisfaction of Memotain and Ortho-Flex tech retainers”.

What did they do?

They did a multicentre, two-arm parallel group randomised controlled trial. The PICO was


Patients who had completed a course of fixed appliance treatment.


Memotain retainers. These retainers are laser cut from a nitinol sheet, and no chairside bending is needed. It looks great!


Ortho-Flex tech retainers.   These are a 0.039×0.014-inch rectangular chain bonded retainer. This retainer is measured and fitted at the chairside.


The primary outcome was dental relapse measured with Little’s Irregularity Index. Secondary outcomes were failure rate and patient comfort. 

A remote computer-based system did the allocation concealment and randomisation, which was good. As usual, it was not possible to blind the operators, but data collection and model analysis were blinded.

The team did this clinical trial very well.

What did they find?

The study’s main finding was both interesting and unusual. Unfortunately, the researchers had to halt the study due to the high failure rate of the Memotain retainers. All clinical trials have stopping rules in place to minimize the possibility of harm to the participants. In this study, the authors discovered a high failure rate of Memotain retainers, which they felt compromised the effectiveness of the treatment. Consequently, they stopped enrolling participants. This was a reasonable course of action and provided a helpful outcome.

The authors discovered that the failure rate for the upper Memotain retainer was 50%, which is significantly higher than the 17% failure rate of the Ortho-Flex Tech retainers. Additionally, the survival analysis revealed that Memotain retainers were three times more likely to fail than their Ortho-Flex Tech counterparts. In the lower arch, the failure rate for the Memotain was 35% while the Ortho-Flex Tech had a 28% failure rate.

They concluded:

“The Memotain retainer had a higher risk of failure in the maxillary arch than the Ortho-Flex Tech retainers”.

What did I think?

The study team did a well-designed randomized controlled trial (RCT) that addresses a relevant clinical question. I was hopeful that any innovation that could reduce clinical time and result in a well-fitting retainer would be effective. Unfortunately, this was not the case in this trial. I was initially concerned about the high failure rates of both retainers in this study, but a recent systematic review confirmed similar rates. Therefore, this study may add to the evidence that bonded retainers commonly fail.

There could be several reasons for this high failure rate. The most likely is that staff with varying levels of experience fitted the retainers, which is a technique-sensitive area. The authors also suggested that as the Memotain failed mostly at the composite/enamel interface, something inherent in the property of the nitinol wire may cause movement and this type of bond failure.

Nevertheless, the most compelling finding was that the authors had to stop the study due to the high failure rates. This leads us to conclude that this new approach to making retainers has some problems. Therefore, additional developments are necessary.

Final thoughts

In conclusion, this well-designed study highlights the importance of testing innovations before releasing them for clinical use. At present, Memotain may not be an effective retainer.

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Have your say!

  1. How did these memotain appliances fail? Bond failure? NiTi material broke? I have been using the Ortho-Flex material for over 15 years and seldom have a failure; not anywhere close to 17%. I think my success is due to a recommendation from Reliance to micro-etch all the teeth to be bonded to rid of stain and light calculus. Of course, there is always the chance my failures have moved to another state for someone else to repair.

    North Carolina

  2. A failure rate of 20 resp. 50 percent (!) is almost unbelievable. I have never experienced a rate as high as this and I am practicing Orthodontics for over 30 years now. This only lets me conclude, that there is a big flaw in the design of this study.

  3. Excellent article: in Australia I had started a lot of discussion re: Ortho Flex vs other fixed options : the so called “hygienic” scalloped one and the YOAT machine. Have there been recent articles on the latter 2?
    My ”gold” standard has been Ortho Flex with failure rates only around 5-7%

  4. I am preparing a manuscript detailing the outcomes of over one hundred consecutive lower arch cases and approximately sixty upper arch cases, all treated with Memotain from canine to canine. This work was rigorously examined by a student at the University of Geneva. We set our observation milestones at six and twelve months post-debonding, meticulously recording failures as per the methodology of a published study. Our findings revealed a 95% success rate per tooth, with a slight increase in complications for central and lateral incisors (5-6% failure rate) and around 2% for canines. Notably, no significant differences were observed between the upper and lower arches.

    When evaluating patient outcomes rather than individual teeth, we noted approximately 85% of cases had no events at six months, a statistic that remained stable at twelve months, with an overall incidence of uneventful cases at around 70%.

    These results diverge significantly and more reassuringly from those reported. The documented 50% failure rate likely reflects very likely variables tied to operator skill or technique, as I employed identical 3M products for bonding, performed by myself and my assistants. Although lacking a control group, it’s my view that the skepticism towards CAD-CAM solutions, which are inherently more anatomically accurate than manual fixed retainers, may be overstated. Thus, I advocate for a nuanced consideration of these outcomes, especially since a perceived 50% failure rate contradicts the precision we observed.

    By the way, I encourage every practitioner to meticulously catalog each failure for an accurate evaluation rather than relying on a mere gut feeling. In my experience, the actual failure rate was surprisingly higher than what self-expected (at least it was in my case).

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