Should we worry about the cytotoxic effect of orthodontic retainers?

Recent research highlights the potential cytotoxic effects of plastic aligners and retainers, suggesting that these devices may release toxic substances. However, few studies have investigated the cytotoxic and genotoxic effects of Hawley and ESSIX appliances. This new trial provides concerning information on this topic.

It’s important to start this post with some background information. The authors note that certain materials used to create removable retention appliances may have cytotoxic effects. For example, the organic component of acrylic resin used for Hawley retainers is polymethylmethacrylate (MMA). It’s crucial to understand that not all of the monomer is converted into the polymer. This means that some residual monomer remains in the appliance.

When we consider Essix retainers, they utilise several polymers. The use of these materials releases xenoestrogens, one of which is Bisphenol A (BPA). This has teratogenic and carcinogenic effects on tissues and organs.

A team from Gaziantep, Turkey did this study. The AJO-DDO published their paper.

What did they ask?

They did this study to;

“Investigate the cytotoxic and genotoxic effects of Hawley and Essix retainers”.

What did they do?

They did a randomised controlled trial with a 1:1 allocation.

The PICO was

Participants

50 orthodontic patients aged 14-25 years old

Intervention

Hawley retainers

Comparator

Essix retainer

Outcome

Analysis of salivary samples and swabs taken before retainer fitting (TB0), after one month (TB1), and after two months (TB2). They measured several biomarkers and investigated harvested cells for signs of damage.

The team randomly allocated the participants to the interventions using a coin toss. I could not find any information on how they concealed the allocation.

What did they find?

They presented a significant amount of quite complex data. As I am not a basic scientist, I found it rather tricky to interpret. Consequently, you can regard my interpretation of this as being at the level of an interested layperson. I hope this is acceptable?

There were no differences in the age or gender of the two groups.

In the results, they highlighted the levels of salivary 8-OHdG, which is an indicator of oxidative damage to DNA. They found that these levels increased in the Hawley group and decreased in the Essix group. Consequently, this was higher in the Hawley group.

When they looked at cytology, they found higher levels of cell damage in the Essix group 14-21 days after appliance fitting.

Their overall conclusion was.

“For both appliances, there was an increase in nuclear degeneration. The Hawley increased the 8-OHdG levels and the Essix reduced this level”.

What did I think?

This study was interesting. However, I must admit that I lack an adequate understanding of basic scientific research to thoroughly discuss the methods and outcomes that were assessed. I will have to rely on the AJO referees to provide that analysis for us.

From the perspective of someone familiar with clinical trials, I believe it would have been useful to include data from a control group of patients who were fitted with bonded retainers. This would clearly identify that the changes etc were linked to the removable retainers.

The authors offered a comprehensive discussion of their methods and made comparisons with other studies. There seems to be a consensus about the potential effects of plastic appliances. However, I noticed a lack of information on the clinical significance of their findings. Addressing this aspect would have been very useful.

Nevertheless, the findings related to cell damage are potentially significant. I support the authors’ suggestion for further research in this area. We need reassurance that the long-term use of plastic appliances is not causing harm. This research is becoming increasingly important as our awareness of potential risks continues to grow.