First published July 1, 2021.
DentalSlim Diet Control is a small dental device developed by researchers at the University of Otago in New Zealand that uses magnets and locking bolts to stop the mouth opening more than about 2 millimetres, so the wearer can only take liquids. In a two-week pilot study with seven people, published in the British Dental Journal in June 2021, participants lost an average of 6.36 kg. When the university promoted it as a world-first weight-loss tool, the internet reacted with outrage, and the researchers clarified that it was meant for short, supervised use before surgery, not as a general diet aid.
How the device works
A dental professional fits small metal attachments to the upper and lower back teeth (the first molars). Closed-field magnets and custom bolts hold the jaws almost shut. Wearers can still speak and breathe normally, and they can drink through the narrow gap, so food has to come as a liquid diet. The device can be removed and refitted, and it has an emergency release that the wearer can operate; none of the trial participants needed to use it.
The project was led by Professor Paul Brunton, then Otago’s Pro-Vice-Chancellor of Health Sciences, with UK partners Dr Jonathan Bodansky and Dr Richard Hall of Leeds. Brunton argued that the main obstacle to weight loss is sticking to a diet, and that the device enforces that by design.
What the study found, and its limits
The pilot followed seven healthy adults with obesity in Dunedin. For two weeks they wore the device and followed a commercially available liquid diet. Comfort and quality of life were checked at day 1, day 7, day 14 and two weeks after removal.
- Weight: an average loss of 6.36 kg (about 14 lb), roughly 5.1% of body weight, with wide variation between people.
- Daily life: participants had some difficulty pronouncing words and occasionally felt tense or embarrassed. The paper notes that at times they found life in general less satisfying.
- Motivation: in interviews, participants said they were happy with the result and keen to keep losing weight.
Seven people over two weeks is a very small, short study. It cannot show whether weight stays off, whether the device is safe for wider use, or how it compares with other approaches. Rapid early weight loss on a liquid diet is largely expected, and much of it can return once normal eating resumes. The journal later issued a correction notice for the paper in December 2021.
The backlash on social media
The university’s press release described the device as a world-first tool against obesity, and quoted Brunton calling it a non-invasive, reversible and economical alternative to surgery. Within hours of the announcement being shared on Twitter in late June 2021, hundreds of people responded, many comparing it to a medieval torture device or a muzzle.
Brilliant, I'd like to submit my idea for a device to help short people be taller. pic.twitter.com/5WYp26VbJ3
— Ika Makimaki (fish monkey) (@pezmico) June 28, 2021
This research team is like “you know, the Human Centipede guy actually made some valid points”
— mäther! (@carlysintothat) June 28, 2021
(This post is no longer available on X.)
Some replies questioned whether it was ethical or even legal; others turned the idea back on the researchers with dark humour.
90% sure this is in breach of a few health and war crime laws
— AusSyndie🏴🚩 (@AusSyndicalist) June 28, 2021
Have you considered wiring the professors fingers together so they can do less of this?
— SnarkyMcSnark (@snarky_mk) June 28, 2021
A common thread was concern about ethics in research on people with obesity, who already face a great deal of stigma.
And this, kids, is why ethics needs to be taught in science.
— Justin Boot ∞ (@Polymathically) June 28, 2021
Good God, I thought medicine was past these kinds of torture devices.
Critics also pointed to the line in the paper about participants feeling embarrassed and finding life less satisfying, which seemed at odds with the claim that the device had no adverse consequences. Some dietitians and eating-disorder advocates reportedly warned that forcibly restricting food intake could encourage unhealthy relationships with eating and does not address the many causes of obesity.
The university’s response
Facing the criticism, the University of Otago issued a clarification. It said the device was not meant as a quick fix or a long-term weight-loss tool, but was “aimed to assist people who need to undergo surgery and who cannot have the surgery until they have lost weight.” Some operations carry higher risks for patients with a very high body weight, and surgeons may ask them to lose weight first.
The university described a phased approach: wear the device for two or three weeks, have the magnets disengaged for a period of less restricted eating, and then resume, with a dietitian guiding the whole process.
After two or three weeks they can have the magnets disengaged and device removed. They could then have a period with a less restricted diet and then go back into treatment. This would allow for a phased approach to weight loss supported by advice from a dietician.
— University of Otago (@otago) June 28, 2021
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Is jaw restriction a new idea?
Not really. From the 1970s and 1980s, some doctors tried jaw wiring for weight loss, fixing the jaws together with wires so patients could only drink. Reported outcomes were disappointing in the long run: many people regained the weight once the wires came off, and the method raised safety concerns, for example around vomiting with the jaws held shut. DentalSlim’s designers presented their magnet system as easier to fit, release and remove than wires, but the basic approach of forced liquid intake is similar.
What this means for anyone trying to lose weight
- DentalSlim was a research prototype tested on seven people, not an established treatment.
- Very rapid weight loss through severe restriction is hard to sustain and can carry risks.
- Lasting change usually comes from approaches people can keep up: diet, activity, sleep and, for some, medicines or surgery.
- If you are thinking about any weight-loss treatment, especially before an operation, talk to a doctor.
The story is a reminder of how much the framing of a press release matters. A narrow pilot study for a specific medical situation was presented as a world first for weight loss, and the reaction followed the headline rather than the research.
Sources: Brunton et al., British Dental Journal (25 June 2021); University of Otago press release; earlier coverage by IFLScience.
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