Interview: Project Stealth, inside the mouth

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Unique and discreet: UK designers have developed a prototype mouth wearable device that aims to take security and authentication beyond the eyes of hackers. (Image: Project Stealth Tech)
Jeremy Booth, Dental Tribune International

Jeremy Booth, Dental Tribune International

Wed. 2. September 2020


What if we could replace the cumbersome process of validation for our devices, banking and other secure entry points with a flick of the tongue? According to the designers behind UK-based Project Stealth Tech, the inside of our mouths is not only a rich source of unique biometrics, but also offers concealment by default. Dental Tribune International spoke with Paul Mendieta, one of the four graduates of the Royal College of Art in London who developed the Stealth mouth wearable, which is worn on the palatal rugae. Mendieta says that the prototype device aims to take authentication inside the mouth and that further uses for the technology are under development.

Paul, thanks for speaking with us. Could you please tell us about Project Stealth and the technology behind it?
We started the project with an interest in mouth interfaces. We were mainly fascinated by the mouth’s potential for being an independent communication channel, its richness in valuable biological indicators and its discreet nature. We went through an explorative journey of experiments with mouth gestures, digitally simulated senses and wearing experience. Building on the insights that we gained, we invented a mouth wearable—named Stealth—as a concealed multifactor authentication interface.

What is the wearable made of, and how easily and comfortably can it be fitted, worn and removed?
We made our first proof of concept prototypes with a fast-setting silicone-based polyvinylsiloxane (PVS) material. We chose this material for its shape memory properties and its acceptable capability of sealing the electronics. By the material being shaped to the palatal rugae, the device creates a vacuum effect that enables it to stay in place without any extra fixture. The interaction in the way that the user wears and removes the product is the same as a retainer, the difference being that our device auto-fits to the palate. When we tested the wearable on people, they were surprised by how comfortable a mouth roof-mounted piece could be.

Our next step is to select the most appropriate material. Our current options are PVS, thermoplastic nylon, or acrylic, and our selection will depend on how long the device stays inside the mouth.

For multifactor authentication scenarios, the Stealth device has to be put inside the mouth on the morning of the day on which an authentication service is required—such as at a bank, an entry point in an enterprise, or in a healthcare setting—and the user interacts with the device in order to gain access. Otherwise, the wearable can either stay passive inside the mouth or be stored in a self-cleaning case, depending on the user’s preference. It can be taken out once the user is at home and charged overnight.

Stealth fits into place on the palatal rugae and its interface (left) is commanded by the tongue. (Image: Project Stealth Tech)

Given the complexities of the oral cavity, what were the most important physical design parameters for Stealth?
To make sure the fitting works, the size of the device had to be controlled, which was also important to prevent asphyxia and choking. We are now working on miniaturising the components for smaller weight and size.

The mouth is quite sensitive, so it is essential to make the wearable comfortable so that people want to put it into their mouths. We have learned that the wearable should be customised to an individual’s mouth and be flexible—unlike a retainer—because people show resistance towards wearing something that includes metal fixings.

Understanding the physical feedback that the tongue can sense is very important for designing the interface. An efficient and enjoyable interface should be based on careful consideration of the tactile experience and position of the gesture sensors.

Another parameter was the dimensional stability of the materials that we used for our prototypes. For example, a silicone base material would keep its stability for seven days, whereas thermoplastic nylon, such as Valplast, could maintain its shape for over a year.

Hygiene is another crucial parameter. Dentists told us that the material we use should be as smooth on the surface as possible to prevent bacteria from accumulating. Of course, a natural cleaning routine should be designed around it.

What can you tell us about mouth biometrics and their application in identity authentication?
The mouth is home to many biometrics. Studies have shown that tongue print, teeth, palatal rugae, and even saliva can be used as biometrics for identifying people. We started to look at palatal rugae because of the palate’s overall stability and positional potential for a mouth wearable. Our palate is as unique as our fingerprints. Palatal rugoscopy studies mainly focus on forensic identification, and there is no existing device for direct scanning and verifying of the palatal biometrics. We proposed a novel way of using a mouth wearable to scan and store the holder’s palatal biometric, but we understand that there is still a long way to go in sensor development and model building.

“With its capability of input and output, the tongue is a perfect alternative for communicating information without speaking”

Besides physical biometrics, we realised that behavioural biometrics inside the mouth would potentially be another identification method: how we place our tongue, for example, and the changes in temperature, pH level, etc.

The user’s tongue commands the interface of your wearable and acts as a source of data. How reliable and unique are our tongues?
Our tongue is able to sense tastes, temperature, texture, etc. We chose taste delivery, since in our initial prototypes, we were able to convey information such as a phone access password. Our own experiments, and research by Dr Nimesha Ranasinghe, have shown that, even though digitally simulated tastes might be perceived differently by individuals, the device can be calibrated to deliver differentiable tastes. The tongue is also trainable and has the strongest versatility and is able to perform gestures like pressing and sliding. With its capability of input and output, the tongue is a perfect alternative for communicating information without speaking. Besides, it is the only input–output channel that is concealed by default.

What are the potential uses for this technology in improving oral health?
Currently, our technology development is not focusing on improving oral health. We are leveraging the properties of the mouth to create a device capable of using mouth biometrics for authentication and identity applications. Another application would be using saliva biomarkers for monitoring health-related markers and indicators, such as hydration, stress and inflammation.

Nevertheless, we have explored other potential use cases for our technology that are more related to oral health: treating dysphagia, for example, by using speech and lingual therapy to learn new swallowing techniques and tone tongue muscles, or treating snoring using myofunctional therapy. Oral drug delivery is another potential application that we have explored, whereby a mouth wearable could perform local, sustained release of a drug for treatment of oral disease.

London graduates Paul Mendieta (pictured), Beren Kayali, Lu Ye, and Lea Marolt Sonnenschein are the designers behind the Stealth mouth wearable. (Image: Project Stealth Tech)

What kinds of feedback have you had from dentists or other medical professionals?
We have met with several dentists throughout our development process. At the moment, we are in a continuous conversation with one dentist adviser to guide us through the process of defining the material for our next prototyping stage. Dentists are already very familiar with different kinds of retainers and electronics inside the mouth. With their expertise, two key concerns have been raised and need to be addressed by our technology: hygiene and fixation. Hygiene is going to depend predominantly on the material. For example, our current prototypes are made with sheets of PVS or addition silicone, which can be simply cleaned with a 70% solution of alcohol. Now we will be evaluating and testing our design with new materials such as acrylic and thermoplastic nylon (Valplast), which have different cleaning protocols, although from our adviser’s perspective, hygiene is an issue that is easy to solve, considering that the materials we are testing are already used in dentures, retainers and dental impressions. In terms of fixating the device to the palatal rugae, we are leveraging the vacuum effect created by the rugae ridges and the silicone that we are currently using. Our experiments show that the force created by the effect is strong enough to hold our device in place. Nevertheless, we are also planning to test Bertoni screw products in case we need to increase the fixation strength.

Project Stealth is working on another project that uses saliva as a biomarker for athletic performance. What can you tell us about this?
Health prevention is only as effective as our capacity to understand the human body. In today’s world, real-time data collection and continuous data analytics have become an uprising tool to reach a deeper understanding of complex topics in high-performance sports, including human mobility, mental state and physiological status. We are using our patent pending technology to develop a mouth wearable that helps athletes to track their physiological status. The combination of our technology with biochemical sensors has the potential to be better than current cumbersome diagnosis systems like blood tests, by providing them with a comfortable real-time saliva biomarker reader to monitor and deliver the data to any digital platform.

“The field of mouth wearable technology is relatively new and unexplored”

Our mission is to enable biosensing technology to positively impact the high-performance sports industry by providing coaches, clinical sport professionals, researchers and athletes with meaningful data to better understand physiological changes. It would allow them to design better training cycles and customise medical interventions.

Around £300 million (€333 million) is spent on salaries for injured players in the English Premier League each year and even more significant numbers in the US National Football League and National Basketball Association. The economic impact is evident not just in the salaries, but also in the decreased performance of the team. Studies show that, in some sports, 42% of injuries are potentially avoidable. Curbing the incidence of these injuries would not just provide a marginal gain; it could be a game-changer.

How far along is the development of mouth wearables, and how has Project Stealth advanced this field of research?
The field of mouth wearable technology is relatively new and unexplored. There are many considerations when designing a product that goes inside our body, and this usually scares off researchers, investors and ventures. Therefore, our mission is to create a platform that enables knowledge and science around the mouth to have a feasible host for their new findings. For example, in the last five years, many advances in replacing saliva testing instead of blood testing have been made and validated; unfortunately, there are no developments in the incorporation of that knowledge into a product that could benefit society. Therefore, Project Stealth Tech wants to take the risk that no one has yet taken and concentrate first on developing a device that can embed mouth technology in a comfortable, non-intrusive and safe way. Also, we want something that people want to use, something that is functional but at the same time exciting and fun to wear.

Since Project Stealth is a hardware company, we are focusing on validating the best material to be used for the device. The hardware miniaturisation process is moving confidently into reaching the size milestones of our product requirements. We have secured an academic partnership with the Dyson School of Design Engineering to develop a tailor-made biocompatible battery, and more, which we unfortunately cannot yet disclose to the public.


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