Tiny oral sensor may one day help dentists assess their patients’ oral and overall health

 Omenetto, Kaplan and Tao created a thin, water-soluble silk backing for McAlpine’s bacterial sensor—a film that’s strong enough to hold the sensor components in place, but soft and pliable enough to wrap easily around the irregular contours of a tooth. To apply the sensor, McAlpine says, you need only to wet the surface of the entire assembly—silk, sensor and all—and then press it onto the tooth. Once there, the silk backing will dissolve within 15 or 20 minutes, leaving behind the sensor, a rectangle of interwoven gold and black electrodes about half the size of a postage stamp and about as thick as a sheet of paper. The advantage of being attached directly to a tooth means that the sensor is in direct contact with bacteria in the mouth—an ideal way to monitor oral health. Because the sensor doesn’t carry any onboard batteries, it must be both read and powered simultaneously through a built-in antenna. Using a custom-made handheld device about the size of a TV remote, McAlpine’s team can "ping" that antenna with radio waves, causing it to resonate electronically and send back information that the device then uses to determine if bacteria are present. Window on the Body Right now the sensor can only detect gram-negative bacteria, the general class of bacteria responsible for periodontal disease. Once its detection ability is honed, it eventually might help dentists track exactly when and where certain bacteria are present in the mouth so that they can develop customized treatment plans for patients with chronic periodontal disease. "A sensor like this could give you a panoramic view of what’s happening over a number of hours or even days," says Gerard Kugel, D85, L93, a professor of prosthodontics and operative dentistry and associate dean for research at Tufts School of Dental Medicine. "If you could tell when bacteria levels are spiking, you could shape your course of treatment accordingly. For example, if I saw a patient had a high caries rate and their bacteria level was high for an entire week, I might put them on fluoride rinses and cavity varnishes, or even prescribe an antibiotic." In addition to monitoring oral health, Kugel believes the tooth tattoo might be useful for monitoring a patient’s overall health. Biological markers for many diseases—from stomach ulcers to AIDS—appear in human saliva, he says. So if a sensor could be modified to react to those markers, it potentially could help dentists identify problems early on and refer patients to a physician before a condition becomes serious. "The mouth is a window to the rest of the body," Kugel says. "You can spot a lot of potential health problems through saliva, and it’s a much less invasive way to do diagnostic tests than drawing blood." Before the tooth tattoos can undergo clinical testing, however, researchers will have to overcome some limitations. In order for the sensor to detect specific strains of bacteria, McAlpine says, his team will need to create new peptides or similar molecules that bond with only one particular strain. Constructing those won’t be easy. McAlpine notes that he’ll need to work with biologists to build them from the ground up, a process that could require the development of entirely new methods for assembling organic molecules in the lab. The sensor’s physical size is also a consideration: the prototype is a bit too large for use in humans (the team tested it on a cow tooth), so making the whole package smaller will be another challenge. And, Kugel notes, thickness is a factor, too. It’ll be important to determine if patients will accept having a foreign object, no matter how thin, attached to their teeth. "People are very sensitive," Kugel says. "They can feel objects in the mouth that are 50 or 60 microns across"—about the thickness of a sheet of paper. "If it’s at all irritating to a patient, he or she will complain about it. You’d need to make sure it’s actually comfortable enough to leave in place for long periods of time."