By pulsing near-infrared light at different frequencies, the device can also explore different depths under the enamel. For example, a lower frequency of 5 hertz would allow a deep probe because it gives the heat enough time to radiate back to the surface, while 1,000 hertz would be a relatively shallow probe. Throughout the whole process, the temperature of the tooth rises by two ºC.

Detecting the earliest signs of decay could bring big changes to dentistry. "You need to lose about 30 percent of the mineral before you begin to see it on an x-ray; that's why these new technologies are so exciting," says Christopher Fox, executive director of the International Association for Dental Research, based in Alexandria, Virginia, and a 20-year industry veteran. "If we can detect early mineral loss, we have different intervention technologies we can use to prevent getting to that drill and fill point."

Fox calls Quantum's approach "very interesting" but says that x-rays will always be needed to assess periodontal health, such as the deterioration of bone structure around the teeth.

Still, Abrams says that the device could dramatically reduce the use of x-rays. In one study, published in the journal Caries Research, 52 human teeth were subjected to a range of tests--including radiographs, visual inspection, and laser-induced fluorescence--that looked at tooth decay on biting surfaces. Quantum's system caught "very early lesions" in enamel about 80 percent of the time. Its sensitivity was 33 percent higher than laser fluorescence and 2.8 times higher than a radiograph. Abrams says studies that focus on areas between the teeth and subsurface are ongoing, and he expects that the sensitivity compared with laser fluorescence will be much higher.

Researchers plan to spend the next 15 months engineering a version of the device small enough to be used in dentists' offices, with the first clinical prototype likely to be introduced in the summer of 2008, followed by a clinical trial.