Tooth decay often goes undetected until too late. Early signs of damage are usually hidden from sight and it is unhealthy to take too many X-rays. Now researchers working for the National Institutes of Health (NIH) in the US have discovered that infrared light – with a wavelength of 1310 nanometres – can pass straight through a tooth, providing a safe and simple way to probe for hidden decay. Most light frequencies bounce off enamel, meaning they cannot probe below the surface. But the NIH research found that, for a narrow band of infrared, reflection is 30 times less than normal. An infrared diode shines light through a tooth and a Charge-Coupled Device (CCD) sensor on the other side measures the light that passes through. Any decay inside the tooth creates small pores that scatter the infrared light, causing a dark shadow to appear in the resulting image. The image quality could be further improved by polarising the infrared light before sending it through a tooth, the researchers suggest. This is because any hidden pores should also depolarise this light, making for better image contrast. Tests show that an infrared diode can shine light through 5 millimetres of enamel, providing an image as clear as an X-ray, but without exposing the patient to harmful radiation.
December 5, 2006
Original web page at New Scientist