Abstract: An apparatus for detecting biological deposits on the surface of a tooth. The device has illumination means to direct exciting radiation onto a test tooth surface and detection means to detect fluorescence emission from the test tooth surface at a wavelength associated with that of auto fluorescence emission from clean tooth surface. The intensity of the said fluorescence emission from the test tooth surface is compared with an intensity of auto fluorescence emission from clean tooth surface and the comparison is associated with the presence of deposits on the test tooth surface. The device is preferably embodied in a toothbrush which indicates to the user that deposits are present and are being removed.