The outer surface of the tooth is made of enamel, a hard surface which protects the soft inner dentin from decay. Often there are natural defects in the enamel which allow the bacteria of the mouth to gain access to the dentine.

X-rays and examination with dental instruments may not reveal the decay because the anatomy of the defect can prevent the instrument or an x-ray from reaching the problem area.

A laser light consists of a uniform light. When a laser light is pointed into the potential problem area it will reflect differently for a solid dentin and decayed dentin. The Diagnodent laser measuring device records these differences and gives both a numerical and acoustic signal of the variations in the reflected light. By reading the varying numbers it is possible to find areas of decay. It is reported that the accuracy for this method of decay detection (in these areas) is in the range of 90% while traditional methods are in the range of 60%.