All tissue and cells are made of tiny particles. Some of these particles give off small amounts of light. This light is called fluorescence. Researchers have learned that cancerous cells and normal cells give off different amounts and different types of fluorescence and also reflect light differently. Researchers need to better understand whether fluorescence and reflectance of light from tissues in the mouth can be used to tell whether areas of the mouth are abnormal. This information may help doctors detect pre-cancers and early cancer.