Yellow spots can be caused by many things. It could be staining, plaque or tartar. If it is along or near the gumline it might be the root surface of the tooth becoming exposed. The roots are usually darker than the crown or enamel portion of the tooth. It might also be a thinner area of enamel, allowing more of the dentin layer of the tooth to show through. Please see your family dentist to have it evaluated These are only a few causes of yellow spots on the teeth. It might also be a cavity. Have your dentist evaluate the exact cause and what needs to be done, if anything.