Can an iron supplement in the elderly turn teeth black?

Yes: Liquid forms of iron supplement tend to stain the teeth. To prevent these stains, mix each dose in water and/or drink water after each dose. You may use a straw to help keep the iron supplement from getting on the teeth. iron stains on teeth can usually be removed by brushing with baking soda or hydrogen peroxide.

Root dying or dead: In the elderly the most common cause of a tooth turning black is that the root has died.