Tooth decay and dead teeth are the most common reasons why a tooth might turn black. Other reasons may include the consumption of certain foods and drinks, tobacco use, poor dental hygiene, taking certain medications and various diseases.
Tooth death occurs when the nerve and other living tissue inside of a tooth has died. Sometimes, this may be a result of nerve extraction that occurs as part of a root canal treatment. A tooth may also die as a result of trauma, such as falling and knocking the teeth, or as a result of dental decay. Teeth may darken to a variety of yellow and gray shades before turning black. Increased consumption of drinks that stain the teeth may contribute to darkening. These include coffee, red wine, Coca-Cola and tea. According to WebMD, white wine stains the teeth as well, especially if drunk before a cup of tea. Different types of medicines may cause tooth discolorations, with the main ones being antibiotics such as doxycycline and tetracycline. Antihypertensive medication can also lead to tooth discoloration. If a dentist uses amalgam for teeth restorations, the teeth may turn gray or black as well. Advanced age and genetics are further causes for tooth discoloration.