Hello there... The blackish discoloration can be due to many reasons like underlying tooth infection, stains etc ... All u can do is visit a nearby dentist and get it diagnosed properly so that it can be treated In a systematic way. Take care ..!!

Hello, Outer or ‘extrinsic’ discoloration of tooth simply stains on the visible outer surface. The actual underlying color of the tooth is unaffected. • Coffee; especially black coffee. Coffee stains more than tea does. • Tea; again, especially when black. • Red wine. • Dark cola drinks and some fruit juices (cranberry and grape for example). • Certain foods such as curries and dark berries. • Smoking (and chewing) tobacco. • Chlorhexidine mouthwash; a common example of what stains teeth, but one that you may not be aware of! • Poor oral hygiene can result in green or black staining. • Iron supplements and some medications. Consult a nearest dentist to get it washed or for bleaching.