Teeth discolouration can be either external or internal. External and internal discolouration have different causes and their treatments are different. Smoking, as well as tea, coffee and soft drink consumption are some of the biggest causes of external staining. At times, irregularities on teeth surfaces may contribute significantly to the uptake of external stains too.
Deep stain could be the result of a dead or infected tooth. External discolouration can be predictably treated with cleaning and whitening, while treatment for intrinsic discolouration will be more complicated. The key to effective treatment is to get a proper examination and diagnosis. Your dentist would be able to identify the causes of your concern and the relevant treatment.