Dark colored teeth cause by? and tooth whitening

Before

After

Generally dark colored teeth that are caused by . 

1, Changing the color of the teeth that occurs within the tooth. Caused by drinking water or eating substances that fluoride is too much. Cause "Fluorosis" or have oral antibiotics "Tetracycline" has been obtained from the pregnant mother. Including material from the tooth filled with a mix of metals. Death due to dental concussion. Dead means tooth does not have blood that make the color not white as natural teeth. This will occur with the tooth decay, and tooth that has previous root canal treatment. This cause are made tooth dark gray or very dark brown, this teeth bleaching can not make whiten teeth,It can be done by Veneer or Facing. 

2, Discoloration of teeth that occurred outside of the teeth, including a dental calculus, stain by tobacco, tea, coffe, red wine, the other stainned food,or the brushing the teeth at the wrong way. Make plans to stain microbes and limestone islands outside of the teeth and cause tooth piecemeal is dark yellow. These cause is not difficult to resolve only scraping teeth or limestone Air Flow avoid tea coffee tobacco and brush teeth in the right way. 

3, Changing the color of teeth associated with age. When people will age more the enamel will thin and dentine have more yellow, so tooth have yellowish color. This cause can solve by bleaching. The dentist should check the condition of the gums and teeth. Tooth fracture on the leakage of material conditions and fill teeth.