change to black color may be because of two reasons... 1. extrinsic stains caused by bacteria in plaque 2. any hit/ trauma resulting in loss of life of the tooth visit a near by dentist to get a perfect idea of the problem

Hi! Change in teeth color is more likely because of progressive plaque(sticky film) layer that accumulates on surface of the teeth. Progressively, Plaque hardens and form a strong layer called as calculus over a period of time, which is yellowish to brownish in color. Normal food we consume has artificial/natural colors incorporated which these sticky films attracts and deposit them leading to color change.