If a single tooth turns dark, this is an indication that the nerve of the tooth has died. Because in this case, tissue inside the tooth decomposes and waste products are deposited that discolor the tooth. The reason for the death of the dental nerve can be a strong external force impact on the tooth – such as hitting a hard object as a result of a fall or a punch on the tooth. On the other hand, the dental nerve may also die off due to deep caries in the tooth. In addition, teeth often develop a dark discoloration after root canal treatment.
In all of these cases, the cause for the discoloration lies inside the tooth and it is not caused by external deposits (e.g. from smoking, coffee, tea, red wine etc.) on the outside of the tooth.