If you have a tooth that looks darker than other teeth, you may have experienced a traumatic injury in the past. The original trauma caused the pulp to bleed. The blood had iron pigment that stained the visible crown of tooth.
Since the pulp has died, root canal treatment is indicated. The opening created at the tongue side of the upper front tooth that allowed Dr. Cancellier to perform the procedure is used as a reservoir for a bleaching agent. It is covered with a temporary filling. You will return in a few weeks for another round of bleach or you will be released to your general dentist for a permanent filling.