Veneer or root canal/bleaching? Tooth has turned gray. (Photos)

Internal beaching, ideally done by an endodontist is the best starting point as they will often be able to start the level of bleaching higher up the canal (further under the gum line) than a general or cosmetic dentist will be able to do. The whole treatment process will also be shorter if the endodontist completes the bleaching. 
If you assess at that stage, the choice should be between veneer, crown and possibly composite bonding depending on the amount of difference between the undamaged tooth and the root treated tooth at that stage. 
Good luck with your treatment - and as others have suggested, do not wait on this as damage to the end of the root is otherwise almost inevitable. 
Kind regards
Thomas Dey, BDS, MSc

I agree with both dentists. Get the root canal done first. I suggest trying the internal bleaching first. It is low cost and can be effective. If it doesn't work do the veneers. You will always have to deal with this tooth getting darker so you might also consider a zirconia crown on this tooth to mask out the color. 

I would consider having endodontic treatment soon as the nerve is degenerating or dead and occasionally we will see resorption and root damage if left for long periods.The dentist will evaluate the tooth for cracks and suggest a treatment approach.  This may be a situation of doing a root canal therapy, internal bleaching and bonding a composite post internally.  If cosmetically acceptable, delaying or not doing a ceramic crown or veneer for now.  It will depend on the amount of cracks and discoloration noted after initial treatment.

When you traumatized your tooth by hitting it on a shopping cart, the nerve was irreversibly  damaged .   It should have root canal treatment as there is a good probability that  infection could develop and lead to an abscess at sometime in the future.   Once a tooth has a root canal, the nerve and the blood supply in the canal  are removed, and without blood supply that tooth becomes more brittle and subject to fracture. For this reason, it is best to have a full crown placed over a tooth that has a root canal.   It is very difficult to match the color of one front tooth to another with a single crown, but it is possible to get very close. If you want to match perfectly, then a veneer or crown could be placed on your other central incisor.   Placing a veneer over a dark tooth may not mask the discoloration due to the thinness of the veneer, so I would not recommend that treatment for your tooth. Hope this helps you make an informed decision.

Hi:The reason for the discoloration is that the nerve of the tooth is dead due to trauma.  Therefore you definitely need to get a root canal to prevent infection in the future.  After the root canal 2 veneers in the front would give you the best long term resultsBest,Dr. Maddahi