Will crown lengthening (removing/shaving down bone) weaken endodontically treated natural teeth?

The normal reason for crown lengthening is to raise the  gum line up to create longer teeth. If the current level of the gum is even with the next tooth there is no reason to crown lengthen the root canaled tooth. Dark endodonticly treated teeth often show through thin gum tissue. There is really no easy way to mask this problem. You may be able to graft additional tissue over the root to block out the darkness, without a picture it is difficult to determine if this is an option for you. Removing the bonded crowns needs to be done carefully with lots of water. This will prevent overheating of the underlying tooth.