Looks like a chunk of tarter to me. When you go to your vet have them take a look at it. Maybe not, I just looked at the second picture and it looks like the tooth is actually smaller on the bottom? I WOULD have the vet look at it fairly soon. Does the dog appear to be in pain? Hard time eating? Gums look normal?
Looks like the enamel on the tooth is worn down or off....that appears to be the very outside of the pulp of the tooth exposed. Def need to go to the Vet ASAP, probably to have it extracted.... Does the dog chew on hard things like bones or rocks? Lots of dogs love chewing on rocks for some reason hehe
I agree the enamel looks worn, if you look at how the upper canine meets with the lower one, it looks like the upper is wearing down the lower. What do the back and inside edges of the upper tooth look like?
