What is this on my doodles teeth?

[Lauren Hayes]

As I was brushing my pups teeth I noticed this same tooth on both sides were looking weird and had this blacking like line which seems to be like a crack since when I rub it with my finger my nail catches in it !  Cavity possibly ?!   Anyone elses doodle pup experience this and if so what was the turn out?

P.S. Our dog eats no wet food and exclusively eats Taste of the wild dog food.sively eats Taste of the wild dog food.

[Rosemary (Ro) and Enzo]

I've tried the same move without any success!

[Ricki and Tara (doodle)]

Me too. I think I need a vet tech to assist. My subjects are not very cooperative. ;)

[Lauren Hayes]

Thanks you all so much <3 Any kits or brand specific for finger toothbrush please do share and I will order tonight online :D!