Small dogs are prone for bad breath my vets says its because of the small mouths food gets trpped in places you wouldnt think, my male chi...was the worst!..and his food was building up in a hole at the back of his teeth like you i cheacked and couldnt find anything I would take to the vet they soon find out they got mirrors that can see right at the back.
Ps i bought every thing out there for bad breath too!..didnt work..
