Mom and I have Grandma and Grandpas 16+ year old chihuahua, she has no teeth. She often times "corrects" my 55 pound Airedale. Its hilarious. Considering the size/age difference, and the fact that she has 0 teeth.
When I was three, we got a female puppy Chihuahua. She lived till I was twenty-one. Her last year was spent mostly sleeping in her little bed. Near the end, she was mostly deaf, blind, and toothless. Ears, eyes, and teeth, just wore out with age. When she lost the ability to walk, I took her in for her last visit to the vet. I cried like a baby right there in the office. My only regret was not going into the room with her. I just couldn't do it.
Throughout her prime, and nearly to the end, she was top dog in a pack that included two German Shepherds. She laid down the law to them, and they accepted her position, mostly (probably) because they were afraid that any action on their part in self-defense would be her end, and they knew it.