He's a four pound chihuahua that I've always compared to an autistic child. These are the things that frighten him: too much outside stimulation, too much touching, fingers curled while you pet him, hand too heavy, a bowl that is different (he won't eat if it isn't a small white bowl), picking him up when he faces you, touching him unexpectedly, looking at him....well just about everything. And now at the age of 12, we think he's beginning to suffer a little from dementia and that shows by him 'asking' to go outside but then forgetting why he's out there so you gotta keep telling him over and over to go to the bathroom or he just stands there staring at you! Totally useless little dog because he's too fearful to even be cuddly, but we just enjoy his weirdness and are glad that we are the family that took him on. Some people would be the wrong fit for a little mutty with issues.
As for 'his own toothbrush' well why not? I'm not sharing mine.
You're very kind for taking him in and giving him such TLC. My dog is beginning to have old age issues like arthritis, senior moments, auto immune disease, etc. My dog before him suffered with Idiopathic Epilepsy, and she also had hip dysplasia and some other health problems. I'm glad she was with us too, because we gave her all the love and care that was needed to keep her safe and comfortable during those difficult times.
People toothbrushes are the wrong size and shape anyway for dogs. You're absolutely correct about wild animals not needing their teeth cleaned due to their natural diet in the wilderness. Animal lovers really care about their pets, and I love to hear that. I often say that I like animals over people in general.