Are Dog Mouths Cleaner Than Human Mouths?

I've always heard that a dog's mouth is cleaner than a human's mouth, which seems absurd to me, partially because my dog chewed on a dead bird today (and that's not the grossest thing that's been in her mouth).

It turns out that statement is untrue, but it's true-ish.

Scienceline.org says:

“It’s like comparing apples and oranges,” says Colin Harvey, a professor of surgery and dentistry at the University of Pennsylvania’s School of Veterinary Medicine. He is also the executive secretary at the American Veterinary Dental College.

And ABC News says:

[Veterinarian Marty] Becker says many of the bacteria in the mouth of a dog are species specific, so it won't harm its owner. 'So a staph or a strep for a human is not transmissible to a dog, if you were to kiss it, and vice versa,' said Becker.

So their mouths aren't cleaner, but their germs aren't likely to be harmful to people.

Mystery solved.