A dogs mouth is not really cleaner than a humans mouth.
I've heard that for years that a dogs mouth is always cleaner than a humans mouth is but that is so not true.
Think about it a dog licks it's private areas clean and also some dogs eat their own poop.
That would make a dogs mouth really dirty and much dirtier than a humans mouth and also some dogs drink from the toilet which is also disgusting.
Humans do not drink from the toilet, lick their own private parts, eat their own poop etc so that would make a humans mouth cleaner than a dogs mouth.
Also most humans brush their teeth often, use mouthwash etc to clean their teeth and mouth.
Dogs do not brush their teeth, use mouthwash etc.
So dogs mouths are not cleaner than a humans and a dog licking a human is disgusting.