As I understand it, as a general rule, a dog's mouth is much "cleaner" (i.e., less bacteria) than a human mouth.
Most of my very limited sexual experience with dogs occurred over a decade ago with a neighbor's dog. After our first encounter (her licking me until I had an orgasm), we mostly just engaged in cuddling and kissing. She loved kissing. That became her favorite activity with me. In my (albeit limited) experience, when a dog kisses you they go deep, sticking their muzzle right into your mouth. To be honest, I didn't really enjoy it that much, but I wanted to make her happy, so I went along with it. Sometimes our kissing sessions would last 20 minutes or more, until I'd had enough. (My mouth would start to get really dry, as if I'd swished my mouth with an astringent, like witch hazel.) If I had let her kiss me as long as she wanted, I'd don't know if we ever would have stopped.
