Do Dogs Have Clean Mouths?
Dogs' mouths are clean enough that you could let them lick you. As a show of affection, dogs sometimes lick you to share comfort and to relieve stress. However, some dog owners might be worried about diseases that such contact might transfer such as rabies, pasteurella, salmonella, novovirus, and others. But this worry is mostly unfounded as these kinds of diseases involve bites and contact with fecal matter. Interestingly, some researches show that canine saliva has antimicrobial properties which gives credence to common beliefs that licking one's wound helps it heal faster. On the other hand, a dog's mouth contains its own world of bacteria but most of these have been determined to be harmless to both dogs and humans as they are a normal part of a dog's oral health. Just make sure to keep your dog away from your open wounds for your peace of mind.
On whether a dog's mouth is cleaner than a human's, the vastly different microbes in their respective mouths and their effects to the other point that such discourse is unnecessary.