Here's the trick: don't treat your mouth like shit and find a good dentist.
If you actually do brush at least twice a day and floss at least daily, not only will you have a nice kissable mouth, you'll have dramatically reduced risk of gum disease, cavities, and other ailments that make the dentist have to do painful things to you.
There are dentists & hygenists who know how to make the process much less painful. They do this through a mix of strong interpersonal skills, the latest equipment, good physical techniques, and genuinely caring about their patients. If your dentist doesn't seem to be on your side, find one who is. Ask friends for recommendations and when you're talking to a prospective new dentist's office, ask about how they reduce the painfulness of common procedures such as cleanings.
Personally, I recommend Dr. Perona in San Francisco. Tell him Dinah sent you.