Who is the Fifth Dentist?

The famous Trident commercials claim that "Four out of five dentists recommend chewing sugarless gum". That always sticks out to people, but my guess is that fifth dentist is the smart one. If you recommend chewing sugary gum and sweets to your patients you're going to be doing a lot more business. I never understood why anyone would trust the word of a dentist. What benefits do they gain when you have perfect dental health?

Dentists are always trying to do unnecessary surgeries to have your wisdom teeth removed so why wouldn't they tell you to gargle with Dr. Pepper every night before bed? You're dealing with people who choose to dig inside stranger's mouths for a living, how can anyone trust them? Dentists are like proctologists, I don't believe a damn thing they say because they work with moist bacteria laden orifices. Too many years of that and you're lucky if only every fifth dentist goes completely insane.