The dentist

A guy and a girl meet at a bar. They get along so well that they decide to go to the girl's
apartment. A few drinks later, the guy takes off his shirt and then washes his hands. He
then takes off his pants and washes his hands.
The girl watches him and says, “You must be a dentist.”
The guy, somewhat surprised says, “Might be, I’ll tell you latter ... what make you say
that?”
The girl replies, "Easy... you keep washing your hands."
One thing leads to another and they make love. After they are finish, the girl says,
“Now I’m certain you’re a great dentist.”
“OK I am.” replies the guy. “How do you know?”
“Simple” girl replies, "I didn't feel a thing!"