"Dentist picks up" joke

A guy and a girl met at a bar.
They're getting along so well that they decide to go to the girl's place.
A few drinks later, the guy takes off his shirt and washes his hands.
He then takes off his pants and washes his hands.
So the girl looks at him and says, 'You must be a dentist!'.
The guy all surprised says, 'Yes, how did you figure that out ?'.
The girl says, 'Easy, you keep washing your hands'.
One thing led to another.
They make love.
After they were done, the girl says, 'You must be a GREAT dentist!'.
The guy was very very surprised, he says, 'Yes, I sure am a great dentist. How did you figure that out??'
The girl says, 'Easy, I didn't feel a thing!'