“How do astronauts brush their teeth in space?”

Astronauts living on the International Space Station still have to brush their teeth every day, preferably twice a day. There’s no “out in space” exemption for dental hygiene. But how do you get the toothbrush wet in zero gravity? Where do you spit without a sink? Why doesn’t all that mess end up in your hair? How do astronauts brush their teeth in space?