The general sign for "dentist" combines the sign TOOTH and PERSON-agent.
DENTIST (TOOTH + PERSON-agent)
Note: In context you can drop the "PERSON-agent" sign and just sign "TOOTH." You use a double motion as if tapping your tooth twice -- but you don't actually make contact with the tooth. For example, if you sign "I/me GO TOOTH" it is obvious that you are saying that you are going to the "dentist."
Note: A lot of people "initialize" the sign DENTIST by doing it with a "D" hand. If you do that version, you should not add the PERSON-agent sign. I don't recommend using the initialized version since the traditional ASL sign is very easily recognized.
Another version of "dentist" is to hit (lightly) the side of your mouth a couple times with the pinkie-side of your fist.
Sample sentence: "How often do you go to the dentist?" = YOU GO DENTIST HOW OFTEN?"
Notes: