Goes to a dentist, awful, that I have left (7)
I believe the answer is:
attends
'goes to' is the definition.
('attend' can be a synonym of 'go to')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for attends that I've seen before include "to listen carefully" , "Appears" , "ministers" , "Heeds" , "Listens" .)