Type of hygiene (4)
I believe the answer is:
oral
'type of hygiene' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oral that I've seen before include "language exam" , "Ant; tourist (dial.)" , "'Spoken, not written (4)'" , "Unwritten examination" , "Spoken, of the mouth" .)