Powder used in dental cleaning (4)
I believe the answer is:
'powder' is the definition.
(talcing is a kind of powdering)
'in dental cleaning' is the wordplay.
'in' indicates a hidden word.
'TALC' is hidden within 'dental cleaning'.
'used' is the link.
(Other definitions for talc that I've seen before include "Mineral used as a toiletry" , "Soft stuff" , "Cosmetic powder" , "Powder used as toiletry" , "Powdered mineral" .)