Some hero dentists are wearing away (7)
I believe the answer is:
erodent
'are wearing away' is the definition.
(I've seen this before)
'some hero dentists' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'ERODENT' can be found hidden inside 'hero dentists'.
(Other definitions for erodent that I've seen before include "Caustic" , "wearing away" , "Corrosive" , "eating away" .)