Tooth damage around filling of gold (5)
I believe the answer is:
molar
'tooth' is the definition.
(molar is a kind of tooth)
'damage around filling of gold' is the wordplay.
'damage' becomes 'mar' (to mar is to spoil or damage).
'around' indicates putting letters inside.
'filling of' means to look at the middle letters (the letters which fill the inside of the word).
The centre of 'gold' is 'ol'.
'mar' enclosing 'ol' is 'MOLAR'.
(Other definitions for molar that I've seen before include "Type of tooth" , "of ivory, perhaps" , "that could be capped" , "Dealing with masses" , "part of the daily grind" .)