Turning pale, question filling for dental problem (6)
I believe the answer is:
plaque
'dental problem' is the definition.
(I've seen this before)
'turning pale question filling' is the wordplay.
'turning' indicates anagramming the letters.
'question' becomes 'qu' (abbreviation).
'filling' indicates putting letters inside.
'pale' is an anagram of 'plae'.
'plae' placed around 'qu' is 'PLAQUE'.
'for' is the link.
(Other definitions for plaque that I've seen before include "Unhygienic substance that forms on teeth" , "Commemorative tablet - unwanted film on teeth" , "Unhygienic stuff that grows on teeth" , "Memorial slab" , "film in bad taste?" .)