It's blown up if dental treatment is required (8)
I believe the answer is:
inflated
'it's blown up' is the definition.
('inflate' can be a synonym of 'blow up')
'if dental treatment is required' is the wordplay.
'treatment is required' indicates an anagram (letters must be treated).
'if'+'dental'='ifdental'
'ifdental' with letters rearranged gives 'INFLATED'.
(Other definitions for inflated that I've seen before include "Blown up" , "Blew up" , "Filled with air or gas to distend" , "Flan diet (anag.)" , "Pompous" .)