Article stopping tooth decay in birds (8)
I believe the answer is:
canaries
'birds' is the definition.
(canary is a kind of bird)
'article stopping tooth decay' is the wordplay.
'article' becomes 'an' (indefinite article).
'stopping' is an insertion indicator (stopping can mean blocking a gap).
'tooth decay' becomes 'caries' (dental caries).
'an' placed within 'caries' is 'CANARIES'.
'in' acts as a link.
(Other definitions for canaries that I've seen before include "Atlantic islands - cagebirds" , "Small yellow finches" , "The birds can arise" , "The birds forewarn of danger in the mines" , "Mediterranean islands and yellow birds" .)