Worries about one finding tooth decay (6)
I believe the answer is:
caries
'tooth decay' is the definition.
(term for decay of a tooth or bone)
'worries about one' is the wordplay.
'worries' becomes 'cares' (I've seen this in another clue).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'cares' going around 'i' is 'CARIES'.
'finding' is the link.
(Other definitions for caries that I've seen before include "Decay of bone or teeth" , "I scare easily with tooth decay" , "Decayed areas in teeth" , "Decay in bones or teeth (6)" , "Dental cavities" .)