Answer:

decay

Answer	Crossword Clue
DECAY	Go bad
DECAY	Fall into ruin
DECAY	Urban ...

DECAY	Dentist's concern
DECAY	Rot
DECAY	Dental problem
DECAY	Dental concern
DECAY	Progressive decline
DECAY	Deteriorate
DECAY	Break down
DECAY	Dental woe

DECAY	Crumble away
DECAY	Cavity cause
DECAY	Tooth trouble
DECAY	Waste away
DECAY	Go to pot
DECAY	Canine's woe?
DECAY	Dentist's discovery
DECAY	Degenerate

DECAY	Decompose
DECAY	Erode
DECAY	Dentist's concern, and a hint to what the longest answers have in common
DECAY	Rot.
DECAY	"Change and ... in all around I see . . . "
DECAY	Disintegration.
DECAY	Termite result.
DECAY	Gradual failure.

DECAY	Spoil.
DECAY	Gradual decline.
DECAY	Tooth problem
DECAY	Caries
DECAY	Tooth nemesis
DECAY	Crumble
DECAY	Molder
DECAY	Disintegrate

DECAY	Dental damage
DECAY	Go bad, as teeth
DECAY	Reason to drill
DECAY	Cause of radioactivity
DECAY	Go downhill