May need stopping before they get too bad (5)
I believe the answer is:
teeth
'may' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how one could define the other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for teeth that I've seen before include "Dentures" , "Structures in the jaws" , "they add effectiveness" , "Gnashers" , "They're to be found on a gear-wheel" .)