The short potatoes mashed - it may stop cavities (10)
I believe the answer is:
toothpaste
'it may stop cavities' is the definition.
The definition suggests a singular noun which matches the answer.
'the short potatoes mashed' is the wordplay.
'short' means to remove the last letter.
'mashed' is an anagram indicator.
'the' with its last letter removed is 'th'.
'th'+'potatoes'='thpotatoes'
'thpotatoes' is an anagram of 'TOOTHPASTE'.
Can you help me to learn more?
(Other definitions for toothpaste that I've seen before include "Cleaner used in bathroom" , "Dentifrice" , "Cleaning item required" , "Dental cleaner" , "Substance with a fresh flavour" .)