Filth originally inside an incisor unfortunately too deep to pick up? (10)
I believe the answer is:
infrasonic
'too deep to pick up?' is the definition.
(too deep for humans to hear)
'filth originally inside an incisor unfortunately' is the wordplay.
'originally' says to take the initial letters.
'inside' means one lot of letters goes inside another.
'unfortunately' is an anagram indicator (a bad or unfortunate spelling).
The first letter of 'filth' is 'f'.
'an'+'incisor'='anincisor'
'anincisor' is an anagram of 'inrasonic'.
'f' going inside 'inrasonic' is 'INFRASONIC'.
(Other definitions for infrasonic that I've seen before include "too low to be noticed" , "inaudible" .)