Damage a student of teeth (6)
I believe the answer is:
dental
'of teeth' is the definition.
(I've seen this in another clue)
'damage a student' is the wordplay.
'damage' becomes 'dent' (dent is a kind of damage).
'student' becomes 'L' (as in L-plates for learner drivers).
'dent'+'a'+'l'='DENTAL'
(Other definitions for dental that I've seen before include "Consonant" , "sort of surgeon" , "surgery" , "Concerning teeth" , "Concerned with teeth" .)