Incisor’s coating of enamel seen on outside of head (7)
I believe the answer is:
scalpel
'incisor's' is the definition.
(blade for making incisions)
'coating of enamel seen on outside of head' is the wordplay.
'coating of' says to hollow out the word (remove centre letters) (only the letters that coat the word remain).
'seen on' says to put letters next to each other.
'outside of head' becomes 'scalp' (skin covering the head).
'enamel' with its centre taken out is 'el'.
'el' after 'scalp' is 'SCALPEL'.
(Other definitions for scalpel that I've seen before include "Surgeon's blade" , "One making cuts in hospital" , "Small surgical knife" , "Surgical blade" , "Theatrical knife?" .)