Preserved dent in formation (6)
I believe the answer is:
tinned
'preserved' is the definition.
(similar in meaning)
'dent in formation' is the wordplay.
'formation' is an anagram indicator.
'dent'+'in'='dentin'
'dentin' is an anagram of 'TINNED'.
(Other definitions for tinned that I've seen before include "Canned" , "Sealed in a can" , "In cans" .)