Material found in teeth or in a plant (5)
I believe the answer is:
ivory
'material' is the definition.
(ivory is a kind of material)
'or in a plant' is the wordplay.
'in' means one lot of letters goes inside another.
'a plant' becomes 'ivy' (ivy is a kind of plant).
'or' inserted into 'ivy' is 'IVORY'.
'found in teeth' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ivory that I've seen before include "Yellowish white - material from tusks" , "Elephant tusk material" , "Key material" , "Piano-key" , "Material from tusks of certain mammals" .)