Crown covering (6)
I believe the answer is:
enamel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">crown covering</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for enamel that I've seen before include "found on crowns" , "protective coat" , "Glassy substance" , "Glassy coating" , "Hard white substance covering the crown of a tooth" .)