Tablet that's stuck on teeth (6)
I believe the answer is:
plaque
I believe this clue is a double definition.
'tablet' is the first definition.
(thesaurus)
'that's stuck on teeth' is the second definition.
(Other definitions for plaque that I've seen before include "Memorial plate" , "Unhygienic stuff that grows on teeth" , "Memorial slab" , "Film on tooth" , "Sticky deposit on teeth" .)