The most common and most likely answer to this crossword clue is the 6 letter word PLAQUE
I've seen this crossword clue in Financial Times
P
L
A
Q
U
E
More clues leading to the result PLAQUE
- Tablet that’s stuck on teeth
- On-set film panel marking celebrity
- It commemorates an unpleasant mixture of bacteria and saliva
- Tablet’s coating causing harm in mouth
- Trophy filling could be the result
- Tablet for oral condition caused by bacteria?
- Tablet for a dental problem
- Place with a “Quebec” sign
- Undesirable film panel
- Calculus marker
Buddy explains!

The straight part
We know that "Undesirable film/panel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case undesirable film/panel = plaque.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PLAQUE mean?
PLAQUE noun- Any flat, thin piece of clay, ivory, metal, etc., used for ornament, or for painting pictures upon, as a dish, plate, slab, etc., hung upon a wall; also, a smaller decoration worn by a person, such as a brooch.
- A piece of flat metal with writing on it, attached to a building, monument, or other structure to remind people of a person or an event.
- A small card representing an amount of money, used for betting in casinos; a sort of gaming chip.
- A clearing in a bacterial lawn caused by a virus.
- In the Hornbostel–Sachs classification system: any flat, thin musical instrument.
- A broad patch of abnormal tissue distinguishable from surrounding tissue, especially a broad papule on the skin.
- An abnormal accumulation of material in or on an organ of the body, often associated with disease.