Professional set-up looking down in the mouth (6,8)

I believe the answer is:

dental practice

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This could be a double definition.

'professional set-up looking' is the first definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe there's a link between them I don't understand?

'down in the mouth' is the second definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I can't see?

Can you help me to learn more?

I've seen this clue in The Daily Express.

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