Waste lying in sad teeth — who's needed? (6,9)

I believe the answer is:

dental hygienist

'who's needed?' is the definition.
I can't tell whether this defines the answer.

'waste lying in sad teeth' is the wordplay.
'waste' indicates an anagram (I've seen 'wasting' mean this (waste can mean to destroy)).
'lying'+'in'+'sad'+'teeth'='lyinginsadteeth'
'lyinginsadteeth' is an anagram of 'DENTAL HYGIENIST'.

I've seen this clue in The Times.

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