Chopper with built-in obsolescence? (4,5)

I believe the answer is:

baby tooth

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'obsolescence?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'chopper with built' is the wordplay.
'chopper' becomes 'tooth' (I've seen this before).
'with' says to put letters next to each other.
'built' becomes 'baby' (I can't explain this - if you can you should give a lot more credence to this answer).
'tooth' after 'baby' is 'BABY-TOOTH'.

'in' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.

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