About cards for teeth (7)

I believe the answer is:

canines

I'm a little stuck... Click here to teach me more about this clue!

'teeth' is the definition.
(canine is a kind of tooth)

'about cards' is the wordplay.
'about' becomes 'ca' (short for circa).
'cards' becomes 'nines' (I can't justify this - if you can you should give a lot more credence to this answer).
'ca'+'nines'='CANINES'

'for' is the link.

Can you help me to learn more?

(Another definition for canines that I've seen is " Dogs -- teeth".)

I've seen this clue in the Sydney Morning Herald.

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