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Why are wisdom teeth called 親知{おやし}らず in Japanese?

The literal meaning seems to be something like "unknown to the parents".

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up vote 11 down vote accepted

From the wikipedia article:


Translation (please edit where appropriate):

In contrast to baby teeth, wisdom teeth often start to grow in after you become independent of your parents. Therefore, your parents do not know about them. This is the reason they are called 親知らず. Also, if you think of baby teeth as the "parents" of permanent teeth, 親知らず do not have corresponding baby teeth, as a result, some people claim that 親知らず means teeth which do not have corresponding baby teeth.

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The name seems appropriate to me. A parent may know about the initial set of teeth that their children have. However, wisdom teeth begin to grow around 18+ years of age. The child is now an adult, so the parents typically will not know about these extra teeth coming in at such a late period.

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In the olden days people died early and usually by the time the wisdom teeth would break through the parents would have died already.

Thus 親知らず meaning "not knowing your parents".

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Dono's answer seems equally plausible and agrees with the explanation on the Japanese Wikipedia page: ja.wikipedia.org/wiki/親知らず. My answer is what an old Japanese woman told me once... – Earthliŋ Sep 5 '12 at 3:10
Yes, this is much like something I was sure I read at some point. However my google searching only turned up this which disagreed. – MatthewD Sep 5 '12 at 3:11
This answer agrees with an episode of Sayonara Zetsubou Sensei I saw, but unfortunately nothing that could be considered expert evidence. Sounds like an urban legend? – AlbeyAmakiir Sep 5 '12 at 5:52

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