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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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2012-09-05T02:55:47.050
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question
etymology
Why are wisdom teeth called 親知らず in Japanese?
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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2012-09-05T03:04:21.740
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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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2012-09-05T03:05:42.003
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2012-09-05T03:05:42.003
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answer
From [the wikipedia
article](http://ja.wikipedia.org/wiki/%E8%A6%AA%E7%9F%A5%E3%82%89%E3%81%9A):

>
> 赤ん坊の歯の生え始めと違い、多くの場合親元を離れてから生え始めるため、親が歯の生え始めを知ることはない。そのため親知らずという名が付いた。また、乳歯が永久歯の「親」と考えると、親知らずには、対応する乳歯が存在しないので、「対応する乳歯が無い＝親知らず」として命名された、という説もある。

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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2012-09-05T03:10:43.157
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