Why are wisdom teeth called 親知らず in Japanese?

Question

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".

Answer 1

From the wikipedia article:

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.

Answer 2

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.

Answer 3

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".