Why Do Roots of Baby Teeth Look So Long?

The bottom baby front teeth (Fig.1 A) usually fall out by themselves at the age of 6.  Elaine is 7 years old.  Her front teeth are stable, while the permanent teeth are behind (Fig.1: #1).  The baby teeth need removal immediately so that the adult teeth may reposition themselves.  When the baby teeth are out, they look extremely long without any root resorption (Fig.2, as compared to normal ones (Fig.4)).

Fig.3 is cross section of development of baby and adult front teeth.  Normally the former is more or less immediately above the latter (a).  When the adult tooth starts to move up (b), the root of the baby tooth becomes resorbed and shortened (red saw-teethed).  As the permanent tooth keeps growing, it eventually causes complete root resorption of the baby one (c).

In Elaine's case, the permanent tooth is too behind the baby one (d).  When the former grows, it does not cause root resorption of its predecessor (e, f).

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Xin Wei, DDS, PhD, MS 1st edition 07/17/2016, last revision 07/17/2016