Please help! what is the difference of crown to root ratio between deciduous and permanent teeth?

Crown to root ratios: If you re-post the question stating why you are asking the question, you will probably get a more helpful and to the point answer. Crown to root ratio is important as to strength of teeth and foundation in bone. Overwhelmingly, permanent teeth are larger, have bigger roots and are therefore stronger.

It's the same ratio: The crown to root ratio for permanent teeth and primary teeth are the same: one third of the total length of a tooth is the crown and two-thirds is the root. Obviously, the entire tooth of a deciduous tooth is smaller compared to the permanent tooth.

Correct: Dr doyon is absolutely correct. When a baby tooth falls out the root has disolved away. Ask your dentist to see x-rays of baby teeth that have not begun the resorption process to see normal crown-root ratio.