Why don't all baby teeth have permanant teeth under them?

They should: All 20 baby should under normal circumstances have permanent teeth to replace them. Occasionally one or more permanent teeth may be congenitally missing.

Congenital : Occasionally patients will have a congenital lack of development of permanent teeth. This is called oligodontia. This can be managed sometimes by orthodontically repositioning teeth or possible dental implants in the future.

Not that unusual: Not having some permanent development of permanent teeth is not that rare. If you have been going to the dentist from childhood on and getting x-rays, i assume that you should have been informed of this (or your parents.).

Missing 'big' teeth : Some people are born missing some permanent teeth. We don't know why. Usually these baby teeth will not fall out on their own. Some people can keep the baby teeth into adulthood if they keep them cavity free. Women who have missing permanent teeth may have a slightly higher risk of ovarian cancer so screenings by your doctor for cancer should start eary in life.

They should: The 20 baby teeth are supposed to have 20 permanent teeth under them. Sometimes 1 or more are congenitally missing and it may be mother nature's way of dealing with the reduction of our jaw size over eons of time. Missing permanent teeth can be addressed with either orthodontic space closure or a prosthetic replacement. See your Dentist and/or an Orthodontist for advice.