Those teeth are alive. Every time you chew and put pressure on them, it makes them act like a pump, taking in and putting out blood, lymph and saliva through all those dentin tubules. Teeth are very much alive. Once the root is drilled out, that sucker is dead and any "repair" will only be of the encapsular type, seeking to protect the rest of the body from the dead structure. Problem is, that the body is not equipped to deal with a dead tooth still in the mouth. In nature, they fall out. Keeping a dead tooth in only serves as a site for infection and a wide range of changes to occur in that milieu, which just happens to be connected with the rest of the bones. Personally, I don't want any local infections near any portal to my bones, regardless of what any MD's might say. Just my opinion !