Teeth are very rarely lost in this day and age, because every effort is made to save them. There are a number of reasons why teeth may need to be removed:
When there has previously been a lot of decay and very little of the tooth remains. For example root filled teeth with post crowns or broken teeth.
The supporting bone around the tooth is lost due to pocketing and infection.
Teeth that have been root canal treated can be prone to persistent infection resulting in a poor prognosis and are often better removed.
Such as when a tooth is buried under the gum or has come through in the wrong place.
Whatever the cause of the problem, the end result is the root of the tooth is removed. Dental implant therapy is the replacement of the root with an artificial root that is made from titanium. This procedure can be used to replace one tooth, several teeth, or all the teeth.
When any part of the body is put out of use, it tends to wither away. If we take a tooth away the gum will shrink, underneath the bone that used to support the tooth will find itself with no reason to stay and will also shrink away.
There are some factors that speed up the bone loss process. One of these is the use of dentures when you clench; dentures squeeze the blood out of the gum. This reduces the blood supplying the bone and causes accelerated shrinkage. In addition teeth that are associated with infection may result in faster loss of bone. This is why diseased teeth should be removed soon so that bone is not lost.