Over the course of a lifetime, many people lose teeth. What most people do not know is that your body will reabsorb the bone at the site of the missing tooth, using the minerals elsewhere in the body. If you are missing all your teeth, over time your jaws can deteriorate dramatically. The diagram in the sidebar shows the progression from normal, healthy jaw with teeth (top) to the severely deteriorated jaw (bottom). This deterioration can lead to a condition called "facial collapse".
If a patient has a jawbone like that pictured at the bottom of the diagram, they will find it very uncomfortable to wear a conventional removable denture. With such a limited ridge of bone left, the soft tissues of the mouth bear all the pressure of the teeth, and the denture itself will move around a great deal, as there is no stable surface for it to rest on. This inevitably causes irritation and soreness, usually to the degree that dentures can no longer be tolerated.
Ideally, missing teeth should be addressed as quickly as possible, to prevent this kind of deterioration. If the bone has deteriorated to such a severe point that dentures are no longer a viable option, the patient would likely need bone grafts to make the jaws strong enough to accept an implant. Obviously, this makes the entire procedure much more complex, and much more expensive. Dental insurance almost never covers the cost of dental implants or the bone grafting surgery.
The good news is that once the dental implants are in place, the body senses their presence and responds by building up the bone to support the "tooth". If the damage is not too severe, dental implants can halt and even reverse the damage done by years of missing teeth.