Dentists, psychologists and neurologists in Stockholm and Umeå in Sweden and Tromsø in northern Norway, are cooperating on the Betula Project, a study of age, memory, senility and health. The Betula Project has been going on for nearly 20 years in Sweden, and has Center of Excellence status.

A study of around 2,000 persons in Umeå revealed a clear tendency that those who kept a full set of teeth had better powers of memory than those who lost teeth.

"We have tested the problem from every angle and reached the same result," said Professor Jan Bergdahl at the Institute for Clinical Odontology at the University of Tromsø. Bergdahl is both a dentist and psychologist and works closely with the research centers in Umeå and Stockholm.

Their conclusion that older persons with their own teeth have better memory that those without is now going to international publication.

Researchers in Japan achieved similar findings on tests with mice and monkeys, with mice learning to find food in labyrinths but forgetting this knowledge when their teeth were pulled.

"We know that own teeth are important for elderly health. Chewing brings oxygen-rich blood to the head and one chews better and harder with one's own teeth," Bergdahl said.

The Norwegian-Swedish researchers will now examine if the number of teeth is significant, and if certain teeth have a more important role for memory than others. They will also examine if titanium implants have an impact on memory, and if there are genetic components to memory and tooth loss.

In Norway and Sweden it was quite common until about 50 years ago to pull all teeth and get dentures as soon as a first tooth rotted.