The main cause of tooth decay is bacteria or germs in the mouth which turns sugar into lactic acid.
The acid then destroys teeth.
But now US scientists say they can genetically modify (GM) the bacteria so it doesn't produce the acid.
The GM germs would be squirted in your mouth.
Five minutes later you'd be protected from tooth decay for life.
So far tests on animals have worked and human trials are to start in the UK and America by the end of 2002.