Bugs escaping from the mouth employ a survival trick that can trigger deadly blood clots, research has shown.
The link between bacteria that cause dental plaque and heart disease and strokes is well known.
Scientists have now discovered just why it is that the microbes pose a far bigger risk than receding gums.
Once let loose in the blood they deploy a protein that forces platelets to bind together and shield the bugs with clots.
Professor Howard Jenkinson, from the University of Bristol, said: "When the platelets clump together they completely encase the bacteria. This provides a protective cover not only from the immune system, but also from antibiotics that might be used to treat infection.
"Unfortunately, as well as helping out the bacteria, platelet clumping can cause small blood clots, growths on the heart valves, or inflammation of blood vessels that can block the blood supply to the heart and brain."
He said bacteria can "wreak havoc" if not kept in check by brushing and flossing.