Today, most dental professionals know that periodontal disease results from a bacterial infection. Some even know the names of some of the notorious red group of periodontal pathogens, like Porphyromonas gingivalis, Treponema denticola and Tannerella Forsythus.  There are about a dozen more, lesser-known pathogens, including Prevotella intermedia and Fusobacterium nucleatum that yet haven’t achieved the notoriety of the so-called red group.

What’s less understood is that none of these pathogens can cause periodontal disease alone. Just as it takes a village to raise a child, it takes a cooperative assembly of different pathogens to cause an infection. Individually, they’re harmless. It’s only when large numbers of these bacteria come together in organized groups called biofilms that they become pathogenic.

Why?  Because almost all periodontal pathogens are anaerobic. By the way, that doesn’t mean they are killed by oxygen. In microbiology, anaerobic bacteria grow best in a low oxygen environment. They can live at higher oxygen levels, but they reproduce more slowly. Sulci less than 4 mm are typically aerobic. The higher oxygen level inhibits their growth as does competition with aerobic bacteria (bacteria that grow best in an oxygenated environment.)

So, when oxygen levels are about 3% or higher, growth is inhibited and they live as planktonic (free-swimming, unorganized, individual) bacteria. In low numbers, they’re no match for the host defenses. They don’t even bother activating the genes that make them pathogenic. It would be a waste of energy.

However, if the oxygen level drops, as it does in the absence of good dental hygiene, the reproductive rate surges.

How do planktonic bacteria know when there are enough of own species around to make becoming pathogenic worthwhile? Well, they can count, sort of. Each bacterium secretes small molecules called autoinducers. They also have receptors on their membranes to detect autoinducers. When the detection rate exceeds some threshold, they know that they’re surrounded by enough brethren species to collectively overcome the host defenses. That level triggers the genes that enable the formation of biofilms and activation of pathogenic genes that overcome the host’s defenses.

The key to preventing periodontal infections thus lies in keeping the sulci aerobic and the number of pathogenic species low. It’s not about calculus. That’s inert. It’s all about eliminating pathogenic species or at least keeping their numbers in check.

Next blog:  How do biofilms overcome host defenses.  It’s not what most people think. It’s less like an open war than a stealthy fifth column.