Dental plaque is a sticky film made mostly of bacteria, but it also contains proteins, sugars, and acids that all work together to cling to your teeth. It’s not just a single substance. Plaque is a living ecosystem, technically called a biofilm, with hundreds of bacterial species embedded in a self-made matrix of carbohydrates, proteins, lipids, and DNA. If you searched this wondering about arterial plaque (the kind that clogs blood vessels), that’s a completely different material, and it’s covered below.
The Bacterial Community in Dental Plaque
Your mouth hosts hundreds of bacterial species, and plaque is where many of them live. The specific mix varies from person to person and even from tooth to tooth, but several genera consistently show up. In people with cavities, bacteria like Prevotella, Veillonella, and Abiotrophia tend to appear in higher numbers. In people with healthy teeth, Rothia and Corynebacterium are more dominant.
Interestingly, Streptococcus mutans, the bacterium most famously linked to cavities, is present at extremely low levels in most people. One study of adolescents found it in only 40% of those who actually had cavities, and when it did appear, it made up just 0.16% of the bacterial population. Cavities, it turns out, aren’t caused by a single villain but by shifts in the overall community that favor acid-producing species.
The Sticky Matrix Holding It Together
Bacteria alone wouldn’t stick to your teeth very well. What makes plaque so stubbornly adhesive is the matrix surrounding those bacteria, a scaffolding they build from their own secretions and from materials in your saliva. This matrix is made up of four main components: carbohydrates, proteins, lipids, and nucleic acids (strands of DNA and RNA released by bacteria as they grow and die).
The carbohydrate portion is the best understood. When you eat sugar, especially sucrose, plaque bacteria use enzymes to convert it into sticky polysaccharides called glucans and fructans. These act like glue, anchoring the biofilm to tooth enamel and making it harder to rinse away. Other sugar-based polymers in the matrix help bacteria stick to each other, building the plaque into a thicker, more organized structure.
The protein portion includes adhesins (molecules bacteria use to grip surfaces), structural fibers called amyloids, and proteins that help organize the biofilm’s architecture. Lipids from bacterial cell walls and membranes also get woven into the matrix, especially when cells die and release their contents. Together, these components create a protective environment where bacteria can thrive, sheltered from saliva, mouthwash, and even antibiotics.
How Plaque Produces Acid
The real damage from plaque comes not from the film itself but from what the bacteria inside it produce. When you eat carbohydrates, plaque bacteria ferment those sugars and generate organic acids, primarily lactic acid. These acids get trapped between the plaque and your tooth surface, creating a concentrated acidic pocket right against the enamel.
Tooth enamel begins to dissolve when the pH at its surface drops below about 5.5. For the softer dentin underneath (exposed if you have receding gums or worn enamel), the threshold is even higher, around 6.0. Every time you eat something sugary or starchy, plaque bacteria can push the local pH below these levels within minutes. If the plaque stays in place and the acid exposure happens repeatedly, minerals leach out of the enamel faster than saliva can replace them. That’s how cavities begin.
How Fast Plaque Forms
Plaque starts building within minutes of brushing. First, a thin protein layer from your saliva coats the tooth surface. Bacteria begin colonizing this layer almost immediately, and during the first one to four hours, they reproduce roughly once per hour. That’s an aggressive growth rate. By 24 hours, the biofilm is well established, and bacterial reproduction slows to once every 12 to 15 hours as the community matures and resources become scarcer.
If plaque isn’t removed, minerals from your saliva (calcium and phosphate) gradually harden it into calculus, commonly called tartar. This mineralization can begin within 24 hours of plaque formation and typically reaches 60% to 90% calcification within about 12 days. Once plaque hardens into tartar, brushing and flossing can’t remove it. Only a dental professional can scrape it off.
What’s in Arterial Plaque
Arterial plaque is an entirely different substance from dental plaque, though they share the same name. It builds up inside artery walls and is the hallmark of atherosclerosis, the condition behind most heart attacks and strokes. The composition is a mix of cholesterol, other fats, proteins, calcium, and inflammatory cells.
The process starts when low-density lipoprotein (LDL cholesterol) accumulates in the inner lining of an artery wall. Immune cells called macrophages move in to clean up the cholesterol, but they absorb so much of it that they become bloated “foam cells.” These foam cells pile up, forming a fatty streak. Over time, smooth muscle cells migrate into the area, and the body lays down fibrous connective tissue, mainly collagen, creating a cap over the fatty core.
Chemical analysis of arterial plaque shows it contains free cholesterol, cholesterol esters, and phospholipids, with roughly 30% of those lipids in an oxidized form. Fatty hydroxides, ketones, and hydroperoxides are also present. In advanced plaques, calcium deposits can make the lesion hard and rigid, similar to bone.
Stable vs. Vulnerable Arterial Plaque
Not all arterial plaques are equally dangerous. What matters most is the structure, not just the size. A stable plaque has a thick fibrous cap rich in collagen, which keeps its contents sealed away from the bloodstream. A vulnerable plaque has a large lipid core and a thin cap. Plaques with a cap thinner than 65 micrometers (about the width of a human hair) are classified as “thin-cap fibroatheromas” and carry the highest risk of rupturing.
When a vulnerable plaque ruptures, its fatty, thrombogenic core is exposed to flowing blood, triggering a clot that can block the artery. Studies have found that 91% of plaques with blood clots forming on them had a lipid core occupying more than 40% of the total plaque volume. The weakest point is typically the “shoulder” region at the edge of the cap, where the fibrous covering is thinnest. Critically, the plaques most likely to rupture aren’t necessarily the ones that cause the most narrowing of the artery, which is why some heart attacks seem to come without warning.