Dental Plaque: The Bacterial Biofilm That Drives Cavities and Gum Disease

Dental plaque is a biofilm -- a structured community of microorganisms, overwhelmingly bacteria but also some fungi, embedded in a self-produced matrix of polysaccharides and glycoproteins -- that grows on tooth surfaces. By dry weight it is roughly 70% microbial cells and 30% matrix. As a biofilm, plaque is far more resistant to disruption than free-floating bacteria; see Biofilms: The Bacterial Communities 1000× More Resistant to Antibiotics. Formation follows a predictable sequence. Within minutes of a clean, salivary proteins coat the enamel as an acquired pellicle. Early colonizers, mostly Streptococcus species, bind loosely to this film and multiply into micro-colonies, secreting slime that anchors them. Over the first few days the community matures: gram-positive cocci dominate at first, then filamentous rods appear, and by one to two weeks gram-negative anaerobes and spirochetes such as Porphyromonas gingivalis and Treponema establish themselves. The central cavity-causing organism is Streptococcus mutans. Its enzyme glucansucrase (a glucosyltransferase) splits dietary sucrose, fermenting the fructose for energy and polymerizing the glucose into sticky dextran, an extracellular polysaccharide that cements bacteria to enamel and builds the plaque matrix. Fermentation of these sugars produces acid, which demineralizes the enamel surface and, repeated over time, causes dental caries (tooth decay). Fluoride counters this by making enamel more acid-resistant -- see How Fluoride Strengthens Enamel: The Hydroxyapatite to Fluorapatite Swap. Plaque also harms the gums. Accumulation at the gumline triggers gingivitis, a reversible inflammation; if plaque persists, it can progress to periodontitis, in which bacterial activity and the body's own osteoclasts destroy the bone supporting the teeth. Plaque is part of the normal mouth ecosystem, not a sign of a dirty mouth -- see The Oral Microbiome: Why a Healthy Mouth Is Not a Sterile One -- but it must be controlled. Left in place, plaque absorbs calcium and phosphate from saliva and mineralizes into calculus (tartar), a hard yellow-brown deposit that begins hardening within a couple of days and reaches most of its final hardness by about two weeks. Once mineralized, calculus bonds tightly to the tooth and cannot be brushed or flossed off; only professional scaling removes it. The primary defense is daily mechanical disruption of soft plaque before it mineralizes: brushing and interdental cleaning, as covered in Correct Toothbrushing Technique Matters More Than Toothpaste Choice. Antiseptic rinses such as Chlorhexidine: The Gold-Standard Antiplaque Mouthwash (and Why It's Short-Term) suppress plaque chemically but do not replace mechanical removal.