The term “plaque” in a medical context refers broadly to an abnormal patch, deposit, or build-up that adheres to a surface within the body. This material often consists of aggregated or hardened biological substances, creating a localized accumulation. The exact composition and location of the build-up determine the specific health implications. Therefore, the word is used across several distinct physiological systems.
Plaque on Teeth
Dental plaque is a soft, sticky, colorless film that forms naturally on the surface of teeth, representing a complex microbial community known as a biofilm. It is composed primarily of bacteria embedded within a matrix of polymers derived from bacterial products and saliva components. Formation begins almost immediately after cleaning, as salivary proteins precipitate to create a thin acellular layer called the acquired pellicle. Bacteria then adhere to this pellicle.
Initial colonizers like Streptococcus species begin the foundation of the biofilm. As the bacteria multiply, the mass matures, with the dry weight of the plaque consisting of about 70% microorganisms. These bacteria metabolize dietary sugars, producing acids that cause the demineralization of tooth enamel, leading to dental caries, or cavities.
If soft plaque is not regularly removed through mechanical cleaning, it begins to mineralize due to the accumulation and deposition of calcium and phosphate ions from the saliva. This hardening process results in the formation of dental calculus, commonly known as tartar, which cannot be removed by simple brushing. The presence of plaque and calculus near the gumline irritates the gingiva, initiating an inflammatory response called gingivitis. Sustained inflammation can progress to periodontitis, a severe condition involving the destruction of the bone and tissues supporting the teeth.
Plaque in Arteries
Plaque that forms within the walls of arteries is known as atherosclerotic plaque, defining the progressive disease atherosclerosis. This complex deposit accumulates in the inner lining of the artery wall, known as the intima. Its composition includes a mix of fatty substances, cholesterol, cellular waste products, calcium, and fibrin.
The process begins when the endothelial lining of the artery is damaged, often by high blood pressure or elevated low-density lipoprotein (LDL) cholesterol. LDL particles then penetrate the arterial wall and become trapped, where they are modified, typically through oxidation. Circulating monocytes are recruited to the site, transforming into macrophages that engulf the modified LDL.
These cholesterol-laden macrophages are known as foam cells, and their accumulation forms the initial fatty streak, the earliest stage of atherosclerotic plaque. The plaque then develops a fibrous cap composed of smooth muscle cells and extracellular matrix, covering a core of lipid-laden cells and debris. This build-up thickens and stiffens the artery wall, narrowing the channel and reducing the supply of oxygen-rich blood.
Atherosclerotic plaque presents a significant danger, particularly when classified as unstable. Unstable plaques have a thin fibrous cap and a large lipid core, making them prone to rupture. When rupture occurs, the thrombogenic material in the core is exposed to the bloodstream, triggering the rapid formation of a blood clot, or thrombus. If this clot completely blocks the artery, it can lead to a sudden and life-threatening event such as a heart attack (in a coronary artery) or a stroke (in an artery supplying the brain).
Plaque in Other Health Contexts
The term “plaque” is also used to describe abnormal patches or deposits in other parts of the body, notably the skin and the brain. In neurological health, amyloid plaques are a characteristic feature of Alzheimer’s disease. These are extracellular deposits found between nerve cells, primarily composed of aggregated fragments of the protein beta-amyloid.
The accumulation of these misfolded protein aggregates is thought to disrupt communication between neurons and contribute to cognitive decline. Amyloid plaques often form alongside neurofibrillary tangles, which are twisted filaments of the protein tau found inside the nerve cells. Both lesions are hallmarks used to characterize the progression of the disease.
Plaque is also a term used in dermatology, particularly for plaque psoriasis, the most common form of the chronic skin condition. In this context, a plaque is a raised, inflamed, and well-demarcated patch of skin, often covered with silvery-white scales. Formation is driven by an immune system malfunction that causes skin cells to grow much faster than normal, leading to a rapid build-up on the skin’s surface. These patches can be itchy and painful and are typically found on the elbows, knees, scalp, and lower back.