Occlusion means a blockage or closure. In medicine, it most often refers to something blocking a blood vessel, but the term also appears in dentistry (how your teeth fit together) and in other contexts like bowel obstructions. The word comes from the Latin “occludere,” meaning to shut up or close off. Understanding which type of occlusion is being discussed matters because the causes, symptoms, and treatments differ dramatically depending on where in the body it occurs.
Vascular Occlusion: Blocked Blood Vessels
The most common medical use of “occlusion” describes a blood vessel that has become partially or fully blocked. When a vessel is partially narrowed, doctors call it a stenosis. When it’s completely blocked, that’s a total occlusion. The distinction matters: a total occlusion in a leg artery, for instance, involves dense fibrous plaque that makes it much harder to treat than a narrowing. Interestingly, though, patients treated for partial narrowings actually have a higher rate of re-narrowing afterward (28%) compared to those treated for total blockages (12%).
Three factors drive most vascular occlusions, a combination known as Virchow’s triad: abnormal blood flow (such as sluggish circulation from sitting still too long), damage to the blood vessel wall, and changes in the blood’s clotting components. When a clot forms inside a vessel and stays put, that’s thrombosis. When a clot breaks loose and travels to block a vessel somewhere else, that’s an embolism. Together, these are among the most preventable complications in hospitalized patients.
Where Vascular Occlusions Happen
Heart (Coronary Occlusion)
A blocked coronary artery is the classic cause of a heart attack. On imaging, doctors can distinguish a complete occlusion from a severe narrowing primarily by measuring the length of the blockage. Complete occlusions in the coronary arteries average about 16.6 mm long, while severe narrowings average only 4.6 mm. Any lesion 9 mm or longer is almost certainly a complete occlusion rather than a narrowing. This measurement helps guide treatment decisions, since the two conditions require different approaches.
Legs (Peripheral Artery Occlusion)
When arteries in the legs become blocked, the condition is called peripheral artery disease (PAD). Symptoms go well beyond leg pain during walking. You might notice foot pain at rest, numbness or tingling, hair loss on the legs, skin that turns bluish, wounds that won’t heal, poor walking endurance, trouble standing from a chair, or even erectile dysfunction. Doctors use a simple test called the ankle-brachial index (ABI), which compares blood pressure at the ankle to blood pressure in the arm. A normal reading falls between 1.00 and 1.40. Values between 0.41 and 0.90 indicate mild to moderate PAD, while anything below 0.40 signals severe disease.
Eyes (Retinal Occlusion)
A blocked vein or artery in the retina can rob you of vision in one eye. Symptoms typically come on suddenly or build over hours to days and include blurry vision or outright vision loss, dark floating spots or lines in your visual field, and in more severe cases, pain or pressure in the affected eye. Retinal occlusion usually strikes one eye only, which is one reason people sometimes delay seeking care.
Intestines (Bowel Occlusion)
An intestinal occlusion, more commonly called a bowel obstruction, happens when something physically blocks the passage of food through the digestive tract. In adults, the most common culprits are adhesions (bands of scar tissue that form after abdominal or pelvic surgery), hernias, and colon cancer. In children, the leading cause is intussusception, where one segment of intestine telescopes into another. Other causes include Crohn’s disease, diverticulitis, twisting of the colon, and impacted stool.
There’s also a condition called paralytic ileus that mimics a mechanical blockage but involves no physical obstruction at all. Instead, the muscles or nerves controlling intestinal movement stop working properly, and food and fluid simply stop moving through. The symptoms can look identical, but the treatment is very different.
How Vascular Occlusions Are Detected
The imaging method depends on where the suspected blockage is. For veins in the legs, traditional contrast-dye imaging (venography) has long been the gold standard, though ultrasound is now used widely as a first-line test because it’s noninvasive and readily available. For coronary arteries, CT angiography can identify blockages and measure their length to determine severity. The ABI test for peripheral artery disease requires nothing more than a blood pressure cuff and a handheld ultrasound probe, making it one of the simplest screening tools in medicine.
Dental Occlusion: How Your Teeth Meet
In dentistry, occlusion simply means the way your upper and lower teeth come together when you bite down. A normal bite is classified as Class I, where the upper and lower molars align in a specific interlocking pattern. When the alignment is off, it’s called malocclusion, and dentists categorize it using Angle’s classification system. Class II malocclusion means the lower jaw sits too far back relative to the upper jaw, creating what’s sometimes called an overbite. Class III means the lower jaw juts forward, resulting in an underbite.
These classifications apply to both adult and baby teeth, though a modified system using lowercase Roman numerals (i, ii, iii) is used for children’s primary teeth. Dentists also recognize “half cusp” variations and “subdivisions,” where the bite relationship differs on the left and right sides of the mouth. Malocclusion can affect chewing, speech, jaw comfort, and long-term tooth wear.
One area of ongoing debate is whether adjusting the bite (occlusal equilibration) helps with jaw pain and temporomandibular disorders. Current evidence does not support irreversible bite adjustments as a treatment for TMD, so most practitioners favor reversible approaches like bite splints when jaw pain is present.
Occlusion vs. Stenosis
These two terms describe a spectrum. Stenosis is a narrowing: blood can still flow through, just in reduced amounts. Occlusion is a complete closure: no blood gets past the blockage. In practice, a severe stenosis and a total occlusion can produce similar symptoms, but total occlusions are generally harder to treat because the dense, fibrous tissue filling the vessel is difficult to penetrate with surgical wires and tools. Knowing which one you’re dealing with shapes everything from the urgency of treatment to the technique a specialist will use.