An untreated cavity, or dental caries, is a permanent breakdown of tooth structure caused by acid-producing bacteria in the mouth. This bacterial activity creates a localized hole by dissolving the mineral content of the tooth’s hard tissues. Since the body cannot regenerate lost tooth structure, a cavity is a progressive disease that will only worsen without intervention. The ongoing bacterial invasion acts as a destructive mechanism, deepening the decay over time.
Progression Through Enamel and Dentin
The earliest stage of decay involves the hard, outer layer of the tooth, the enamel. Once bacteria penetrate this enamel barrier, the decay reaches the underlying layer known as dentin. Dentin is softer, less mineralized, and contains millions of microscopic tubules that lead directly toward the tooth’s center. Because of this porous structure, decay accelerates significantly once it breaches the dentin-enamel junction.
At this stage, the patient often experiences hypersensitivity, particularly when consuming sweet, hot, or cold foods or drinks. The fluid movement within the dentinal tubules transmits these external stimuli as sharp, temporary discomfort. If treatment is initiated while the decay is confined to the dentin, a simple filling is usually sufficient to remove the infected material and restore the tooth’s integrity. Continued neglect allows the bacteria to drill deeper through the dentin.
Deep Infection and Nerve Death
The infection reaches the pulp chamber, the innermost core of the tooth, containing the nerves and blood vessels. This bacterial breach triggers a severe inflammatory response called pulpitis. Because the dental pulp is encased within rigid walls, the resulting swelling creates intense internal pressure. This pressure compresses the nerve and blood vessels.
This pressure typically causes severe, constant, throbbing pain that is often spontaneous and can intensify when lying down at night. This pain signals an irreversible injury to the pulp tissue, leading quickly to the death of the nerve and blood vessels, known as pulp necrosis. Once the nerve dies, the pain may temporarily subside, but the tooth remains infected. At this advanced stage, a standard filling cannot resolve the issue, and the infected pulp must be removed via root canal therapy to save the tooth.
Dental Abscess and Jawbone Damage
Following the death of the pulp tissue, bacteria and their toxic byproducts spread down the root canal, eventually exiting the tip of the root. This infection contaminates the surrounding bone and gum tissue, leading to the formation of a periapical abscess, a localized pocket of pus. Symptoms of an acute abscess include facial swelling, fever, and a persistent bad taste in the mouth if the infection drains through the gum.
The chronic bacterial infection near the root tip initiates a destructive process in the surrounding alveolar bone. The body’s immune response releases inflammatory chemicals that dissolve the jawbone tissue supporting the tooth. This localized bone loss weakens the tooth’s attachment and may be visible on dental radiographs as a dark area around the root. If the infection and bone destruction are too extensive, the tooth must be extracted to eliminate the source of infection.
Rare Systemic Complications
When the localized infection is left untreated, bacteria can breach the jawbone and soft tissue, leading to serious systemic consequences. One rare complication is cellulitis, a rapidly spreading bacterial infection of the soft tissues beneath the skin of the face or neck. Cellulitis causes swelling and, if it affects the floor of the mouth, can lead to a potentially life-threatening condition called Ludwig’s Angina, which obstructs the airway.
Bacteria from the dental abscess can enter the bloodstream, traveling to distant parts of the body. This can lead to conditions such as endocarditis, an infection of the heart’s lining, or, most severely, sepsis. Sepsis is a generalized, life-threatening response to infection that causes widespread inflammation and organ dysfunction, requiring immediate medical intervention.