A root canal infection occurs when the innermost soft tissue of a tooth, the dental pulp, is invaded by microorganisms. This specialized tissue contains nerves, blood vessels, and connective tissue that sustain the tooth’s vitality. While the hard enamel and underlying dentin typically protect this sterile environment, a breach allows bacteria from the mouth to infiltrate. The infection is a bacterial colonization of this confined space, leading to inflammation and eventual death of the pulp tissue.
Deep Decay and Cavity Progression
The most frequent path for bacteria to reach the dental pulp is through untreated dental decay. This decay begins when acid-producing bacteria erode the tooth’s hard outer layer, the enamel. If not treated early, the acids continue to dissolve the underlying dentin, which leads directly toward the pulp chamber.
As the decay progresses deeper, it creates a direct channel for the oral bacteria to infect the pulp tissue. Once the pulp is exposed, the bacteria trigger a severe inflammatory response called pulpitis. Because the pulp is encased in rigid walls, the swelling causes a pressure buildup that constricts the blood supply to the tissue.
This lack of blood flow, combined with the active infection, ultimately causes the pulp to die, a condition known as pulp necrosis. The dead tissue becomes a breeding ground for bacteria, which can multiply and spread past the tip of the root into the surrounding jawbone, forming an abscess.
Cracks, Fractures, and Physical Trauma
Sudden mechanical damage to a tooth can provide a rapid entry point for bacteria. Cracks and fractures, often caused by trauma or biting hard objects, can extend from the tooth’s chewing surface deep into the dentin. Even hairline fractures can allow oral microbes and fluids to seep down to the vulnerable pulp.
The constant movement of the tooth’s fractured segments during chewing further irritates the pulp, accelerating the inflammatory process. If the crack reaches the pulp chamber, bacteria quickly colonize the sterile environment, leading to infection.
A different mechanism occurs with severe blunt force trauma, such as a sports injury, which can jar the tooth without necessarily fracturing the crown. Such an impact can physically sever the delicate bundle of nerves and blood vessels where they enter the tooth at the root tip.
When the blood supply is cut off, the pulp tissue dies due to lack of oxygen and nutrients, leading to necrosis. This non-bacterial death creates a defenseless environment for any bacteria that later enter the tooth to cause a full infection.
Leakage and Recurrent Infection
A root canal infection can also arise due to the failure of prior dental work, often related to microleakage. Microleakage refers to the microscopic gaps that form between an existing restoration, such as a filling or crown, and the natural tooth structure. These minute spaces allow saliva, food debris, and bacteria to penetrate beneath the restoration’s seal.
Over time, this infiltration leads to secondary decay, which begins at the margin of the restoration and progresses inward toward the pulp. The breakdown of bonding material, wear and tear, or polymerization shrinkage can all contribute to this seal compromise. Once the secondary decay reaches the pulp, the tooth becomes infected despite the presence of a restoration.
The repeated stress from multiple dental procedures on the same tooth can also irritate the pulp, making it more susceptible to infection. Advanced gum disease, or periodontitis, can progress so deeply that the bacterial infection travels up the outside of the root and accesses the pulp through small side canals.