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How can tooth decay spread from enamel to the pulp?

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A labeled cross section illustration of an adult human molar shows the tooth's crown and root, with layers including enamel, dentin, and pulp, as well as gum, cementum, blood vessels, periodontal ligament, lateral canals, and nerve. — tooth Cross section of an adult human molar.

Tooth decay, or caries, begins when bacteria in the mouth ferment sugars and starches from food debris, creating acids that demineralize and destroy the enamel—the tooth's hard, inorganic outer layer.12

Once the enamel is breached, the decay progresses into the dentine, the middle layer that forms the bulk of the tooth. In this stage, the protein structure of the dentine is broken down through enzymatic action and bacterial invasion. If left untreated, the decay continues to advance through the dentine until it reaches the pulp, the innermost soft tissue containing nerves and blood vessels. This progression poses a significant risk of infection, often necessitating root canal therapy to remove the diseased tissue and preserve the tooth.2134

Maintaining good oral hygiene, such as regular brushing and flossing, is essential to prevent this progression and protect the health of the tooth's interior.32