Dental caries, commonly known as a cavity, begins as a bacterial infection that erodes the hard structure of a tooth. This condition is progressive; unlike a cut or bruise, a cavity cannot heal itself because the enamel, the tooth’s outer layer, lacks living cells capable of regeneration. Neglecting this active infection allows the decay to tunnel deeper into the tooth’s core, leading to a sequential breakdown of tissue and escalating health consequences. The trajectory of an untreated cavity moves from minor structural damage to severe pain, localized infection, and eventually, systemic health risks.
The Progression from Enamel Decay to Dentin Exposure
A tooth is composed of three main layers: the hard outer enamel, the softer dentin beneath it, and the innermost pulp containing the nerve and blood vessels. Decay begins when oral bacteria metabolize sugars and produce acids that demineralize the enamel, creating a small lesion. This initial stage is often asymptomatic because the enamel has no sensory nerves.
Once the decay breaches the enamel barrier and reaches the dentin, the rate of damage significantly accelerates. Dentin is less mineralized and softer than enamel, offering less resistance to bacterial invasion. This layer contains millions of microscopic tunnels, called dentinal tubules, that connect directly to the tooth’s pulp chamber.
When decay reaches these tubules, it provides a pathway for external stimuli to affect the internal nerve. Symptoms typically appear here, manifesting as a sharp, short-lived sensitivity when consuming hot, cold, or sweet foods. If left untreated, the decay continues its rapid advance along the dentinal tubules, moving closer to the tooth’s vulnerable center.
Severe Pain and Internal Nerve Infection
The infection progresses to its most painful stage when bacteria penetrate the dentin and invade the dental pulp. The pulp contains the nerve, connective tissue, and blood supply. The resulting inflammation, known as pulpitis, is confined within the rigid walls of the tooth, leading to intense pressure and throbbing pain.
Early-stage pulpitis may be reversible, causing sensitivity that resolves quickly after the stimulus is removed, and can sometimes be corrected with a deep filling. However, as the bacterial load increases, the condition becomes irreversible, signaling that the nerve tissue is dying. At this point, the pain becomes spontaneous, often intensifying at night or lingering after exposure to heat.
The only way to resolve irreversible pulpitis is to remove the infected pulp tissue through a root canal procedure or to extract the tooth entirely. Ignoring the pain ensures that the bacteria will consume the entire pulp, causing the nerve to die and the infection to spread out of the tooth’s root tip.
Development of Abscess and Localized Infection Spread
As the bacteria exit the root tip, they enter the bone and soft tissues surrounding the tooth, leading to the formation of a periapical abscess. An abscess is a localized pocket of pus that forms as the body attempts to contain the infection. This pus accumulation creates significant pressure within the jawbone, often causing the surrounding gum tissue to swell and making the tooth feel “high” when biting.
The pressure may eventually force the pus to create a small opening, known as a fistula or “gum boil,” on the gum line to drain the infection. While this drainage can temporarily relieve the pain, the infection remains active in the bone.
If the infection continues, it can spread locally beyond the immediate site, leading to osteomyelitis, an infection within the jawbone itself, or cellulitis, a serious bacterial infection of the soft tissues of the face and neck. These infections cause visible facial swelling and tenderness.
Systemic Health Risks and Tooth Loss
When the body can no longer contain the abscess, bacteria can travel through the bloodstream, leading to life-threatening conditions. Sepsis, or blood poisoning, is a systemic response to infection that can cause organ failure. A dental infection can spread to the brain via the venous sinuses, potentially causing cavernous sinus thrombosis.
Chronic, untreated dental infections contribute to systemic inflammation, which has been linked to the worsening of conditions like cardiovascular disease.
Ultimately, the tooth itself will become non-restorable, forcing an extraction. This results in permanent tooth loss, which can lead to neighboring teeth shifting out of alignment and bone loss in the jaw. An untreated cavity progresses from a minor dental issue to a potentially life-threatening medical concern.