A cavity, known scientifically as dental caries, is a hole that forms in a tooth as a result of acid erosion caused by bacteria. These bacteria consume sugars and starches, producing acids that slowly dissolve the tooth’s hard outer layers. Ignoring this damage allows the infection to deepen and spread throughout the tooth’s structure and beyond. The trajectory of an untreated cavity is a predictable progression of worsening damage, increased pain, and escalating health consequences. Understanding this sequence highlights why early intervention is important for maintaining oral health.
Progression from Enamel to Dentin
The initial phase of decay begins when acid penetrates the enamel, the tooth’s protective outer shell. This layer has no nerves, which is why decay at this stage often presents without pain or noticeable symptoms. Once the bacterial acid breaches the enamel, the infection reaches the dentin, the layer immediately beneath it.
Dentin is much softer than enamel and is composed of microscopic tubes called dentinal tubules. These tubules contain fluid and connect directly to the tooth’s inner nerve center. This softer structure allows the decay to accelerate rapidly, as bacteria encounter less resistance.
The porous nature of the dentin explains the first common symptom of untreated decay: increased sensitivity. When the cavity exposes the dentin, external stimuli like hot or cold drinks can travel through the tubules to irritate the nerve. This temporary discomfort serves as the earliest warning sign that the tooth’s protective layers have been compromised.
Infection Reaches the Pulp
As the decay continues through the dentin, it eventually reaches the pulp, the innermost chamber of the tooth. This central area contains the tooth’s nerves, blood vessels, and connective tissue. The arrival of bacteria here triggers a severe inflammatory response called pulpitis.
The rigid walls of the tooth prevent the swollen pulp from expanding, leading to a rapid buildup of pressure. This intense, confined pressure directly irritates the nerves, causing the spontaneous, throbbing, and constant pain associated with a toothache. This pain is often severe enough to disrupt sleep.
If the infection remains untreated, the pressure eventually cuts off the blood supply, leading to the death of the nerves and pulp tissue, known as pulp necrosis. Paradoxically, the nerve’s death can sometimes result in a temporary cessation of intense pain.
This temporary relief is misleading, as the infection has progressed to a more dangerous stage. The dead tissue and bacteria remain inside the tooth, multiplying and spreading down the root canals. The infection then exits the tip of the root, entering the jawbone and surrounding tissues.
Localized and Systemic Complications
When the infection extends past the end of the root, it forms a periapical dental abscess, a localized pocket of pus and debris within the jawbone. This abscess creates a chronic source of infection that damages the tissues supporting the tooth. Chronic inflammation can eventually lead to the destruction and loss of the bone around the tooth.
The pressure from the abscess can cause the infection to break out from the bone, leading to visible, painful swelling in the gums, face, or neck, known as cellulitis. If the infection involves upper back teeth, it may spread into the maxillary sinuses, causing a sinus infection.
The most serious consequences arise if the infection spreads into the body’s deeper tissues and bloodstream. Although rare, an untreated dental abscess can lead to life-threatening systemic conditions. Bacteria can enter the circulatory system, resulting in sepsis, a severe inflammatory response that can cause organ failure.
Systemic Risks
Infections in the lower jaw can track down into the neck and throat spaces, potentially causing Ludwig’s angina. This serious condition involves swelling on the floor of the mouth that can obstruct the airway. Bacteria can also travel to distant sites, leading to the formation of a brain abscess or causing infective endocarditis in individuals with pre-existing heart conditions.
The Shift in Required Treatment
The initial treatment for a small cavity is straightforward, involving a simple dental filling to clean out the decay and restore the tooth’s structure. This procedure is minimally invasive and relatively inexpensive. Delaying this treatment fundamentally changes the complexity and cost of the required interventions.
Once the infection has reached the pulp, a simple filling is no longer adequate to save the tooth. Treatment shifts to root canal therapy, which involves removing the infected pulp and nerves and sealing the root canals. A dental crown is often required afterward to protect the now-brittle tooth structure from fracturing.
If the tooth is too structurally compromised or the infection has caused excessive bone loss, the only viable option becomes extraction, the complete removal of the tooth. Losing a tooth then necessitates further intervention to maintain proper function and alignment of the remaining teeth.
Replacing a missing tooth requires a bridge or a dental implant. These procedures are significantly more involved, costly, and time-consuming than a root canal or the initial filling. Neglecting a small cavity sets off a cascade of biological damage that inevitably leads to more invasive, more expensive, and more complex treatments.