When only a single tooth appears darker than the rest, the cause is typically an issue originating from within the tooth structure, known as intrinsic discoloration. This is distinct from extrinsic staining that affects all teeth due to external factors like coffee or tobacco. A localized color change, often appearing gray, brown, or black, indicates a problem in the pulp, the tooth’s innermost layer containing nerves and blood vessels. This isolated darkening suggests a specific event, like an injury or localized decay, has compromised the tooth’s internal health.
Why Only One Tooth Changes Color
The most frequent cause for a single tooth to darken is dental trauma, such as a blow to the mouth, which may have occurred months or even years earlier. This impact can rupture the blood vessels within the pulp chamber, leading to internal bleeding. The tooth essentially develops an internal bruise, which starts the discoloration process.
The characteristic gray or dark appearance develops as the blood components break down. Hemoglobin degrades into highly pigmented molecules like hematin. These breakdown products then seep into the microscopic channels of the dentin, called dentinal tubules, staining the tooth from the inside out.
If the trauma is severe enough, it can cause pulp necrosis, meaning the nerve and blood supply have died. In this non-vital state, bacteria may contribute to the discoloration by converting iron released from the degrading blood into black ferric sulfide. This compound intensifies the dark, often grayish-black, hue visible through the enamel.
Other, less common causes of single tooth discoloration include deep, localized tooth decay that has penetrated close to the pulp. A tooth that has previously undergone root canal treatment may also darken if remnants of pulp tissue or certain root-filling materials were left in the crown. These residual materials can degrade over time, leaching pigments into the surrounding dentin.
Understanding the Implications of Darkening
A discolored tooth is a significant sign of underlying pathology, even if it is not causing pain. While a healthy tooth remains sensitive to temperature changes, the absence of a painful response does not mean the tooth is healthy; a non-vital tooth with a dead pulp will no longer react to heat or cold. The darkening is a physical manifestation that the pulpal tissue has been damaged beyond repair.
If a necrotic pulp is left untreated, it provides an ideal environment for bacteria to multiply. This infection can spread beyond the root tip into the surrounding jawbone, potentially leading to a periapical abscess, which is a pocket of pus. An abscess can cause swelling, persistent pain, and may compromise the health of the jaw structure if the infection becomes chronic.
When a dentist examines a dark tooth, they perform diagnostic tests to determine the pulp’s status. These include thermal pulp testing, where the tooth is exposed to cold to check for a living nerve response. A percussion test, involving a gentle tap on the tooth, may also be performed, as a non-vital tooth can become tender to pressure. Finally, a dental X-ray checks for signs of bone loss or inflammation at the root tip, confirming periapical pathology.
Restoring Tooth Color
The first step in treating a discolored tooth with a dead pulp is to address the underlying infection through a root canal procedure. This treatment involves removing the necrotic tissue from the pulp chamber and root canal system, cleaning the internal space, and sealing it to prevent future infection. Only after the tooth’s health is stabilized can the cosmetic issue of discoloration be addressed.
The most conservative method for lightening a non-vital, discolored tooth is internal bleaching, commonly known as the “walking bleach technique.” A bleaching agent, often a paste containing sodium perborate, is placed inside the cleaned pulp chamber. The access cavity is then temporarily sealed, allowing the agent to work from the inside out over several days.
The bleaching agent oxidizes the pigmented compounds trapped in the dentinal tubules, breaking them down into colorless molecules. This process is repeated until the tooth matches the adjacent teeth. If internal bleaching is unsuccessful, or if the tooth is severely weakened, alternative restorative options are considered. These involve covering the tooth with indirect restorations like a porcelain veneer or a full-coverage crown to mask the discoloration.