When a single tooth shifts from its natural white or yellow shade to a distinct grey, it signals a change happening deep within the tooth structure. Unlike extrinsic stains that accumulate on the enamel surface, grey discoloration is an intrinsic issue, meaning the pigment resides within the dentin, the dense tissue beneath the enamel. This change represents an alteration in the tooth’s internal biology, prompting individuals to seek professional dental assessment.
The Primary Cause: Pulp Necrosis Following Trauma
The most frequent cause of localized grey or dark discoloration in a single tooth is a prior physical injury. Even a minor impact, such as a fall or a blow to the mouth, can damage the neurovascular bundle that supplies the dental pulp, the soft tissue inside the tooth’s core. This trauma compromises the tooth’s blood supply, leading to intrapulpal hemorrhage within the pulp chamber, even if the outer tooth structure remains unbroken.
The resulting color change is a chemical process that occurs as the pulp tissue dies, a process known as necrosis. Blood trapped inside the dentinal tubules—microscopic channels extending outward from the pulp—begins to break down. Red blood cells lyse, releasing hemoglobin into the surrounding dentin.
As the hemoglobin degrades, its iron content reacts with hydrogen sulfide, a byproduct of bacterial metabolism or tissue decomposition within the non-vital pulp. This reaction forms dark iron sulfide pigments. These pigments penetrate the dentinal tubules, making the tooth crown appear dark or slate grey. This discoloration is often delayed, sometimes appearing weeks or months after the initial injury occurred.
Other Sources of Discoloration
Grey discoloration can also stem from factors unrelated to physical injury, including previous dental procedures and systemic conditions. Iatrogenic causes, or those resulting from dental treatment, often involve materials used during root canal therapy. Certain older endodontic sealers and filling materials, such as zinc oxide eugenol or some mineral trioxide aggregate (MTA) compounds, can leach metallic ions into the dentin.
When these ions oxidize, they cause intrinsic staining that can turn the tooth a dark grey or blackish hue. This issue is localized to the treated tooth and depends on the specific materials used and the cleaning of the pulp chamber crown.
Grey discoloration can also be a systemic issue tied to development, such as the historical use of tetracycline antibiotics during tooth formation (from the second trimester of pregnancy through approximately age eight). The tetracycline molecule binds irreversibly to calcium ions within the developing dentin. While this initially causes a yellow-green color, light exposure over time oxidizes the compound, resulting in permanent, diffuse blue-grey or brown-grey banding across multiple teeth. A genetic condition like dentinogenesis imperfecta can also cause teeth to appear grey or blue-grey due to defects in the dentin structure.
What the Grey Color Indicates
When the grey discoloration is localized to one tooth and has appeared following a history of trauma, it is a strong clinical sign of pulp non-vitality. This means the soft tissue inside the tooth has died, and the tooth is no longer biologically active. The persistent dark color is essentially a visible marker of the degradation products that have saturated the internal dentin.
A non-vital tooth is a concern because it is susceptible to developing chronic infection, even if it is currently asymptomatic. The necrotic tissue and bacteria within the root canal system can eventually lead to periapical pathology, which is an infection at the root tip. This infection can destroy the bone supporting the tooth, potentially leading to an abscess or cyst formation.
The presence of a localized grey tooth signals the need for an immediate dental assessment, including clinical examination and X-rays, to evaluate the periapical health of the tooth. This intrinsic change indicates a potential biological problem that requires intervention to prevent the spread of infection and preserve the tooth structure.
Options for Correcting the Color
Once a grey tooth has been thoroughly assessed and the underlying issue of non-vitality has been addressed—typically through root canal therapy to remove the necrotic tissue and seal the canal—cosmetic correction can proceed. The most conservative and often effective option for a single, non-vital tooth is internal bleaching. This technique, sometimes called the “walking bleach” method, involves placing a bleaching agent, such as a mixture of sodium perborate and water or hydrogen peroxide, directly into the cleaned-out pulp chamber.
The bleaching agent is sealed inside the tooth for several days to a week, where it works from the inside out to oxidize the dark iron sulfide pigments within the dentinal tubules. This process is repeated until the desired shade is achieved, effectively reversing the internal staining without requiring external tooth reduction.
If the discoloration is too severe, or if the tooth requires additional structural support, external restorations offer a viable alternative. A dental veneer involves bonding a thin, custom-made layer of porcelain or composite resin to the front surface of the tooth, which effectively masks the underlying grey color. For teeth that are heavily damaged or structurally weakened, a full-coverage crown may be recommended. The crown encapsulates the entire remaining tooth structure, providing both strength and a complete, aesthetically pleasing color correction.