When teeth turn grey, it signals a change deeper than the surface-level staining seen with coffee or tobacco. Unlike common yellowing that affects the outer enamel, grey discoloration often indicates an internal alteration within the tooth structure. This darker hue is generally a sign that a substance has become incorporated into the dentin, the dense layer beneath the enamel, or that the tooth’s internal health has been severely compromised. Investigating the origins of this grey color is important because it can point to past trauma, systemic exposure, or underlying health conditions.
Discoloration from Internal Trauma
The most common reason for a single tooth to turn grey is the death of the dental pulp, known as pulp necrosis. This condition frequently occurs following a traumatic injury, such as a severe impact, or from extensive tooth decay that reaches the nerve. The trauma ruptures the blood vessels supplying the pulp, cutting off the tooth’s lifeline.
When blood cells within the pulp chamber break down, they release iron-containing compounds, specifically iron sulfides. These breakdown products are forced into the microscopic tubules of the dentin, causing internal staining. This gives the tooth a distinct dark or grey-blue appearance, which may not become noticeable until weeks or even months after the initial injury. The color change signals that the tooth is no longer biologically active and requires immediate dental evaluation.
The degree of discoloration varies depending on the severity of the trauma and the amount of blood products trapped inside the tooth structure. Unlike external stains, this internal discoloration cannot be removed with conventional whitening products.
Systemic and Medication-Related Causes
Certain substances, when ingested during tooth development, can become integrated into the mineral structure and cause widespread grey discoloration. The most well-known example is exposure to tetracycline antibiotics, once commonly prescribed to children and pregnant women. If exposure occurs while the dentin and enamel are forming (from the second trimester of pregnancy up to about eight years of age), the drug binds to calcium ions in the developing tooth.
Initially, affected teeth may appear fluorescent yellow upon eruption, but light exposure causes the bound tetracycline to oxidize over time. This chemical reaction darkens the substance, resulting in permanent discoloration ranging from brown to a deep blue-grey color. The staining is typically seen as horizontal bands across the tooth, corresponding precisely to the period of drug exposure.
Excessive exposure to fluoride, a condition called fluorosis, can also lead to discoloration that presents as mottled grey or brown, in addition to chalky white patches. This systemic exposure causes defects in the enamel’s formation, altering its light-reflecting properties and sometimes incorporating dark intrinsic stains.
Influence of Dental Restorations
Discoloration can originate from materials placed by a dentist, particularly silver amalgam fillings. Amalgam, a dark alloy, can visibly darken the entire tooth structure depending on the filling’s size and location.
In some cases, the bulk of the opaque metal shows through the translucent outer layers of the enamel and dentin. More commonly, the metal components of the amalgam filling slowly corrode over many years. This corrosion causes metallic ions to migrate and leach into the surrounding dentinal tubules, staining the tooth tissue a noticeable grey-blue hue.
While localized staining on the gums is called an “amalgam tattoo,” the slow seepage of ions into the tooth structure causes a diffuse grey shadow. This intrinsic discoloration is embedded within the tooth as the metal degrades and spreads throughout the microscopic structure.
Inherited Structural Conditions and Aging
The natural composition and slow wear of teeth also contribute to a grey appearance over time, often affecting the entire dentition. One rare cause is a genetic disorder like Dentinogenesis Imperfecta (DI), which directly impairs dentin formation. Because the dentin layer is poorly mineralized and abnormally soft, teeth affected by DI often exhibit a characteristic blue-grey or opalescent appearance.
The weak dentin causes the overlying enamel to chip away easily, further exposing the abnormal dentin and intensifying the grey or translucent look. These teeth are structurally compromised, leading to rapid wear and a bulbous shape.
Aging also contributes to a general darkening and greying due to the natural wearing down of the enamel layer. As the hard, white enamel becomes thinner, the underlying dentin, which is naturally more yellow-grey, becomes more visible. The continuous formation of secondary dentin throughout life also causes the pulp chamber to shrink, increasing the density of the opaque dentin and contributing to a darker appearance.