When a tooth unexpectedly turns black inside, it signals an issue originating deep within the tooth structure, specifically the dentin or the pulp chamber. This intrinsic discoloration is not caused by surface stains, but by internal changes indicating underlying pathology. The dark color is a visible alarm that the living tissue inside the tooth has been compromised, requiring prompt professional attention to prevent further damage or infection spread.
Primary Causes of Internal Tooth Discoloration
The most frequent cause for a tooth turning dark is pulp necrosis, the death of the tooth’s innermost tissue containing nerves and blood vessels. When the pulp dies, trapped blood cells break down, releasing hemoglobin. This hemoglobin degrades, and the iron component combines with hydrogen sulfide to form black iron sulfide. This compound saturates the surrounding dentin, causing the tooth to appear dark gray or black over time.
A sudden, forceful blow or trauma to the tooth can also trigger this discoloration process due to an internal hemorrhage. The impact ruptures the tiny blood vessels in the pulp, forcing blood into the microscopic dentinal tubules. This effect is akin to a bruise on the tooth, and as the blood products break down, iron sulfides are formed and permanently stain the dentin. The color change is often delayed, appearing weeks, months, or even years after the initial injury.
Deep, untreated dental decay that progresses to the pulp chamber allows bacteria to infect the soft tissue. The resulting inflammation and infection compromise the blood supply, leading to tissue death and the release of staining compounds. This prolonged process results in a gradual darkening as the infection deepens.
In some cases, older silver amalgam fillings can cause a dark shadow due to metallic ions leaching into the surrounding dentin. This is typically a gray or blue-gray discoloration caused by corrosion products, rather than the deep black associated with pulp death.
How Dentists Determine the Source
The diagnostic process begins with a thorough visual and physical examination, checking the affected tooth for swelling, tenderness, or signs of fracture. Dentists use percussion testing, gently tapping the tooth to gauge sensitivity, and palpation to check for tenderness near the root tip. These initial assessments help localize the source of the problem and differentiate it from issues in neighboring teeth.
Dental X-rays are a necessary tool for visualizing the internal structure of the tooth and the surrounding bone. A key sign of a necrotic pulp is the presence of a periapical radiolucency, which appears as a dark, circular area at the tip of the tooth root. This shadow represents the breakdown of bone tissue caused by the body’s defensive response to the infection leaking out of the dead pulp.
To confirm the pulp’s status, dentists perform pulp vitality testing, most commonly using a cold stimulus. A specialized spray, often ethyl chloride, is applied to a cotton pellet and then briefly placed on the tooth surface. A healthy tooth will elicit a sharp, immediate, but short-lived response, while a necrotic tooth will produce no sensation. The electric pulp tester is an alternative that sends a mild electrical current through the tooth; a lack of response confirms the absence of functional nerve fibers.
Professional Treatment Options
Once pulp necrosis is confirmed, the standard procedure is root canal therapy, which aims to save the natural tooth. This involves drilling an access hole into the crown to remove dead pulp tissue, bacteria, and staining compounds from the internal chamber and root canals. The canals are thoroughly cleaned, disinfected, and then filled with an inert material, typically gutta-percha, before the access hole is sealed.
Extraction becomes the necessary option when the tooth is too structurally compromised to be saved by a root canal. This occurs if the tooth has a severe vertical root fracture, extensive decay that has destroyed too much tooth structure, or if the surrounding bone loss from a long-standing infection is too significant. While extraction resolves the infection, it necessitates a subsequent prosthetic replacement, such as an implant or bridge, to prevent neighboring teeth from shifting.
After a successful root canal, dark staining in the dentin can be addressed with internal bleaching, also known as non-vital bleaching. This conservative technique involves placing a strong oxidizing agent, like a mixture of sodium perborate and water, directly inside the pulp chamber through the access cavity. The bleaching agent is sealed inside the tooth for several days in a procedure called the “walking bleach” technique. This process chemically breaks down the dark pigments, lightening the tooth color from the inside out.