Teeth may be darkened by a buildup of surface stains (extrinsic staining), which hides the natural tooth color; or the tooth itself may discolor (intrinsic staining).
Causes of extrinsic staining include:
- Dental plaque: Usually virtually invisible on the tooth surface. However, plaque may become stained by chromogenic bacteria such as Actinomyces species.
- Calculus: Neglected plaque will eventually calcify, and lead to the formation of a hard deposit on the teeth, especially around the gumline. The color of calculus varies, and may be grey, yellow, black or brown.
- Tobacco: The smoke of tabacco products contains (and also smokeless tobacco products), which tends form a yellow-brown-black stains around the necks of the teeth above the gumline.
- Betel chewing.
- Ingesting colored liquids like sports drinks, cola, coffee, tea, and red wine can cause the discoloration of teeth.
- Metallic compounds: Exposure to such metallic compounds may be in the form of medication or other environmental exposure. examples include iron (black stain), iodine (black), copper (green), nickel (green), cadmium (yellow-brown).
Causes of intrinsic staining include:
- Dental Caries: tooth decay.
- Dental Trauma: which may cause staining either as a result of pulp necrosis or internal resorption. Alternatively the tooth may become darker without pulp necrosis.
- Enamel hypoplasia.
- Dentinogenesis imperfecta.
- Tetracycline and minocycline: Tetracycline is a broad spectrum antibiotic, and its derivative minocycline is common in the treatment of acne. The drug is able to chelate calcium ions and is incorporated into teeth, cartilage and bone. Ingestion during the years of tooth development causes yellow-green discoloration of dentin visible through the enamel which is fluorescent under ultraviolet light. Later, the tetracycline is oxidized and the staining becomes more brown and no longer fluoresces under UV light.
- Hemolytic desease of the newborn.
Cause of extrinsic and intrinsic staining include:
- Age: the tooth enamel becomes thinner over time, which allows the dentin to shine through.
- Bruxism(clenching and grinding of the teeth): It can lead to micro-cracking of the incisal edges of the teeth. Extrinsic stains may settle more readily into these cracks, and a thin layer of enamel can be left. This thin enamel layer is partially transparent, allowing the dark background of the mouth to shine through, affording a darker appearance of the incisal edge.