Staining and discolouration

Tooth discolouration and staining is primarily due to two sources of stain: intrinsic and extrinsic (see Figure 2). In essence, tooth whitening primarily targets those intrinsic stains in which cannot be removed through mechanics such as a debridement (clean) or prophylaxis, in the dental office. Below explains in-depth the differences between the two sources of which contribute to such discolouration of the tooth's surface.

Extrinsic stainingedit

Extrinsic staining, is largely due to environmental factors including smoking, pigments in beverages and foods, antibiotics, and metals such as iron or copper. Coloured compounds from these sources are adsorbed into acquired dental pellicle or directly onto the surface of the tooth causing a stain to appear.

• Dental plaque: Dental plaque is a clear biofilm of bacteria that naturally forms in the mouth, particularly along the gumline, and it occurs due to the normal development and defences of the immune system. Although usually virtually invisible on the tooth surface, plaque may become stained by chromogenic bacteria such as Actinomyces species. Prolonged dental plaque accumulation on the tooth surface can lead to enamel demineralisation and formation of white spot lesions which appear as an opaque milk-coloured lesion. The acidic by-products of fermentable carbohydrates derived from high-sugar foods contribute to greater proportions of bacteria, such as Streptococcus mutans and Lactobacillus in dental plaque. Higher consumption of fermentable carbohydrates will promote demineralisation and increase the risk of developing white spot lesions.
• Calculus: neglected plaque will eventually calcify, and lead to the formation of a hard deposit on the teeth, especially around the gumline. The organic matrix of dental plaque and calcified tissues undergo a series of chemical and morphological changes that lead to calcification of the dental plaque and therefore leading to the formation of calculus. The color of calculus varies, and may be grey, yellow, black, or brown. The colour of calculus depends on how long it has been present in the oral cavity for; it typically starts off yellow and over time the calculus will begin to stain a darker colour and become more tenacious and difficult to remove.
• Tobacco: tar in the smoke from tobacco products (and also smokeless tobacco products) tends to form a yellow-brown-black stain around the necks of the teeth above the gumline. The nicotine and tar in tobacco, combined with oxygen, turns yellow and over time will absorb into the pores of enamel and stain the teeth yellow. The dark brown to black stains along the gum line of the teeth are the result of the porous nature of calculus immediately picking up the stains from nicotine and tar.
• Betel chewing. Betel chewing produces blood-red saliva that stains the teeth red-brown to nearly black. The extract gel of betel leaf contain tannin, a chromogenic agent that causes discolouration of the tooth enamel.
• Tannin is also present in coffee, tea, and red wine and produces a chromogenic agent that can discolor teeth. Large consumptions of tannin-containing beverages stain the dental enamel brown due to the chromogenic nature.
• Certain foods, including curries and tomato-based sauces, can cause teeth staining.
• Certain topical medications: Chlorhexidine (antiseptic mouthwash) binds to tannins, meaning that prolonged use in persons who consume coffee, tea or red wine is associated with extrinsic staining (i.e. removable staining) of teeth. Chlorhexidine mouthwash has a natural liking for sulphate and acidic groups commonly found in areas where plaque accumulates such as along the gumline, on the dorsum of the tongue and cavities. Chlorhexidine is retained in these areas and stain yellow-brown. The stains are not permanent and can be removed with proper brushing.
• Metallic compounds. Exposure to such metallic compounds may be in the form of medication or occupational exposure. Examples include iron (black stain), iodine (black), copper (green), nickel (green), and cadmium (yellow-brown). Sources of exposure to metal include placing metal into the oral cavity, metal-containing dust inhalation, or oral administration of drugs. Metals can enter the bony structure of the tooth, causing permanent discolouration, or can bind to the pellicle causing surface stain.

Removal of extrinsic stainingedit

Extrinsic staining may be removed through various treatment methods:

• Prophylaxis: dental prophylaxis includes the removal of extrinsic staining using a slow-speed rotary handpiece and a rubber cup with abrasive paste, mostly containing fluoride.citation needed The abrasive nature of the prophy paste, as it is known, acts to remove extrinsic staining using the action of the slow-speed handpiece and the paste against the tooth. Adversely, the action of the rubber cup together with the abrasive nature of the paste, removes around one micron of enamel from the tooth surface every time a prophylaxis is performed. This method of stain removal may only take place in the dental office.
• Toothpaste: there are many available on the market that implement both peroxide as well as abrasive particles such as silica gel to help remove extrinsic stains while the peroxide acts on intrinsic staining. This method of stain removal may take place at home as well as in a dental office.
• Micro-abrasion: allows a dental professional to make use of an instrument which emits a powder, water and compressed air to remove biofilm, and extrinsic staining. This stain removal method can only be undertaken in a dental office, not at home.

Intrinsic stainingedit

Intrinsic staining primarily occurs during the tooth development either before birth or at early childhood. Intrinsic stains are those that cannot be removed through mechanical measures such as debridement or a prophylactic stain removal. As the age of the person increases, the teeth can also appear yellower over time. Below are examples of intrinsic sources of stains:

• Tooth wear and ageing: Tooth wear is a progressive loss of enamel and dentine due to tooth erosion, abrasion and attrition. As enamel wears down, dentine becomes more apparent and chromogenic agents are penetrated in the tooth more easily. The natural production of secondary dentine also gradually darkens teeth with age.
• Dental caries (tooth decay): The evidence regarding carious tooth discolouration is inconclusive, however the most reliable evidence suggests that carious lesion allows for exogenous agents to enter dentine and hence increased absorption of chromogenic agents causing discolouration to the tooth.
• Restorative materials: The materials used during root canal treatments, such as eugenol and phenolic compounds, contain pigment that stain dentine. Restorations using amalgam also penetrate dentine tubules with tin over time therefore causing dark stains to the tooth. 
• 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: Enamel hypoplasia causes enamel to be thin and weak. It produces a yellow-brown discolouration and can also cause the enamel's smooth surface to be rough and pitted which causes the tooth to be susceptible to extrinsic staining, tooth sensitivity, malocclusion, and dental caries. The evidence regarding enamel hypoplasia is inconclusive, however the most likely cause is infection or trauma caused to the primary dentition. Disturbances to the developing tooth germ during neonatal and early childhood stages such as maternal vitamin D deficiency, infection, and medication intake can cause enamel hypoplasia.
• Pulpal hyperemia: Pulpal hyperemia refers to inflammation of a traumatised tooth which can be caused by a stimuli such as trauma, thermal shock, or dental caries. Pulpal hyperemia is reversible and produces a red hue seen initially after trauma which has the ability to disappear if the tooth becomes revascularized.
• Fluorosis: Dental fluorosis causes enamel to become opaque, chalky white, and porous. The enamel can break down and cause the exposed subsurface enamel to become mottled and produce extrinsic dark brown-black stains. Dental fluorosis occurs due to excessive ingestion of fluoride or overexposure to fluoride during the development of enamel which usually occurs between the ages of one to four. Fluoridated drinking water, fluoride supplements, topical fluoride (fluoride toothpastes), and formula prescribed for children can increase the risk of dental fluorosis. Fluoride is considered an important factor in the management and prevention of dental caries, the safe level for daily fluoride intake is 0.05 to 0.07 mg/kg/day.
• Dentinogenesis imperfecta: Dentinogenesis imperfecta is a hereditary dentine defect, associated with osteogenesis imperfecta, which causes the tooth to become discoloured usually blue or brown in colour and translucent giving teeth an opalescent sheen. The condition is autosomal dominant which means that the condition runs in the family.
• Amelogenesis imperfecta: The appearance of amelogenesis imperfecta depends on the type of amelogenesis, there are 14 different subtypes and can vary from the appearance of hypoplasia to hypomineralisation which can produce different appearances of enamel from white mottling to yellow brown appearances.
• 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 dentine 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.
• Porphyria: A rare metabolic disorder in which the body fails to adequately metabolise porphyrins, which leads to accumulation or excretion of porphyrins into teeth. The excretion of porphyrins produces purple-red pigments in teeth.
• Hemolytic disease of the newborn: This disease occurs when a newborn's red blood cells are being attacked by antibodies from the mother caused by an incompatibility between the mother and baby's blood. This condition can produce green staining of teeth due to jaundice, which is an inability to excrete bilirubin properly.
• Root resorption: Root resorption is clinically asymptomatic, however can produce a pink appearance at the amelocemental junction.
• Alkaptonuria: Metabolic disorder which promotes the accumulation of homogentisic acid in the body and may cause brown colour pigmentation in the teeth, gums, and buccal mucosa.