Teeth differ from one person to another. Some people have defects on the outer covering of the tooth enamel: microscopic cracks and holes that can make coloured substances stick more to the enamel’s surface.
Also, a genetic condition where a person has less saliva than what is normal is predisposed to staining. Saliva washes away debris from food and drinks. If the person produces less saliva, then the mouth is washed infrequently.
Teeth gradually stain yellow with ageing, but poor dental habits are more responsible for this.
The following are sources of exterior stains of the teeth:
1. Food
All food can deposit leftover materials and pigments on the teeth causing gradual yellowing of the teeth through time. Some food may also cause immediate staining due to natural pigments (e.g. berries) or due to food colouring (e.g. sweets)
2. Beverage
Beverages that contain tannic acid (e.g. coffee and tea) or other acids such as phosphoric (e.g. cola drinks) can cause brownish stains on the teeth. The acid reacts with the enamel and stains the teeth yellow. Red wine is not highly acidic being an alcohol, but bacteria living in the mouth can react with it changing it to an acid.
3. Exposure to metallic salts
People who work in chemical factories may inhale fumes of metallic salts such as copper, nickel, potassium, calcium, sodium, silicon, magnesium, and phosphorus causing green stains on the teeth.
4. Tobacco Use
Smoking or chewing tobacco can leave brown to black stains on the middle surface of the tooth down to the gums. These stains are hard to remove and get worse with prolonged smoking.
5. Bacteria
Colour-producing bacteria (chromogenic) cause orange to red stains. Black stain, the most common stain caused by bacteria is caused by Actinomyces sp. Fluorescent bacteria produce green stains on the teeth. Bacteria react on the food we eat and excess acids can react with the enamel of the tooth and cause plaque and eventually tooth decay.
6. Medicated mouthwash
Some medications delivered as mouthwash can gradually stain the teeth as well. These include Iodine-containing, Chlorhexidine, Iron-containing (black), Potassium Permanganate (violet-black), Silver Nitrate (black), and Stannous Flouride (brown) mouthwashes.