With the development of economy and the improvement of national health, modern people's requirements for teeth are no longer just pathological or functional. If they can have white and bright teeth, they can not only add points to their overall appearance, but also increase their self-confidence. The factors causing tooth discoloration can be divided into two categories: internal cause and external cause.

Endogenous factors such as tetracycline staining, fluorosis, pulp necrosis, etc. External factors, such as smoking, dyeing caused by eat areca or dark diet, and tooth aging.

If tetracycline is taken in the process of tooth calcification, it will cause teeth to be dyed gray, brown, purple or even different colors. If drinking water contains excessive fluoride, it will form yellow-brown lines or spots on the tooth surface, which is called dental fluorosis;

And teeth with necrotic pulp will be darker than other normal teeth. The central part of the tooth is the pulp cavity, which contains nerves and blood vessels and is covered with ivory and enamel.

Ivory is yellow, while enamel is transparent. The thicker the enamel, the whiter the teeth. Because westerners have bigger teeth and thicker enamel, their teeth are relatively whiter than those in the East.

In the process of aging, due to the wear of enamel, teeth will appear ivory yellow. Exogenous dyes, such as tobacco stains, betel nut stains or coffee and tea dyes, can be removed by polishing or sandblasting.

Tooth bleaching technology began in 1960' s and was first implemented in clinic. After the whole gum is isolated and protected by rubber barrier and moisture-proof device, 35% hydrogen peroxide is coated on the tooth surface, and then the action of the drug is stimulated by heating with a light source, about one hour at a time, and taken twice or three times.