There are many reasons for tooth coloring and yellowing, generally speaking, there are two types of endogenous and exogenous: exogenous coloring is due to the presence of a variety of bacteria on the surface of the teeth, which secrete many sticky substances on the surface of the teeth, tea scale in the daily diet, tobacco stains, as well as certain minerals in drinking water and minerals in people’s saliva adsorbed on these sticky substances to form plaque and tartar, gradually making the teeth yellow or black. Endogenous staining is formed during the development of teeth, such as tetracycline deposited in the dentin, which makes the teeth yellow, brown or dark gray, called tetracycline teeth; if the drinking water contains too much fluoride, it may also lead to dental fluorosis, with white nightmare-colored, brownish-brown plaque on the tooth surface; if the pulp is necrotic, the metabolites from the bacterial decomposition of the pulp, as well as the dehydration of the teeth themselves will also discolor the teeth. Generally speaking, exogenous coloring can usually be removed by scaling; while endogenous coloring requires professional whitening methods, and there are essentially only two types of tooth whitening methods, one is chemical bleaching, and the other is whitening through restorative methods of masking. Specifically, there are the following types: Home whitening: bleaching agents such as carbamide peroxide are used by patients themselves at home in specially designed trays. It usually takes about 3 weeks of treatment. Cold light whitening: The principle is to irradiate special wavelength blue light onto the special whitening agent applied on the teeth, which causes the whitening agent to oxidize and reduce the pigment deposited on the surface and deeper layers of the teeth over the years through the dentin tubules in the shortest possible time, so that the teeth tend to be white. It is suitable for medium and mild tetracycline teeth, smoky teeth, tea-stained teeth, cola teeth and other pigmented teeth, and usually achieves teeth whitening in about half an hour, so that you can’t help but always want to show your beautiful teeth and show a charming smile. The whitening effect can last for about 2 years. Porcelain veneers or resin veneers: Under the condition of preserving the living pulp and grinding less or no teeth, we use precision casting technology or the latest computerized ultra-precision sculpture cutting equipment and technology to produce “dental veneers” or resin veneers that fit perfectly with the prepared teeth and are similar to the tooth enamel, and then use special bonding The veneers are then bonded to the teeth using special bonding materials. These veneers are suitable for whitening and restoring moderate to severe tooth discoloration, chipped teeth and malocclusion. Porcelain veneers have the advantages of less dental damage, excellent aesthetic performance, and no adverse stimulation to the periodontium, which is the mainstream direction of dental esthetics in western developed countries. All-porcelain or porcelain crowns: porcelain teeth (crowns) was an important method of cosmetic dental restoration, but in recent years, with the promotion of its application, some of the disadvantages of porcelain teeth gradually revealed, such as easy to cause gum inflammation, gingival margin black line, allergic reactions, another porcelain teeth due to its inner crown for the metal opaque thus affecting its aesthetics, in addition, porcelain teeth in the metal will affect some special checks such as magnetic resonance imaging (MRI). (MRI). All-porcelain teeth have the advantages that porcelain teeth do not have. All-porcelain materials are biocompatible and do not cause gum inflammation and gingival margin staining because they do not contain metal materials, and can transmit light and therefore have better aesthetics. All-porcelain crowns are suitable for the whitening and restoration of heavily discolored teeth, tooth defects and malformed teeth that cannot be used in the above whitening methods.