Extrinsic tooth stains forms in the enamel while for the most part, intrinsic stains that show trough the enamel occur in the dentin. First, the tooth enamel is a highly mineralized very hard part of the tooth composed of strand of rod-like crystalline materials. These rods while very tightly packed have microscopic gaps in between them. What it does not bleach are crowns, veneers, restorations and other materials relative to tooth repairs. So while the teeth are becoming whiter with every application, those that are not retain its original color and results to uneven coloration. The best part is, unlike most cosmetic procedures, teeth whitening are really very inexpensive. Red wine may be good for the heart but it contains a high concentration of tannins that causes staining fast. DNA. All teeth are translucent to some degree. There are people though that are born with teeth that are more translucent than most. Teeth that are more translucent tend to show more staining than those with more opaque teeth. As people age, the teeth also suffers considerably. The teeth will crack or will have chips. And the veneers can be used to address this concern. Porcelain veneers are also best for use on uneven teeth due to tooth grinding, and can be used to correct the abnormal spacing in between the teeth. The use of veneers is not actually recommended for all concerns relating to the teeth. This is the leading organization and entity that you would want to listen to with regards to any products related to dental care. They often select products that comply with their standards. And if the organization is to be consulted, it is best to ask for assistance from your dentist before buying impulsively. Except when there is a special tooth and gum problem, where the teeth is prone to hypersensitivity and where the gum is easily irritated, over the counter teeth whitening ranks among the safest in cosmetic enhancement. Teeth whitening gels, strips, pens, gurgles and other treatments are generally designed for self help and the mix is generally very mild.