Because of this, permanent teeth come in varying shades from white to off-white and sometimes to yellowish. It could shade darker as the person grows older, perfectly normal. While the darkening of the teeth as it ages is mainly due to the changes in the teeth's mineral structure, the enamel at the same time gets less porous and less shiny making it more susceptible to stains from bacterial pigments, medication, tobacco, wine, coffee, tea and food. Extending the time off gels or rinses in the mouth will not improve the affectivity of the products. After each treatment do not drink carbonated beverages for at least two hours to get better results and protect the teeth. Teeth whitening products are very affordable that customers sometimes overdo the practice that more may be better. While there are 16 shades of teeth, they are divided into two basic types, the yellowish and the greenish. Stains on teeth that are greenish-grey in cast are harder to remove while those that have a yellow cast tend to whiten faster. Since teeth whitening and bleaching are among the simplest cosmetic procedures and provided you do not have cracks crowns porcelain veneers, special teeth and gum conditions, home kits are advisable provided you start with a low mixture of bleaching agents and water. Increased teeth sensitivity This is more likely to happen when the treatment is done in a clinic or a health spa because bleaching agents that are used are more concentrated than home bleaching kits. More concentration of the bleaching agents however means faster results compared to home treatment methods that are very much "watered down" to insure safety. These rods while very tightly packed have microscopic gaps in between them. The density of the crystalline rods differs from individual to individual and explains the reason why some tooth enamel are tougher than another person's enamel. Nonetheless, all most all of us are born with bright shiny teeth. Also it should be remembered that these procedures are not best for pregnant women. Once the women gave birth and has finished the lactating stage, then that is the time that whitening procedures are safer. For those with allergies, consider a stop first on the plans to have teeth whitening. This is especially true for everyone who is allergic to peroxide.