People generally consider whiter teeth as an indicator of good health and hygiene.  This has not been always the case especially in earlier cultures. In

Japan, for example, blackened teeth or ohaguro were thought to make a woman beautiful. During those times, Japanese women who usually come from wealthy families would stain their teeth using dye as part of their make-up. The dye was made usually from soaking iron in tea or rice wine known as sake but there were also cases when the dye contained lead, making it hazardous or even lethal. It was only during the 19th century that Japanese women stopped dyeing their teeth after their empress appeared in public with her white teeth showing.

 People’s preference for white teeth, however, is not without scientific basis.  Children’s milk teeth are generally whiter than that of adults mainly due to the difference in the mineral structure of the enamel as well as their less exposure to food pigments, bacteria and tobacco. Subconsciously, people began associating whiter teeth to youth and good health. Teeth whitening are a part of the larger field of cosmetic dentistry. During teeth whitening, bleaching agents such as hydrogen peroxide (the same one used to whiten hair) are applied to the enamel penetrating its crystal structure and lightening the shade of the stain deposits by oxidation.  In time, the bleach also acts on the inner dentine layer as well.   

There are generally two types of teeth whitening methods: in-office bleaching and at-home bleaching.

1.  In-house bleaching:

Uses a higher concentration of hydrogen peroxide and produces quick results but with higher risks of chemical burns to the soft tissues of the mouth. 

2.  At-home bleaching:

Uses a lower concentration of hydrogen peroxide in mouth strips that are placed in contact with the teeth. This has a slower effect but safer to use. 

  Whitening gels with lower peroxide concentrations (equivalent 3.6% hydrogen peroxide) used for at-home bleaching are confirmed to be safe by most studies.  Higher concentrations can potentially weaken the enamel but the presence of fluoride in these gels can balance this effect.  It is advised to use whitening gels less frequently if teeth sensitivity occurs as well as reducing the treatment time. Dentists also prescribe fluoride to further protect the enamel. Although questionable to some researchers, some dentists are now using high-intensity light treatment along with the whitening gels to speed up the treatment time. While teeth whitening have become a very successful trend nowadays, there are still people who prefer conventional brushing using their fluoride toothpastes and regular flossing aside from periodic visits to the dental clinic for oral prophylaxis. Some whitening toothpastes available today include pumice powder to increase the abrasive action of the toothbrush on the enamel and remove the dark protein layer called pellicles as well as other stains caused by foreign deposits. Some concerns regarding the use of abrasives include scratching of the enamel, leaving marks where more materials can get deposited and provide additional areas for bacteria and food particles.