This film can be removed chemically as well as by scraping by a dentist. Brushing helps to clean the teeth stains to some extent and there are special abrasive toothpastes which help further the process. Teeth whitening toothpastes are also available which are effective in cleaning such stains on our teeth enamel. Our teeth enamel is porous in nature.
Hydroxyapatite crystals in the form of microscopic hexagonal "rods" make up the enamel. The accumulation of the foreign substances over the years gets into the pores and settles on the inner layer where it is very difficult to scrape them. Though these deep stains are actually quite harmless, they do not look good. Thus to get rid of these tough stains, people seek the help of professional teeth whitening procedures. During such teeth whitening procedures, a bleaching chemical agent is used called carbamide peroxide or hydrogen peroxide.
This is present in a tooth whitener and it triggers a chemical - rather an oxidation reaction - which manage to break the staining compounds. The chemical compound carbamide peroxide breaks within the mouth into urea and hydrogen peroxide. The hydrogen peroxide plays a vital role in the teeth whitening process.