The plastic whitening strips contain a thin layer of peroxide gel and are shaped to fit the buccal/labial surfaces of teeth. Many different types of whitening strips are available on the market, after being introduced in the late 1980s. Specific whitening strip products have their own set of instructions however the strips are typically applied twice daily for 30 minutes for 14 days. In several days, tooth colour can lighten by 1 or 2 shades. The tooth whitening endpoint does depend on the frequency of use and ingredients of the product.