Teeth often become darker due to a variety of reasons. Adult teeth are generally darker than a child’s deciduous teeth. The mineral structure of the teeth changes with age, causing the enamel in the teeth to become less porous. Many substances can stain the teeth, such as coffee, tea and tobacco. Drugs like tetracycline can also discolor the teeth. The methods of whitening teeth include gel bleaching, light-accelerated bleaching and natural bleaching.
Gels are the most common method of bleaching teeth, and they may be divided into high-concentration and low-concentration gels. High-concentration gels typically use carbamide peroxide or hydrogen peroxide as the oxidizing agent that whitens teeth. Gels containing carbamide peroxide have a concentration between 10 percent and 44 percent, while hydrogen peroxide solutions have a concentration between 3 percent and 16 percent. High-concentration gels use trays to retain the gel around the teeth according to a prescribed schedule, typically 20 minutes at a time.
Low-concentration gels are typically found in mouth guards and strips that are commercially available. They are usually applied to the teeth for several hours each day for up to two weeks. Low-concentration gels are much less effective at whitening teeth than high-concentration gels.
Light-accelerated bleaching combines high-concentration whitening gels with certain types of light to reduce the treatment period. The lighting source must emit high-energy photons to effectively increase the reaction rate of the oxidizing agent, with blue light generally being the most efficient. However, it cannot produce a great deal of heat as this could burn the surrounding tissue. Halogen, light-emitted diodes and plasma arcs are the most common sources of lighting used in light-accelerated bleaching. This treatment typically consists of a single session in a clinical setting that lasts no longer than an hour.
Many naturally-occurring substances can also whiten teeth effectively. Malic acid is one of the most common natural whitening agents and is found in many fruits such as apples and strawberries. Citric acid found in fruits such as lemons, limes and oranges can also whiten teeth. These acids can be used simply by eating the relevant fruits, although you can increase their effectiveness by brushing the pulp or juice directly onto your teeth. This method must be used with caution to avoid damaging the enamel in your teeth, especially when using lemon juice. Baking soda is also a common method of whitening teeth that relies on abrasion.