Tooth Whitening / Bleaching
Tooth whitening is a process by which the teeth are made whiter using peroxide-based bleaching gels of varying concentrations (from about 8% to over 30%, depending on how it is applied). The process has become popular in recent years as our image-conscious society strives to maintain a more youthful appearance. Bleaching solutions generally contain carbamide peroxide and hydrogen peroxide as the active bleaching ingredients.
Carbamide peroxide breaks down into hydrogen peroxide and urea upon exposure to water (including saliva). Other ingredients include stabilizers (which help prevent decomposition of the bleaching ingredients), preservatives (to prolong the shelf life/effectiveness of the product), and pH (acid) balancers.
Bleaching teeth works because tooth enamel is somewhat porous (see fluoride treatments), allowing the bleach solution to penetrate its surface and neutralize pigmented molecules from coffee, cigarettes, colored beverages, and other external sources.
It’s important to realize that dental materials generally cannot be lightened with bleach. If you have fillings, veneers or crowns on any of the teeth that are visible when you talk and smile, lightening the shade of the teeth by bleaching can make those restorations obvious (they’ll appear dark). Such restorations may need to be replaced following tooth whitening procedures, generally at additional cost.
The underlying dentin layer of teeth naturally darkens with age, due to continuous deposit of secondary dentin by the odontoblast cells living in the hollow interior of teeth (pulp). Overbleaching teeth can make enamel more transparent, allowing the darker underlying dentin to show-through.
The secondary dentin formation process accelerates during times of stress on the teeth. Tooth stressors include decay, drilling on the teeth, a clenching and grinding habit (bruxism), and trauma and injuries to the teeth (chipped teeth, cracked teeth, and bruised periodontal ligaments). Accelerated secondary dentin formation is called reparative dentin, which can be brownish red in color. This is because tooth stressors increase blood flow into the tooth. Blood is rich in iron, a reddish pigment, which is incorporated into the newly forming dentin and the pores of the original dentin. These pigments are not generally removed by externally bleaching the teeth.
If a tooth undergoes more stress than the pulp tissues (nerve and blood vessels) inside it are capable of withstanding, the tooth may die and require root canal (endodontic) treatment. If the tooth has taken on a dark shade that makes it stand out among the adjacent teeth, the tooth can be bleached from the inside following root canal treatment. The process simply involves placing bleach solution inside the tooth and placing a temporary filling over it until the tooth lightens. Dentists call this process internal bleaching or walking bleach.
In general, bleaching the teeth is an option for people whose tooth enamel has yellowed or darkened over time, and who have no contraindications to the whitening materials or processes. Internal bleaching is often recommended for people who have a single tooth which has darkened and had a root canal treatment.