Tooth Whitening / Bleaching
What is Tooth Whitening?
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.
The process of Tooth Whitening
A dentist should examine your teeth to see whether you have any fillings, crowns, veneers or other tooth restorations visible in your smile. If you do, you should realize that those will not bleach and may appear darker if you choose to bleach your teeth. Replacement of those restorations may be necessary.
Your health history should be reviewed with a dentist. If you are pregnant or nursing, you shouldn’t bleach your teeth. If your dentist says you are a candidate for tooth whitening, there are generally two ways you can whiten: at home, or in a dental office.
Whitening your teeth at home
If you elect to bleach your teeth at home, you again have several options. You may purchase over-the-counter bleach kits with the same active ingredients as dentist-dispensed systems. The disadvantages of over-the-counter kits include one-size-fits-all trays, which do not closely adapt to the teeth and may promote sensitivity and gingival irritation. Whitening strips can be messy and difficult to adapt to the teeth, resulting in wasted bleaching gel and possible sensitivity. They also may not cover all of the teeth that are visible when you talk and speak.
Custom bleaching trays made by your dentist
A dentist can make custom trays that provide the best adaptation to your teeth, which can minimize waste and gingival irritation.
At your first appointment, impressions of your teeth are made, usually by a dental auxiliary. This usually takes about ten minutes. You will be asked to return at a later time for delivery of your bleaching “kit.” The dental auxiliary will perform the following in the lab:
- Stone cast replicas of the teeth are made from the impressions.
- Sheets of polyethylene or vinyl are heated until formable, then vacuum-formed over the stone casts to create trays into which the bleaching gel will be dispensed.
- The bleach trays are trimmed to follow the contours of the gingiva where the teeth and gums intersect.
At your next appointment, the starting shade of your teeth will typically be recorded. The trays will be tried onto your teeth for proper fit, and to be sure they cover all of areas of your teeth to be bleached. Any overextended areas can be trimmed. You will be shown how to apply the bleach, how much to use, and given instructions on frequency of use. Potential complications (like sensitivity) and ways to address them will be discussed. You may be asked to return for one or more follow-up visits.
Tooth whitening at the dentists’ office
If your dentist bleaches your teeth in-office, the procedure is generally as follows though it may vary by individual dental office and patient.
- Risks and benefits of the higher concentration bleach materials and possible accelerants (e.g. laser, UV light, etc.) used for in-office whitening should be discussed with your dentist ahead of the procedure.
- The teeth will be isolated with a rubber dam or “paint-on” isolation barrier to protect the gum tissues, lips and cheeks (oral mucosa) from exposure to the bleaching solution, and UV light (if used).
- Concentrated bleach solution (30% or more) is applied to the teeth and left for 20-30 minutes, while the teeth are exposed to a bleaching accelerant (laser, UV, etc.)
- The bleach is rinsed from the teeth and the isolation barrier is removed.
- Isolating the teeth from mouth moisture during the bleaching process causes some dehydration of the tooth to occur. Dehydration itself causes the teeth to lighten temporarily. Therefore, when you leave the dentist’s office, your teeth are likely to be whiter than they will remain. Even a few hours after the appointment, you may notice that your teeth are not as white as when you left the dentist’s office.
- Some people return to the dentist’s office for an additional application of the bleach, and even after multiple applications may be dissatisfied with the outcome for the cost involved.
- Advantages to in-office bleaching include the rapidity with which whitening is achieved; and the protection from the oral soft tissues (gums, lips, cheeks) from the bleach. Disadvantages include the cost (which may be twice that of home bleaching); the noticeable relapse toward the darker shades when the teeth rehydrate; and, there have been reports of patients being sunburned from UV lamps which may be used to accelerate the bleach.
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