Remark from GODENTA :
Remember that only natural teeth substance could be
bleached / whitened, on artificial material of crowns, bridges, fillings, onlays, inlays, the process will generally not have any effect.
Dental bleaching, also known as tooth whitening, is a common procedure in general dentistry but most especially in the field of cosmetic dentistry.
A child's deciduous teeth are generally whiter than the adult teeth that follow. As a person ages the adult teeth often become darker due to changes in the mineral structure of the tooth, as the enamel becomes less porous.
Teeth can also become stained by bacterial pigments, foodstuffs and tobacco. Certain antibiotic medications (like tetracycline) can also lead to teeth stains or a reduction in the brilliance of the enamel.
There are three methods to whiten teeth: bleaching gel, laser bleaching, and natural bleaching. Traditionally, at-home whitening is done with bleaching gel which is applied to the teeth using thin guard trays. Oxidizing agents such as hydrogen peroxide or carbamide peroxide are used to lighten the shade of the tooth. The oxidizing agent penetrates the porosities in the rod-like crystal structure of enamel and oxidizes interprismatic stain deposits; over a period of time, the dentin layer, lying underneath the enamel, is also bleached. Laser bleaching uses light energy to accelerate the process of bleaching in a dental office. The effects of bleaching can last for several months, but may vary depending on the lifestyle of the patient. Factors which will decrease whitening include smoking and the ingestion of dark colored liquids like coffee, tea and red wine.
Internal staining of dentin can discolor the teeth from inside out. Internal bleaching can remedy this. If heavy staining or tetracycline damage is present on a patient's teeth, and whitening is ineffective, there are other methods of whitening teeth. Bonding, when a thin coating of composite material is applied to the front of a person's teeth and then cured with a blue light can be performed to mask the staining. A veneer can also mask tooth discoloration.
There are two main methods of gel bleaching--one performed with high-concentration gel, and another with low-concentration agents. High-concentration bleaching can be accomplished either in the dental office, or at home. Performing the procedure at home is accomplished using high-concentration carbamide peroxide ,which is readily available online or in dental stores and is much more cost-effective than the in-office procedure. Whitening is performed by applying a high concentration of oxidizing agent to the teeth with thin plastic trays for a short period of time, which produces quick results. The application trays ideally should be well-fitted to retain the bleaching gel, ensuring even and full tooth exposure to the gel. Trays will typically stay on the teeth for about 15–20 minutes. Trays are then removed and the procedure is repeated up to two more times. Most in-office bleaching procedures use a light-cured protective layer that is carefully painted on the gums and papilla (the tips of the gums between the teeth) in order to reduce the risk of chemical burns to the soft tissues. The bleaching agent is either carbamide peroxide, which breaks down in the mouth to form hydrogen peroxide, or hydrogen peroxide itself. The bleaching gel typically contains between 10-30% carbamide peroxide (15% is recommended) which is roughly equivalent to 3-10% hydrogen peroxide concentration.
Low-concentration whitening is far less effective, and is generally only performed at home. Low-concentration whitening involves purchasing a thin mouthguard or strip that holds a relatively low concentration of oxidizing agent next to the teeth for as long as several hours a day for a period of 5 to 14 days. Results can vary, depending on which application is chosen, with some people achieving whiter teeth in a few days, and others seeing very little results or no results at all. Whitening is potentially better at a dentist because the strip or mouth-guard does not completely conform to the shape of the teeth, sometimes leaving the tips of the teeth (near the gumline) unbleached. The bleaching agent is typically less than 10% hydrogen peroxide equivalent, so irritation to the soft tissue around teeth is minimized. Dentists as well as some dental laboratories can fabricate custom fitted whitening trays that will greatly improve the results achieved with an over-the-counter whitening method.
A typical course of bleaching can produce dramatic improvements in the cosmetic appearance of most stained teeth; however, some stains do not respond to bleaching. Tetracycline staining may require prolonged bleaching, as it takes longer for the bleach to reach the dentine layer. White-spot decalcifications may also be highlighted and become more noticeable. Bleaching is least effective if teeth have white spots, decay or infected gums. It is also least effective when the original tooth color is grayish. Bleaching is most effective with yellow discolored teeth.
Laser bleaching, also known as power bleaching, uses light energy to accelerate the process of bleaching in a dental office. Different types of energy can be used in this procedure. The ideal source of energy should be high energy to excite the peroxide molecules without overheating the pulp of the tooth, creating an inflammatory response. The use of an argon laser to safely and effectively speed up the whitening process is ideal for laser bleaching. An argon laser is preferred over the use of an arc lamp (the traditional dental method of light-activated bleaching) or infrared laser because it does not exhibit any of the heat or UV ray emissions of the arc lamp. Chemical burns, which are occasionally a side-effect of gel bleaching, or heat-induced sensitivity, are not a factor with argon laser whitening. Most laser teeth whitening treatments can be done in approximately 1 hour, in a single visit to a dental physician, (depending on the condition of a person’s teeth).
Side effects of teeth bleaching include: chemical burns with gel bleaching (if a high-concentration oxidizing agent contacts unprotected tissues, which may bleach or discolor mucous membranes), sensitive teeth, and overbleaching (known in the profession as "over white teeth") aka "Hyperodonto-oxidation". Rebound, or teeth losing the bleached effect and darkening, is also an issue, with some studies showing the rebound effect over 30 days. A recent study by Kugel et al. has shown that as much as 4 shades of lightness can be lost over 30 days with light-activated/office bleaching[citation needed.
Home tooth bleaching treatments can very slightly reduce tooth enamel. There have been long term Tetracycline studies done where patients received high concentration bleach, over night, for 6 months. These studies show that even over long term exposure, the amount of reduction in tooth enamel is insignificant.
The side effects that occur most often are a temporary increase in tooth sensitivity and mild irritation of the soft tissues of the mouth, particularly the gums. Tooth sensitivity often occurs during early stages of the bleaching treatment. Tissue irritation most commonly results from an ill-fitting mouthpiece tray rather than the tooth-bleaching agent. Both of these conditions usually are temporary and disappear within 1 to 3 days of stopping or completing treatment.
Individuals with sensitive teeth and gums, receding gums and/or defective restorations should consult with their dentist prior to using a tooth whitening system. People who are sensitive to hydrogen peroxide (the whitening agent) should not try a bleaching product without first consulting a dentist. Also, prolonged exposure to bleaching agents may damage tooth enamel. This is especially the case with home remedy whitening products that contain fruit acids.
Bleaching is not recommended in children under the age of 16. This is because the pulp chamber, or nerve of the tooth, is enlarged until this age. Tooth whitening under this condition could irritate the pulp or cause it to become sensitive. Tooth whitening is also not recommended in pregnant or lactating women.
Tooth whitening does not usually change the color of fillings and other restorative materials. It does not affect porcelain, other ceramics, or dental gold. However, it can slightly affect restorations made with composite materials, cements and dental amalgams. Tooth whitening can restore color of fillings, porcelain, and other ceramics when they become stained by foods, drinks, and smoking, among other activities.
Internal bleaching procedures are performed on devitalized teeth that have undergone endodontic therapy but are discolored due to internal staining of the tooth structure by blood and other fluids that leached in. Unlike external bleaching which brightens teeth from the outside in, internal bleaching brightens teeth from the inside out. Bleaching the tooth internally involves drilling a hole to the pulp chamber, cleaning, sealing, and filling the root canal with a rubber-like substance, and placing a peroxide gel into the pulp chamber so that the gel can work directly inside the tooth on the dentin layer.
In this variation of whitening the peroxide is sealed within the tooth over a period of some days and replaced as needed, the so called "walking bleach" technique.
Various chemical and physical agents can be used to whiten teeth. Toothpaste typically has small particles of silica, aluminum oxide, calcium carbonate, or calcium phosphate to grind off stains formed by colored molecules that have lodged onto the teeth from food. Unlike bleaches, whitening toothpaste does not alter the intrinsic color of teeth.
Bleaching solutions contain peroxide which bleaches the tooth enamel to change its color. Off-the-shelf products typically rely on a carbamide peroxide solution varying in concentration from 10% to 22%. Bleaching solutions may be applied directly to the teeth, embedded in a plastic strip that is placed on the teeth or use a gel held in place by a mouthguard. Because the concentration is typically low to avoid toxicity, whitening often takes several weeks. A tooth whitening agent that also remineralizes teeth is under development.
Whitening treatments used by dentists are much more concentrated, containing substances with more than 30% hydrogen peroxide, and require protection of the soft tissues.
Whitening teeth for aesthetic purposes has been dated back to the Ancient Egyptians, where a mixture of ground pumice and wine vinegar was brushed on the teeth with a rudimentary toothbrush. The ancient Romans used human urine by the belief that it kept the teeth white and firmly in place, a practice that continued into the eighteenth century. Whitening in the medieval ages was done by barbers, where the teeth would be filed down and nitric acid applied to the teeth. This was a dangerous procedure, considering the massive tooth damage this practice caused.
Generally, consumer organizations and health sector professionals recommend that bleaching products should only be used after consultation with a dentist, while the cosmetic industry and its organizations argue that, since bleaching products are basically safe, they should be freely available over the counter.
Also, regulations concerning bleaching products' availability and concentration in peroxide are more restrictive in the European Union than in North America.[