The subconscious impact of a white smile — radiant health, happiness, warmth and invitation are part of the human condition. Beyond personal and social perceptions a contagious smile makes you feel and be perceived as a winner. This phenomenon has been reinforced with the spread of American culture worldwide, where an especially white smile has even been coined a “Hollywood smile.” Social acceptance has created an ever increasing public demand for whiter teeth, considered to be one of the keys to an attractive smile. Where does this perception come from? White teeth are subconsciously associated with youth and virility and are more desirable. Today whiter, brighter, straighter, lighter teeth have become a norm. Moreover dentists have had to create a special shade of “whiter than white” which even in the profession is known as “Hollywood white.”
Whitening to the Rescue
A child’s deciduous (baby) teeth are generally whiter than the adult teeth that follow. With age adult teeth often become darker. Discolored teeth cause aesthetic impairment and psychological trauma. Attempts to whiten teeth as a result of tooth discoloration are myriad and date back centuries. Anything and everything from chewing gum to sophisticated dental restorative treatment has been and is being utilized.
Tooth whitening by bleaching is a successful, conservative, relatively inexpensive and safe alternative with few side effects, which for the most part are readily controllable.
Causes of Tooth Discoloration
Tooth discoloration may be described as intrinsic, extrinsic or a combination of both. It varies in appearance, cause, severity, position and adherence to the teeth. Intrinsic (internal) tooth discoloration is caused by changes in the structure of enamel or dentine or by incorporation of chromogenic (color generating) material into tooth tissue, either during tooth formation or after eruption. Wear of teeth, thickening of dentin due to aging or as a consequence of pulp inflammation affect the light-transmitting properties of enamel and dentin, resulting in a gradual discoloration.
Aging results in changes in the mineral structure of the tooth; the enamel, the outer covering loses its beautiful and youthful translucency, becoming less porous; and the underlying dentin, which forms the body of the teeth thickens and becomes more yellow. Intrinsic discoloration is also caused by exposure to high levels of fluoride, tetracycline antibiotic administration during childhood, inherited developmental disorders and jaundice in childhood. After eruption, tooth decay, restorations, pulp death (root canal problems) and trauma to developing teeth, are the main causes of intrinsic discoloration.
Extrinsic staining mainly results from dietary factors and smoking; foods containing tannins such as red wine, coffee and tea can give rise to extrinsic stain. Carotenes, pigments in oranges and carrots, and tobacco use, whether it is smoking or chewing, also give rise to extrinsic stain.
How Does Modern Whitening Work?
The first publications describing techniques and chemicals for bleaching “non-vital” (root canal treated) teeth appeared in the latter half of the 19th Century. The bleaching agent of choice was chloride of lime. Other agents described for the bleaching of non-vital teeth included aluminum chloride and hydrogen peroxide, used either alone or in combination with heat. The active ingredient common to all the early medicaments was an oxidizing agent. Concern about the side effects of some of these agents was justified because some chemicals used were very poisonous, such as cyanide of potassium.
The observation that carbamide peroxide caused lightening of teeth was made in the late 1960s by an orthodontist (Klusmier), who had prescribed an antiseptic containing 10% carbamide peroxide to be used in a tray for the treatment of gingivitis (inflammation of the gums). Believe it or not, this technique pioneered the method of home bleaching today, which only achieved general acceptance decades later. In a nutshell, carbamide peroxide and its breakdown products, hydrogen peroxide and urea bleach the colored organic molecules between the enamel crystals and in the dentin therefore leaving the teeth whiter looking.
Professionally Applied or “In-Office” Tooth Whitening
Sometimes known as “Power Bleaching,” this is the procedure of choice for whitening teeth. It is indicated where general whitening of the teeth is required but especially for severely stained teeth, for example by tetracycline, or prior to veneering or crowning teeth where severe discoloration is present. The whitening of the external surfaces of vital (living) teeth accomplishes complete lightening during treatment in the dental office under direct supervision of the dentist. Power bleaching of vital teeth generally uses a high concentration of peroxide solution, (35-45% hydrogen peroxide) placed directly on the teeth, often supplemented by a heat or light source to activate or enhance peroxide release [Figure 1].
The Magic’s in the “Gel”
These systems use a gel applied with custom tailored trays specially fitted to the individual’s mouth. When using the stronger professionally applied agents the dentist will isolate the gums and membranes (skin) of the mouth with a “rubber dam,” silicone barrier material or protective gel to prevent irritation [Figure 2]. When activated by mixing the components of the gel, hydrogen peroxide gas is liberated which is responsible for the whitening effect. The better systems contain a buffer which keeps the gel from becoming acidic thereby preventing damage to the enamel.
Dull to bright in minutes. The combination of chemicals in the gel can lighten teeth up to ten shades in about an hour. Most testers have recorded an improvement of three to eight shades and note that some people may need up to four treatments to achieve the level of whiteness they desire. There are several professional bleaching systems available all with slight variations in the bleaching gels, light systems as well as the time and number of applications required to produce the appropriate level of lightening.
Risking sensitivity? Higher concentrations of peroxide provide a more rapid bleaching effect; however they may increase the risk of tooth sensitivity, a good reason for a dental professional to carry out the procedure in-office. In addition to concentration, the degree of whitening is also related to the amount of time that the bleaching agent is in contact with the tooth surface; the longer the time, the greater the lightening effect and the greater the likelihood of sensitivity. Tooth sensitivity, generally to hot and cold, normally persists for no more than four days after the cessation of bleaching.
Prevention of sensitivity: Recently the effect of the addition of amorphous calcium phosphate (ACP) to a 16% carbamide peroxide gel has been reported to significantly reduce sensitivity. Another approach to reducing sensitivity is by the addition of desensitizing agents such as potassium nitrate or fluoride, in the form of stannous fluoride, to produce “sensitive-formula” gels. However it can take some time to see results with these two agents.
Home Whitening Systems
“Take home” whitening is the more commonly used technique because it is easy to perform and is less expensive. It generally involves the use of a 6-16% solution of carbamide peroxide in a gel form (approximately equal to 3.4-7% hydrogen peroxide) delivered to the tooth surface by a custom made, vacuum formed, plastic bleaching tray which can be made in your dentists office.
Manufacturers have offered carbamide peroxide in a variety of different concentrations, ranging from 10% to over 20%, but the best combination of safety, limited side effects and speed of action is obtained with a 10% solution of carbamide peroxide approved by the ADA (American Dental Association).
It is generally agreed that most teeth are susceptible to bleaching. The process of home bleaching requires longer contact time compared to power bleaching, but it is safe and the results are generally excellent. General recommendations are for 30 minute applications twice a day. The first subjective change in tooth color is generally observed after two to four sessions of bleaching. In a clinical study of custom tray vital bleaching with 10% carbamide peroxide, 92% of subjects experienced some lightening of teeth after a six-week period. Another clinical trial examined the amount of change in shades of lightness using 10% carbamide peroxide nightly for two weeks and reported that lightness increased by, on average, eight shade units. The dentists or manufacturers guidelines should be followed exactly and not exceeded to avoid damage to the teeth and oral (skin) membranes.
Whitening strips are easier to use than some other products. They generally contain 10% carbamide peroxide gel or less. They come in the form of strips and look like clear band aids that are applied to the tooth surfaces. They should be worn twice a day for 30 minutes each time, for seven days. On average, they claim to lighten more than three shades. Results claim to last about 12 months. Whitening strips containing 6% carbamide peroxide gels take about two weeks to work at 30 minutes per day.
“Paint on” or “Brush on” whitening formulas are also available. These consist of gels that are painted onto the teeth before bed for two weeks. Some claim that this can whiten teeth two to five shades. However these gels can increase salivation and may make your mouth feel goopy, but are relatively inexpensive.
If you are willing to pay more for convenience, some systems consist of individual tubes of 6% gel that each come with a small brush. The gel is squeezed onto the brush and then scrubbed onto the teeth. It does not have to be removed.
When it comes to over-the-counter whitening products, teeth-whitening strips and paint-on whiteners are preferred to over-the-counter “mouth-tray” whiteners, however best results are always attained through a qualified dentist. Since the mouth trays are one-size-fits-all, they can be ill fitting. The trays are filled with gel and worn 45 minutes a day for one week. On average, teeth become two shades whiter. Some find the trays to be messy or uncomfortable. Many tray systems are available.
Whitening Gum is another novelty to hit the market. It doesn’t contain peroxide, but it does have a “patented technology” that supposedly breaks up surface stains. To see an effect, you need to chew two pieces for at least 20 minutes, four times a day — not a problem if you are a habitual gum chewer, otherwise it could become a bit tiring.
