Tooth whitening

Tooth whitening or tooth bleaching is the process of lightening the colour of human teeth. Whitening is often desirable when teeth become yellowed over time for a number of reasons, and can be achieved by changing the intrinsic or extrinsic colour of the tooth enamel. The chemical degradation of the chromogens within or on the tooth is termed as bleaching. Reflecting less light, these smaller molecules create a "whitening effect". Additionally, the perceived brightness of the tooth can change depending on the brightness and colour of the background. This can be attributed to secondary dentin formation and thinning of enamel due to tooth wear which contributes to a significant decrease in lightness and increase in yellowness. Below explains in-depth the differences between the two sources of which contribute to such discolouration of the tooth's surface. alt=|thumb|443x443px|Figure 2. Examples of tooth staining. Extrinsic staining examples: A. Smoking; B. Wine stain; and C. Food stain. Intrinsic staining examples: D. Age yellowing; E. Decay; F. Orthodontic white spot lesion; G. Mild fluorosis; H. Amalgam restoration; I. Tetracycline stain; J. Genetic (amelogenesis imperfecta); K. and non-vital colouring.

Extrinsic staining

Extrinsic staining, is largely due to environmental factors including smoking, pigments in beverages and foods, antibiotics, and metals such as iron or copper. Coloured compounds from these sources are adsorbed into acquired dental pellicle or directly onto the surface of the tooth causing a stain to appear.

Dental plaque: Dental plaque is a clear biofilm of bacteria that naturally forms in the mouth, particularly along the gumline, and it occurs due to the normal development and defences of the immune system. Although usually virtually invisible on the tooth surface, plaque may become stained by chromogenic bacteria such as Actinomyces species. The acidic by-products of fermentable carbohydrates derived from high-sugar foods contribute to greater proportions of bacteria, such as Streptococcus mutans and Lactobacillus in dental plaque. Higher consumption of fermentable carbohydrates will promote demineralisation and increase the risk of developing white spot lesions. The color of calculus varies, and may be grey, yellow, black, or brown. The colour of calculus depends on how long it has been present in the oral cavity for; it typically starts off yellow and over time the calculus will begin to stain a darker colour and become more tenacious and difficult to remove.
Tobacco: tar in the smoke from tobacco products (and also smokeless tobacco products) tends to form a yellow-brown-black stain around the necks of the teeth above the gumline. Betel chewing produces blood-red saliva that stains the teeth red-brown to nearly black. The extract gel of betel leaf contain tannin, a chromogenic agent that causes discolouration of the tooth enamel.
Tannin is also present in coffee, tea, and red wine and produces a chromogenic agent that can discolor teeth.
Certain foods, including curries and tomato-based sauces, can cause teeth staining.
Certain topical medications: Chlorhexidine (antiseptic mouthwash) binds to tannins, meaning that prolonged use in persons who consume coffee, tea or red wine is associated with extrinsic staining (i.e. removable staining) of teeth. Chlorhexidine mouthwash has a natural liking for sulphate and acidic groups commonly found in areas where plaque accumulates such as along the gumline, on the dorsum of the tongue and cavities. Chlorhexidine is retained in these areas and stain yellow-brown. The stains are not permanent and can be removed with proper brushing.
Metallic compounds. Exposure to such metallic compounds may be in the form of medication or occupational exposure. Examples include iron (black stain), iodine (black), copper (green), nickel (green), and cadmium (yellow-brown). Sources of exposure to metal include placing metal into the oral cavity, metal-containing dust inhalation, or oral administration of drugs. Metals can enter the bony structure of the tooth, causing permanent discolouration, or can bind to the pellicle causing surface stain. The abrasive nature of the prophy paste, as it is known, acts to remove extrinsic staining using the action of the slow-speed handpiece and the paste against the tooth. Adversely, the action of the rubber cup together with the abrasive nature of the paste, removes around one micron of enamel from the tooth surface every time a prophylaxis is performed. This method of stain removal may only take place in the dental office.
Micro-abrasion: allows a dental professional to make use of an instrument which emits a powder, water and compressed air to remove biofilm, and extrinsic staining. This stain removal method can only be undertaken in a dental office, not at home.
Toothpaste: there are many available on the market that implement both peroxide as well as abrasive particles, such as silica gel, to help remove extrinsic stains, while the peroxide acts on intrinsic staining. This method of stain removal may take place at home as well as in a dental office.

Intrinsic staining

Intrinsic staining primarily occurs during the tooth development either before birth or at early childhood. Intrinsic stains are those that cannot be removed through mechanical measures such as debridement or a prophylactic stain removal. As the age of the person increases, the teeth can also appear yellower over time. Below are examples of intrinsic sources of stains:

Tooth wear and aging: Tooth wear is a progressive loss of enamel and dentine due to tooth erosion, abrasion and attrition. As enamel wears down, dentine becomes more apparent and chromogenic agents are penetrated in the tooth more easily. The natural production of secondary dentine also gradually darkens teeth with age.
Dental cavities (tooth decay): The evidence regarding enamel hypoplasia is inconclusive, however the most likely cause is infection or trauma caused to the primary dentition. Disturbances to the developing tooth germ during neonatal and early childhood stages such as maternal vitamin D deficiency, infection, and medication intake can cause enamel hypoplasia. and produces a red hue seen initially after trauma which has the ability to disappear if the tooth becomes revascularized. Dental fluorosis occurs due to excessive ingestion of fluoride or overexposure to fluoride during the development of enamel which usually occurs between the ages of one and four. Fluoridated drinking water, fluoride supplements, topical fluoride (fluoride toothpastes), and formula prescribed for children can increase the risk of dental fluorosis. Fluoride is considered an important factor in the management and prevention of dental cavities, the safe level for daily fluoride intake is 0.05 to 0.07 mg/kg/day.
Dentinogenesis imperfecta: The drug is able to chelate calcium ions and is incorporated into teeth, cartilage, and bone. Ingestion during the years of tooth development causes yellow-green discoloration of dentine visible through the enamel which is fluorescent under ultraviolet light. Later, the tetracycline is oxidized and the staining becomes more brown and no longer fluoresces under UV light.
Porphyria:
Hemolytic disease of the newborn:
Root resorption: Root resorption is clinically asymptomatic; however, it can produce a pink appearance at the amelocemental junction.

Methods

Prior to proceeding to tooth whitening alternatives, it is advised that the patient comes into the dental office to have a comprehensive oral examination that consists of a full medical, dental, and social history. This will allow the clinician to see if there is any treatment that needs to be done such as restorations to remove cavities, and to assess whether or not the patient will be a good candidate to have the whitening done. The clinician would then debride (clean) the tooth surface with an ultrasonic scaler, hand instruments, and potentially a prophy paste to remove extrinsic stains as mentioned above. This will allow a clean surface for maximum benefits of whichever tooth whitening method the patient chooses. These shades may be reached after a single in office appointment, or may take longer, depending on the individual. The effects of bleaching can last for several months, but may vary depending on the lifestyle of the patient. Consuming tooth staining foods or drinks that have a strong colour may compromise effectiveness of the treatment. These include food and drinks containing tannins such as; coffee, tea, red wines, and curry.

In-office bleaching procedures generally use a light-cured protective layer that is carefully painted on the gums and papilla (the tips of the gums between the teeth) 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% and 44% carbamide peroxide, which is roughly equivalent to a 3% to 16% hydrogen peroxide concentration. The legal percentage of hydrogen peroxide allowed to be given is 0.1–6%. Bleaching agents are only allowed to be given by dental practitioners, dental therapists, and dental hygienists.

Bleaching is least effective when the original tooth color is grayish and may require custom bleaching trays. Bleaching is most effective with yellow discolored teeth. If heavy staining or tetracycline damage is present on a patient's teeth, and whitening is ineffective (tetracycline staining may require prolonged bleaching, as it takes longer for the bleach to reach the dentine layer), there are other methods of masking the stain. Bonding, which also masks tooth stains, is when a thin coating of composite material is applied to the front of a person's teeth and then cured with a blue light. A veneer can also mask tooth discoloration.

In-chair whitening is faster and more effective in comparison to the take-home bleaching options. Some clinicians also make custom bleaching trays, which can take up to a week to create. After the whitening treatment is completed, the patient is able to use these trays for maintenance of their bleaching with at-home kits or for use with desensitising products.

Light-accelerated bleaching

Power or light-accelerated bleaching uses light energy which is intended to accelerate the process of bleaching in a dental office. Different types of energy can be used in this procedure, with the most common being halogen, LED, or plasma arc. Use of light during bleaching increases the risk of tooth sensitivity and may not be any more effective than bleaching without light when high concentrations of hydrogen peroxide are used. A 2015 study showed that the use of a light activator does not improve bleaching, has no measurable effect, and rather is likely to increase the temperature of the associated tissues, resulting in damage.

The ideal source of energy should be high energy to excite the peroxide molecules without overheating the pulp of the tooth. Lights are typically within the blue light spectrum as this has been found to contain the most effective wavelengths for initiating the hydrogen peroxide reaction. A power bleaching treatment typically involves isolation of soft tissue with a resin-based, light-curable barrier, application of a professional dental-grade hydrogen peroxide whitening gel (25–38% hydrogen peroxide), and exposure to the light source for 6–15 minutes. Recent technical advances have minimized heat and UV emissions, allowing for a shorter patient preparation procedure.

For any whitening treatments, it is recommended that a comprehensive examination of the patient is done including the use of radiographs to aid in the diagnosis of the current condition of the mouth, including any allergies that may be present. The patient will need to have a healthy mouth and free of periodontal disease or cavities and to have had a debridement/clean done to remove any tartar or plaque build up.

It is recommended to avoid smoking, drinking red wine, eating or drinking any deeply coloured foods after this as the teeth may stain considerably straight after treatment.

Internal bleaching

Internal bleaching is a process which occurs after a tooth has been endodontically treated. This means that the tooth will have had the nerve of the tooth extirpated or removed through a root canal treatment at the dentist or by a specialist endodontist. Internal bleaching is often sought after in teeth which have been endodontically treated as tooth discolouration becomes a problem due to the lack of nerve supply to that tooth. It is common to have this internal bleaching done on an anterior tooth (a front tooth that you can see when smiling and talking). A way around this is by sealing off the bleaching agent inside the tooth itself and replacing it every few weeks until the desired shade has been achieved. The amount of time between appointments varies from patient to patient and with operator preference until the desired shade has been achieved. Even though this is a great option, the disadvantage of this treatment is a risk of internal root resorption of the tooth that is being internally bleached. This may not occur in every patient or every tooth, and its occurrence is difficult to determine prior to completing the treatment. At home whitening methods include over-the-counter strips and gels, whitening rinses, whitening toothpastes, and tray-based tooth whiteners.

Strips and gels

The plastic whitening strips contain a thin layer of peroxide gel and are shaped to fit the buccal/labial surfaces of teeth. Tooth whitening toothpaste that have excessive abrasivity are harmful to dental tissue, therefore baking soda is a desirable alternative.

Intrinsic tooth staining
Aesthetics
Dental fluorosis
Endodontic treatment (internal bleaching)
Tetracycline staining

Contraindications

Some groups are advised to carry out tooth whitening with caution as they may be at higher risk of adverse effects.

Patients with unrealistic expectations
Allergy to peroxide
Pre-existing sensitive teeth
Cracks or exposed dentine
Enamel development defects
Acid erosion
Receding gums (gingival recession) and yellow roots
Sensitive gums
Defective dental restorations
Tooth decay. White-spot decalcification may be highlighted and become more noticeable directly following a whitening process, but with further applications the other parts of the teeth usually become more white and the spots less noticeable.
Active periapical pathology
Untreated periodontal disease
Pregnant or lactating women
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. Younger people are also more susceptible to abusing bleaching.
Individuals with poor oral hygiene

Risks

Some of the common side effects involved in teeth whitening are increased sensitivity of the teeth, gum irritation, and extrinsic teeth discolouration. Exposure to cold, hot, or sweet stimuli may further exacerbate the intensity of the hypersensitive response. Amongst those who receive in-office whitening treatment, between 67 and 78% of the individuals experience sensitivity after the procedure where hydrogen peroxide and heat is utilized. Although it varies from person to person, sensitivity after whitening treatment can last up to 4–39 days.

Potassium nitrate and sodium fluoride in toothpastes are used to ease discomfort following bleaching, however, there is no evidence to suggest that this is a permanent method to eradicate the issue of hypersensitivity.

Irritation of mucous membranes

Hydrogen peroxide is an irritant and cytotoxic. Hydrogen peroxide with concentrations of 10% or higher can cause tissue damage, be corrosive to mucous membranes and cause burning sensation to the skin. Chemical burns can commonly occur whilst bleaching, irritation and discolouration of the mucous membranes may occur if a high concentration of oxidising agent comes in to contact with unprotected tissue. Poorly fitting bleaching trays are amongst the most common reasons for chemical burns. The temporary burning induced by whitening treatments can be reduced by using custom-made plastic trays or nightguards provided by the dental professional. This prevents the leakage of solution onto the surrounding mucosa.

Uneven results

Uneven results are quite common after bleaching. Consuming less foods and drinks that cause surface staining of teeth can contribute to attaining a good result from tooth whitening.

Return to original pre-treatment shade

Nearly half the initial change in colour provided by an intensive in-office treatment (i.e., one hour treatment in a dentist's chair) may be lost in seven days. Rebound is experienced when a large proportion of the tooth whitening has come from tooth dehydration (also a significant factor in causing sensitivity). As the tooth rehydrates, tooth colour "rebounds", back toward where it started.

Over-bleaching

Over-bleaching, more often known as the "bleached effect", occurs among treatments that promise a large change over a short period of time e.g., hours. Over-bleaching can emit a translucent and brittle appearance.

Damage to enamel

Teeth enamel can have an adverse negative effect by whitening treatment. Evidence from studies show that carbamide peroxide present in whitening gels can damage the enamel surface. Although this effect is not as damaging as phosphoric acid etch, the increased irregularity of the teeth surface makes the teeth more susceptible to extrinsic staining, thus having an increased detrimental effect on the aesthetics. The increased porosity and changes in surface roughness may have an impact on the formation of supra- and subgingival plaque, thus increasing the adhesion of bacterial species such as Streptococcus mutans and Streptococcus sobrinus, significant contributors to dental cavities. The release of amalgam components is said to be due to active oxidation. This increase in amalgam mercury release is proportional to the concentration of carbamide peroxide. Many studies have found that 10–16% carbamide peroxide tooth bleaching gels (containing approximately 3.6–5.76% hydrogen peroxide) leads to an increase in the surface roughness and porosity of composite resins. However, the saliva may exert a protective effect. In addition, changes in the reflectance of the composite have been analysed following whitening with high concentration (30–35%) hydrogen peroxide.

Bleachorexia

Bleachorexia is the term that is used to describe an individual that develops an unhealthy obsession with teeth whitening. Patients need to actively participate in their treatment and follow the guidelines given by the dentist accurately. Erratic or inaccurate use of the bleaching trays could cause harm to the patient such as blistering or sensitivity of the teeth and the surrounding soft tissue. Inconsistent use of the bleaching trays can lead to the slowing and irregularity of the whitening process. Some patients with a substantial gag reflex may not be able to tolerate the trays and would need to consider other methods of teeth whitening. The downside is that these radicals have certain local harmful effects, such as enamel erosion, changes in the microhardness of the teeth, gum irritation, post-bleaching hypersensitivity, and burning sensations. The following side effects are also known:

Even during treatment, there is often very painful sensitivity to the bleaching agent. Freshly treated teeth can be sensitive to sweets, acids, and temperature, which can be quite painful. However, these symptoms are usually temporary and subside within a few days after treatment.
The long-term effects of higher concentration bleaching agents (>6% H<sub>2</sub>O<sub>2</sub> or equivalent) on the pulp, dentin, enamel, and oral soft tissues are not yet clarified. These bleaching agents are potentially harmful and should be used with caution only in dental practice.
Bleaching can deplete minerals from the teeth, leading to demineralization and the temporary breakdown of the protein pellicle (the protective layer of the tooth). This can result in more or less pronounced white spots, which usually normalize within days after treatment. Remineralization can be supported by special gels.
Bleaching can weaken the tooth structure. Internal bleaching can lead to tooth brittleness and root resorption.

Peroxycarboxylic Acids-Based Bleaching Agents

Bleaching agents based on peroxycarboxylic acids (PAP) can be chosen as an effective vehicle for tooth whitening. PAP has proven to be almost harmless to enamel with a safe and reliable bleaching effect. In the clinical application of PAP for tooth whitening, oxidation reactions also occur, and color molecules are bleached through chemical-physical processes. However, the reaction occurs without the formation of free radicals. This is the major and decisive difference, as free radicals are the main cause of tooth sensitivity and gum irritation in tooth whitening with hydrogen peroxide-based bleaching agents.

Other risks

Evidence suggests that hydrogen peroxide might act as a tumour promoter. Although cervical root resorption is more evidently observed in thermocatalytic bleaching methods, intracoronal internal bleaching may also lead to tooth root resorption. Recently, the genotoxic potential of hydrogen peroxide was evaluated. The results indicated that the oral health products that contain or release hydrogen peroxide up to 3.6% will not increase the cancerous risk of an individual, hence, it is safe to use in moderation.

Maintenance

Despite achieving the results of treatment, stains can return within an initial couple of months of treatment. Various methods may be employed to prolong the treatment results, such as:

Brush or flush out mouth with water after eating and drinking
Floss to remove plaque and biofilms between the teeth
Take special care during the first 2 days – the first 24–48 hours after the whitening procedure is seen as the most crucial period in which you must protect for your teeth the most. Hence, it is vital that non-staining drinks or foods are eaten during this time as enamel is prone to adhere to stains.
Drink fluids that may cause staining through a straw
Depending on the method used to whiten the teeth, re-treatment every six months or after a year may be required. If an individual is a smoker or they consume beverages with the capacity to stain, regular re-treatments would be required.

History

Teeth whitening remedies have been present since ancient times. Despite seeming absurd, some methods were somewhat effective in their results.

Ancient Roman dentists believed in using urine with goat milk to make their teeth look whiter. Pearly white teeth symbolized beauty and marked wealth. In the Auyrveda medicine system, oil pulling was used as an oral therapy. For this process today, swish coconut or olive oil in your mouth for up to 20 minutes each day. In the late 17th century, many people reached out to barbers, who used a file to file down the teeth before applying an acid that would, in fact, whiten the teeth. Although the procedure was successful, the teeth would become completely eroded and more prone to becoming decayed. Guy de Chauliac suggested the following to whiten the teeth: "Clean the teeth gently with a mixture of honey and burnt salt to which some vinegar has been added." In 1877, oxalic acid was proposed for whitening, followed by calcium hypochlorite. By 1940s and 1950s, ether and hydrogen peroxide gels were used to whiten vital teeth, whereas non-vital teeth were whitened using pyrozone and sodium perborate. The US Food and Drug Administration only endorses gels that are under 6% hydrogen peroxide or 16% or less of carbamide peroxide. The Scientific Committee on Consumer Safety of the EU consider gels containing higher fixations can be dangerous.

As per European Council guidelines, only a certified dental professional can lawfully give tooth whitening products utilizing 0.1–6% hydrogen peroxide, provided the patient is 18 years of age or older. In 2010, the UK General Dental Council became concerned of the "risk to patient safety from poor quality tooth whitening being carried out by untrained or poorly trained staff." A public attitudes survey, conducted by the GDC, showed that 83% of people support "policies of regulating tooth whitening to protect patient safety and prosecuting illegal practice."

According to research, tooth whitening can produce positive changes in young participants' Oral Health Related Quality of Life (OHRQoL) in aesthetic areas such as smiling, laughing, and showing teeth without embarrassment. However, its main side-effect, tooth sensitivity, negatively affects quality of life.