From Volume 44, Issue 1, January 2017 | Pages 56-63
Improving patients' aesthetics is an important request in daily practice. Tooth whitening is a treatment option available for improving aesthetics. This paper will pose questions asked by our patients on bleaching techniques and outcomes and offer appropriate up-to-date answers.
Tooth discoloration is a common problem affecting patients of all ages. The dental profession has used numerous chemicals and methods to remove discoloration from teeth over many years.1
Dental bleaching is a chemical process that uses oxidizing agents on tooth surfaces to penetrate the enamel and dentine, resulting in a change of colour.2
Numerous techniques and products with different concentrations are available to the profession and direct over-the-counter (OTC) products are available to the patient.3
The aim of this article is to answer frequently asked questions about bleaching.
Tooth colour is determined by a combination of the different optical properties of enamel, dentine and pulp. Tooth discolorations vary in aetiology, appearance and severity, and are categorized as intrinsic or extrinsic. Some of these occur during tooth formation and others afterwards. It is important to identify the correct aetiology in order to obtain an effective treatment.4,5
Extrinsic stains are superficial discolorations of the tooth surface or restorative material resulting from an accumulation and adherence of foreign particles of various origins (including tobacco, coffee, tea, red wine, medications such as iron supplements, chlorhexidine, chromogenic type bacteria, tannin) (Table1).
| Origin | Agent | Colour |
|---|---|---|
| Biofilm | Food residue | White-yellow |
| Dietary coloration | Wine, soda, tea, coffee | Brown-black |
| Bacterial coloration | Penicillium – Aspergillus | Orange-green |
| Antiseptic coloration | Chlorhexidine | Brown |
| Medication | Iron | Brown-black |
Extrinsic stains can consist of multiple colours such as brown, black, green, orange and grey metallic. Brown stains are thin pigmented pellicles usually located on the buccal surfaces of maxillary incisors. The specific origin of the brown staining has not been determined but tannin depositions from tea and coffee are suspected. Dark brown to black stains are often the result of tobacco and are usually located on the gingival third of teeth and on any enamel defects. Green stains are found on the buccal aspect of maxillary incisors. It is thought that bacteria or fungi such as penicillium or aspergillus cause this coloration in the presence of light. These stains are commonly found in children and more commonly affect females. Orange stains, which are uncommon, are due to chromogenic bacteria. Chlorhexidine discolorations are typically brown and occur on the teeth and composite restorations after prolonged use (more than 14 days).6
Intrinsic stains may be caused by trauma to a developing permanent tooth. The trauma causes damage to the blood supply, which may result in degeneration of pulpal tissues, and subsequent loss of vitality. The blood pigments left behind infiltrate the dentinal tubules leading to significant tooth discoloration. Other forms of intrinsic staining include tetracycline, fluorosis, amelogenesis and dentinogenesis imperfecta, MIH (molar incisor hypomineralization), hypoplasia, erythroblastosis fetalis and porphyria. Additionally, discoloration due to the ageing process may be considered intrinsic. As teeth age, more secondary dentine is formed and the more translucent enamel layer thins. The combination of less enamel and darker, opaque dentine creates an older-looking, darker tooth7 (Table 2).
| Origin | Causes | Colour |
|---|---|---|
| Physiologic origin | Ageing | Yellow |
| Pathologic origin | Amelogenesis |
Dark brown |
| Iatrogenic origin | Amalgam |
Grey, black |
Although extrinsic discoloration can be removed with a prophylactic cleaning, intrinsic staining necessitates chemical bleaching.8
Vital bleaching is contra-indicated in the following situations:
If the patient is undergoing radiation or chemotherapy, for melanoma, using photosensitive drugs or photosynthesis herbal remedies, vital bleaching is contra-indicated.
Pregnant and breast-feeding women: there is no scientific or supported proof of any harmful side-effect. It may be advised to postpone all bleaching procedures.6
The safety of tooth bleaching for children and adolescents is an important issue. The European safety regulator advises that products containing or releasing between 0.1% and 6% hydrogen peroxide cannot be used on any person under 18 years of age. Therefore, it is not recommended to undertake any bleaching procedure for children and adolescents until they have reached their 18th birthday. Moreover, for 8–13 year-old children,9 bleaching may cause pain because the pulp chambers and dentine tubules are much larger than they are in adults.
Previous allergic problems, which may include ingredients in bleaching materials, may contra-indicate bleaching treatment.6
Quality of enamel: bleaching is inappropriate when surface, thickness and health of enamel is compromised. For this reason, cavities, micro-cracks and thinned enamel, seen in many systemic diseases or in some older people,6 need to be treated before undergoing any whitening procedure, to prevent any hypersensitivity.
Patients with periodontal problems such as recession and periodontitis are generally discouraged from undergoing a tooth whitening procedure owing to cementum exposure and hypersensitivity.
Vital bleaching is contra-indicated for patients with a heavy smoking habit because of a rapid recurrence of the discoloration.
Several publications show that, during the bleaching process, the enamel undergoes a reduction in micro-hardness that could be attributed to the dissolution of the calcium phosphate components of the enamel.10,11 The amount of calcium lost from teeth after 12 hours of bleaching treatment was similar to that lost from teeth exposed to a soft drink or juice for a few minutes.12 But, once the bleaching process is terminated, a process of re-calcification occurs, thereby filling in the spaces created by the enamel rod prism dissolution. Whether or not the re-calcified enamel is of the same quality originally deposited into the enamel matrix remains uncertain.13
Three main different agents are used for bleaching:
Carbamide peroxide is used in most of the home bleaching kits. It breaks down into a solution of hydrogen peroxide (H2O2) and a solution of urea (CH4N2O). It is important to note that knowing the concentration of carbamine peroxide allows you to calculate the concentration of the active hydrogen peroxide on the tooth surface. The ratio between them is 1/3; for example 10% carbamide peroxide is equivalent to 3.6% hydrogen peroxide.3
Most of the bleaching agents contain hydrogen peroxide in some form. The hydrogen peroxide breaks down into water and oxygen that penetrate the tooth and liberate the pigment molecule causing the tooth to whiten. Data accumulated during the last two decades demonstrate that, when used properly, peroxide-based tooth whitening is safe and effective; however, potential adverse effects can occur with inappropriate application, abuse, or the use of inappropriate whitening products.14
These materials contain sodium perborate as the active ingredient. They are also reported to contain hydroxylite, sodium chloride, oxygen and sodium fluoride and other materials. It is reported that they do not contain or produce hydrogen peroxide.1 The reactive oxygen and the free radical species promotes a whitening effect on the dental hard tissues because these reactive molecules attack the long-chained, dark-coloured chromophore molecules and split them into smaller, less coloured and more diffusible molecules.
There are several methods used for vital teeth bleaching:
Researchers have shown two contradictory opinions regarding the use of a light source.15,16 On the one hand, some of them defend the use of light,17,18,19 while others conclude that it offers no benefits.20,21
The theoretical advantage of the light source might be the increase in the hydrogen peroxide temperature, thus accelerating the reaction and formation of hydroxyl and oxygen-free radicals. A temperature rise of 10 °C increases the speed of hydrogen peroxide decomposition by 2.2 times. To increase the interaction of visible light with the bleaching gel, manufacturers incorporate colouring agents or pigments into their products, which have colours capable of promoting maximum absorption of light and subsequent conversion into heat. The equipment uses different light sources, such as halogen, Plasma arc, light emitting diode (LED), ultraviolet lamp, laser (Argon, Diode, Neodymium-YAG) and hybrid light. The assumed benefit is that the procedure is less time-consuming. However, the colour may rebound after treatment.22
The use of the light source is not necessary to enhance the whitening process.
Over-the-counter treatments include dentifrices, whitening strips, paint or brush applications, and whitening kits complete with a preformed or semi-molded tray. The toothpastes marketed as whitening products typically contain a mild abrasive to remove surface stains and some contain a minimal amount of peroxide. The exposure time to the toothpaste is minimal. Therefore, any potential whitening is minimal. Whitening strips use 3–6.5% hydrogen peroxide. Minimal research exists on these products and, because they can be bought and used indiscriminately by patients, the risk of inappropriate use is high. Over-the-counter bleaching products are frequently associated with gingival irritation and tooth sensitivity, despite low concentrations of peroxide agents. However, any adverse effects associated with the use of the whitening gel and tray are temporary, easily controlled, and often disappear within a short time.23
The main factors affecting the success of vital bleaching are: the initial colour of the teeth, the patient responsiveness and the material's concentration.
The initial colour of the teeth affects the treatment duration. Teeth exhibiting yellow or orange intrinsic discolorations usually respond better and faster to vital bleaching than teeth exhibiting bluish-grey discolorations.
The compliance of the patient to the treatment, their oral hygiene and smoking habits will influence the longevity of the bleaching effect.
The effectiveness of the treatment depends upon the length of time that the bleaching agent is in contact with the surface of the tooth and the concentration of the peroxide used. Currently, concentrations of 10%–45% of carbamide peroxide are available. In general, the lower concentrations are employed for at-home treatment, whereas the higher concentrations of hydrogen peroxide are reserved for the practitioner.
All patients receive instructions to avoid any substance that could stain teeth during all the treatment period, eg coffee, black tea, cola, mustard, ketchup, red wine, soy sauce, chocolate, red fruits, tomato sauce, beets, etc. Beyond these, patients were instructed to avoid other substances that could stain teeth such as consumption of tobacco products, food and beverages with acidic pH levels.
The level of sensitivity ranges from slight to unbearable and may differ from one patient to another. In clinical studies, tooth sensitivity during bleaching has been reported in a range of 18%–78% of patients, using either at-home tray delivery or in-office procedures. The carbamide demineralization process may extend all the way to the dentine-enamel junction. Under such conditions cold temperatures could be transferred to the dentine surfaces through any open channels. The resultant negative pressure on the ends of the odontoblastic processes could create pain sensation.
If the patient experiences sensitivity during tooth bleaching, the options to manage this may include the use of non-steroidal anti-inflammatory drugs (NSAIDs)24 or the application of a desensitizer based on fluoride, casein phosphopeptide-amorphous calcium phosphate25,26,27,28 or potassium nitrate.29 This desensitizer must be applied to the surfaces of the teeth immediately after removal of the carbamide-filled tray and will eliminate the sensitivity by covering the orifices of the dentinal tubule, thereby sealing them. It is thought that these materials penetrate deep into the dentinal tubule forming a series of bridges across the tubule itself. These bridges prevent movement of the fluids surrounding the odontoblastic process, thereby eliminating the potential for sensitivity.
If sensitivity is a problem during treatment it may be necessary to select an alternate bleaching product, change the delivery system, treatment duration or treatment interval, or even discontinue treatment.
When using the ‘At Home Technique’, a weekly visit is necessary to observe any initial bleaching results, and 2–5 weeks are required to obtain the desired results,6 as shown in Figure 1. Usually, 8 syringes of 1.2 ml are necessary for a normal treatment; 4 for the upper and 4 for the lower arch. For more severe cases (such as tetracycline discoloration), the time and quantity are at least doubled (Figures 2–5).
As bleaching proceeds, a point is reached at which only hydrophilic colourless structures exist. This is called the saturation point. Whitening then slows down dramatically and the bleaching process begins to break down the carbon backbones of proteins and other carbon-containing materials. Compounds with hydroxyl groups (usually colourless) are split, breaking the material into yet smaller constituents. Mineral reduction of enamel becomes rapid, with the remaining material being quickly converted into carbon dioxide and water. It is therefore critical for the dentist to know that bleaching must be stopped at or before the saturation point. Clinically, if the patient visits the dentist two successive times with no colour change, the dentist can conclude that the saturation point has been reached.
As for the repetition of the procedure, it is important that the patient understands that bleaching is not a permanent treatment and that some periodic re-bleaching will be required, even if the patient is avoiding staining agents. Usually retreatment can be accomplished with either one in-office session or a 3-week sequence of wearing a tray once a year.5
While each person responds differently to VTW, every patient will experience some degree of relapse, depending on a patient's habits and hygiene.
During the treatment, the teeth absorb peroxide. The peroxide releases oxygen inside the teeth structure and the oxygen oxidizes the discolorations and eliminates them. Right at the end, tiny bubbles of oxygen stay inside the teeth. These bubbles will make the teeth appear a little bit whiter. They will dissipate over a period of 2–3 weeks resulting in colour stability.
Afterwards, the teeth continue to absorb stains. Foods, including coffee, red wine, blueberries and soda have dark pigments that are absorbed by the teeth. In addition to foods, the hygiene and smoking habits have more negative effects on the longevity of bleaching. The teeth will return to their pre-bleaching colour in 3–4 years.3 To prevent this relapse from occurring we can periodically re-bleach the teeth.
The result of residual oxygen or peroxide residue in the tooth structure inhibits the set of bonding resin by preventing the formation of resin tag in etched enamel. This can be prevented by delaying any adhesive procedure, such as direct composite or indirect veneers, for at least two weeks after completion of the bleaching procedure and obtaining colour stability.30
In some countries, different whitening products and concentrations are allowed. The new regulations in Europe allow the use of hydrogen peroxide and other compounds or mixtures that release hydrogen peroxide, including carbamide peroxide and zinc peroxide to be used for tooth whitening. The maximum concentration that may be used for tooth whitening under the regulations is 6% present or released. In very broad terms, a percentage expressed in terms of carbamide peroxide content will release approximately one third of that level of hydrogen peroxide. So, the commonly used products containing 16% carbamide peroxide would be permitted under the revised regulations. According to the European Regulations, tooth whitening compounds containing or releasing up to 6% hydrogen peroxide are legal under the following conditions:
Tooth bleaching is one of the most conservative and cost-effective dental treatments to improve or enhance a person's smile. However, tooth bleaching is not risk-free and many clinical data are available on the side-effects of tooth bleaching.
The basis of this article is to address questions frequently raised by dentists and patients on tooth bleaching. A limited number of questions were addressed. Answers and recommendations are provided to help answer rising issues raised in daily practice.
Finally we can conclude the following:
