Given the recent rise in cosmetic dentistry over the last few years, I plan to investigate one of the most common procedures, tooth whitening. In this report, I will;
Try to discover why patients choose to have their teeth whitened and when vital tooth whitening is indicated (types of staining-extrinsic and intrinsic)
Try and find out the mechanism of tooth whitening and what the most common bleaching agents are (hydrogen peroxide and carbamide peroxide)
Explore the different ways in which tooth bleaching is carried out (take-home trays, in-office power bleaching and over the counter treatments) and which system is the most recommended according to a variety of studies
Identify the main side effects to tooth bleaching, and if this has any impact on a patient’s decision for undertaking the procedure
Draw my own conclusion, based on previously carried out clinical trials and current professional opinion, on which is the ‘best’ method to use.
Tooth whitening is an effective, widely accessible method for removing stains and discolouration, which is very popular amongst patients and has minimal side effects. Of the different methods of delivery, it appears that take-home tray systems are the best, as they have the greatest efficacy and are the most tolerated by patients.
Tooth bleaching is not a new procedure, and reportedly was in use more than a hundred years ago, using hypochloric acid to treat dental fluorosis [Khin, 2007]. Since then the technology has evolved to become more advance and specific, responding to the recent increased demand from patients for aesthetic procedures including orthodontics, ceramic crowns, tooth-coloured restorations, as well as tooth whitening. Such procedures often have little or no effect on the functionality of the dentition and are therefore often disregarded as an important dental issue by professionals, yet there is a high demand for more competitive aesthetic procedures by patients indicating that is very important to them.
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According to Kershaw et al (2008), “physical appearance plays a key role in human social interaction and the smile and teeth are important features in determining the attractiveness of a face” and that more attractive people are perceived as “more popular, sociable, extraverted, sexually attractive and happy”. It therefore follows that people request whitening, as discoloured and decayed teeth are seen as associated with “lower levels of social competence, intellectual ability, psychological adjustment, and relationship satisfaction” [Kershaw et al, 2008] as well as unattractive.
An investigation by Alkhatib et al (2004) assessed people’s perception of their own teeth discolouration, and found that half the population saw themselves with some form of discolouration, with 31% rating their discolouration as ‘mild severity’. They found people’s dissatisfaction with their teeth positively correlated to their perceived discolouration and that, interestingly, females we less likely to perceive their own discolouration than males. This is perhaps because women are more aware of their physical appearance in general and so are more likely to have work done previously to correct any issues they have.
Nevertheless, it is clear that people observe tooth colour as an important dental issue. This, as well as tooth whitening being relatively, quick, inexpensive and widely accessible could explain why it is the most popular cosmetic dental treatment, and currently in such high demand. Thus, there is a wide variety of research undertaken recently, to better understand how whitening works, which are the best methods of whitening and if there are any associated risks.
Causes of tooth discolouration
The natural colour of teeth is “associated with the light scattering and adsorption properties of the enamel and dentine” [Joiner, 2006] with the dentine attributing to a greater part of the colour and the main cause for the yellowish tinge to teeth. This could explain why teeth tend to look more ‘yellow’ with age, as throughout life the quantity of dentine increases since secondary dentine is continually being laid down. Such discolouration is referred to as intrinsic staining which is due to changes within the tooth structure. As well as ageing, other intrinsic factors include metabolic diseases, systemic factors and prescriptive drug staining (figure 1) [Pretty et al, 2006]. The intrinsic factors can be incorporated into the tooth pre-erruptively (during tooth morphogenesis) or post-erruptively (after morphogenesis) [Minoux & Serfaty, 2008].
Extrinsic staining is more superficial and affects the enamel or pellicle layer on the outside of the tooth surface. It normally forms on sites where patients find it more challenging to brush, such as interproximal and lingual areas. The staining is often caused by high intake of caffeinated drinks or tannins in diet or smoking [Pretty et al, 2006]. Further causes are illustrated in figure 1. Mild extrinsic staining can sometimes be removed by shop bought products like whitening toothpastes, or can be removed professionally using ultrasonic scaling and polishing and therefore don’t always require bleaching.
The nature of the staining needs to be determined in order to select the best bleaching system and maximise the effects of the treatment, as some types of intrinsic staining will not be affected by bleaching. These are highlighted in bold in figure 1. Methods other than bleaching, such as composite or porcelain veneering, can therefore be used instead to treat the discolouration.
Types of staining
Congenital erythopoeitic prohyria
Pulpal Heamorrhagic products
Extrinsic ~ non-metallic
Extrinsic ~ metallic
Silver nitrate salt
A table to show the different factors which could cause tooth discolouration.
[Pretty et al, 2006]
Tooth whitening- how does it work?
In vital tooth bleaching, a gel or liquid preparation is applied externally to the tooth surfaces. The contents of the preparation vary depending on the delivery system, but in general, in-office power bleaching contains hydrogen peroxide and clinician supervised take home systems contain either hydrogen peroxide (HP) or carbamide peroxide (CP), a hydrogen peroxide precursor. The HP diffuses easily into enamel and dentine due to its molecular weight, and can act from there. [Matis et al, 2009]
The nature of the exact mechanism is still not clearly understood, however it is thought that there are several likely reactions that occur, depending on what the environmental conditions are like.
In alkaline conditions, the hydrogen peroxide can undergo ionic dissociation (see equations 1 and 2, figure 2) to produce hydroxyl radicals. However, in take home tray systems where carbamide peroxide (CP) is often used, the breakdown of CP to HP when it comes into contact with water involves the production of urea, which in turn breaks down into carbon dioxide and ammonia. These products cause the pH in the tray to decrease [Minoux & Serfaty, 2008]. In these more acidic conditions, HP undergoes anionic dissociation or homolytic cleavage (equation 3, figure 2), particularly promoted by UV light or high temperatures, to produce free radicals which act as powerful oxidisers. To become more stable, the oxidative agents disrupt double bonds within organic molecules (such as carbon, oxygen and nitrogen) which act as electron donators. These double bonds are vital in molecules which generate colour in organic molecules, also known as chromophores, and when the double bond is broken it either causes a change in the size of the chromophore, therefore reducing the absorption energy of the molecule from a longer visible light wavelength to a shorter one and making the molecule appear lighter [Minoux & Serfaty, 2008] or it causes the pigment molecules to break down and diffuse out into the environment [Thickett & Cobourne, 2009].
As well as anionic dissociation, HP can also undergo photo dissociation, which is light activated. This is why in-office bleaching techniques often use light curing systems, so try to speed up the bleaching process, by producing more oxidising agents faster from HP.
Equations 1 and 2 show ionic dissociation of hydrogen peroxide under alkaline conditions to produce hydroxyl radicals
Equation 3 show the homolytic cleavage of hydrogen peroxide under acidic conditions and the presence of UV light, producing hydroxyl radicals
Equations 4 and 5 show the chain reaction which can follow on from equation 3, producing perhydroxyl and superoxide radicals.
[Minoux & Serfaty, 2008]
Bleach delivery systems
At present, there are 3 major bleaching systems used for vital teeth; Home bleaching kits which can be bought by patients over the counter, in-office systems used by the practitioner in the surgery and clinician assisted home systems.
Home bleaching systems
These products are readily available over the counter in most pharmacies and drug stores. They are most often bought by patients who choose to have their teeth whitened but present with no obvious discolouration of their teeth and simply want a brighter and more ‘youthful’ smile to improve their facial appearance [Pretty et al, 2006]. These shop-bought whitening kits are therefore suitable for them as legally in the UK the product can only contain up to 0.1% hydrogen peroxide [Thickett & Cobourne, 2009] and so this low concentration will produce minimal effect but still remove any mild discolouration or maintain white teeth.
The delivery of the treatment varies greatly depending on the manufacturer and country, but examples include whitening strips, paint on brush applications, dentifrices and kits containing a pre-moulded tray [Brunton et al, 2006]. (For a list of different branded products available in the UK, refer to figure 3).
These products are often very affordable, but little research exists on their effectiveness. According to Li (2003), to produce the same effect as professional whitening, the products have to be used for much longer. However, as the product relies solely on patient use the risk of inappropriate use is high.
In- office bleaching systems
These products are only available in the clinic, as they contain much higher levels of peroxides and are more technique sensitive so can only be applied by a professional. The high concentration of peroxides means that this procedure is more suited to people with high levels of staining which cannot be removed with ultrasonic scaling etc.
The power bleaching technique involves a 30-35% hydrogen peroxide preparation in the form of a liquid, gel or powder being placed directly onto teeth [Thickett & Cobourne, 2009]. (Refer to figure 3 for a list of branded products currently available in the UK.) As the preparation is so highly caustic, tissue protection must be used, either rubber dam or a light cured resin shield. [Pretty et al, 2006] The activation of the hydrogen peroxide preparation depends on the system being used, but it could be either light activated (with a light cure or specially designed unit), chemically activated (in the mixing process) or a combination of the two.
Patients are often very satisfied with power bleaching results as they are visible immediately after treatment. It also requires minimal patient compliance. However, it is time consuming and need several visits to the dentist in order to ensure complete effectiveness of the treatment. The costs are also higher than those which can be purchased over the counter or take home systems. [Khin, 2007]
Clinician-assisted home systems
This technique involves the use of a bleach preparation being worn in a mouthguard, made specifically for the patient by the clinician, generally overnight for a specific amount of time depending on the instructions from the practitioner and manufacturer.
Alginate impressions of the patient’s teeth are taken by the clinician and normally sent away for a mouthguard to be made. The patient is then advised on how to apply the solution to the mouthguard, how to wear the guard and the exact instructions on how often to apply the treatment. On the whole, most systems appear to be based on wearing the guard daily for 2-4 hours in the day and overnight, for a couple of weeks. However, the length of time the guard should be worn for depends on the severity and type of staining, so relies on the judgement of the practitioner and their advice to the patient. For example, if the patient suffers from extreme tetracycline staining during tooth development, they may need to wear the guard for up to six months [Pretty et al, 2006].
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This system has the advantage of being convenient for the patient as it can be applied when it is most suitable for them. They are also more economical than clinician supervised systems and don’t require frequent visits to the dentist, which can be time consuming and uncomfortable due to the use of rubber dam. However, this system involves high patient compliance. The patient needs to be motivated to persevere with the duration of the course advised. This can be difficult as results are not immediately visible, and the patients often give up. This reliance on the patient also means that there is an increased risk of misuse of the product [Khin, 2007]. Some patients with a strong gag reflex can find the tray uncomfortable and may not tolerate it well.
It has also been suggested in a review by Matis et al (2009) that home systems could also be recommended as a follow up to in-office bleaching “to ensure long term effectiveness” of the treatment.
Home – Clinician assisted
Nite White® ACP Bleaching Gel
iWhite Light Activated Teeth Whitening Kit
Aquafresh White TraysTM
Sapphire Professional Home Whitening System
Pola Zing Advanced Tooth Whitening System
Colgate Simply White and Visible White
Home – over the counter
Colgate Simply White
Crest night effects
Rembrandt Whitening Strips
ON-THE-GO Whitening Click-Pen
Pola Paint Advanced Tooth Whitening System
BriteSmile Whitening Pen
In office dual activated
Figure 3. A table showing current products available on the market in the UK for tooth whitening; at- home and in-office systems. [Thickett & Cobourne, 2009]
Which system is the best?
The type of bleaching advised for patients depends greatly on a variety of factors. The nature of the staining is very important (intrinsic or extrinsic) as is the severity of staining. If the staining is mild, then less concentrated bleach could be advised, perhaps in a clinician supervised take home system. If the staining is more severe, then stronger bleach could be suggested, such as the 30-35% concentrations of hydrogen peroxide in in-office power bleaching.
The preference of the patient is also a factor to consider. Some, perhaps with time or economical constraints, may prefer to use a take-home system. Others who want a slightly brighter smile quickly could get an over the counter the counter system.
However, the efficacy and longevity of the systems are also another consideration as patients will not want to spend time and money on a procedure which doesn’t work effectively. There are a number of studies which have been carried out to determine which of the products currently on the market are the most effective. Efficacy of vital tooth whitening is usually determined by the number of shades the tooth has been lightened, for how long after the procedure this remains and any possible side effects, and depends on the bleaching agent and method used [Bizhang et al, 2009].
Tooth colour can be measured visually using a shade guide often provided by manufacturers with their products or by spectrophotometry which is a method to measure the wavelengths of visible light [Joiner et al, 2008] as the longer the wavelength, the darker the colour. Thus spectrophotometry can be used to measure shades of teeth more precisely and therefore the exact degree of whitening that the procedure has produced. Precision like this is used in clinical trials, whereas shade guides, which are much more approximate, can be used in clinics before and after whitening to show patients how much their teeth have been lightened.
In a study by Matis et al (2007), they evaluated eight different in-office systems and their longevity after six weeks. They found that all the systems had an effect and produced whiter teeth with a mean reversal of 65% after six weeks. However, the more successful products were found to have a longer contact time with teeth, and that the catalysing of hydrogen peroxide is more important than concentration. Therefore, it can be suggested that when using in-office bleaching, a light or chemically activated system is advised to enhance the effects of treatment.
In a second study by Matis et al (2009), they tested the efficacy of in-office tooth whitening when followed up by at- home tray whitening. They found that the effects of in office bleaching are more rapid, but has increased reversal (within two weeks) whereas the effects of at-home tray bleaching takes longer but have less chance of reversal. Therefore, when following up in-office bleaching with at-home tray whitening, they found that patients had better whitening after twelve weeks than when not followed up with tray whitening. They suggest that the two systems should be used in unison, to give rapid whitening and increase its effect. They also showed that a treatment plan of three fifteen minute treatments is better than one treatment of forty minutes, and produced fewer side effects.
A paper by Matis et al (2009) reviewed the effectiveness of various tooth whitening systems, including in-office, at-home tray and over the counter systems. They concluded that the most effective method was when the product was placed in trays and used overnight. Second most effective was when the product was used in trays for shorter periods of time during the day. They also found that “two weeks after completing the bleaching treatment, over-the-counter tooth whitening was as effective as in office tooth whitening”.
The effect of three different bleaching methods was investigated by Bizhang et al (2009) over three months; 10% carbamide peroxide gel used at home in a tray, 15% preparation of hydrogen peroxide for in-office use and 6% whitestrips. Significant differences were found between in-office and whitestrips and home trays and whitestrips but not between 10% carbamide peroxide for home use and 15% hydrogen peroxide for in-office use. The whitestrips provided least whitening of all and it was also noted that the subjects preferred the at-home tray method the best.
It is not just the delivery method which is an important factor, but also the agents used. The use of daytime bleach was investigated by Mokhlis et al (2000). They compared 20% carbamide peroxide against 7.5% hydrogen peroxide when used in trays at home and found that after two weeks, teeth whitened with carbamide peroxide were lighter than hydrogen peroxide. However, after twelve weeks there was no significant difference between the two in colour or sensitivity. Therefore, they concluded that both chemicals are equally suitable and effective for use in at-home trays.
The concentrations of the agents used, and if this has any major effect, is debatable. Although Matis et al (2007) suggested that the concentration is not as relevant as the contact time and the fact that the agents should be catalysed, it has since been suggested by Bizhang et al (2009) that concentration is still important. The effect of the concentrations of carbamide peroxide was analysed by Meireles et al (2009). The outcome after a one year investigation of 10% versus 16% carbamide peroxide used in at-home trays was that both concentrations produced the same median lighter shade than at baseline after one year, although there was more reversal on treatment with 16% carbamide peroxide. Therefore they suggest that concentration shows little difference in the long run.
This was also shown by Braun et al (2007), who tested the effects of 10% and 17% carbamide peroxide on enamel tooth surfaces. They concluded that both concentrations significantly whitened teeth with the only difference being that the higher concentration lightened teeth faster. Nevertheless, they did suggest that the lower concentrations should be used, to try to limit side effects such as hypersensitivity.
As shown, there are many trials and research carried out to evaluate tooth whitening products, and which are the ‘best’. There appears to be no outstanding system, as it depends on a variety of variables such as the needs of the patient, the teeth being bleached, the nature of the staining, the system being used, the concentration of the agent, the type of agent, the method of activation, and any adverse effects produced. However, there does seem to be more evidence to suggest that it is more advantageous to use at-home tray systems, as they are more convenient for the patient and have longer lasting effects than other systems.
As with any procedure, there are always some adverse effects which can be produced, and may affect some patients. In a review by Khin (2007), she highlighted that the main side effect of vital tooth bleaching is tooth sensitivity, seen in between 55-75% of patients who undertake the treatment. One suggestion for post-whitening hypersensitivity is that the by-products of hydrogen peroxide/carbamide peroxide degradation (water and oxygen/urea) diffuse down dentinal tubules to the pulp. These by products then irritate the nerves in pulp and effectively cause reversible pulpits, accounting for the hypersensitivity [Hewlett, 2007].
The second suggestion is that the glycerine gel that bleaching agents are often carried by dehydrates the tooth. Glycerine exerts osmotic pressures on the dentine, causing fluid movement in the dentinal tubules and causing sensitivity, as suggested by Brännstöm [Hewlett, 2007]. Manufacturers now replace glycerine with water-soluble based solutions, to try and overcome this problem.
The pain experienced during a whitening procedure was investigated by Krause et al (2008) by asking patients to describe the pain when using either 17% or 10% carbamide peroxide. They found that there was a positive correlation between the concentration of the agent and the intensity of pain. They therefore suggested that lower concentrations should be used in practice, as they still provide the same results as higher concentrations, just not as quickly. A preliminary study by Chakaron et al (2009) investigated the use of 600 mg ibuprofen to minimise pain and sensitivity. They showed that it helped reduce pain during treatment, but not after. This is something which could be further investigated, to see if this could be used to help patients during the procedures.
The most common suggestion for avoiding bleaching hypersensitivity is to use potassium nitrate toothpaste twice a day for two weeks before carrying out the procedure [Hewlett, 2007] or in the tray for 10-30 minutes before the treatment [Khin, 2007] to desensitise the teeth. It is also suggested to keep the number of applications to a minimum.
Another side effect of tooth bleaching is gingival irritation, caused by prolonged contact of the gingiva with the gel. This can be from either in-office power bleaching or take-home trays. In in-office systems gingival protection is used to minimise the negative effect on the gingiva, however, it is more difficult to protect the gingiva in take-home tray systems as the patient is applying the product themselves. Therefore the clinician could minimise irritation by properly trimming the tray so that the gel will only come into contact with the hard surfaces of the tooth and not the gingiva.
In some patients it has been reported that they experienced some minor orthodontic movement when using take-home trays. This could have been due to the trays being made of rather rigid material, which put pressure on teeth to move, also causing sensitivity [Hewlett, 2007]. Trays are now made of more flexible materials to try to reduce pressure on teeth.
There can also be an adverse effect on restorations. If the marginal seal of the restoration is leaking there is an increased chance bleaching agents to penetrate deep into the dentine and pulp and therefore there is an increased risk of hypersensitivity. It has been recommended to replace failing restorations prior to bleaching [Hewlett, 2007].
There has been much debate on whether or not tooth bleaching has a negative effect on the composition of enamel and dentine. This is attributed to the free radicals produced during the dissociation of hydrogen peroxide being capable of disrupting the lipids and proteins (the organic component) in the tooth [Minoux & Serfaty, 2008]. A study by Markovic et al (2007) used laser scanning microscopy in vitro to investigate the micromorphology of the enamel surface after treatment with 10% or 16% carbamide peroxide. The results showed that the roughness of the enamel surface increased for both concentrations, indicating “loss of organic matrix after exposure to hydrogen peroxide”.
However, an in vitro by Delfino et al (2009), in which they tested 10% carbamide peroxide, 16% carbamide peroxide, 6.5% hydrogen peroxide and 6.5% hydrogen peroxide whitening strips showed that there was “no change to either the enamel surface microhardness or the enamel subsurface microhardness”. This was also illustrated by Mielczarek et al (2008), who compared the effects of 14% hydrogen peroxide whitestrips, 20% hydrogen peroxide (take-home tray system) and 38% hydrogen peroxide (in-office system) on enamel surfaces. They concluded that none of the systems demonstrated any “deleterious effects on surface roughness”.
These studies are only examples of many which have been carried out to determine the exact effect on tooth surfaces, and show that it is still unclear whether there is a detrimental effect.
Based on all the research that I have found, it appears that tooth whitening is a safe, inexpensive, and accessible method for patients to remove discolouration and gain a whiter, brighter smile. The type of staining, if any, which the patient presents with must be assessed first, as the types determine which system must be used, if at all as some staining cannot be removed with bleaching.
Though the exact nature of whitening is not fully understood, extensive studies have shown that the main side effect is hypersensitivity, which is quite common amongst patients undertaking the procedure but can vary considerably in pain intensity. The bleaching agents used, especially in in-office systems, are also rather caustic due to their concentration, and can burn the soft tissues in the mouth unless they are protected fist.
There are three main methods of tooth bleaching, each with their own advantages and disadvantages. Over the counter systems contain a minimal concentration of hydrogen peroxide, and therefore have little effect on the colour of teeth. In-office bleaching is much more effective, as contain 30-35% hydrogen peroxide, and show effects immediately.
Clinician-assisted take home trays are more convenient for the patient, as they can be used at their own convenience. It is also cheaper than in-office whitening, and studies have shown that the effects are just as good, if not better, than in-office whitening, and have the least reversal.
Therefore, in my opinion, take-home trays are the best system to use, as it is better tolerated by patients as it is more convenient and cheaper, and clinical studies have concluded that they are very effective at lightening teeth and have less chance of reversal.
Clinical Trials and studies are still being carried out, to try and determine the exact nature of tooth whitening, and therefore to maximise the effect. New procedures are also being tested, such as laser tooth whitening, which preliminary reports have shown to be very effective [Lin et al, 2008].
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