Open main menu

Wikipedia β

Tooth whitening (termed tooth bleaching when utilizing bleach), is either restoration of natural tooth shade or whitening beyond natural tooth shade, depending on the definition used.

Tooth whitening
Office Teeth Whitening.jpg
Professional laser teeth whitening

Restoration of the underlying, natural tooth shade is possible by simply removing surface (extrinsic) stains (e.g. from tea, coffee, red wine and tobacco) and calculus (tartar). This is achieved by having the teeth cleaned by a dental professional (commonly termed "scaling and polishing"), or at home by various oral hygiene methods. Calculus is difficult to remove without a professional clean.

To whiten the natural tooth shade, bleaching is suggested. It is a common procedure in cosmetic dentistry, and a number of different techniques are used by dental professionals. Many different products are also marketed for home use. Techniques include bleaching strips, bleaching pen, bleaching gel, and laser tooth whitening. Bleaching methods generally use either hydrogen peroxide or carbamide peroxide which breaks down into hydrogen peroxide. Common side effects of bleaching are increased sensitivity of the teeth and irritation of the gums.


Natural tooth shadeEdit

1: crown, 2: root, 3: enamel, 4: dentin and dentin tubules, 5: pulp chamber, 6: blood vessels and nerve within root canal, 7: periodontal ligament, 8: apex and periapical region, 9: alveolar bone

The perception of tooth color is the result of a complex interaction of factors such as lighting conditions, translucency, opacity, light scattering, gloss and the human eye and brain.[1] Teeth are composed of a surface enamel layer, which is whiter and semitransparent, and an underlying dentin layer, which is darker and less transparent. These are calcified, hard tissues comparable to bone. The natural shade of teeth is best considered as such; an off-white, bone-color rather than pure white. Public opinion of what is normal tooth shade tends to be distorted. Portrayals of cosmetically enhanced teeth are common in the media. In one report, the most common tooth shade in the general population ranged from A1 to A3 on the VITA classical A1-D4 shade guide.[2]

Females generally have slightly whiter teeth than males, partly because females' teeth are smaller, and therefore there is less bulk of dentin, partially visible through the enamel layer. For the same reason, larger teeth such as the molars and the canine (cuspid) teeth tend to be darker. Baby teeth (deciduous teeth) are generally whiter than the adult teeth that follow, again due to differences in the ratio of enamel to dentin. 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[citation needed] and phosphate-deficient. The enamel layer may also be gradually thinned or even perforated by the various forms of tooth wear.

Tooth staining and discolorationEdit

Internal resorption of the left maxillary lateral incisor (right in photograph), giving rise to the appearance termed "Pink tooth of Mummery"

Teeth may be darkened by a buildup of surface stains (extrinsic staining), which hides the natural tooth color; or the tooth itself may discolor (intrinsic staining).[3]

Causes of extrinsic staining include:

  • Dental plaque: although usually virtually invisible on the tooth surface, plaque may become stained by chromogenic bacteria such as Actinomyces species.[4]
  • Calculus: neglected plaque will eventually calcify, and lead to the formation of a hard deposit on the teeth, especially around the gumline. The color of calculus varies, and may be grey, yellow, black or brown[4]
  • Tobacco: tar in 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[4]
  • Betel chewing.[5]
  • Certain foods and drinks. food-goods and vegetables rich with carotenoids or xanthonoids.[citation needed] Ingesting colored liquids like sports drinks, cola, coffee, tea, and red wine can discolor teeth.[6]
  • 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.[7]
  • Metallic compounds. Exposure to such metallic compounds may be in the form of medication or other environmental exposure. examples include iron (black stain), iodine (black), copper (green), nickel (green), cadmium (yellow-brown).[3]

Causes of intrinsic staining include:

Cause of extrinsic and intrinsic staining include:

  • Age: the tooth enamel becomes thinner over time, which allows the dentin to shine through [11]
  • Bruxism (clenching and grinding of the teeth) can lead to micro-cracking of the incisal edges of the teeth. Extrinsic stains may settle more readily into these cracks, and a thin layer of enamel can be left. This thin enamel layer is partially transparent, allowing the dark background of the mouth to shine through, affording a darker appearance of the incisal edge.


Whitening methods include in-office bleaching (applied by a dental professional), and treatments which the individual carries out at home (either supplied by a dental professional or available over the counter). In some countries non dental professionals also carry out tooth whitening procedures for consumers.

Bleaching solutions generally contain hydrogen peroxide or carbamide peroxide, which bleaches the tooth enamel to change its color.[12] Off-the-shelf products typically rely on a carbamide peroxide solution varying in concentration from 10% to 44%. 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. Carbamide peroxide reacts with water to form hydrogen peroxide. Carbamide peroxide has about a third of the strength of hydrogen peroxide. This means that a 15% solution of carbamide peroxide is the rough equivalent of a 5% solution of hydrogen peroxide. The peroxide oxidizing agent penetrates the porosities in the rod-like crystal structure of enamel and breaks down stain deposits in the dentin.

Other bleaching agents include 6-phthalimido peroxy hexanoic acid (PAP)[citation needed] (however, there is no evidence for its effectiveness) and sodium perborate.[13]


VITA classical A1-D4 shade guide arranged according to value
VITA classical A1-D4 shade guide arranged according to chroma; A: red-brown, B: red-yellow, C: grey, D: red-grey

Before the treatment, the dentist may examine the patient: taking a health and dental history (including allergies and sensitivities), observe hard and soft tissues, placement and conditions of restorations, and sometimes x-rays to determine the nature and depth of possible irregularities.

The whitening shade guides are used to measure tooth color. These shades determine the effectiveness of the whitening procedure, which may vary from two to seven shades.[14] The effects of bleaching can last for several months, but may vary depending on the lifestyle of the patient.

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.

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 dentin 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.

Light-accelerated bleachingEdit

Power or light-accelerated bleaching, sometimes colloquially referred to as laser bleaching (a common misconception since lasers are an older technology that was used before current technologies were developed), 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.[15] Recent research has shown that the use of a light activator does not improve bleaching and has no measurable effect.[16]

The ideal source of energy should be high energy to excite the peroxide molecules without overheating the pulp of the tooth.[17] 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 ultraviolet emissions, allowing for a shorter patient preparation procedure.

Nanoparticle Catalysts for Reduced Hydrogen Peroxide ConcentrationEdit

A recent addition to the field is new light-accelerated bleaching agents containing lower concentrations of hydrogen peroxide with a titanium oxide nanoparticle based catalyst. Reduced concentrations of hydrogen peroxide cause lower incidences of tooth hypersensitivity.[18] The nanoparticles act as photocatalysts, and their size prevents them from diffusing deeply into the tooth. When exposed to light, the catalysts produce a rapid, localized breakdown of hydrogen peroxide into highly reactive radicals. Due to the extremely short lifetimes of the free radicals, they are able to produce bleaching effects similar to much higher concentration bleaching agents within the outer layers of the teeth where the nanoparticle catalysts are located. This provides effective tooth whitening while reducing the required concentration of hydrogen peroxide and other reactive byproducts at the tooth pulp.

Internal bleachingEdit

Internal staining of dentin can discolor the teeth from inside out. Internal bleaching can remedy this on root canal treated teeth. Internal bleaching procedures are performed on devitalized teeth that have undergone endodontic treatment (root canal treatment) but are discolored due to internal staining of the tooth structure by blood and other fluids that leaked 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 gutta-percha points, and placing a peroxide gel or sodium perborate tetrahydrate into the pulp chamber so they can work directly inside the tooth on the dentin layer.[citation needed] In this variation of whitening the whitening agent is sealed within the tooth over a period of some days and replaced as needed, the so-called "walking bleach" technique.[citation needed]. A seal should be placed over the root filling material to minimise microleakage. There is a small risk of external resorption.

An alternative to the walking bleach procedure is the inside-out bleach where the bleaching cavity is left open and the patient issued with a custom-formed tray to place and retain the agent, typically a carbamide peroxide gel inside the cavity. On review once sufficient shade change has occurred the access cavity can be sealed, typically with a dental composite.

At homeEdit

At-home whitening methods include gels, chewing gums, rinses, toothpastes, paint-on films, and whitening strips.[19][20] Most over-the-counter methods utilize either carbamide peroxide or hydrogen peroxide.[20] Although there is some evidence that such products will whiten the teeth compared to placebo, the majority of the published scientific studies were short term and are subject to a high risk of bias as the research was sponsored or conducted by the manufacturers.[20] There is no long term evidence of the effectiveness or potential risks of such products.[20] Any demonstrable difference in the short term efficiency of such products seems to be related to concentration of the active ingredient.[20] In addition, many products produced for use at home are supplied with an LED light although recent research has shown that the use of a light activator does not improve bleaching and has no measurable effect.[16]

Whitening toothpastesEdit

Toothpastes (dentifrices) which are advertised as "whitening" rarely contain carbamide peroxide, hydrogen peroxide or any other bleaching agent.[21] Rather, they are abrasive (usually containing alumina, dicalcium phosphate dehydrate, calcium carbonate or silica), intended to remove surface stains from the tooth surface.[21] Sometimes they contain enzymes purported to break down the biofilm on teeth.[21] Unlike bleaches, whitening toothpaste does not alter the intrinsic color of teeth. Excessive or long term use of abrasive toothpastes will cause dental abrasion, thinning the enamel layer[21] and slowly darkening the appearance of the tooth as the dentin layer becomes more noticeable.

Natural (alternative) methodsEdit

One purported method of naturally whitening the teeth is through the use of malic acid.[22][unreliable medical source?][23][unreliable medical source?] The juice of apples, especially green apples, contains malic acid. On the other hand excessive consumption of acidic beverages will slowly dissolve the enamel layer, making the underlying yellower dentin show through more noticeably, leading to darkening of the tooth's appearance. One study indicates that malic acid is a weak tooth whitening agent.[24]


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

  • Pre-existing sensitive teeth
  • Acid erosion
  • Receding gums (gingival recession)
  • Sensitive gums
  • Sensitive to hydrogen peroxide
  • 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.
  • 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.[21]
  • Persons with visible white fillings or crowns. 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 will not restore color of fillings, porcelain, and other ceramics when they become stained by foods, drinks, and smoking, as these products are only effective on natural tooth structure. As such, a shade mismatch may be created as the natural tooth surfaces increase in whiteness and the restorations stay the same shade. Whitener does not work where bonding has been used and neither is it effective on tooth-color filling. Other options to deal with such cases are the porcelain veneers or dental bonding.[25]


The most common side effects associated with tooth bleaching are increased sensitivity of the teeth and irritation of the gums, which tend to resolve once the bleaching is stopped.[20]


The low pH of bleach opens up dentinal tubules and may result in dentine hypersensitivity, bringing about hypersensitive teeth.[26] It manifests as increased sensitivity to stimuli such as hot, cold or sweet. Tooth sensitivity often occurs during early stages of the bleaching treatment. Recurrent treatments or use of desensitising toothpastes may alleviate discomfort, though there may be occurrences where the severity of pain discontinues further treatment. Potassium nitrate and sodium fluoride are used to reduce tooth sensitivity following bleaching.[27]

Irritation of mucous membranesEdit

Hydrogen peroxide is an irritant and cytotoxic. At concentrations of 10% or higher, hydrogen peroxide is potentially corrosive to mucous membranes or skin and can cause a burning sensation and tissue damage.[28] Chemical burns from gel bleaching (if a high-concentration oxidizing agent contacts unprotected tissues, which may bleach or discolor mucous membranes). Tissue irritation most commonly results from an ill-fitting mouthpiece tray rather than the tooth-bleaching agent.

Uneven resultsEdit

After teeth bleaching, it is normal to have uneven results. With time, the color will appear more even. To avoid this from happening it is important to avoid making some common post-bleaching mistakes, such as consuming foods and beverages that stain the surface of your teeth.

Return to original pre-treatment shadeEdit

Nearly half the initial change in color provided by an intensive in-office treatment (i.e., 1 hour treatment in a dentist's chair) may be lost in seven days.[29] Rebound is experienced when a large proportion of the tooth whitening has come from tooth dehydration (also a significant factor in causing sensitivity).[30] As the tooth rehydrates, tooth color 'rebounds' back toward where it started.[31]


Overbleaching, known in the profession as "bleached effect", particularly with the intensive treatments (products that provide a large change in tooth colour over a very short treatment period, e.g., 1 hour). Too much bleaching will cause the teeth to appear very translucent.[32]

Damage to enamelEdit

Home tooth bleaching treatments can have significant negative effects on tooth enamel.[33] This is especially the case with home remedy whitening products that contain fruit acids and brushing with abrasives such as baking soda.


When bleaching is abused and an individual develops an unhealthy obsession with whitening, the term bleachorexia or whitening junky has been used.[21] The condition is characterized by repeated bleaching even though the teeth are already white and will not get any whiter.[32] This condition is somewhat similar to body dismorphic disorder. The individual perceives their teeth never to be white enough, despite repeated bleaching. A person with bleachorexia will typically continually request more bleaching services or products from the dental professional.[32] It has been recommended that a target shade be agreed before starting bleaching treatment to help with this problem.[32]


Although treatment results can be rapid, stains can reappear within the first few months and years of treatment. In order to maintain your whitened smile, there are multiple ways to protect your teeth and prolong the treatment.[34]

  • Brush or rinse mouth immediately after eating and drinking[35]
  • Chewing gum
  • Floss to remove plaque
  • Use whitening tooth paste once or twice a week to avoid surface stains
  • Drink harsh beverages through a straw[36]
  • Do touch up treatments


There has been interest in white teeth since ancient times.[32] Ancient Romans used urine and goat milk in an attempt to make and keep their teeth whiter.[citation needed] 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."[32] In 1877 oxalic acid was proposed for whitening, followed by calcium hypochlorite.[32] Peroxide was first used for tooth whitening in 1884.[32]

Society and cultureEdit

Teeth whitening has become the most marketed and requested procedure in cosmetic dentistry. More than 100 million Americans whiten their teeth one way or another; spending an estimated $15 billion in 2010.[37] The US Food and Drug Administration only approves gels that are under 6% hydrogen peroxide or 16% or less of carbamide peroxide. The Scientific Committee for Consumer Protection of the EU consider gels containing higher concentrations than these to be unsafe.[38]

In Brazil, all bleaching products are classed as cosmetics (Degree II) in legislature.[21] There are concerns that this will result in increasing misuse of bleaching products and consequently there have been calls for reclassification.[21]

See alsoEdit


  1. ^ Joiner, A (2004). "Tooth colour: a review of the literature.". Journal of dentistry. 32 (Suppl 1): 3–12. PMID 14738829. doi:10.1016/j.jdent.2003.10.013. 
  2. ^ Herekar M; Mangalvedhekar M; Fernandes A (Dec 2010). "The Most Prevalent Tooth Shade in a Particular Population: A survey". Journal of the Indian Dental Association. 4 (12). 
  3. ^ a b c d e Chi AC, Damm DD, Neville BW, Allen CA, Bouquot J (11 June 2008). Oral and Maxillofacial Pathology. Elsevier Health Sciences. pp. 70–74. ISBN 978-1-4377-2197-3. 
  4. ^ a b c d e f Rajendran A; Sundaram S (10 February 2014). Shafer's Textbook of Oral Pathology (7th ed.). Elsevier Health Sciences APAC. pp. 386, 387. ISBN 978-81-312-3800-4. 
  5. ^ a b c Crispian Scully (21 July 2014). Scully's Medical Problems in Dentistry. Elsevier Health Sciences UK. ISBN 978-0-7020-5963-6. 
  6. ^ "Facts About Tooth Staining and Discoloration". Retrieved 2017-09-28. 
  7. ^ Scully C (2013). Oral and maxillofacial medicine : the basis of diagnosis and treatment (3rd ed.). Edinburgh: Churchill Livingstone. pp. 39, 41. ISBN 9780702049484. 
  8. ^ a b Sánchez, AR; Rogers RS, 3rd; Sheridan, PJ (October 2004). "Tetracycline and other tetracycline-derivative staining of the teeth and oral cavity.". International Journal of Dermatology. 43 (10): 709–15. PMID 15485524. doi:10.1111/j.1365-4632.2004.02108.x. 
  9. ^ Good, ML; Hussey, DL (August 2003). "Minocycline: stain devil?". The British journal of dermatology. 149 (2): 237–9. PMID 12932226. doi:10.1046/j.1365-2133.2003.05497.x. 
  10. ^ Ibsen OAC; Phelan JA (14 April 2014). Oral Pathology for the Dental Hygienist. Elsevier Health Sciences. p. 173. ISBN 978-0-323-29130-9. 
  11. ^ "Tooth Discoloration". Retrieved 2015-10-26. 
  12. ^ "Tooth Whiteners containing hydrogen peroxide summary by GreenFacts of the European Commission SCCP assessment". GreenFacts. Retrieved 2008-05-04. 
  13. ^ Valera, Marcia Carneiro; Camargo, Carlos Henrique Ribeiro; Carvalho, Cláudio Antonio Talge; Oliveira, Luciane Dias de; Camargo, Samira Esteves Afonso; Rodrigues, Cristiana Martins. "Effectiveness of carbamide peroxide and sodium perborate in non-vital discolored teeth". Journal of Applied Oral Science. 17 (3): 254–261. doi:10.1590/S1678-77572009000300024. 
  14. ^ Delgado, E; Hernández-Cott, PL; Stewart, B; Collins, M; De Vizio, W (2007). "Tooth-whitening efficacy of custom tray-delivered 9% hydrogen peroxide and 20% carbamide peroxide during daytime use: A 14-day clinical trial". Puerto Rico Health Sciences Journal. 26 (4): 367–72. PMID 18246965. 
  15. ^ He, LB; Shao, MY; Tan, K; Xu, X; Li, JY (August 2012). "The effects of light on bleaching and tooth sensitivity during in-office vital bleaching: a systematic review and meta-analysis.". Journal of Dentistry. 40 (8): 644–53. PMID 22525016. doi:10.1016/j.jdent.2012.04.010. 
  16. ^ a b Baroudi, Kusai; Hassan, Nadia Aly (2015). "The effect of light-activation sources on tooth bleaching". Nigerian Medical Journal. 55 (5). doi:10.4103/0300-1652.140316. The in-office bleaching treatment of vital teeth did not show improvement with the use of light activator sources for the purpose of accelerating the process of the bleaching gel and achieving better results. 
  17. ^ Grace Sun, Lasers and Light Amplification in Dentistry. Dental Clinics of North America, Vol. 44 No. 4, October 2000.
  18. ^ Bortolatto, J. F.; Pretel, H.; Floros, M. C.; Luizzi, A. C. C.; Dantas, A. a. R.; Fernandez, E.; Moncada, G.; Oliveira, O. B. de (2014-07-01). "Low Concentration H2O2/TiO_N in Office Bleaching A Randomized Clinical Trial". Journal of Dental Research. 93 (7 suppl): 66S–71S. ISSN 0022-0345. PMC 4293723 . PMID 24868014. doi:10.1177/0022034514537466. 
  19. ^ "Statement on the Safety and Effectiveness of Tooth Whitening Products". American Dental Association. Retrieved 2010-07-05. 
  20. ^ a b c d e f Hasson, H; Ismail, AI; Neiva, G (18 October 2006). "Home-based chemically-induced whitening of teeth in adults.". The Cochrane Database of Systematic Reviews (4): CD006202. PMID 17054282. doi:10.1002/14651858.CD006202. 
  21. ^ a b c d e f g h Demarco, FF; Meireles, SS; Masotti, AS (2009). "Over-the-counter whitening agents: a concise review.". Brazilian Oral Research. 23 Suppl 1: 64–70. PMID 19838560. doi:10.1590/s1806-83242009000500010. 
  22. ^ "How to Whiten Your Teeth Naturally". Retrieved 2012-02-12. 
  23. ^ "Foods That Whiten Teeth Naturally". Retrieved 2012-02-12. 
  24. ^ "Efficacy of Do-It-Yourself Whitening as Compared to Conventional Tooth Whitening Modalities: An In Vitro Study". 
  25. ^ "Tooth Whitening Treatments". Retrieved 2010-07-05. 
  26. ^ Ricketts, David. Advanced Operative Dentistry, A Practical Approach. Churchill Livingstone Elsevier. 
  27. ^ Wang, Y; Gao, J; Jiang, T; Liang, S; Zhou, Y; Matis, BA (August 2015). "Evaluation of the efficacy of potassium nitrate and sodium fluoride as desensitizing agents during tooth bleaching treatment-A systematic review and meta-analysis.". Journal of Dentistry. 43 (8): 913–23. PMID 25913140. doi:10.1016/j.jdent.2015.03.015. 
  28. ^ Li, Y (1996). "Biological properties of peroxide-containing tooth whiteners". Food and Chemical Toxicology. 34 (9): 887–904. PMID 8972882. doi:10.1016/s0278-6915(96)00044-0. 
  29. ^ Kugel, G; Ferreira, S; Sharma, S; Barker, ML; Gerlach, RW (2009). "Clinical trial assessing light enhancement of in-office tooth whitening". Journal of Esthetic and Restorative Dentistry. 21 (5): 336–47. PMID 19796303. doi:10.1111/j.1708-8240.2009.00287.x. 
  30. ^ Kugel, G; Ferreira, S (2005). "The art and science of tooth whitening". Journal of the Massachusetts Dental Society. 53 (4): 34–7. PMID 15828604. 
  31. ^ Betke, H; Kahler, E; Reitz, A; Hartmann, G; Lennon, A; Attin, T (2006). "Influence of bleaching agents and desensitizing varnishes on the water content of dentin". Operative dentistry. 31 (5): 536–42. PMID 17024940. doi:10.2341/05-89. 
  32. ^ a b c d e f g h Freedman GA (15 December 2011). "Chapter 14: Bleaching". Contemporary Esthetic Dentistry. Elsevier Health Sciences. ISBN 0-323-08823-6. 
  33. ^ Azer, SS; Machado, C; Sanchez, E; Rashid, R (2009). "Effect of home bleaching systems on enamel nanohardness and elastic modulus". Journal of Dentistry. 37 (3): 185–90. PMID 19108942. doi:10.1016/j.jdent.2008.11.005. 
  34. ^ "Teeth Whitening - Cost, Types, Results & Risks". DocShop. Retrieved 2015-10-27. 
  35. ^ "Tips for Keeping Teeth White". WebMD. Retrieved 2015-10-27. 
  36. ^ "Maintaining Your White Smile Article | Whitening Basics | Colgate® Oral Care Information Whitening & Bonding". Retrieved 2015-10-27. 
  37. ^ Krupp, Charla. (2008). How Not To Look Old. New York: Springboard Press, p.95.
  38. ^ Antoniadou M, Koniaris A, Margaritis V, Kakaboura A. Tooth whitening efficacy of self-directed whitening agents vs 10% carbamide peroxide:a randomized clinical study. J Dent Oral Craniofac Res 2015;1(2):31-35 (doi 10.15761/DOCR.1000107).