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Table of Contents
INVITED REVIEW
Year : 2016  |  Volume : 6  |  Issue : 1  |  Page : 3-13

An overview of vital teeth bleaching


Department of Conservative Dentistry and Endodontics, KLE VKIDS, Belagavi, Karnataka, India

Date of Web Publication10-Aug-2016

Correspondence Address:
Sonal Bakul Joshi
Department of Conservative Dentistry and Endodontics, KLE VKIDS, Belagavi, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2229-5194.188155

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   Abstract 

The virtue of "the perfect smile" is an easily achievable task with a better understanding of materials and diseases along with advances within the technology. Discolored teeth can often be corrected totally or partially by bleaching. Since bleaching is conservative, noninvasive, and inexpensive, it is the most opted treatment protocol by the masses. To achieve instant whitening with no risks and relapse, there have been developments of innovative technologies and promising products. This article aims to keep in pace with these newer trends and to provide an insight on the present day clinical challenges of vital tooth bleaching.

Keywords: Hydrogen peroxide, mechanism, techniques, tooth discoloration, tooth whitening


How to cite this article:
Joshi SB. An overview of vital teeth bleaching. J Interdiscip Dentistry 2016;6:3-13

How to cite this URL:
Joshi SB. An overview of vital teeth bleaching. J Interdiscip Dentistry [serial online] 2016 [cited 2019 Dec 14];6:3-13. Available from: http://www.jidonline.com/text.asp?2016/6/1/3/188155


   Introduction Top


Today's dentist has an array of treatment options to harmonize a smile with discolored vital teeth. The spectrum of treatment ranges from invasive options such as crowns, veneers, and placement of direct restorations to minimally invasive therapies such as macroabrasion, microabrasion, and bleaching to merely prophylaxis. [1] From the number of services listed to enhance the appearance of the discolored teeth, bleaching is an extremely promising option. It is, in fact, both the clinicians' and patients' answer to a safe conservative approach to tackle discolorations, hence gaining wider acceptance. [2]


   History Top


The pursuit of whiter teeth dates back to the Babylonian era. An Assyrio-Babylonian Cuneiform tablet dating from the dawn of recorded history reads:
"If a man's teeth become yellow. thou shalt bray together 'salt of Akkad,' ammi, lolium, pine-turpine with these, with thy fingers shalt bur his teeth." [3]

In 1300s, it was the most sought after dental treatment apart from extractions. The enamel was abraded with a coarse metal file and a solution of "aquatortis," a nitric acid solution, was applied to whiten the teeth. Since 1800s to early 1900s, nearly sixty documents have been published regarding bleaching. These articles claimed to have understood the chemical aspect while seeking to further investigate its safety. [4]

Vital teeth were bleached in the 1860s, using oxalic acid [4] on the external surfaces of the teeth. [5] Later, hydrogen peroxide (HP) [6] or pyrozone [7] was used instead of oxalic acid. Higher concentrations of HP were applied on the tooth in a liquid form in the office. [6] The safety instructions, the steps to ensure the comfort of the patient including the covering of the eyes, were recognized by the dentists. Number of applications with a 3-day minimal interval between appointments and prognosis of the treatment were well documented. Due to the World War I, era of depression, and the World War II, few articles were published from 1913 to 1940. [8] In 1990s, HP was introduced in a gel form that could be applied more conveniently to the teeth by means of gauze pieces. [9] Currently, HP is used in office as gels or in a powder-liquid form in the concentrations ranging from 15% to 40%. [10],[11] Heated instruments or high-intensity light sources were used as adjuncts to accelerate the bleaching process. [12] Researchers have attempted to substitute high-intensity light sources by the desire of conventional halogen lights, plasma arc lamps, xenon-halogen lights, LED lights, and LASERs. [13]

In the late 1960s, accidently, a home bleaching technique was stumbled upon by Dr. B. Klusemeir, an orthodontist. He designed a custom fitting tray and prescribed an over-the-counter (OTC) oral antiseptic, Gly-Oxide (Marion Merrell Dow, Kansas City, MO, USA), containing 10% of carbamide peroxide (CP). It dawned on him that along with the improvement in the gingival health, the teeth were also whitened. Gly-Oxide was substituted by proxigel; a combination of 10% CP, water, glycerin, and carbopol. This combination resulted in a slow release of 10% CP, and was hence preferred. [14],[15] In 1992, Haywood and Heymann in their article described this technique 20 years later as nightguard vital bleaching (NGVB). "White and Brite" (Omni International, Albertson, NY, USA) was introduced as a new home bleaching product. Subsequently, many whitening products surfaced. [4]

OTC bleaching products were first marketed in the United States in the 1990s. These products contained lower concentrations of HP or CP. Consumers could hence avail bleaching products directly, OTC thus offered a solution of whiter teeth to a wider section of the society. [12]


   Mechanism of tooth bleaching Top


Tooth whitening is any process that lightens the color of the tooth. [16] The causes of discoloration are varied and complex. [8] The color-producing stains are typically organic compounds that possess extended conjugated chains of alternating single or double bonds and often include heteroatoms, carbonyl and phenyl rings in conjugated system, and are referred to as chromophores. [17] Bleaching is the chemical degradation of the chromogens.

In vital dental bleaching, HP is the active ingredient, which is commonly delivered as HP or CP in commercial agents. CP is a stable complex that breaks down in contact with water to release HP and urea and thus, the chemistry of these agents is that of HP. [18]

The basic mechanism of whitening by HP remains unexplained. From the available literature, three distinct phases can be attributed to the changed perception of tooth color. The first phase is ascribed to the diffusion of HP through the highly permeable interprismatic spaces within enamel and dentinal tubules. [19],[20] HP circulates within the tooth for around 2 weeks after its application, [12] thus repeated replenishment of the material can be evaded. [21],[22],[23]

The second phase is based mainly on the interactions of HP with the organic chromophores and is represented as the "Chromophore Theory." [24] HP, as it diffuses into the tooth, dissociates to produce free oxygen radicals. Depending on the kind of breakage of its chemical bonds, the radical ions formed include hydroxyl radical, hydroperoxyl radical, hydroperoxyl anion, superoxide radical anion, and superoxide radical cation. The temperature, pH, light, and presence of metal cations influence the reactivity of the radicals. [25],[26] Using light or LASERs, the number of hydroxyl ions increases. [27] The discolored teeth appear bleached when the highly reactive oxygen radicals break one or more of the double bonds, clear, or oxidize the chemical moieties in the conjugated chains of the chromophores. [17] These reactions result in products, which are polar in nature and lower in molecular weight and are hence easily removed from the tooth in an aqueous environment. [26] In addition, the newly formed products are also lighter in shade than the original stained molecule. Ideally, HP should limit its oxidizing action only to organic chro

mophores. However, some researchers have opined significant changes in the calcium phosphate ratio, suggesting an alteration within the inorganic components of hydroxyapatite. [28],[29] On the other hand, many studies have concluded that the altered calcium phosphate ratio is clinically insignificant and could be reversed with additives of fluoride or calcium. [30],[31],[32],[33],[34],[35]

The third phase is associated to perceiving the color change through an altered tooth surface that reflects light differently. [26] An object appears brighter when it reflects light through its rough or light surface. A rough surface postoperatively may result in superior digital color reading, [36],[37],[38],[39] owing to its increased reflective spectra. Sizable articles have documented changes within the surface topography of bleached teeth, hence justifying the whitening. [40],[41],[42],[43],[44],[45],[46],[47],[48] However, extensive investigations by scanning electron microscope (SEM), profilometry, and atomic force microscopy (AFM) have also suggested no effects on the surface topography of bleached teeth. [15],[49],[50],[51],[52],[53] In fact, articles attribute the modification of organic matrix within enamel by the demineralization and not the surface roughness to whiten the tooth. [30],[33],[36],[54] Crystallographic studies emphasize the association of hydroxyapatite crystals of the enamel, with optical properties of the bleached tooth. It has been suggested that the hue of the tooth is related with the size of the crystals, and the carbonization of these hydroxyapatite crystals is inter-linked with the chroma of the tooth. The value of the tooth is associated with both size and carbonization. This understanding led to a major innovation by incorporating chemicals such as blue covarine into whitening agents. Recent studies have indicated that deposition of this product on the tooth surface produces a decrease in the chroma in the yellow-blue axis and hence, increases the measured whiteness index. The studies on the optical properties suggest reviewing the mechanism of bleaching as "Chromophore Theory," [26] which is not supposedly the sole reason for tooth whitening.


   Types of stains Top


The apparent color of a tooth is a combination of its innate color along with the stains present within and on the tooth surface. [55],[56] The chromogens when deposited on the surface of the tooth or within the pellicle layer discolor the tooth and are termed extrinsic stains. [8] Extrinsic stains occur when chromogens such as tobacco, tea, coffee, red wine, medicines, spices, and plaque attach directly to the tooth. Chromogens such as polyvalent metal salts such as iron supplements and cation antiseptics such as chlorhexidine may combine with tea and attach to the tooth indirectly, creating black or brown characteristic stains. [57] Prophylactic procedures may remove extrinsic stains; however, the more persistent stains respond successfully to bleaching. [58]

Chromogens, which are deposited within the tooth bulk mostly in the dentin, are termed intrinsic stains and are of systemic or pulpal origin. [59],[60] Iatrogenic, traumatic, metabolic, inherited, and aging stains are the subdivisions of intrinsic staining. Tetracycline ingestion during tooth formation depicts itself as classical banded appearance in yellow, brown, blue, black, or gray, depending on severity. [8] The color is derived by photo-oxidation of the tetracycline molecule bound within the tooth structure. [61] Not so severe cases are possibly treated by bleaching over a period of 3-6 months. [62],[63],[64],[65] Very severe tetracycline stains may not be amendable to bleaching alone and may require a combination of bleaching along with veneers to mask the color. [64] The prognosis is poorest for teeth stained dark gray or blue and involving the neck of the tooth. Almost all materials used in endodontics may stain the teeth. [66] Minocycline, a tetracycline derivative, which is commonly prescribed to treat acne, has been reported to stain adult teeth. [67]

Discolorations owing to trauma are observed due to enamel hypoplasia, pulpal hemorrhage, pulp canal obliteration, [68] and tooth resorption. Bleaching does not erase the white spots resulting from enamel hypoplasia, but whitens the remaining tooth. The white spot merges within the bleached tooth, making it lesser obvious. [64] Bleaching reverses the discolorations due to pulpal hemorrhage and pulp canal obliteration.

Aging is a common cause for discoloration. Secondary and tertiary dentin deposition, thinning of enamel, and accumulation of dietary stains result in darker teeth in geriatrics, which are predictably bleached. [64]

Fluorosis may depict with varying severities. Discolorations due to simple-to-moderate fluorosis can be treated with bleaching. Hypomineralization when reaches dentinoenamel junction may result in posteruptive breakdown (PEB), [69] staining the tooth dark brown to black. PEB-stained teeth require a combination of bleaching, microabrasion, followed by veneers to camouflage the discoloration. [62]

Defects within the tooth such as cracks, leaky restorative margins, caries, and trauma with time permit the percolation of extrinsic stains within the tooth. This mechanism is categorized as "stain internalization." [70]


   Composition of commercial bleaching agents Top


Majority of the current bleaching agents consist of both active and inactive ingredients. The active ingredient includes HP or CP compounds. [18],[71] CP is equally efficient in tooth whitening when compared with equivalent HP content and is delivered in similar format and formulation. [72],[73],[74]

Sodium percarbonate is another source of HP, painted onto the teeth in a product containing silicone polymer. [75] The efficacy of sodium percarbonate versus HP in the same product format, content, and conditions has not been reported. [18]

The active ingredients in different concentrations are combined with the inactive ingredients for their commercial use.

The major inactive ingredients are:

Thickening agents

Carbopol (carboxypolymethylene) is a high molecular weight polyacrylic acid polymer. It is the most commonly used thickening agent in bleaching materials. It increases the viscosity aiding in the retention of bleaching gel in the tray. Second, it causes a slow release of active oxygen from HP, thus increasing the bleaching period up to four times, [34] and hence decreasing the frequency of replacement during bleaching treatment. [12]

Polyx is another thickening agent with its composition being a trade secret. It enhances the activity of the material and tray design. [12]

Carrier

Glycerin, as a carrier, enhances viscosity and eases manipulation. Dehydration caused by glycerin may be depicted as a loss of translucency. The dehydration and swallowing of glycerin in the solution or gel is responsible for sore throat, which is another side effect, reported by clinicians. [12]

Propylene glycol is the other carrier commonly used. Along with maintaining moisture, it aids in dissolving other ingredients. [71]

Surfactant and pigment dispersant

The addition of surfactant or pigment dispersant [76] increases the effectiveness of bleaching. [77] The surfactant allows the diffusion of HP across the gel and tooth boundary by increasing the surface wetness. The pigment dispersant holds the pigments within the gel in suspension.

Preservatives

Sodium benzoate and methyl propyl paraben when used as a preservative prevent bacterial growth within the gels. [71] Solutions containing preservatives such as citroxain, phosphoric acids, citric acid, or sodium stannate sequestrate transitional metals, spacing out the breakdown of HP. These preservatives enhance the durability and stability of the gels and have mildly acidic pH.

Flavorings

Flavorings are substances when added to the gel increase the patient's acceptance by improving the taste. For example, banana, melon, peppermint, spearmint, wintergreen, sassafras, anise, and sweetener such as saccharine. [71]

Additives

To escalate the bleaching procedure and/or minimize its side effects, various additives are incorporated within bleaching gels. [8]

Potassium nitrate

It is superior in comparison to other additives. Five percent potassium nitrate acts like an anesthetic by halting the nerve from repolarizing after it has depolarized in the pain cycle. [64] Hence, it decreases the postoperative sensitivity without reducing the bleaching effect. It is effective even in light-activated bleaching. [77],[78],[79],[80]

Fluoride

Fluoride increases the microhardness of the substrate enamel. [81],[82] Fluoridated bleaching gels result in lesser demineralization without altering bleaching efficiency. [83] The fluoridated bleaching gels maintain micro tensile bond strength, assisting subsequent restorative procedures. [84] Fluoride blocks the dentinal tubules resulting in slowing down of the dentinal fluid flow, hence decreasing sensitivity. [64]

Amorphous calcium phosphate-casein phosphopeptide

The addition of amorphous calcium phosphate-casein phosphopeptide (ACP-CPP) within bleaching gels significantly reduces sensitivity by remineralization [85] and even enhances the bleaching outcome. [84] ACP-CPP causes protein binding and deposition of phosphate and calcium ions in exposed dentinal tubules, ensuing rapid desensitization. Patients using ACP-CPP gel had lesser bleaching effect compared to those using potassium nitrate-modified gel with similar reduction in sensitivity. [86] The ACP-CPP-added gel enhances the lustrous shine to the teeth. [71]


   Patient selection for vital tooth bleaching Top


Bleaching, though promising, may not guarantee success in all cases or may fail to satisfy patient's high expectations. The indications and contraindications are basically the same for both in-office and home bleaching. Patient's lifestyle, current levels of tooth sensitivity, the type of discoloration, baseline shade of the teeth, and time available for bleaching are important factors to be contemplated while selecting the bleaching technique. [87] Patients with decay, periapical lesion, and sensitivity should seek treatment for the same prior to bleaching. [8] Bleaching is contraindicated in pregnant women as the effects of bleaching materials on fetus are yet to be investigated. [87]

Erasing stains is not time-specific as some stains are more responsive to bleaching than others. Analysis of reports, studies, cases, and personal experiences has correlated stains and their response to bleaching with functions as a guideline to assist the clinician in predicting success. [8],[71],[87] It has been demonstrated that teeth with yellow hue with no or developmental pathologies are bleached more efficiently. Younger patients experience a greater magnitude of whitening. Gender had no significant influence in the whitening response of the tooth. [88] Tobacco stains and other brown stains respond to longer bleaching regimens, as they are not easy to bleach. [64] There is a correlation of the sclera of the eye and tooth to be bleached. If the discolored teeth were lighter than the sclera, the probability of success would be lesser. [12]


   Types of whitening system Top


Discolorations are treated by either removal of extrinsic stains, bleaching, or both. [8] The whitening agents and systems used are classified in accordance to the chemicals used, mode of application/delivery, or mode of action. The American Academy of Cosmetic Dentistry categorized systems on the basis of the mode of application/delivery. [89]

Whitening toothpaste

Whitening paste in comparison to standard toothpaste contains higher amounts of abrasives and detergents, which make it very effective in removing extrinsic stains, significantly improving the appearance of teeth but not the underlying color. [90] Some whitening toothpastes contain a low concentration of CP or HP that can bleach the tooth by one or two shades. [16] The dual-chambered technology permits HP to be included within the dentifrice. The product permits the addition of 1% HP and is only stable as they are separate and mixed on the brush. Adapting to a better understanding of the application of color science, blue covarine is incorporated within silica toothpaste making the tooth measurably and perceivably whiter. [91]

Over-the-counter whitening strips and gels

The strips and gels are two groups of novel tooth whitening system. Strips are thin layers of 5.3% HP gel on polyethylene strips, shaped to cover the anterior teeth from canine to canine. They were introduced in 1980 and have reported effective whitening in comparison to home bleaching with 10% CP in trays. [92] The concentration of HP is on the rise with 6.5% HP-coated strips available. [16] They are advocated to be used for 14 days. The 5.3% strips are applied twice daily for 30 min and 6.5% HP for 30 min in a day. It is difficult to place the strips on malaligned teeth; in addition, they are irritating to the gingiva. [93] A novel trayless system was introduced comprising 10% HP as thin membrane system (Treswhite Ultradent Products). [16] It ensures an increased comfort as it has a gel barrier at the margin of the gingiva. As the strips require no dispensing, an error at this stage is avoided and is hassle-free as it is disposed after every use. [94]

Whitening gels comprise peroxide, which is applied with specific brushes directly onto the surfaces of the teeth. They are recommended to be used for 20-30 min, twice a day for 14 days. The brushes are discarded as per the manufacturer's instruction, which reduces microbial contamination and peroxide inactivation. [95]

Whitening strip products and gels lighten the teeth by 1-2 shades. [16]

Whitening rinses

The rinse comprises HP, which reacts with the stains, lightening the tooth by 1-2 shades. [16] Manufacturers recommend rinsing for 3 months twice daily for 60 s each.

Tray-based tooth whiteners

Tray-based tooth whiteners are available both professionally and OTC. OTC trays are stock trays that are not comfortable, as they do not adapt to every mouth. Professional trays are fitted trays, in which CP or HP is dispensed at home by the patient, while the concentration and the results are monitored by the dentist. [16] This dentist-monitored bleaching technique or NGVB is most opted for as it is safe, cost-effective, easy, and has a high success rate, qualifying it as a gold standard against which other techniques are judged. [87] Lower concentration of the bleaching agent is recommended to be used for longer time durations for more number of sessions. [87] Higher concentrations of viscous bleaching agents to whiten the teeth pronto are linked with an increased risk of thermal sensitivity. Depending on the patient's lifestyle, availability of time, and sensitivity, dentist can recommend bleaching during the day or night. [87] Occlusal pressure and increased salivary flow may dilute gels when used during the day. [96] As home bleaching demands compliant patients, it witnesses a high dropout rate. [2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13] Overzealous patients with a strong urge for whiter teeth replenish the gel frequently or use the trays for a longer period of time leading to thermal sensitivity. [4] For selected cases with different chromas within the same arch, lower and higher concentrations of the bleaching agents can be used simultaneously for lighter and darker teeth, respectively. [87]

An alginate impression is recorded to deliver bleaching trays. Standard trays are made of poly (vinyl acetate) polyethylene sheets with a thickness of 0.9 mm. Reservoirs are placed to hold greater thickness of material to contact teeth. Trays with reservoirs are preferred for viscous materials, bulbous teeth, and darker teeth. However, trays with or without reservoir show no difference in the rate of bleaching. [97] The trays could be scalloped following the tooth/gingiva interface, minimizing soft tissue contact and gingival irritation. Unfortunately, this design washes the gel with the ingress of saliva and may also irritate the lip or tongue. Trays that are cut 2 mm over the incisors in a straight line or nonscalloped have a better seal. [98] Trays are modified as per the individual cases, in those with gingival recession or sensitivity, borders are cut back. In cases with crowns or teeth that do not require to be bleached, windows are cut in trays. The trays for bruxers are made from sheets of 1.5 mm thickness, and for those prone to gagging, thinner sheets of 0.5 mm are used. [87]

A stepwise demonstration of the placement of bleach within the tray as per manufacturer's instructions is given to the patients. Brushing and flossing teeth prior to loading the tray is emphasized. Excess material extruded from the tray is removed with cotton wool rolls, toothbrush, cotton bud, or finger. Patients should be instructed to merely clean the tray and store it in a dry place till its use again. Patients should be instructed to discontinue treatment temporarily if irritation within the gingiva or sensitivity sets in. Sensitivity set can be treated by incorporating desensitizing protocols. Desensitizing toothpaste containing potassium nitrate can be rubbed or brushed against the affected teeth. Neutral fluoride gels, potassium nitrate gels, or desensitizing toothpaste can be worn overnight in the bleaching tray. Preloaded trays of potassium nitrate and neutral fluoride can be used prior to bleach as recommended by manufacturers, relief is almost immediate. The protocol of bleach could be altered by using the same bleach on alternate days or decreased time periods. A lower concentration bleach could be prescribed which may prolong the duration of treatment but will ensure comfort for the patients. [87]

Patients could anticipate banding of teeth in the initial phase of bleaching, especially with higher concentration of bleach and in lower incisors. [99] The color evens out as the treatment progresses. Bleaching an arch at a time creates an obvious contrast motivating bleaching of lower arch too. The shade of teeth should be reassessed and compared to baseline and noted with patients' consent.

In-office bleaching

Higher concentrations of HP (25-40%) are used in the clinics to achieve quicker tooth lightening. [71],[100] In-office bleach, with its immediate positive outcome, can kick-start a home bleaching regimen. [100] It overcomes the problems of patient compliance, manual dexterity, [87] and is ideal for those patients with high gag reflex. [100] It prevents patients from the distaste of the bleaching gel. The treatment in office mandatorily needs isolation and protection, [100] owing to the caustic nature of the high concentration of HP. In-office bleaching results in dehydration; as a result, the shade lightens far more in comparison to baseline shade. On rehydration, the results may be misinterpreted owing to an increased rebound. The clinician can halt the treatment as and when required as he or she is in complete control throughout the procedure.

HP is potent in the first 30 min of mixing, after which the free radicals are depleted. [100] Depending on the manufacturers' instructions, products are applied in 2-3 mm thickness on the labial surfaces of teeth for a period ranging from 3 to 20 min. The contact of the bleach with the teeth is usually for three periods of 10 min, each termed as "passes." Using gels is advantageous as it contains 10-20% water, which prevents dehydration while bleaching unlike liquid and liquid powder products. The consistency of the material permits it to remain in intimate contact with the tooth, [101] thus minimizing harm to soft tissues. A thick band of light-cured resin barrier is painted in-between teeth and around the tooth, onto the gingiva for its protection. The isolation of the oral structures depends on the type of power bleaching or the dentists' preference.

Fresh gel is replenished on the surface after suctioning and wiping the tooth clean. The inadvertent leakage of bleach may cause blanching and burning of tissues. Immediately, the area of concern should be washed with copious amount of water followed by the application of neutralizing agent such as Vitamin E supplied with the kit. Treatment can resume after careful placement of the barrier for recommended bleaching passes. Postbleaching, teeth are polished with diamond-polishing pastes to increase luster and coated with an application of neutral fluoride gel, especially in patients who experience sensitivity. Postbleach shade and photographs with tabs are taken to aid documentation. To stabilize the shade, home bleaching is recommended after in-office bleach.

The oxidation potential of HP can be intensified by exposure to heat, LASERs, or intense blue light with a spectrum of wavelength between 480 nm and 520 nm, either to activate the bleaching agent or decrease the time required for bleaching. Various types of curing lights used in bleaching are as follows:

Halogen-curing lights

Demetron 501 (Kerr Dental Ltd., Peterborough, UK) has been used for activating many different bleaching systems such as Pola Office (SDI, Victoria 3153, Australia) and Quick White Net (DMDS UK, Canterbury, UK). The light in its bleaching mode is applied for 30 s/tooth; the application includes three 10- min passes. Products such as Opalescence Xtra (Ultradent Products, South Jordan, Utah, USA) have carotene mixed within the bleaching agent, which allows for conversion of light energy into heat. This heat increases the further breakdown of HP into free radicals by increasing its activity. [102]

Plasma arc lamps

Plasma arc lamps significantly contribute to effective bleaching using HP without thermal changes as it releases energetic ions, free electrons, and hydroxyl radicals. [103] Activation is by three 10-min passes with whitening mode activation for 3 s/tooth. A burst of lower intensity light with a gap of 5 s may be used to activate both arches together with a 10-min pass in a full-smile adaptor. [100]

Xenon-Halogen technology

It is a xenon-halogen light having a blue-green spectrum. [102] A full-smile illuminator is kept a few centimeters ahead of teeth in the usual protocol of three 10-min passes to activate 35% HP. There has been a controversy regarding the efficacy and safety of a combination of 22% CP and 38% HP for three 20-min passes using this technology.

Diode LASERs

Nearly, 35-50% HP may be used for tooth bleaching in combination with 830 nm or 980 nm diode lasers. The blue dye present in the powder absorbs thermal energy from the light source to heat up the gel causing an increased breakdown, thus increasing its activity. [104] Three 10-min passes are used at 1-2 W of energy for 30 s/tooth. Eye protective glasses are a must with the use of lasers.

Metal halide lamp

The metal halide light has an infrared filter and emits insignificant amounts of ultraviolet light, minimizing heat on the surface of the tooth. The Zoom light (Discus Dental, Culver City, CA 90232, USA) is an example of such a curing unit. The bleaching gel comprising two parts of 25% HP with an activator is used in a dual arch technique with three 20-min passes. This is followed by an application of sodium fluoride gel. [105],[106]

Chemical activation

Opalescence Xtra Boost (Ultradent Products, South Jordan, Utah, USA) has gels placed within two syringes. One syringe contains 38% HP and the second syringe contains a proprietary agent. When mixed, the gel is chemically activated. The agent increases the pH to 7, enhancing the activation of the bleach. It is used for three passes of 10-15 min each. The teeth are lightened by 6-10 shades. [100]


   Dual activation Top


Ferrous and manganese sulfate have been added to the bleaching gel to allow for chemical and light activation, respectively. An example of the same is Hi Lite (Shofu Dental Products, Tonbridge, Kent, UK). The bleaching time is, thus, reduced to 7-9 min. [9],[10],[11],[12],[13],[14],[15] The HP gel changes color from blue to green to cream, and finally, chalky on completion of activation. A maximum of 6 passes are recommended in a session. [100]

Ultrasonic technology

Using ultrasonic energy, an expedite method of in-office bleaching has been recently introduced. SoniWhite Whitening System (DMDS UK, Canterbury, UK) utilizes ultrasonic energy to enhance bleaching by placing 6-7.5% HP within custom-made trays in either arch for approximately two cycles of 5 min each. It is thought that ultrasonic energy may result in an increased production of free radicals. [100]

Other than hastening the chemical reaction, the current research on whitening literature observes no added benefits from attempts to use other sources with respect to the whitening achieved, persistence to bleaching, or avoidance to tooth sensitivity from the treatment. [16]


   Assissted/waiting room bleaching technique Top


DenMat introduced assisted bleaching technique, in which 35% of CP was used cautiously under close supervision. Assisted bleaching is indicated to initiate home bleaching and accustom the patients to handle the trays. This technique is also used as an adjunct to accelerate vital tooth bleaching. Nearly, 35% CP is loaded in a custom-made tray; the efficacy of CP may be enhanced by holding the syringe under hot water prior to its loading. The tray is placed in the patients' mouth and the patients are asked to be seated in the waiting room for 30 min. [12]


   Compressive bleaching technique Top


This technique was reported by Miara to enable the permeation of nascent oxygen radicals through the enamel under guided pressure. [107] This procedure involves using a custom-made tray to place 35% HP bleaching gel and sealing of the edges with light-cured resin material. A halogen or plasma arc lamp is used for activation. However, there are few studies supporting this method; there are definite concerns about the penetration of HP into pulp chamber after 15-20 min. [108] The hypothesis that nascent oxygen is indeed forced into the tooth requires to be authenticated. [100]


   Combining bleaching techniques Top


A combination of both in-office and home bleaching may improve the prognosis of tooth with stains of varying etiologies or cases of tetracycline staining. It is also a method of motivating the patients, whose compliance is questionable. It may also be used in cases where a nonvital discolored tooth is involved or there is a single tooth with multiple stains.

Every tooth has a final level of lightness termed "inherent lightness potential." It is the end point of bleaching for that tooth. [109] Research points to 6 weeks window of bleach, independent of the concentration and kind of peroxide used to reach the end point.


   Postoperative instructions for vital bleached teeth Top


Avoid acidic drinks, fruits, tea, coffee, and smoking for 48 h postbleach. Avoid disappointment, as shade relapse is to follow. Quicker the drop of shade, more is the rebound. In in-office bleach, shade regression of about half a shade tends to occur within a week or 10 days postbleaching. [99]


   Postoperative sensitivity Top


Tooth sensitivity while bleaching is the most commonly reported adverse reaction. Studies have reported sensitivity in the patients during bleaching ranging from 18% to 78%, when treated either at home or in-office. [102],[110],[111] Clinical observations conclude that this sensitivity is transient, with no long-term effects. [112] Potassium nitrate desensitizing toothpaste can be recommended [110] to decrease sensitivity using a medium hardness toothbrush. Bleaching trays can be loaded with 5% potassium nitrate-containing toothpaste and worn for 10-30 min a day, 2 weeks before initiating the treatment. [113],[114] Five percent potassium nitrate professionally dispensed in syringes can be loaded in bleaching trays, or preloaded potassium nitrate bleaching trays can be recommended while bleaching and used for immediate relief. ACP-CPP can be burnished onto the surface of teeth postbleach in the operatory. ACP-CPP can be loaded within the tray and worn for 3 min to reduce sensitivity and add luster. [115] Neutral fluoride gel can also be applied. [100]


   Maintenance of bleached teeth Top


Patients are recommended to use a whitening toothpaste and dental floss with a powered toothbrush. Food, beverages, and habits that stain the teeth should be evaded. Women are advised to wear a brighter shade of lipstick to make the teeth appear whiter. A touch up is a must to restore the shade. Depending on the relapse, the touch up is recommended in 6 months or after a year or 2. [116]


   Conclusion Top


The amalgamation of minimal intervention and desire for a flawless smile has widened the scope of whitening vital discolored teeth. In succession, recent years have witnessed a flood of newer products and procedures. Although most teeth bleach promisingly, the predictability depends on multiple factors and is variable. [1] Professionally dispensed bleaching treatment that includes HP- and CP-based bleaching are safe and effective methods when manufacturers' instructions are followed. [16] A careful monitoring and supervision is critical for achieving a successful and safe tooth whitening outcome. Home bleaching is a safer, cost-effective option for whitening teeth. In-office bleach is a viable, esthetic treatment option for an immediate effect on discolored teeth. [117] Further work is essential to unequivocally demonstrate the benefits of light-activated bleach. [15] Tooth sensitivity and gingival irritation; the common risks associated with tooth whitening are transient and may be treated with professional help as needed. [16]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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This article has been cited by
1 Annual review of selected scientific literature: Report of the committee on scientific investigation of the American Academy of Restorative Dentistry
Terence E. Donovan,Riccardo Marzola,Kevin R. Murphy,David R. Cagna,Frederick Eichmiller,James R. McKee,James E. Metz,Jean-Pierre Albouy,Mathias Troeltzsch
The Journal of Prosthetic Dentistry. 2017;
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