Bleaching Procedures

Society, in general, is more concerned about beauty and perfect looks than ever before. In particular, the “perfect smile” has gained more and more importance, including straight and light-colored teeth. Tooth whitening has become a veritable business, of both the dental profession that offers vital in-office bleaching procedures, as well as of commercial companies that sell over-the-counter tooth “whitening” products. Whereas vital tooth bleaching aims to lighten the entire arch, nonvital bleaching procedures are used to treat individual discolored teeth so that they will blend in with adjacent teeth.

Etiology of Tooth Discolorations

Discoloration of teeth can be attributed to various etiologies. Discoloration was described as “any change in the hue, color, or translucency of a tooth due to any cause.” Great differences exist in severity, localization, and appearance. Intrinsic discolorations are incorporated into the tooth structure. Extrinsic discolorations are attached to the tooth surface. Intrinsic and extrinsic discolorations may exist in combination and can affect enamel, dentin, or the pulp. Tooth discolorations may be hereditary, related to patient behavior, age, and disease, or caused iatrogenically by dental and medical treatment ( Table 27-1 ).

TABLE 27-1
Overview of Intrinsic and Extrinsic Discolorations
Color of Stain Extrinsic Intrinsic (Single Tooth) Intrinsic (Multiple Teeth)
Black Betel nut
Chromogenic bacteria
Coffee
Dental plaque
Metals
Tea
Tobacco
Wine
Amalgam restorations
Glass ionomer restorations
Pulpal trauma with hemorrhage
Minocycline (revascularization procedures)
Metals (silver, gold, alloys)
Minocycline (oral)
Tetracycline (oral)
Gray Metals (silver, gold, alloys)
Silicate compounds (e.g., MTA)
Dentinogenesis imperfecta
Thalassemia
Brown/reddish Coffee
Dental plaque
Doxycycline
Drugs (e.g., khat, marijuana)
Iodine
Metals/halides
Oral rinses (e.g., chlorhexidine)
Other foods
Tea
Tobacco
Wine
Caries (active, arrested)
Cervical root resorption
Composite resin, glass ionomer restorations
Dental trauma
Endodontic irrigation solutions
Iodine
Minocycline (revascularization procedures)
Pulpal trauma with hemorrhage
Resorcinol-formaldehyde resin
Amelogenesis imperfecta
Congenital erythropoietic porphyria
Dental trauma
Dentinogenesis imperfecta
Fluorosis
Infection during enamel formation
Tetracycline (oral)
Thalassemia
Green Chromogenic bacteria
Metals
Tea
Hyperbilirubinemia
Thalassemia
Orange Chromogenic bacteria
Metals
Doxycycline
Yellow Caries (active)
Composite resin, glass ionomer restorations
Dental trauma
Aging
Amelogenesis imperfecta
Dentinogenesis imperfecta
Dental trauma
Dentinal dysplasia
Fluorosis
Hemolytic diseases
Hemoglobin, heme
Hyperbilirubinemia
Nutrition deficiency (e.g., rickets, scurvy)
White Caries (incipient)
Dental trauma
Calcification due to trauma
Fluorosis
Infection during enamel formation
Nutrition deficiency (e.g., rickets, scurvy)

Systemic Intrinsic Causes

Genetic Causes

Amelogenesis imperfecta (AI) describes a group of hereditary conditions associated with mutations in five genes—AMEL (amelogenin), ENAM (enamelin), MMP20 (matrix metalloproteinaise-20), KLK4 (kallikrein-4), and FAM83H—affecting the structure and appearance of enamel in the primary and secondary dentition. Enamelin defects may cause variable hypoplasia ranging from local pitting to generalized thinning of the enamel. Amelogenin defects can lead to abnormal maturation and mineralization defects; disorganized, hypoplastic enamel; or other phenotypic variations ranging from hypoplasia to hypomaturation or hypomineralization. Clinical appearance and morphologic structure of the enamel can be affected by discoloration as well as increase sensitivity and fragility. Due to the impaired mineralization resulting from the developmental changes in the enamel matrix formation, discoloring agents in the oral cavity may gain easy access to the mineral structure. The tooth color may be brown or yellow. Bleaching attempts may be, although successful, of a temporary nature and seen as an adjunct to comprehensive restorative treatment.

Dentinogenesis imperfecta (DGI) and dentinal dysplasia (DD) are a group of hereditary autosomal dominant genetic dentine disorders, characterized by an abnormal dentine structure. Either primary or both, primary and secondary dentitions may be affected. Dentinogenesis imperfecta is most commonly categorized into three subtypes: DGI type I, DGI type II, and DGI type III; dentinal dysplasia is categorized into two subtypes: DD type I and DD type II. DGI type I is associated with osteogenesis imperfecta and involves mutations in the collagen type 1 encoding genes COL1A1 and COL1A2. With the exception of DD type I, all other forms of dentinogenesis imperfecta and dentinal dysplasia are related to mutations in the gene encoding dentine sialophosphoprotein (DSPP). All patients affected by osteogenesis imperfecta also suffer from brittle bones. Patients with dentinogenesis imperfecta have weaker teeth that are more prone to fracture. Patients suffering from DGI type I, DGI type II, and DGI type III have teeth with yellow-brown, deep amber, or blue-gray discolorations and higher translucency. Bleaching treatment will have minimal to no effect; comprehensive restorative treatment is indicated, but it is difficult to execute due to the compromised tooth structure.

Other diseases causing tooth discoloration include porphyria, erythroblastosis fetalis or thalassemia, and sickle cell anemia. Congenital erythropoietic porphyria is a disease resulting from abnormalities in the synthesis of porphyrins, organic compounds essential for the function of hemoglobin. It may result in reddish or brownish discoloration. Erythroblastosis fetalis is a hemolytic disease wherein fetal erythrocytes in Rh-positive fetuses or newborns of Rh-negative mothers are destroyed by antigens that cross the placenta, leading to hyperbilirubinemia. Bilirubin, a yellow breakdown product of hemoglobin, is incorporated into developing teeth, creating yellow-green and blue-green discolorations. Thalassemia, a blood disease causing characteristic malformations of the skull and long bones, and sickle cell anemia, a hereditary blood disorder displaying an abnormality of the oxygen-carrying hemoglobin molecule causing red blood cell malformations, may result in intrinsic blue, green, and brown discolorations.

Disease-Related Causes

High fevers experienced during the ages of tooth development may cause chronologic enamel hypoplasia leading to banding type discolorations on the tooth surface. Vitamin and mineral deficiencies may induce hypoplasia. Rickets, a vitamin D deficiency, may lead to white hypoplasias resulting from osteomalacia, developmental anomalies in the bones. Scurvy, vitamin C deficiency in conjunction with vitamin A deficiency, and disturbances of phosphorus uptake can cause enamel hypoplasias.

Metabolic Causes

Enamel hypoplasia may also occur after excessive exposure to fluoride during tooth formation. This exposure can lead to alterations in the mineralized tooth structure, especially in the enamel matrix, and give the appearance of a mottled tooth. The extent of hypoplasia directly correlates with the fluoride uptake during tooth formation and will impact the degree of discoloration. Shades of discoloration may vary greatly and can range from white spots with opaque or chalky appearances to yellow or brown stains on the facial side of the affected tooth, in severe cases with surface pitting of the enamel. No damage to the shape of the crown can be found. It can be related to amelogenesis imperfecta or hereditary hypophosphatemia. Tumors, infections, or trauma may be contributing factors. In situations of moderate severity, external bleaching may be sufficient, whereas in severe cases, a restorative approach may be indicated.

Drug-Related Causes

Tetracycline is an antibiotic used to treat diseases such as urinary tract infections, chlamydia, and acne. It was frequently used from the 1950s through the early 1980s. In particular in young children, it causes gray or brown, deep, dark stains that may affect the entire tooth or occur as a pattern of horizontal stripes. Many adults also currently suffer from tetracycline stains on their teeth. Tetracycline induces discolorations in permanent teeth manifest during tooth development, when tetracycline becomes calcified in the tooth, generating the characteristic stains. The discolorations are embedded in enamel and dentin. Children are susceptible to tetracycline discolorations from the time they are in utero until the age of 8. Because tooth development starts prior to birth, women are advised to avoid taking tetracycline during pregnancy. Tetracycline stains are obvious and were viewed as always permanent in the past. However, several studies reported successful cases after application of a walking bleach technique and even prolonged bleaching with car­bamide peroxide. The walking bleach technique will, however, require intentional devitalization and endodontic treatment of the tooth to allow for the application of the bleaching agent into the pulp chamber. A patient must be thoroughly informed about the risks, advantages; and disadvantages of this treatment. Today, “power bleaching” and veneers are among the suggested treatments for tetracycline stains. Nevertheless, great care must be taken to avoid issues with bonding systems after the application of bleaching agents. Severe cases of tetracycline discoloration may require full coverage restorations.

Local Intrinsic Causes

Pulpal Hemorrhage

Dental trauma may lead to the rupture of intrapulpal blood vessels with subsequent intrapulpal hemorrhage and the release of blood components into the dentinal tubules. The hemolysis of erythrocytes will result in the degradation of hemoglobin into globin and the heme protein, containing an iron atom. The iron, in the form of iron sulfides, may reach dentinal tubules, causing stains and discolorations in the surrounding dentin. Depending on whether the pulp recovers or becomes necrotic, the discoloration may revert or persist. If the pulp survives, the tooth may eventually revert to its initial shade; however, in situations where pulp necrosis takes place, the discoloration may remain and become worse. Intracoronal bleaching has proved effective in these situations.

Pulp Necrosis

Irritation of the dental pulp can happen chemically, mechanically, or by microbial insult, especially by bacteria and their toxic by-products. After initial inflammation, the pulp develops local microabscesses followed by tissue necrosis and eventually complete necrosis. Disintegration products from pulp necrosis may become incorporated into dentinal tubules and cause discoloration of the surrounding dentin. The intensity of the discoloration appears proportional to the time the discoloring agents remain in the pulp chamber. These types of discolorations tend to respond favorably to intracoronal bleaching.

Pulp Tissue Remnants

Remnant pulp tissue that was left behind after endodontic therapy will eventually disintegrate and may discolor tooth structure. As a clinical consequence, pulp horns and all other pulp tissues in the access chambers should be carefully removed during treatment.

Restorative Materials

Metallic filling materials, such as amalgam or gold, may cause discolorations. Gold fillings—for example, gold foil compaction fillings, inlays, or onlays, but also pins or posts—mostly cause color changes, reducing tooth translucency and adding dark hues through thin remaining tooth portions. Amalgam fillings, over time, will undergo corrosive changes and degradation, with by-products causing color alterations in tooth structure. For any metallic filling that remains visible through existing tooth structure, removal of the filling and exchange with an aesthetic filling material is the preferred choice. Effective dentinal discolorations by amalgam can be bleached but may be prone to recurrence. Composite resin restorations may leak at the margins and allow for discoloring agents to penetrate into the tooth and dentinal tubules.

Intracanal Medicaments and Root Filling Materials

A variety of endodontic medications and filling materials may be responsible for discolorations. Silver points, historically used for root fillings, can cause gray, dark discolorations in teeth and the surrounding tissues due to corrosive processes. Gutta-percha was reported to cause a light pink discoloration. Resorcinol-formaldehyde resin paste (“Russian Red”) was reported to cause discolorations ranging from pink to dark burgundy. Phenols or iodine containing intracanal medications (e.g., camphorated monochlorophenol [CMCP] or iodine-potassium-iodine [IKI]) may reside in the root canal space and start gradual discolorations by penetration of dentinal tubules through oxidation.

Endodontic sealers, particularly those containing metallic compounds (e.g., silver), can cause dark discoloration, either if the material is incompletely removed from pulp chambers and access cavities or because some components interact with moist dentine over time. For example, AH26 (Dentsply De Trey, Konstanz, Germany), an epoxy resin cement, contains bismuth trioxide as a filler and radiopacifier. Within dentin, various bismuth compounds that range in color from green to black may occur and cause discoloration. The corrosion of silver in the sealer may cause a gray to black discoloration. In addition, incomplete removal of AH26 can cause discoloration in reaction with intracanal medicaments. Epiphany (SybronEndo, Orange, CA), an adhesive root canal cement, showed signs of tooth discoloration.

Mineral trioxide aggregate (MTA), a dental material known for excellent biocompatibility, is used for apexifications, perforation repair, root-end filling, and revascularization procedures. MTA may discolor teeth and adjacent soft tissues. The discoloring effects were shown for both gray and white formulations.

Antibiotic pastes in various combinations are used to initiate revascularization of immature necrotic teeth. In particular, use of the triple antibiotic combination of metronidazole, minocycline, and ciprofloxacin has produced cases of dark discolorations of hard tissue structure. Minocycline, a tetracycline derivate, binds calcium ions of the root dentin and forms an insoluble complex. Other medications shown to induce discolorations include corticosteroid preparations or formocresol and iodoform-based medications. Repeated applications of formocresol will penetrate dentin and cementum, particularly in the teeth of younger patients.

Discolorations may also occur due to irrigation solutions. Sodium hypochlorite can discolor dentin based on its destructive effect on erythrocytes and the ability to crystallize on the dentin surface. In contact with chlorhexidine, sodium hypochlorite forms a dark brown precipitate containing para-chloroaniline, which can only be removed by mechanical action. MTAD (a mixture of a tetracycline isomer, citric acid and a detergent; Dentsply Tulsa Dental, Tulsa, OK) can cause brown discolorations, probably caused by dentinal absorption and release of the doxycycline.

Dental Caries

Progressing caries can cause tooth discoloration. Early stages of caries are characterized by white, opaque enamel lesions. If caries arrests, the lesion may darken by taking up pigments from exogenous sources, frequently rendering it a deep dark brown or black color. Explanations for discoloration include the formation of melanin or lipofuscin; the sugar-protein reaction also known as the Maillard reaction or nonenzymatic browning ; melanin or food dye uptake into the lesion, or compounds diffusing ahead of the bacterial penetration of demineralized dentine. Dietary chromogens entering the dentine is seen at least as a co-staining factor facilitated by the increased porosity of the hard tissues by the carious process.

Calcific Metamorphosis/Dystrophic Calcification

Calcific metamorphosis can be caused by trauma, resulting in obliteration of the pulp with mineralized tissue. Odontoblasts can become destroyed by the traumatic impact and replaced by cells from adult stem cell populations in the pulp. These cells may initiate rapid deposition of reparative dentin, resulting in yellowish or yellow-brownish discolorations. Anterior teeth are mostly affected. The reparative dentin may occupy the entire pulp chamber, and in certain cases also major parts of the root canal system, resulting in a loss of translucency of the crown. Depending on whether or not the remaining uncalcified portions of the pulp remain vital, endodontic therapy may be indicated, yet difficult to execute, depending on the extent of the calcification. Dystrophic calcification involves the formation of foci of calcification frequently found in the aging pulp, usually in perivascular or perineural locations.

Root Resorption

Cervical root resorptions can lead to pink discolorations of teeth. The granulation tissue of the resorptive defect may be visible through a thin dental enamel layer, giving the characteristic “pink spot” appearance. Treatment involves the removal if the granulation tissue, etching with trichloroacetic acid to remove tissue remnants, and an adhesive restoration of the defect. The treatment may involve a surgical exposure of the resorption or, in severe cases, extraction of the tooth.

Aging

Aging-related tooth discolorations are the result of a physiologic process attributed to the uptake of discoloring agents into the hard tissue structure over time. Age-related changes such as incisal wear, craze lines, or cracks allow for easier penetration. Furthermore, over time, enamel becomes thinner, and the change in ratio between dentin and enamel structure results in additional optical darkening of the teeth. Extracoronal bleaching can partially whiten age-related stains.

Extrinsic Causes

Extrinsic stains are food-, beverage-, or smoking-related superficial stains and discolorations. Pigments from beverages such as coffee or tea or tar from smoking may cause dark, brownish discolorations. Extensive consumption of oranges, carrots, licorice, or chocolate may lead to food-related stains. In areas with diverse populations, betel chewing and areca nut use may be prevalent. In particular, people with origins in Southeast and East Asia, India, Nepal, Bangladesh, Sri Lanka, Pakistan, and parts of China, Melanesia, Taiwan, and the Pacific Islands may be affected. Consistent chewing of betel nut and related substances may cause large-scale black discolorations. Discoloring agents are also included in marijuana. The effects of staining may be accelerated or enhanced if demineralization from acidic food or poor oral hygiene creates rougher tooth surfaces. In general, extrinsic stains respond well to scaling, polishing, or bleaching.

Treatment Planning for Internal Bleaching

The etiology of tooth discolorations may vary greatly. The outcome of bleaching procedures is also very dependent on the nature of the discolorations. Prior to any bleaching procedures, the situation must be carefully assessed and potential bleaching outcomes discussed with the patient, together with the patient’s expectations. If bleaching procedures are indicated, they should be integrated into the overall treatment plan. The referring dentists may have to be made part of the conversation, if applicable. To establish a correct diagnosis, the patient’s dental and medical histories need to be assessed, including family history, genetic or systemic disorders, past and current medications, as well as any history of dental or facial trauma or orthodontic, restorative, and endodontic treatment. Radiographic analysis, including periapical and bitewing radiographs (as well as, if applicable, CBCT) is indicated. The assessment of the pulpal and periapical status is a prerequisite. Particular to treatment planning bleaching procedures, the dentition must be evaluated for caries prevalence and type, plaque control, and tooth surface stains, as well as the type, quality, and extent of existing restorations. Transillumination may aid in finding dental decay or pulp chamber calcifications.

Contraindications of Bleaching

Tooth bleaching is not indicated for every situation and every patient. A thorough investigation and diagnosis of the patient’s history and clinical situation may surface issues with the underlying stain that imply that a good aesthetic outcome is either impossible or difficult to achieve. The patient’s aesthetic expectations should be critically evaluated and the prognosis for the treatment discussed thoroughly. This includes potentially unrealistic expectations by the patient, either due to the clinical facts or the patient’s over-expectations. The clinician should be aware of any psychological or emotional problems that a patient may have with the current clinical situation and should advise patients if a bleaching procedure is not in their best interest. All findings and discussions with the patient should be well documented for legal purposes and future reference.

The patient must be made aware of additional dental procedures, such as restorative, periodontal, endodontic, or ortho­dontic treatments that may be necessary to achieve a desired aesthetic goal. Bleaching of teeth with white or brown spot discolorations could increase the existing contrast. Teeth with existing decay or discolored or leaking older restorations may require technique variations or new restorative procedures to remove diseased hard tissue structures to match the adjacent tooth aesthetically.

Patients with confirmed severe attrition, abrasion, abfractions or erosion, caries, or insufficient restorations may experience dentin hypersensitivity prior to a bleaching procedure. This sensitivity could be strongly enhanced by an in-office or at-home external bleaching procedure, particularly if patients can control the amount of bleaching agent used. Clinicians are advised to resolve the underlying issues prior to engaging in tooth whitening procedures. Patients with suspected or confirmed bulimia should not receive bleaching procedures. The underlying psychological condition must be resolved prior to treatment. Most patients suffering from bulimia require veneers or full coverage restorations.

If orthodontic treatment with fixed orthodontic appliances is scheduled, no bleaching procedures should take place 2 to 3 weeks prior to any adhesive placement of brackets. The oxygen released from the peroxide compounds will interfere with the bonding strength of the composite resins to hard tissue structure.

Alternatives to Bleaching

Microabrasion is an alternative to bleaching with peroxide compounds for superficial irregularities and shallow intrinsic stains in the enamel surface. Briefly, the technique involves mixing 18% hydrochloric acid solution with fine pumice powder to form a thick paste and applying it to the stained tooth surface. A rotating rubber cup in a slow speed handpiece with light pressure is used to distribute the paste. Liquid or sheet rubber dam placement is mandatory. Prior to using the rubber cup, the paste should be placed on the tooth for about 5 seconds, followed by the rubber cup activation for 15 seconds. While the enamel is carefully monitored for any damages, this procedure is repeated for up to 12 to 15 times, depending on the effectiveness of the stain removal. If the stain is not fully removed after this many applications, the procedure should be terminated to avoid permanent enamel damage. Copious irrigation with water is used to remove excessive paste material. The application of topical fluoride for several minutes concludes the procedure. Several case reports with successful long-term follow-up have been reported.

Chemistry of Bleaching

The most common classification for tooth discoloration was described by Nathoo and defines three classes:

  • Nathoo type 1 (N1): The discoloring agent (chromogen) binds to the tooth surface, with a color similar to that of dental stains caused by chromogenic bacteria, coffee, tea, wine, and metals.

  • Nathoo type 2 (N2): The discoloring agent is a Nathoo type 1 food stain that changes color to darker after binding to the tooth surface for a certain amount of time.

  • Nathoo type 3 (N3): A prechromogen or in its base state colorless material binds to the tooth and causes a stain after a chemical reaction. These types of stains are often due to carbohydrate-rich foods (e.g., apples, potatoes), stannous fluoride, or chlorhexidine.

Tooth bleaching involves the alteration of light-absorbing or light-reflecting properties of enamel and dentin stains, resulting in apparent whitening. In-office bleaching, internally and externally, has been practiced since the early 20th century, employing peroxide compounds. At-home bleaching procedures were only introduced in the 1980s. Historically, a variety of bleaching materials has been tried, including substances such as oxalic acid or chlorine. Requirements for active tooth bleaching ingredients include a quick reaction with the stain components, fewer reactions with oral hard and soft tissues, ease of use, and an acceptable shelf life. Alkaline bleaching solutions may cause less demineralization damage than acidic solutions and are less likely to penetrate the pulp. Bleaching materials should cause as minimal oxidative damage to tissues as possible ( Fig. 27-1 ).

FIG. 27-1
Chemistry of tooth whitening with hydrogen peroxide. Breakdown of pigmented organic materials consisting of carbon ring structures with unsaturated, double carbon bonds to hydrophilic, nonpigmented carbon structures with saturated carbon bonds, resulting in effective whitening. Further degradation over this step may complete disintegration of the organic matrix with the release of carbon dioxide and water.
(Modified from Cohen S, Burns C: Cohen’s pathways of the pulp , ed 8, Part III, Chapter 21 , Fig. 21-1 . St. Louis, 2002, Mosby.)

Contemporary bleaching techniques rely on oxidative proc­esses that actively break down pigmenting molecules. Oxidation is initiated by active peroxide compounds. Peroxides and oxygen radicals are reactive free agents that are formed in all body cells that use oxygen. Reactive oxygen is, however, usually only found in low concentrations. Natural antioxidants, such as vitamin E, prevent the accumulation. Cell damage may occur if reactive oxygen reacts with iron or copper ions.

The active peroxides in concurrent bleaching techniques primarily derive from hydrogen peroxide and carbamide peroxide for external, vital bleaching and sodium peroxide for internal, nonvital bleaching. Hydrogen peroxide (H 2 O 2 ) is the simplest peroxide, and in its pure form is a colorless liquid of a slightly higher viscosity than water. It can be utilized for in-office as well as at-home bleaching procedures. An increase in temperature accelerates the speed of the bleaching reaction. Hydrogen peroxide is more effective as a bleaching agent at pH values that are close to the dissociation constant. Enzymes such as peroxidases can break down hydrogen peroxide into oxygen and water. High concentrations of hydrogen peroxide must be handled with great care. If accidentally brought into contact with soft tissues, it is caustic and may cause chemical burns by free oxygen radicals. For external bleaching procedures, the use of a rubber dam with additional blockout isolation around the gingival margins is mandatory to avoid iatrogenic complications. Typically, at-home concentrations range from 3% to 7.5%; however, some exceptionally strong concentrations can reach 14%. In-office concentrations may range from 25% to 38%. Hydrogen peroxide was shown not to induce significant changes in the organic and inorganic relative contents of enamel, but to whiten teeth by oxidizing the organic matrix.

Carbamide peroxide (CH 6 N 2 O 3 ), or urea hydrogen peroxide, will break down into carbamide and hydrogen peroxide in aqueous solution. It is an efficient bleaching agent. The carbamide portion urea is well tolerated by the human body. Carbamide peroxide is available as crystallized powder or white crystals that contain H 2 O 2 in a concentration of about 35%. Most common home bleaching products contain car­bamide peroxide at about 10% strength, but it can reach up to 30% (equivalent to 3.5% to 8.6% hydrogen peroxide). Car­bamide peroxide can be used for internal bleaching. At 35%, it shows very low extraradicular diffusion rates compared to hydrogen peroxide and sodium perborate. Common bleaching preparations may contain glycerin or propylene glycol, sodium stannate, phosphoric or citric acid, and flavor additives. Carbopol, a water-soluble polyacrylic acid polymer, may be added as a thickening agent. It prolongs the release of active peroxide. At room and oral temperatures, the reaction of carbamyl peroxide takes place at a slower rate compared to hydrogen peroxide. The release of oxygen from hydrogen peroxide occurs within seconds of contacting tooth surfaces, whereas carbamide peroxide remains active for 40 to 90 minutes.

Sodium perborate (NaBO 3 ) comes in different preparations, mostly as a stable, dry powder or as a gel. It is available as a monohydrate, trihydrate, and tetrahydrate, with varying contents of oxygen. Depending on the oxygen content of the preparation, the compounds have a different bleaching effi­ciacy. The perborate ion comprises 95% of the molecule and provides close to 10% of the available oxygen. Acids, water, and warm air initiate its decomposition to sodium metaborate, hydrogen peroxide, and nascent oxygen. The pH of sodium perborate solutions used for dental bleaching is alkaline. Because sodium perborate can be more easily controlled, it is considered safer to work with than hydrogen peroxide and more popular for intracoronal bleaching.

In an aqueous solution, due to heat or in an acidic environment, both carbamide peroxide and sodium perborate decompose and release hydrogen peroxide. Hydrogen peroxide then diffuses through enamel and dentin. Subsequently, the oxidative process provides for lightening of stains in comparison to the surrounding tooth structure. Double bonds of complex molecular chains with high molecular weight pigments are broken down by the chemical reactions with the free radicals. As a consequence, the change in pigment configuration and size leads to a change in the wavelength of the reflected light and the change of the stain to a lighter color. In a best-case scenario, this leads to an effective reduction or elimination of the discoloration. However, after the bleaching process a shade rebound effect may be observed, resulting from a reformation of double bonds of the molecules.

Walking Bleach Technique

The walking bleach technique was described early on as leaving a mix of sodium perborate and distilled water in the pulp chamber for a period of several days, with the access cavity sealed with a temporary restoration. Later on, the use of 30% hydrogen peroxide instead of water was suggested to provide better bleaching effectiveness. The mix of sodium perborate with water or, alternatively, anesthetic solution remains the most commonly used technique for internal bleaching of nonvital teeth. The enhancement of the mixture with 30% hydrogen peroxide is being used less due to concerns of cervical root resorption but remains an option for stains resistant to whitening that require stronger chemical compounds to achieve good bleaching results.

Walking Bleach Clinical Protocol

  • 1.

    Prior to initiating the bleaching procedure, a diagnosis must be made following thorough evaluation of the etiology and the origin of the stain. The patient must be informed about the history, the procedures involved in the treatment, the expected outcome of the procedure, and the potential for rediscoloration.

  • 2.

    The endodontic status of the tooth must be assessed clinically and radiographically. In the case of symptoms, the presence of periapical pathology, or an insufficient root filling, retreatment of the existing endodontic filling is advised, unless the apical periodontitis is on a tooth with a history of recent, well-executed root canal treatment or is verifiably in the process of healing.

  • 3.

    Existing coronal restorations need to be checked for quality and shade and replaced if defective. In certain situations, the reason for discoloration may be a leaking restoration or discolored filling materials. Replacement of a defective restoration and cleaning of the access chamber may resolve the discoloration.

  • 4.

    Clinical photographs should be taken at the beginning, throughout, and at the end of the treatment with the tooth next to a shade guide to act as a reference for the practitioner and the patient.

  • 5.

    Rubber dam isolation is mandatory. It is important to provide a seal at the gingival margin to prevent leakage of bleaching agents into the surrounding soft tissues. Depending on whether a single tooth or multiple teeth are being isolated, this may involve the placement of clamps, wedges, ligatures, floss, or light curing blockout material. Local or topical anesthesia may be applied if the patient is sensitive to the discomfort exerted during the isolation procedures.

  • 6.

    The access cavity needs to be prepared so that all restorative filling materials, root-filling material and sealer remnants, and necrotic pulp tissues remnants are completely removed. This procedure requires good visualization through cavity refinement and the elimination of all undercuts, especially in the area of pulp horns. The practitioner should exercise care to avoid labial perforations.

  • 7.

    Materials should be removed to a level just below the labial gingival margin. Solvents such as xylene, eucalyptus oil, or orange solvent may be used to help clean the pulp chamber. Also, rinsing the cavity with sodium hypochlorite was suggested for cleanliness and disinfection or, alternatively, with alcohol to reduce surface tension. Although some studies have recommended cavity treatment with 37% phosphoric acid or EDTA (ethylenediaminetetraacetic acid) to allow for deeper penetration of the bleaching agents, others have suggested that phosphoric acid was unnecessary and offered no better prognosis and no improvement in the bleaching effectiveness of either sodium perborate or a high concentration of hydrogen peroxide. Acidic pretreatment may increase the risk of adverse effects on the periodontium.

  • 8.

    A protective layer of at least a 2-mm thickness should be placed over the root-filling material. To avoid further pigmentation the protective layer should be white or tooth colored. Without this protective layer, bleaching materials may penetrate the root filling toward the apical foramen. Materials that had been suggested include glass-ionomer cements, intermediate restorative material (IRM), Cavit and Coltosol, resin composites, photo-activated temporary resin materials such as Fermit, zinc oxide–eugenol cements, polycarboxylate cements, and zinc phosphate cements. Cavit and IRM provide better sealing than zinc phosphate cement, and Cavit offers a better leakage barrier than IRM. Cavit and Coltosol also provided the most favorable seal when tightly compacted and proved to be superior to Fermit. A protective barrier at the cementoenamel junction (CEJ) will furthermore reduce the risk of cervical root resorption and damage to the periodontal ligament. Ideally, the vertical outline of the protective barrier should be 1 mm coronally to the CEJ to cover lingual, labial, and proximal CEJ areas. Clinically, however, this may be difficult to achieve in confined spaces. A barrier level with the labial CEJ will leave a substantial area of proximal dentinal tubules unprotected. Clinically, Cavit is also easily removable using ultrasonic instruments and chlorhexidine, thus minimizing the amount of tooth structure loss. Glass-ionomer cements may remain in place after the bleaching procedure is completed and do not need to be removed ( Figs. 27-2 and 27-3 ).

    FIG. 27-2
    Walking bleach technique: Placement of barrier material at the CEJ level, bleaching agent, and coronal seal with temporary filling material.

    FIG. 27-3
    Clinical case illustrating the walking bleach technique. A, Situation prior to endodontic treatment and internal bleaching. Discolored maxillary left canine due to pulp necrosis. B, Postoperative situation after endodontic treatment and internal bleaching using the walking bleach technique. C, Preoperative situation. D, Control radiograph after application of sodium perborate for the walking bleach technique. E, Labeling of part D showing placement of barrier material at the CEJ level, bleaching agent, and coronal seal with temporary filling material. F, Postoperative situation after bleaching, permanent coronal seal with adhesive restoration.
    (Courtesy Dr. Helmut Walsch, Munich, Germany.)
  • 9.

    Sodium perborate (tetrahydrate) is mixed with an inert liquid (distilled water, saline, or anesthetic solution) to achieve the consistency of wet sand. Mixing the paste instead with hydrogen peroxide is an option to accelerate the speed of the bleaching process, yet this technique is risky due to the increased possibility of cervical root resorption. If it is required, due to the severity of the stain, it should be used at 3% strength, and it should be refrained from a 30% solution. The long-term results of a sodium perborate and water mix do not significantly differ from mixes with hydrogen peroxide. A plastic instrument or amalgam carrier can be used to place the material in the pulp chamber. It is then carefully condensed with a plugger, without missing areas such as pulp horns ( Fig. 27-4 ).

    FIG. 27-4
    Clinical case illustrating clinical steps of the walking bleach technique. A, Situation prior to endodontic treatment and internal bleaching. Discolored maxillary left central incisor due to dental trauma. B, Postoperative situation after endodontic treatment and internal bleaching using the walking bleach technique. C, Access cavity after barrier placement. D, Application of sodium perborate. E, Temporary coronal seal with adhesive restoration.
    (Courtesy Dr. Mohammed Al-Harbi, Philadelphia, PA.)
  • 10.

    Excessive bleaching material should be removed, the paste carefully dapped with a cotton pellet without removing too much moisture, and a temporary filling material that is ideally 3 mm thick with well-sealing margins placed (Cavit, 3M ESPE, St. Paul, MN). Though some have advocated the use an acid-etched adhesive as a temporary filling to avoid recontamination, restaining, and to offer the best possible prevention from leaking walking bleach, this may not be practical in small cavities where it becomes difficult to selectively etch the enamel without the risk of opening dentinal tubules for hydrogen peroxide and the subsequent risk of cervical resorption. Moreover, because this procedure would have to be repeated at every visit, it would add to the amount of tooth structure loss. Any walking bleach remnants on the external tooth surfaces or the rubber dam isolation need to be removed to avoid irritation of the soft tissues.

  • 11.

    The rubber dam is removed and all tissues inspected.

  • 12.

    The patient should be informed about the procedure. Depending on the reaction of the stain to the bleaching agent, the time to expect results may vary. Usually, a patient should be instructed to return between 3 to 10 days to evaluate the results and to change the walking bleach if necessary. To avoid overbleaching, the patient needs to be instructed to self-monitor the color status of the tooth and to report back earlier than the scheduled appointment date if the color change has reached the desired result or if the temporary filling material is starting to wash out. Although a rarely documented event, it was advocated to instruct the patient about an increased susceptibility to tooth fracture in the time that the tooth is filled with a bleaching agent and not a supportive buildup.

  • 13.

    If desired results cannot be obtained, a mix with 3% H 2 O 2 can be considered. However, the patient needs to be informed about the risks and that most good bleaching results can be accomplished by a sodium perborate and water/anesthetic mix. If the aesthetic outcome with the results is acceptable, a potential for resorption may be minimized.

  • 14.

    If a clinical case does not show improvement after three to four attempts, the diagnosis and treatment plan should be reevaluated for a different etiology.

  • 15.

    At the conclusion of the bleaching procedure, a postoperative radiograph should be taken to check for any adverse effects of the bleaching agents. A permanent adhesive restoration should be placed about 1 to 3 weeks after the last appointment (see next section, Permanent Restoration of Teeth Following Internal Bleaching ).

  • 16.

    The patient should be scheduled for yearly follow-ups to include a clinical examination and periapical radiographs.

Thermocatalytic Bleaching

Heat-activated Superoxol had been advocated for its increased bleaching effect for internal bleaching of endodontically treated teeth. Hydrogen peroxide with a concentration of 30% to 35% is placed in the pulp chamber and activated via heat application with electric heating devices or special lamps. All preparatory steps follow the clinical protocol described previously for the walking bleach technique. However, in lieu of placing a sodium perborate/water mix, the pulp chamber is filled with 30% to 35% hydrogen peroxide and a heating device applied (e.g., Touch’n Heat, System B; SybronEndo, Orange, CA; SuperEndo Alpha, B&L Biotech, Fairfax, VA). The heat application will create foaming of the hydrogen peroxide, with a subsequent release of free radical oxygen. This procedure is repeated in three to four office visits. In addition, some protocols advocate the placement of 30% to 35% hydrogen peroxide in the pulp chamber between the chair-side appointments. Temporary filling placement follows the same steps as outlined earlier for the walking bleach technique. If this technique is used, great care needs to be taken to avoid overheating of teeth, periodontal ligament, and gingival tissues. Regular cooling breaks are recommended. Products such as Vaseline, Orabase, or cocoa butter have been suggested for additional thermal insulation. However, due to the increased risk of cervical root resorption when using this clinical technique, the walking bleach technique is seen as more favorable today. If a decision is made to apply the thermocatalytic technique, the patient must be thoroughly informed about the risks and potential long-term consequences.

Permanent Restoration of Teeth Following Internal Bleaching

A good permanent restoration is one of the foundations of long-term success, as it prevents coronal microleakage from the access cavity and avoids the risk of renewed discoloration through open dentinal tubules. It is generally accepted that an acid-etched and bonded composite resin restoration provides the most favorable results. For preexisting resin composite restorations, a rebonding of the filling has been suggested to reduce the risk of microleakage at the dentinal margins after bleaching with 15% carbamide peroxide. The restoration must be placed at a depth that provides both an adequate seal for the access cavity as well as incisal support. The placement of a white base material below the resin restoration was viewed favorably in situations where the composite resin restoration may compromise the translucency of the tooth. Lighter shade composites were suggested for teeth, with a not entirely satisfactory bleaching result. Consensus exists that the adhesive bond strength between glass-ionomer cements and composite resins to dentin and enamel is temporarily compromised following bleaching procedures by remnants of peroxide or free oxygen, which inhibit resin polymerization. Several remediation techniques have been suggested to overcome the negative influence of hydrogen oxide–containing bleaching agents, including dehydrating agents such as 80% alcohol and the use of acetone-containing adhesives, the application of sodium hypochlorite to dissolve remnants of peroxide, catalases, the antioxidant sodium ascorbate, or the use of alpha-tocopherol. At least 1 week of contact with an aqueous solution was recommended to achieve adequate bonding. Optimal bonding to bleached dentin and enamel was shown to be reestablished after 3 weeks. Calcium hydroxide medication in the pulp cavity was advocated to achieve a buffering effect for an acidic pH that may be present after internal bleaching ; however, it may be unnecessary after a walking bleach technique, due to the weaker nature of sodium perborate compared to Superoxol. Light curing of the composite resin restoration should occur from labial so that shrinkage toward the axial walls can reduce a potential risk of microleakage.

External Bleaching

External bleaching may involve single teeth or entire arches. Whereas internal bleaching requires endodontic treatment of the tooth, external bleaching can also be applied to vital teeth. Steady advancements have been made in external bleaching techniques since its inception. Various techniques exist, including in-office and at-home methods.

In-Office External Bleaching

The in-office or chair-side techniques are completely in the hand of the dental professional. Almost all techniques involve the application of hydrogen peroxide gels of concentrations between 25% and 38%. Liquid solutions at higher concentrations are associated with higher complication rates of soft tissue damage, as they are more difficult to control in terms of handling. Furthermore, high concentrations of hydrogen peroxide solutions are thermodynamically unstable and may explode if not stored in dark bottles in a refrigerator.

Although early techniques also employed heat activation, electric currents, or combinations with other chemicals to make hydrogen peroxide more effective, contemporary techniques commonly use bleaching gels applied on their own or in combination with light activation by special lamps. Patients should undergo a hygiene treatment with cleaning and polishing of the tooth surfaces prior to external bleaching, as well as a careful evaluation of the nature of the stain or the possibility that the discoloration is related to an existing restoration.

If external bleaching is indicated, the treatment involves the placement of a rubber dam, as described in the protocol for the walking bleach technique. Great care must be taken to avoid soft tissue damage. If liquid hydrogen peroxide solutions and no gels are used, the additional placement of gauze to act as a reservoir for hydrogen peroxide is recommended to keep the solution in the proximity of the teeth. More gauze can be placed underneath the rubber dam as an additional safety to catch excess solution before it can damage gingiva, mucosa, or lips. However, these complications can be greatly reduced by a gel application with or without light activation.

Light sources used for bleaching include conventional ultraviolet (UV) bleaching lights, tungsten-halogen and Xe-halogen lights, plasma arc lamps, light-emitting diodes (LED), or laser lights. The wavelengths of the various light sources may range from the high ultraviolet to low visible blue light spectra, and invisible infrared light, such as employed by a CO 2 laser. Although all of these lights have been used to activate the bleaching agent or expedite the whitening effect, there are great differences among them. Limited research on bleaching lights exists, with sometimes controversial results. Although some studies emphasized certain effects after light-activated bleaching, others reported no differences between teeth bleached with and without light activation. In the 1980s, the Fuji HiLite dual-cure material containing 35% hydrogen peroxide was used. When the paste was mixed, it had a green color that would turn white upon activation with a standard UV light upon the release of oxygen. In comparison to other light activation techniques, this was a more time-consuming process and less comfortable for the patient. In addition to light activation alone, various photocatalysts were suggested, including methylene blue and ultraviolet or visible light-activated titanium dioxide.

Tungsten-halogen curing lights are the standard dental curing lights that provide heat and stimulate the initiation of the chemical reaction by activating light-sensitive chemicals in the bleaching agent. Depending on manufacturer recommendations, the individual bleaching time with activation of the gel is 30 to 60 seconds per application per tooth, which is rather time consuming for the patient and the dental professional because up to three passes are recommended. Some products available were based on a premixed 35% hydrogen peroxide gel with carotene that converts light energy to heat upon activation and increased the breakdown of the bleaching agent into active free radicals. Xenon-halogen curing lights are newer generation dental curing lights used to the same effect. Some specialized bleaching lights offer full-arch adaptors. A randomized clinical trial of in-office tooth whitening identified blue light–activated bleaching as the one technique with results most favored by patients.

Xenon plasma arc lamp systems are primarily based on thermal activation and the activation of chemical catalysts in the bleaching gel. The light employed is of high intensity, produces great heat energy, and limits the application to 3-second intervals for up to three passes. Due to the high heat intensity, there is a potential for dental trauma to the pulp and the surrounding tissues, which is why these lights have to be used with great care. Some manufacturers produced lights that allowed an on-off mode setting over 5-second bursts to have a safer and lower-intensity output.

LED lamps emit cold blue light with a wavelength of around 465 nanometers, which allows activation of hydrogen peroxide gels and accelerates the bleaching process. LED lights are placed close to the patient’s teeth for 15- to 20-minute treatments, which may have to be repeated up to three times. Cosmetic specialists with no dental background have adopted this method of bleaching because it offers low risk, as no heat activation is involved.

Lasers are used for tooth bleaching at 830 nm and 980 nm wavelengths for tooth bleaching in combination with 30% to 35% hydrogen peroxide gel. Gels prepared for laser activation may contain fumed silica and a blue dye, the latter absorbing the laser wavelength leading to an increase in temperature and a controlled breakdown of the hydrogen peroxide. Gels are commonly applied in a 2- to 3-mm thickness over the teeth. An application of 1 to 2 W of laser energy for 30 seconds per tooth is recommended. Dental professionals and patients are required to wear protective eyewear while operating lasers. Some studies reported no significant advantage to using laser light for bleaching, whereas others showed a decrease in color regression after a combination of at-home bleaching with an in-office laser-assisted bleaching session in comparison to an at-home bleaching regimen on its own.

“Power Bleaching”

The technique normally termed power bleaching refers to accelerated vital in-office tooth whitening procedures that employ either xenon plasma arc-curing lights or lasers. Either dental hygienists or dental assistants may carry out this procedure, depending on individual licensing issues state by state. In particular, the use of laser lights might be more strictly regulated and may not be allowed to dental professionals other than the dentist. For a delegated procedure, liquid rubber dam is often applied in lieu of a sheet of rubber dam, which would require active retention techniques, such as wedges, floss, or ligatures. Liquid rubber dam can be applied easier without assistance, but it does not give additional protection to gingival tissues or the mucosa.

Power Bleaching Clinical Protocol

  • 1.

    Prior to initiating the bleaching procedure, a diagnosis must confirm that the discolorations can be resolved by external bleaching. The patient must be informed about the history, the procedures involved in the treatment, the expected outcome of the procedure, and the potential for rediscoloration.

  • 2.

    A thorough clinical examination should be performed to detect caries, developmental defects, endodontic or periodontal diseases, and other pathologic conditions in the oral cavity. Existing restorations need to be checked for quality and shade and replaced if defective. For certain teeth, the reason for discoloration may be leaking restorations or discolored filling materials. Replacement of a defective restoration may resolve most of the discoloration.

  • 3.

    Patients should have a hygiene appointment prior to the bleaching session to check for sound gingival tissues and ensure that areas to be bleached are free of calculus or plaque.

  • 4.

    Clinical photographs should be taken in the beginning, throughout, and at the end of the treatment with the tooth next to a shade guide to act as a reference for the practitioner and the patient.

  • 5.

    The patient and dental professionals should wear proper protective eyewear (sunglasses). The patient should be prepared to signal if a tingling sensation to the gingiva, mucosa, lips, or teeth is felt or the temperature is perceived as too hot. As a precaution, vitamin E capsules, a powerful antioxidant, should be ready at hand. In case of an emergency, these can be cut open and the oil inside the capsules applied to the injured tissues with a cotton pellet.

  • 6.

    The teeth should be cleaned again with rubber cups and pumice. The cheeks should be retracted with photo retractors or cotton rolls. The cotton rolls serve as an additional safety feature if any hydrogen peroxide is leaking. Rubber dam isolation is mandatory. This can be either liquid rubber dam (light-cured resin dam) around the gingival margins or ligated sheet rubber dam. Liquid rubber dam bears a higher risk of tissue injury. It is important to create a tight seal at the gingival margin to prevent leakage of bleaching agents. If a sheet rubber dam is used, the inversion of the rubber dam in the sulcus with an air syringe followed by dental floss ligature is recommended.

  • 7.

    The power bleach gel is mixed according to the manufacturer’s recommendation and applied on the labial surfaces of the teeth in a 2- to 3-mm thickness with a disposable brush.

  • 8.

    Depending on the light source, each individual tooth is exposed for up to three passes for 3 to 10 s, according to manufacturer’s recommendations. The gel may stay on the teeth for another 3 to 5 minutes without light activation.

  • 9.

    The gel should be removed with a wet gauze and copious amounts of water, then cleaned with pumice for a second time, and rinsed again to ensure all remnants of the bleaching gel were removed.

  • 10.

    The rubber dam and any remaining cotton rolls and retractors are removed. Water rinses are used again, and all tissues inspected.

  • 11.

    The teeth should be polished and a neutral pH sodium fluoride gel applied.

  • 12.

    The patient should be informed about the procedure. Depending on the individual situation, results may vary. The patient should be instructed that increased sensitivity of the teeth may be present for 2 to 3 days.

  • 13.

    The patient ought to be instructed to refrain from tobacco, coffee, tea, cola, and wine for a period of 2 weeks.

At-Home External Bleaching

For patients who do not want to undergo an in-office procedure, the possibility of at-home external bleaching with custom-made bleaching trays exist. These may be readily available from a pharmacy, requiring only crude adaptation after softening in hot water, or can be fabricated in a dental laboratory. Over-the-counter products most commonly come with bleaching gels, although some come with pastes. Some products are offered as simple, low-strength hydrogen peroxide strips or pastes that can be brushed onto the teeth. Occasionally, pre-rinses are offered. However, these may come at a rather acidic pH, as these solutions may become unstable more easily.

Professional home bleaching involves the fabrication of a well-adapted custom tray after impressions are taken and models are poured. The patient will wear gel loaded in a tray that slowly releases the bleaching agents for several hours or overnight every day for 2 to 6 weeks until a satisfactory result has been achieved.

Trays are usually made using alginate impressions. Upon delivery, trays must be checked for fit, smoothness at the margins, and occlusion. The patient should place several drops of bleaching gel into the tray before every application. The most common bleaching agent for at-home bleaching is 10% to 22% carbamide peroxide with an effective yield of 4% to 7.5% hydrogen peroxide. Patients who wear the trays during the daytime may choose to replace the gel every 2 hours. If any disturbance (e.g., thermal sensitivity, abnormal taste, or tissue irritation) occurs, the patient should stop the procedure and seek advice from the dentist. Patients who use the trays in the daytime should be seen once per week for 3 weeks; nighttime users should be seen every other week for 6 weeks.

The success of at-home bleaching mostly depends on the patient’s cooperation. Risks include potential compliance issues and the possibility of overuse of the bleaching agent. Results with at-home bleaching techniques tend to remain stable for 1 to 10 years.

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Apr 18, 2020 | Posted by in General Dentistry | Comments Off on Bleaching Procedures
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