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.

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 ).

  

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

  

  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 ).

  

  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.

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.