After reading this chapter, the student should be able to:
Identify the causes and nature of tooth discoloration.
Describe means of preventing tooth discolorations.
Differentiate between dentin and enamel discolorations.
Evaluate both the short-term and long-term prognoses of bleaching treatments.
Explain the mechanism of tooth bleaching.
Select the bleaching agent and technique according to the cause of discoloration.
Describe each step of the internal “walking bleach” technique.
Select the appropriate method to restore the access cavity after tooth bleaching.
Describe how bleaching agents may alter tooth structures.
Recognize the potential adverse effects of tooth bleaching and discuss means of prevention.
Bleaching discolored teeth may be internal (within the pulp chamber) or external (on the enamel surface) and involve various approaches. The objectives of treatment are to reduce or eliminate discoloration, improve the degree of coronal translucency, and alleviate present and prevent future clinical signs and symptoms.
To better understand bleaching procedures, you should know the techniques involved, understand the causes of discoloration, recognize the location of the discoloring agent, and apply the correct treatment modality. Also important is the ability to predict the outcome of treatment (i.e., how successfully various discolorations can be treated and how long the esthetic result will last). Therefore before attempting to correct discoloration, there must be a diagnosis (to determine the cause and location of the discoloration), a treatment plan (to select the appropriate bleaching material and technique), and a prognosis (to anticipated short- and long-term success). Patients must be informed of these factors before undergoing the procedure; any discoloration treatment is tempered by the explanation that bleaching bears a certain degree of unpredictability in matching the esthetics of the tooth involved fully and that substantial improvement may or may not occur. However, with proper recognition of the causes of discoloration and careful treatment protocol, no irreversible damage to the crown or root occurs ( ).
Causes of Discoloration
Tooth discolorations may occur during or after enamel and dentin formation. Some discolorations appear after tooth eruption, and others are the result of dental procedures. Acquired (natural) discolorations may be superficial and located on the surface of the tooth or may be embedded and be physically incorporated into tooth hard tissues. Sometimes they result from flaws in enamel formation and structure or a traumatic injury. Inflicted (iatrogenic) discolorations, resulting from certain dental procedures, are usually incorporated into tooth structure and are largely preventable.
Acquired (Natural) Discolorations
Although microorganisms are the main cause of pulpal injury, mechanical or chemical irritation of the pulp may also result in tissue necrosis. Pulp necrosis can occur via stagnation of the vasculature and formation of microabscesses. Red blood cells stagnated in the vasculature will lyse and lead to accumulation of hemoglobin and other pulp breakdown byproducts. These tissue disintegration byproducts are colored compounds that may permeate tubules to stain surrounding dentin. The degree of discoloration is likely related to how long the pulp has been necrotic. , The longer the discoloration compounds are present in the pulp chamber, the greater the discoloration. This type of discoloration can be bleached internally, usually with both short- and long-term success ( Fig. 17.1 ).
Intrapulpal hemorrhage is usually associated with an impact injury to a tooth that results in disrupted coronal blood vessels, hemorrhage into the pulp space, stasis of this extravasated material, and lysis of erythrocytes. Erythrocyte lysis leads to an accumulation of disintegration products, such as iron sulfides. These iron sulfides may permeate dentinal tubules to stain surrounding dentin. Discoloration tends to increase with time.
If the pulp becomes necrotic, the discoloration usually remains. If the pulp survives, the discoloration may resolve and the tooth regains its original shade. Sometimes, mainly in young individuals, a discolored tooth can respond unpredictably to vitality tests. Therefore you should not rely on a single clinical test to establish your diagnosis of the case. If intracoronal discoloration remains despite diagnostic testing indicating presence of a healthy pulp and normal periapex, a porcelain veneer can be considered. Although more invasive, sometimes significantly darker stain may necessitate consideration for elective root canal therapy to remove stain that would not be effectively hidden under a coronal esthetic restoration.
Internal bleaching of discoloration after intrapulpal hemorrhage is usually successful both short term and long term.
Calcific metamorphosis, also known as pulp canal obliteration , is extensive formation of tertiary dentin in the pulp chamber that causes circumferential narrowing of the pulp chamber and root canal. This phenomenon usually follows an impact injury that did not result in pulp necrosis. There is likely temporary disruption of the blood supply with partial destruction of odontoblasts. Odontoblasts are usually replaced by cells that rapidly form irregular dentin on the walls of the pulp chamber and root canal space. As a result, the crowns take on a “flat” and yellow or yellow-brown discolored appearance as they gradually decrease in translucency ( Fig. 17.2 ). The pulp usually remains vital and does not require root canal treatment. However, routine follow-up is recommended as a result of potential of pulp necrosis after a traumatic injury.
If the patient desires color correction, external bleaching should be attempted first. If this is unsuccessful, root canal treatment can be performed, and internal bleaching done. The esthetic prognosis for such treatment is not always predictable. The unpredictability of this procedure results from the bleaching agent addressing discolored pigmentation in the regular structure of the dentinal tubules but not in the bulk of irregular dentin from the aberrant calcification.
In older patients, color changes in the crown occur physiologically as a result of extensive dentin apposition and thinning of and optical changes in the enamel. Food and beverages also have a cumulative discoloring effect because of the inevitable cracking and other changes on the enamel surface and in the underlying dentin. In addition, previously applied restorations that degrade over time cause further discoloration. Bleaching is usually external because the discoloration is primarily on the enamel surface. Success may vary, depending on the causal factor of discoloration.
The most commonly bleached teeth are the maxillary incisors. Maxillary central incisors comprise 69% of internally bleached teeth, whereas maxillary lateral incisors comprise 20% of bleached teeth.
Discolorations may also result from developmental defects or from substances incorporated into enamel or dentin during tooth formation.
Ingestion of excessive amounts of fluoride during tooth formation produces defects in mineralized structures, particularly enamel matrix, with resultant hypoplasia. The severity and degree of subsequent staining generally depend on the degree of hypoplasia, which depends in turn on the patient’s age and the amount of fluoride ingested during odontogenesis. The teeth are not discolored on eruption but may appear chalky. Their surface, however, is porous and gradually absorbs stains from chemicals in the oral cavity.
Because the discoloration is in the porous enamel, such teeth are treated externally. Esthetic success depends mainly on the degree and duration of the discoloration. Some regression and recurrence of discoloration tend to happen but can be corrected with future rebleaching.
Administration or ingestion of certain drugs or chemicals (many of which have not yet been identified) during tooth formation may cause discoloration, which is occasionally severe.
The most common and most dramatic discoloration of this type occurs after tetracycline ingestion, usually in children. Discoloration is bilateral, affecting multiple teeth in both arches. It may range from yellow through brownish to dark gray, depending on the amount, frequency, and type of tetracycline, and the patient’s age (stage of development) during administration.
Tetracycline discoloration has been classified into three groups according to severity. First-degree discoloration is light yellow, light brown, or light gray and occurs uniformly throughout the crown without banding. Second-degree discoloration is more intense and is also without banding. Third-degree discoloration is very intense, and the clinical crown exhibits horizontal color banding. This type of discoloration usually predominates in the cervical region. The location of the band correlates to the part of the dentin that was undergoing formation at the time of systemic tetracycline ingestion. It is therefore recommended to limit systemic tetracycline use in patients with active permanent tooth development.
Tetracycline binds to calcium, which then is incorporated into the hydroxyapatite crystal in both enamel and dentin. Most of the tetracycline, however, is found in dentin. Chronic sun exposure of teeth with the incorporated drug may cause formation of a reddish purple tetracycline oxidation byproduct, resulting in further discoloration of permanent teeth.
A phenomenon of adult-onset tetracycline discoloration has also been reported. It occurs occasionally in mature teeth in patients receiving long-term minocycline therapy, which is usually given for control of cystic acne. The discoloration is gradual because of incorporation of minocycline in continuously forming dentin. Staining generally is not severe.
Two approaches have been used for bleaching tetracycline discoloration. The first, which involves bleaching the external enamel surface, is limited to lighter, yellowish discoloration and requires multiple appointments to achieve a satisfactory result. The second, root canal treatment followed by internal bleaching, is a predictable procedure, is useful for all degrees of discoloration severity (especially linear-band type discoloration), and has proved successful in both the short term and long term.
Defects in Tooth Formation
Defects in tooth formation are confined to the enamel and are either hypocalcific or hypoplastic. Enamel hypocalcification is common, appearing as a distinct brownish or whitish area, often on the facial aspect of a crown. The enamel is well formed and intact on the surface and feels hard to the explorer. Both the whitish and the brownish spots are amenable to correction externally with good results.
Enamel hypoplasia differs from hypocalcification in that the enamel in the former is defective and porous. This condition may be hereditary (amelogenesis imperfecta) or may result from environmental factors. In the hereditary type, both deciduous and permanent dentitions are involved. Defects caused by environmental factors may involve only one or several teeth. Presumably during tooth formation the matrix is altered and does not mineralize properly. The porous enamel readily acquires stains from the oral cavity. Depending on the severity and extent of hypoplasia and the nature of the stain, these teeth may be bleached externally with some degree of success.
Blood Dyscrasias and Other Factors
Various systemic conditions may cause massive lysis of erythrocytes. If this occurs in the pulp at an early age, blood disintegration products are incorporated into the forming dentin causing discoloration. An example of this phenomenon is the severe discoloration of primary teeth that usually follows erythroblastosis fetalis. This disease in the fetus, or newborn, results from Rh incompatibility factors that lead to massive systemic lysis of erythrocytes. Large amounts of hemosiderin pigment then stain the forming dentin of the primary teeth. This discoloration is not correctable by bleaching. However, this type of lysis is now uncommon because of new preventive measures.
High fever during tooth formation may result in linear defined hypoplasia. This condition, known as chronologic hypoplasia, is a temporary disruption in enamel formation that results in a banding type of surface defect that acquires stain. Hyperbilirubinemia, thalassemia, and sickle cell anemia may cause intrinsic bluish, brown, or green discolorations. Amelogenesis imperfecta may result in yellowish or brownish discolorations. Dentinogenesis imperfecta can cause brownish violet, yellowish, or gray discoloration. Porphyria, a metabolic disease, may cause deciduous and permanent teeth to show a red or brownish discoloration. These conditions are also not amenable to bleaching and should be corrected by minimally invasive restorative means.
Other staining factors related to systemic conditions or ingested drugs are rare and may not be identifiable.
Inflicted (Iatrogenic) Discolorations
Discolorations caused by various chemicals and materials used in dentistry are usually avoidable. Many of these discolorations respond well to bleaching, but some are more difficult to correct by bleaching alone.
Endodontically Related Discolorations
Obturating materials are the most common and severe cause of single tooth discoloration. Incomplete removal of materials from the pulp chamber upon completion of treatment often results in dark discoloration ( Figs. 17.3 and 17.4 ). Removing all obturation materials to a level just cervical to the gingival margin can prevent such discoloration. Sometimes, removal of the obturating material 1 to 2 mm further apically is required. Common obturating materials that can lead to stain are sealer remnants, whether of the zinc oxide–eugenol type or resins. These materials may also darken with time. Sealer remnants gradually cause progressive coronal discoloration. The prognosis of bleaching in such cases depends on the components of the sealer. Sealers with metallic components often do not bleach well, and the bleaching effect tends to regress with time.
Remnants of Pulpal Tissue
Pulp fragments remaining in the crown, usually in pulp horns, can cause gradual discoloration. Pulp horns must be exposed and cleaned during access preparation to ensure removal of pulpal remnants and to prevent retention of sealer at a later stage. Internal bleaching in such cases is usually successful.
Several medicaments have the potential to cause internal discoloration of the dentin. , , , These intracanal medications, sealed in the root canal space, are in direct contact with dentin, sometimes for long periods, allowing penetration to dentin tubules and oxidization. These compounds have a tendency to discolor the dentin gradually. Most such discolorations are not marked and are readily and permanently corrected by bleaching. However, discoloration by intracanal medication containing iodoform tends to be more severe.
Restorations are generally metallic or composite. The reasons for discoloration (and therefore the appropriate correction) are quite different.
Amalgam is the worst offender because its dark metallic elements may turn dentin dark gray. If used to restore an access preparation, amalgam often discolors the crown ( Figs. 17.4 and 17.5 ). Such discolorations are difficult to bleach and tend to recur with time. However, bleaching them is worth a try. The result may be an improvement that satisfies the patient. The use of amalgam for tooth restoration is gradually decreasing in many parts of the world.
Discoloration from inappropriately placed metal pins and prefabricated posts in anterior teeth may sometimes occur. This is caused by metal that is visible through the composite or tooth structure. Occasionally, discoloration from amalgam is also caused by visibility of the restoration through translucent tooth structure. In such cases, replacement of old metallic material with an esthetically pleasing restoration will suffice.
Microleakage of composites causes discoloration. Open margins may permit chemicals to permeate gaps between the restoration and tooth structure to stain the underlying dentin. In addition, composites may become discolored with time and alter the shade of the crown. These conditions can sometimes be corrected by replacing the old composite with a new, well-sealed esthetic restoration. In many cases, internal bleaching is carried out first with good results ( Fig. 17.6 ).
Bleaching chemicals may act as either oxidizing or reducing agents. Most bleaching agents are oxidizers, and many preparations are available. Commonly used agents are solutions of hydrogen peroxide of different strengths, sodium perborate, and carbamide peroxide. Sodium perborate and carbamide peroxide are chemical compounds that are gradually degraded to release low levels of hydrogen peroxide. Hydrogen peroxide and carbamide peroxide are mainly indicated for external bleaching, whereas sodium perborate is mostly used for internal bleaching. All have proved effective.
Hydrogen peroxide is a powerful oxidizer that is available in various strengths, but 30% to 35% stabilized solutions (Superoxyl, Perhydrol) are the most common. These high-concentration solutions must be handled with care because they are unstable, lose oxygen quickly, and may explode unless they are refrigerated and stored in a dark container. Also, these are caustic chemicals and will burn tissue on contact.
Although highly concentrated hydrogen peroxide bleaches quickly, other chemicals that release much lower levels of peroxide are available; usually they bleach effectively with longer application periods.
Sodium perborate is available in powder form or in various commercial proprietary combinations. , When fresh, it contains about 95% perborate, corresponding to 9.9% available oxygen. Sodium perborate is stable when dry, but in the presence of acid, warm air, or water, it decomposes to form sodium metaborate, hydrogen peroxide, and nascent oxygen. Various types of sodium perborate preparations are available: monohydrate, trihydrate, and tetrahydrate. They differ in oxygen content, which determines their bleaching efficacy. Commonly used sodium perborate preparations are alkaline; their pH depends on the amount of hydrogen peroxide released and the residual sodium metaborate.
Sodium perborate is more easily controlled and safer than concentrated hydrogen peroxide solutions. , , , , , Therefore in most cases, it should be the material of choice for internal bleaching.
Carbamide peroxide is usually available in concentrations varying between 3% and 15%. Popular commercial preparations contain about 10% carbamide peroxide and have an average pH of 5 to 6.5. They usually also include glycerin or propylene glycol, sodium stannate, phosphoric or citric acid, and flavor. In some preparations, Carbopol, a water-soluble resin, is added to prolong the release of active peroxide and to improve shelf life. Ten percent carbamide peroxide breaks down into urea, ammonia, carbon dioxide, and approximately 3.5% hydrogen peroxide.
Carbamide peroxide and hydrogen peroxide–based systems are mostly used for external bleaching and have been associated with varying degrees of alterations to dental hard tissues and surrounding mucosa. , They may adversely affect the bond strength of composite resins and their marginal seal. Therefore these materials must be used with caution and usually under strict supervision of the dentist.
In the past, a preparation of sodium peroxyborate monohydrate (Amosan), which releases more oxygen than does sodium perborate, was recommended for internal bleaching. Today, this product is not available in all countries, and its clinical use is less common.
Sodium hypochlorite is a common root canal irrigant that is commonly available commercially as a 3% to 8% household bleach. Although used as a household bleaching agent, it does not release enough oxidizer to be effective and is not commonly used for routine tooth bleaching.
Tooth discoloration under existing composites occurs because of:
Open margins of the restoration allowing leakage
Discoloration of the composite itself over time
Excess bonding agent becoming more opaque with time
All of the above
A and B only
In order to prevent discoloration from remaining pulpal tissue, the operator should:
Access the entire pulp chamber and pulp horns to completely débride the tissue
Rely primarily on chemical débridement
Ensure that sealer does not contact any tissue remnants, as sealer will only discolor if in contact with pulp tissue remnants
All of the above
A and B only
The condition caused by a temporary disruption in enamel formation resulting in a banding type of surface defect acquiring stain is known as:
Progressive dentinal hypoplasticity
Chromatic chronologic dimorphism
Acute progressive chromatism
All of the above
When considering internal bleaching of a tooth with pulp necrosis, which of the following is correct:
Tissue disintegration products leach into dentinal tubules to cause stain
The degree of discoloration is related to the duration of pulp necrosis
Dark discolorations have only short-term success when bleached
All of the above
A and B only
What is the current recommended bleaching material used for the “walking bleach” technique?
5.25% sodium hypochlorite
30% hydrogen peroxide
A and B only