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2 Etiology of Discoloration in Endodontically Treated Teeth
J. Perdigão et al.
Systemic Causes of Posteruptive Intrinsic Stains
The developing dentition can be affected by a number of systemic factors, including
metabolic and genetic diseases that cause intrinsic tooth discoloration (Plotino et al.
2008). Systemic factors also include drug-induced discolorations, including those
from the intake of antibiotics and excess fluoride. In the case of fluoride its source
can be either iatrogenic or from natural sources, such as drinking water.
Although most publications refer to aging as a local cause of intrinsic discoloration, the physiological continuous deposition of secondary dentin throughout the
life of an individual may be considered both a systemic and a local cause of intrinsic
discoloration, as reactionary tertiary dentin forms in response to external stimuli,
such as tooth attrition and bacteria from caries lesions. The deposition of both secondary dentin and tertiary dentin results is a narrower pulp space with time. Thicker
dentin affects the light-transmitting properties of teeth, resulting in a gradual darkening of the tooth and increased opacity. In addition, the chemical structure and
physical properties of dental hard tissues change over time.
Local Causes of Posteruptive Intrinsic Stains
Local causes of posteruptive intrinsic stains include intrapulpal hemorrhage, residual
pulpal tissue after endodontic therapy, calcific metamorphosis, endodontic materials,
restorative materials such as amalgam, and root resorption. Other less frequent causes
are trauma to developing teeth and periapical infection of primary teeth (Hattab et al.
1999). Besides being responsible for posteruptive pigmentation of vital teeth (Chap.
6), the antibiotic minocycline also causes discoloration of nonvital teeth. In one case,
minocycline was utilized in the root canal as a component of antibiotic paste resulting
in blue discoloration of immature necrotic permanent teeth in children (Dabbagh et al.
2002). In another case, minocycline was applied as a component of a triple antibiotic
mixture inside a root canal of a tooth with a necrotic pulp, as an attempt to disinfect
the root canal system for revascularization. Minocycline resulted in tooth discoloration 6 weeks after the triple antibiotic paste had been applied (Kim et al. 2010).
Necrotic pulps may cause tooth discoloration as a result of the decomposition of
the pulpal tissues producing colored byproducts that infiltrate the dentinal tubules.
Discoloration related to improper endodontic treatment may be caused by trauma
inflicted during pulp extirpation or obturation materials left in the pulp chamber.
Another cause of discoloration in endodontically treated teeth is the residual pulp
tissue left in the pulp horns when the access to the pulp chamber is under-prepared
(Brown 1965; Faunce 1983). Evidence suggests that stains in endodontically treated
teeth are not just confined to the pulp chamber, but they penetrate into the dentin
substrate showing through dentin and enamel (van der Burgt and Plasschaert 1986).
Fitch (1861) stated, “the disintegration of the red corpuscles of the blood is
another source of discoloration. The hematine, or iron, which is supposed to constitute the pigment of these globules, passes readily into the tubules of the dentine
from the pulp chamber of the tooth, whenever the red disks are disintegrated, and
Intracoronal Whitening of Endodontically Treated Teeth
the discoloration becomes more or less permanent. These red globules may be dissolved or broken up.” Spasser (1961) reported that “in many cases, the hemolysis
of red blood cells with the release of hemoglobin, especially when associated with
hemorrhage following pulp extirpation or trauma” was responsible for the discoloration of endodontically treated teeth. More recently other authors have corroborated this theory. Diffusion of blood components into the dentinal tubules caused
by pulp extirpation or traumatically induced internal pulp bleeding is one of the
causes for discoloration of nonvital teeth (Arens 1989). Products of blood (erythrocytes) decomposition, such as hemosiderin, release iron. The iron can be transformed to ferric sulfide with hydrogen sulfide produced by bacteria, which causes
a dark brownish discoloration of the tooth (Brown 1965; Glockner et al. 1999;
Attin et al. 2003). Other end products of hemoglobin decomposition, biliverdin and
bilirubin, are themselves known causes of color alteration in the skin and mucosae,
being responsible for jaundice in some systemic diseases (Shibahara et al. 2002;
Coronal discoloration of endodontically treated teeth may also be caused by endodontic sealers (Fig. 8.2), such as Grossman’s cement and AH26 silverfree (Dentsply
Caulk) (van der Burgt and Plasschaert 1985; van der Burgt et al. 1986). Temporary
restorative materials, such as classical ZOE, Cavit (3M ESPE), and I.R.M. (Dentsply
Caulk), also result in discoloration of endodontically treated teeth (van der Burgt
et al. 1986). Two mineral trioxide aggregate (MTA)-based endodontic materials,
ProRoot MTA (Dentsply Tulsa Dental Specialties) and MTA Angelus (Angelus
Indústria de Produtos Odontológicos), have also been reported to cause tooth
Fig. 8.2 Clinical case of a recent discoloration (a) caused by endodontic sealer (b) in the pulp
chamber. This tooth lighten with the walk bleach technique using sodium perborate mixed with
distilled water after only one session (c, d)
J. Perdigão et al.
discoloration when used over a period of 12 weeks (Jang et al. 2013). The discoloration was observed at the MTA-dentin interface and intracoronal dentin surface.
Removal of the discolored MTA resolved the discoloration.
Treatment Plan Considerations
When referring to whitening of nonvital teeth, Salvas (1938) wrote, “bleaching
teeth is, at best, more or less of an unsatisfactory operation. Although we may succeed in restoring the color of a tooth, it is seldom permanent.” The unpredictability
of intracoronal whitening has not changed considerably since Salvas wrote these
statements in 1938.
Taking into consideration that the treatment outcome as well as the durability of
the treatment varies for each clinical situation, the patient must be informed of these
inherent limitations of intracoronal whitening. Another detail that the patient must
be aware of is that root dentin does not respond well to bleaching, either external or
internal (Kwon 2011). This is especially significant in case there is gingival recession that has resulted in exposed root surface.
The indications and contraindications for intracoronal whitening are displayed in
Table 8.1. Prior to starting an internal whitening procedure to lighten single or multiple teeth, it is crucial to understand all treatment options available for each specific
clinical case. The prognosis of internal whitening depends on several factors, including the etiology and the duration of the discoloration. Additionally, a history of traumatic injury to the tooth or teeth may be associated with subsequent external cervical
resorption. It is also important to understand that the intrinsic discoloration in endodontically treated teeth affects dentin but not enamel (van der Burgt et al. 1986). A
precise diagnosis relies on accurate clinical and radiographic exams. The presence of
craze lines on the enamel structure and marginal microgaps in existing restorations
may result in seepage of the intracoronal bleaching agents to the surrounding tissues.
For this reason, the use of transillumination to diagnose microgaps and craze lines is
Table 8.1 Indications and contraindications for internal whitening of endodontically treated teeth
Discolorations from pulpal trauma or
Discolorations that do not respond to
external bleaching techniques
Dentin discolorations of various
origins, including endodontic sealers
Inadequate root canal treatment
Untreated caries lesions and abfraction lesions
Loss of coronal tooth structure that prevents sealing of
the bleaching material inside the pulp chamber
Defective restorations or enamel craze lines that may
result in seepage of the bleaching material to the
Patient’s high expectations
Discoloration caused by oxidation of metals (silver,
Discolorations restricted to enamel
Intracoronal Whitening of Endodontically Treated Teeth
extremely important. The treatment plan must be based on existing evidence to
improve the chance of clinical success.
Intraoral photographs are essential to document the baseline color. Although the
color of darkened endodontically treated teeth is not usually within the range of universal shade guides, the clinician may still take a photograph with a tooth tab from
the Vita Classical A1-D4 shade guide (VITA Zahnfabrik H. Rauter GmbH & Co.
KG) next to the darkened tooth. This will provide an excellent comparative reference
for the postoperative versus the preoperative color.
Whitening Techniques for Endodontically Treated Teeth
Superoxol used to be the most commonly used intracoronal bleaching material.
More recently, water has been used (instead of hydrogen peroxide) mixed with
sodium perborate (Ari and Ungör 2002; Plotino et al. 2008). Sodium perborate
(NaBO3) is a white crystalline powder that contains about 95 % of the perborate corresponding to 9.9 % available oxygen (Rotstein and Friedman 1991). In contact with
water, sodium perborate decomposes with the liberation of hydrogen peroxide and
later of oxygen. Sodium perborate is, therefore, a hydrogen peroxide precursor (Ari
and Ungör 2002). Warm air and acidic solutions also initiate the decomposition of
sodium perborate. A thick creamy paste of sodium perborate with water is currently
recommended, left in the pulp chamber for varying periods of time.
Two techniques for bleaching endodontically treated teeth have been used
through the years, namely, the thermocatalytic technique and the walking bleach
technique. Other bleaching techniques include combined thermocatalytic and walking bleach techniques (Freccia et al. 1982).
In the thermocatalytic technique, heat is used to activate the release of nascent oxygen from the oxidizing agent or agents, often hydrogen peroxide and sodium perborate (Ari and Ungör 2002). Several sources of heat have been utilized as adjunct
activation methods, including ultraviolet (UV) lights, infrared lights, flamed instruments, and electrical sources of light and heat. Fischer (1911) reported heating
hydrogen peroxide with a special mercury arc light with a quartz lens, or Kromeyer’s
lamp, to irradiate the teeth with ultraviolet (UV) rays to mimic the sunlight. Prinz
(1924) recommended using heated solutions consisting of sodium perborate and
Superoxol for cleaning the pulp cavity. Dietz (1957) recommended a 20-in. infrared
light for the thermocatalytic technique in case only one appointment was feasible.
In 1963, the use of 30 % hydrogen peroxide with a source of light and heat from a
distance of 5 cm was reported (Weisman 1963).
In light of the risk of side effects from heating hydrogen peroxide in the
pulp chamber space (Madison and Walton 1990), including external cervical
resorption, the thermocatalytic technique is no longer advocated.
J. Perdigão et al.
Walking Bleach Technique
For the walking bleach technique, hydrogen peroxide or water is mixed with sodium
perborate, but heat is not used to trigger the release of nascent oxygen. The use of
an intracoronal mixture of sodium perborate mixed with Superoxol or water has
been described as a successful technique (Kirk 1893; Nutting and Poe 1967; Rotstein
et al. 1993a). Saline and anesthetic have also been used instead of water (Madison
and Walton 1990). Propylene glycol, which is largely used as in the pharmaceutical
and food processing industry as a humectant and preservative, has also been suggested in some countries as a vehicle for the intracoronal bleaching paste in lieu of
water. There is, however, no evidence that propylene glycol is more effective than
water to mix with sodium perborate for internal whitening.
The first description of the walking bleach technique using a mixture of sodium
perborate and distilled water was published in 1938 (Salvas 1938). The mixture was
left in the pulp space for a few days, while the access cavity was sealed with provisional cement. This same technique was revived in 1961 (Spasser 1961) and modified
in 1967 (Nutting and Poe 1967), when 30 % hydrogen peroxide was used instead of
water to improve the bleaching effectiveness of the mixture. Although 30 % hydrogen
peroxide may boost the efficacy of internal whitening, the procedure can be successfully accomplished without hydrogen peroxide (Salvas 1938; Spasser 1961).
Clinically, the walking bleach technique of sodium perborate mixed with water
has been reported to be effective. In 57 out of 95 teeth (60 %), a good or acceptable
result was obtained after one or two visits (Holmstrup et al. 1988). The remaining
38 teeth (40 %) were treated over 3–9 visits. The method used sodium perborate
moistened with water and the access cavity was temporarily restored with Cavit
(3M ESPE) between visits. While 55/69 (79.7 %) of the teeth examined at 3 years
still had a good or acceptable result, 14 teeth (20.3 %) showed recurrence of discoloration that was considered unacceptable. The total number of teeth with an unacceptable result either initially or after 3 years was 25 % of the treated teeth. Despite
recurrence, all examined teeth showed less discoloration than before bleaching.
Interestingly, it has been reported that patients treated with the walking bleach technique brush more often than other patients, developing a superior dental hygiene
regimen (Abou-Rass 1988).
In vitro and clinical studies have shown that three applications of sodium
perborate mixed with water are equally effective as applying sodium perborate and the 30 % hydrogen peroxide solution (Rotstein et al. 1991c; Rotstein
et al. 1993a; Holmstrup et al. 1988).
With the advent of the at-home vital whitening technique (Chap. 6), carbamide
peroxide (also known as urea peroxide) has been advocated for the walking bleach
technique alone or in combination with sodium perborate (de Souza-Zaroni et al.
2009). Aldecoa and Mayordomo (1992) suggested a 4-week treatment with 10 %
carbamide peroxide mixed with sodium perborate as a “second phase” of internal