INTRACORONAL BLEACHING OF NONVITAL TEETH

Ilan Rotstein

INTRODUCTION

Intracoronal bleaching of nonvital teeth involves the use of oxidizing agents within the coronal portion of an endodontically treated tooth to remove tooth discoloration (American Association of Endodontists 2010). It can be successfully carried out even many years after pulp devitalization and discoloration have occurred (see Figure 8.1). The objectives of treatment are to reduce or eliminate discoloration, improve the degree of coronal translucency, and alleviate present and prevent future adverse clinical signs or symptoms (American Association of Endodontists 2010). The successful outcome depends mainly on the cause, correct diagnosis, case selection, and proper application of bleaching technique (Rotstein and Walton 2015).

The methods most commonly used to bleach endodontically treated teeth are the “walking bleach” technique (also known as sealed bleaching) and the thermo/photo bleaching technique (this technique should not be used anymore owing to the high heat generated by the thermocatalytic technique).

There are more choices for nonvital bleaching these days (Table 8.1), and the use of the bleaching tray together with the sealed bleaching technique has opened more options for bleaching teeth (see Chapter 15). In addition, with the restriction of high concentrations of hydrogen peroxide, it is easier to use lower strength bleaching gels such as 10% and 16% carbamide peroxide or 6% hydrogen peroxide together with the bleaching tray, which is applied to the lingual and labial surface of the teeth (see Figure 8.5c–g). This enhances the bleaching action and is much safer. After the barrier is prepared (see Figure 8.1f) the carbamide peroxide is directly placed onto the access cavity. It may be easier to apply the gel with a finer tip on the syringe nozzle for ease of application. Glass ionomer is used as an interim dressing because it has less of a tendency to be expelled once the patient gets home, and also because of the ease of placement and chemical and light curing options. The lower strength concentrations may be used for cases in the EU where the tooth is only slightly darker than its neighbor (see Figure 8.6).

WALKING BLEACH PROCEDURE—SEALED BLEACHING TECHNIQUE

The term walking bleach was first coined in the early 1960s to refer to bleaching action occurring between patients’ visits (Nutting and Poe 1963). Since that time, the technique has evolved and undergone several modifications, mainly by eliminating the use of highly concentrated hydrogen peroxide, making it a very popular and safe technique (Holmstrup et al. 1988, Attin et al. 2003). The walking bleach technique or sealed bleach technique should be attempted first in all cases requiring intracoronal bleaching (Tables 8.2, 8.3, and 8.4). This technique is preferred because it is safe, more comfortable for the patient and requires less chair time (Spasser 1961, Holmstrup et al. 1988).

The technique involves the following steps (see Figures 8.5 and 8.6):

1.  Familiarize the patient with the possible causes of discoloration, the procedure to be followed, the expected outcome, and the possibility of future re-discoloration.

2.  Assess the status of the periapical tissues and the quality of the endodontic obturation (see Figure 8.4). Endodontic failure or questionable obturation should always be re-treated before bleaching.

3.  Assess the quality and shade of any restoration present and replace it if defective. Tooth discoloration frequently is the result of leaking or discolored restorations. In such cases cleaning the pulp chamber and replacing the defective restorations usually suffice, and often a full bleaching procedure would not be required.

4.  Evaluate tooth color with a shade guide and take clinical photographs at the beginning of and throughout the procedure. These provide a point of reference for future comparison.

5.  Isolate the tooth with a dental dam. The dam must fit tightly at the cervical margin of the tooth to prevent possible leakage of the bleaching agent onto the gingival tissue. Interproximal wedges and ligatures may also be used for better isolation.

6.  Remove all restorative material from the access cavity, expose the dentin, and refine the access. Verify that the pulp horns as well as other areas containing pulp tissue are properly exposed and clean. Tissue remaining in the pulp chamber disintegrates gradually and may cause discoloration. Pulp horns must always be included in the access cavity to ensure removal of all pulpal remnants.

7.  Remove all materials to a level just below the labial- gingival margin. Orange solvent, eucalyptus oil, or chloroform on a cotton pellet may be used to dissolve sealer remnants. Etching of dentin with phosphoric acid is unnecessary and may not improve bleaching prognosis (Casey et al. 1989).

8.  Apply a sufficiently thick layer, at least 2 mm (see Figure 8.11), of a protective white cement barrier, such as polycarboxylate cement, zinc phosphate cement, glass ionomer, or intermediate restorative material (IRM) to cover the endodontic obturation. The coronal height of the barrier should protect the dentin tubules and conform to the external epithelial attachment (Steiner and West 1994).

9.  Seal 16% carbamide peroxide gel into the access cavity (see Figures 8.11L and M). It is best to use a bleaching syringe with a finer nozzle tip to allow for ease of placement of the gel.

10.  Although a sodium perborate and 30% hydrogen peroxide (H₂O₂) mixture may bleach faster, in most cases long-term results are similar to those with sodium perborate and water alone, and therefore the mixture need not be used routinely (Holmstrup et al. 1988, Rotstein et al. 1991d, Rotstein et al. 1993a). In addition, use of these two materials—30% hydrogen peroxide and sodium perborate—causes the materials to become synergistic. It is thus not considered appropriate to use this technique recently anymore; there are other, higher concentration materials that are safer and equally effective.

11.  With a plastic instrument, pack the pulp chamber with the paste. Remove excess liquid by tamping with a cotton pellet. This also compresses and pushes the paste into all areas of the pulp chamber. In Europe, sodium perborate is not permitted to be used in dentistry and so carbamide peroxide gel or hydrogen peroxide gel may be sealed into the access cavity at no higher strength than 6% hydrogen peroxide.

12.  Remove excess bleaching paste from undercuts in the pulp horn and gingival area and apply a thick, well-sealed temporary filling directly against the paste and into the undercuts. Carefully pack the temporary filling, at least 3 mm thick, to ensure a good seal. A good seal is essential for a successful bleaching technique. It may be useful to use polytetrafluoroethylene (PTFE) tape as a dressing directly over the gel and then place glass ionomer as an interim restoration.

13.  Remove the dental dam and inform the patient that the bleaching agent works slowly and that significant lightening may not be evident for several days.

14.  Evaluate the patient approximately 2 weeks later; if necessary, repeat the procedure several times. Repeat treatments are similar to the first one.

15.  As an optional procedure, if initial bleaching is not satisfactory, strengthen the walking bleach paste by mixing the sodium perborate with gradually increasing concentrations of hydrogen peroxide (3% to 30%) instead of water. The more potent oxidizers may have an enhanced bleaching effect but are not used routinely because of the possibility of permeation into the tubules and damage to the cervical periodontium by these more caustic agents. In such cases, a protective cream, such as Orabase, Vaseline, or cocoa butter must be applied to the surrounding gingival tissues before dental dam placement.

16.  In most cases, discoloration will improve after one or two treatments. If after three attempts there is no significant improvement, reassess the case for correct diagnosis of the cause of discoloration and treatment plan.

SODIUM PERBORATE BLEACHING MATERIAL

Sodium perborate (NaBO₃) is an oxidizing agent available in a powdered form or as various commercial preparations. When fresh, it contains about 95% perborate, releasing about 9.9% available oxygen. Sodium perborate is stable when dry but, in the presence of acid, warm air, or water, decomposes to form sodium metaborate, hydrogen peroxide, and nascent oxygen. It can act synergistically with hydrogen peroxide (Nutting and Poe 1963).

Various types of sodium perborate preparations are available: monohydrate, trihydrate, and tetrahydrate. They differ in oxygen content, which determines their bleaching efficiency (Weiger et al. 1994). Commonly used sodium perborate preparations are alkaline, and their pH depends on the amount of hydrogen peroxide released and the residual sodium metaborate (Rotstein and Friedman 1991).

Sodium perborate is more easily controlled and safer than high concentrations of hydrogen peroxide solutions. However, sodium perborate has been banned by the European directive. It is not permissible to use any sodium perborate materials in dentistry in Europe.

THERMO/PHOTO BLEACHING PROCEDURES

Thermo/photo bleaching involves placement of the oxidizing agent, usually 30–35% hydrogen peroxide, in the pulp chamber followed by heat application from electric heating devices, light application from specially designed lamps, or both (Buchalla and Attin 2007) (see Figure 8.3). Care must be taken when using these heating devices to avoid overheating the teeth and surrounding tissues. Intermittent treatment with cooling breaks is preferred over one long continuous session. In addition, the surrounding soft tissues should be protected with Vaseline, Orabase, or cocoa butter during treatment to avoid heat damage.

Potential damage from the thermo/photo bleaching approach is external root resorption caused by irritation to the cementum and periodontal ligament. This is possibly attributed to hydrogen peroxide combined with heat (Madison and Walton 1990, Rotstein et al. 1991a). Therefore, application of highly concentrated H₂O₂ and heat during intracoronal bleaching should not be carried out routinely. This technique is now not used much owing to the high heat generated.

In general, the technique involves the following steps:

1.  Familiarize the patient with the probable causes of discoloration, the procedure to be followed, the expected outcome, and the possibility of future rediscoloration.

2.  Assess the status of periapical tissues and the quality of endodontic obturation (see Figure 8.4D). Endodontic failure or questionable obturation should be re-treated before bleaching (see Figures 8.4 and 8.10).

3.  Evaluate tooth color with a shade guide and take clinical photographs before and throughout the procedure. Assess the quality and shade of any restoration present and replace if defective.

4.  Apply a protective cream to the surrounding gingival tissues and isolate the teeth with rubber dam and waxed dental floss ligatures. If a heat lamp is used, avoid placing rubber dam metal clamps; they are subjected to heating and may also be painful to the patient.

5.  Do not use anesthesia.

6.  Position protective sunglasses over the patient’s and operator’s eyes.

7.  Apply a sufficiently thick layer, at least 2 mm, of protective white cement barrier, such as polycarboxylate cement, zinc phosphate cement, glass ionomer, or IRM on top of the endodontic obturation. The coronal height of the barrier should protect the dentin tubules and conform to the external epithelial attachment (Steiner and West 1994). It is best to use glass ionomer as a barrier because it does not interfere with the hydrogen peroxide in the gel.

8.  Soak a small amount of 30–35% hydrogen peroxide solution on a small cotton pellet or a piece of gauze and place it in the pulp chamber. A bleaching gel containing hydrogen peroxide may be used instead of the aqueous solution.

9.  Apply heat with a heating device or a light source. The temperature should be less than the patient can comfortably tolerate, usually between 50°C and 60°C. Re-wet the cotton pellet and pulp chamber with hydrogen peroxide as necessary. If the tooth becomes too sensitive, discontinue the bleaching procedure immediately. Preferably, bleaching should be limited to separate 5-minute periods rather than being performed during a long continuous period (Rotstein et al. 1991b).

10.  Remove the heat or light source and allow the teeth to cool down for at least 5 minutes. Then wash with warm water for 1 minute and remove the dental dam.

11.  Dry the tooth and place walking bleach paste of sodium perborate mixed with water in the pulp chamber.

12.  Recall the patient approximately 2 weeks later and evaluate the effectiveness of bleaching. Take clinical photographs with the same shade guide used in the preoperative photographs for comparison purposes. If necessary, repeat the bleaching procedure.

INTENTIONAL ENDODONTICS AND INTRACORONAL BLEACHING

The technique involves standard endodontic therapy of a vital pulp followed by intracoronal bleaching. It should not be done routinely and should be offered to patients only in limited clinical situations. This technique was mainly advocated for treating severe intrinsic tetracycline discolorations. Such discolorations and other similar stains are incorporated into tooth structure during tooth formation, mostly into the dentin, and therefore are very difficult to treat from the external enamel surface. Intracoronal bleaching of tetracycline-discolored teeth has been shown to be predictable and to improve tooth shade without significant clinical complications (Abou-Rass 1982). These days it is not necessary to intentionally devitalize a tooth merely for the sake of bleaching the tooth because the home bleaching technique can bleach the most severe discoloration over a period of time. Normal home bleaching techniques using higher carbamide peroxide are used instead.

COMPLICATIONS AND ADVERSE EFFECTS

EXTERNAL ROOT RESORPTION

Clinical reports (Harrington and Natkin 1979, Lado et al. 1983, Montgomery 1984, Shearer 1984, Cvek and Lindvall 1985, Goon et al. 1986, Latcham 1986, Friedman et al. 1988, Gimlin and Schindler 1990, Al-Nazhan 1991, Heithersay et al. 1994) and histologic studies (Madison and Walton 1990, Rotstein et al. 1991a, Heller et al. 1992) have shown that intracoronal bleaching may induce external root resorption mainly when 30–35% hydrogen peroxide is being used. The mechanism of bleaching-induced damage to the periodontium or cementum has not been fully elucidated. Presumably, the irritating chemical diffuses via unprotected dentinal tubules and cementum defects (Rotstein et al. 1991c, Koulaouzidou et al. 1996) and causes necrosis of the cementum, inflammation of the periodontal ligament, and finally root resorption. The process may be enhanced if heat is applied (Rotstein et al. 1991b) or in the presence of bacteria (Cvek and Lindvall 1985, Heling et al. 1995). Previous traumatic injury (see Figure 8.7) and age may act as predisposing factors (Harrington and Natkin 1979, Tredwin et al. 2006).

CHEMICAL BURNS

Hydrogen peroxide (30–35%) is highly caustic and can cause chemical burns and sloughing of the gingiva. When such solutions are used, the soft tissues should always be protected with Vaseline, Orabase, or cocoa butter.

High-strength hydrogen peroxide may not be used in Europe. No more than 6% hydrogen peroxide may be used for bleaching in Europe. In this case, 16% carbamide peroxide is sealed into access cavities of teeth. The lower strength has the advantages of causing less chemical burning and less soft tissue discomfort.

DAMAGE TO RESTORATIONS

Bleaching with hydrogen peroxide may affect bonding of composite resins to dental hard tissues (Titley et al. 1993). Scanning electron microscopy observations suggest a possible interaction between composite resin and residual peroxide causing inhibition of polymerization and increase in resin porosity (Titley et al. 1991). This presents a clinical problem when immediate esthetic restoration of the bleached tooth is required. It is therefore recommended that residual hydrogen peroxide be totally eliminated from the pulp chamber before composite placement. This may be done by treating the dentin surface with catalase before bonding (Rotstein 1993). Catalase removes the residual oxygen from the dentin. A glass ionomer restoration can be placed immediately and the rest cut back 2 weeks later for the composite restoration.

It has also been suggested that immersion of peroxide-treated dental tissues in water at 37°C for 7 days prevents the reduction in bond strength (Torneck et al. 1991).

SUGGESTIONS FOR SAFER NONVITAL BLEACHING

See Table 8.5.

•  Isolate tooth effectively. Intracoronal bleaching should always be carried out with dental dam isolation. Interproximal wedges and ligatures may also be used for better protection.

•  Protect oral mucosa. Protective cream, such as Orabase, Vaseline, or cocoa butter, must be applied to the surrounding oral mucosa to prevent damage associated with chemical burns by caustic oxidizers. Animal studies suggest that catalase applied to oral tissues before hydrogen peroxide treatment totally prevents the associated tissue damage (Rotstein et al. 1993b).

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