Internal Tooth Whitening

Indications

Internal tooth whitening is indicated for managing nonvital teeth with internal discoloration following endodontic treatment. Common causes of such discoloration include pulp chamber hemorrhage, pulp necrosis, remnants of pulp tissue, and residual endodontic materials.[5] In these cases, byproducts with chromogenic capacity penetrate the dentinal tubules, leading to discoloration of the surrounding dentin.

Pulp bleeding may occur during pulp extirpation or after trauma. Blood products penetrate the dentinal tubules, causing a temporary pink discoloration of the crown.[6] Subsequently, hemolysis of red blood cells releases iron, which reacts with hydrogen sulfide produced by bacteria to form black ferric sulfide, resulting in grey discoloration.[6] In addition, the breakdown of proteins in a necrotic pulp may cause discoloration.[6] The longer the pulp remains necrotic, the greater the discoloration of the dentin.[5]

Incomplete preparation of the access cavity can lead to the retention of pulp remnants within the pulp chamber, especially in the pulp horns, causing discoloration at the coronal level.[7] Similarly, inadequate removal of root-filling materials from the pulp chamber over teeth can cause tooth discoloration. This inadequate removal typically occurs when the root-filling materials remain elevated above the level of the bone.[5] In such cases, the prognosis of internal tooth bleaching depends on the type and duration of contact with the material. For example, stains from metallic compounds are more challenging to remove.[5] The remaining materials must be entirely removed with burs before bleaching can proceed.[5]

Preparation

Patient Consent

Patients should be informed that complete recovery of natural tooth color cannot be guaranteed. Additionally, comprehensive information regarding potential complications should be provided.

Although rare, external cervical resorption is a noteworthy complication associated with internal tooth whitening. Studies on the etiology of external cervical resorption primarily attribute its development to orthodontic treatment (24.1%), surgical procedures (5.1%), and internal bleaching (3.9%).[8] External cervical resorption is usually asymptomatic and discovered incidentally on radiographic findings. Resorption appears as a radiolucent, dish-shaped near the cementoenamel junction (CEJ) on x-rays. Clinically, the affected tooth may respond well to sensitivity testing and bleed profusely upon probing. Additional clinical findings may include tenderness on percussion and swelling of the interdental papillae.[9]

The primary risk factors for cervical resorption include a history of trauma and bleaching. Although the exact cause of cervical resorption remains unclear, using a lower-concentration bleaching agent is recommended as a preventive measure.[3] In 2011, the Council of the European Union recommended using products that contain or release up to 6% hydrogen peroxide for teeth whitening. However, other countries still permit the use of higher concentrations of hydrogen peroxide.

Pretreatment Considerations

In the preliminary stages of treatment, it is crucial to evaluate the condition of the root canal treatment, as well as the presence of caries and the status of adjacent teeth.[5] The final shade of the tooth after bleaching cannot be predicted accurately. Defective restorations or caries in adjacent teeth should be addressed after completing the bleaching procedure rather than before. Pre- and post-treatment photographs are recommended for documentation and comparison purposes.[5]

Technique or Treatment

The active ingredient in tooth-whitening products is hydrogen peroxide, which can be applied directly or released from compounds such as carbamide peroxide or sodium perborate.[10] Regarding shade guide units, carbamide peroxide and hydrogen peroxide typically yield better outcomes in shade guide units compared to sodium perborate.[11] Hydrogen peroxide releases active oxygen molecules that break down chromophore molecules into smaller, more easily diffusible forms. These altered pigments reflect light differently, resulting in whitening effects. The action of hydrogen peroxide can be enhanced by heat and light.[10]

Walking Bleach Technique

A case study describes the application of the walking bleach technique. The tooth was isolated using a rubber dam, and existing composite materials were removed apically around the gingival margin. Sodium hypochlorite was used for disinfection, followed by placing a 2-mm layer of glass ionomer as a protective barrier. Intraorifice barriers are commonly used in the walking bleach technique to ensure proper coronal sealing, which reduces fracture resistance and prevents cervical resorption.[12][13][14] Common intraorifice barrier materials include glass ionomer cement, resin composite, and mineral trioxide aggregate (MTA). A damp cotton pellet soaked with 40% hydrogen peroxide was placed intracoronally. IRM was used to temporarily seal the access cavity, after which the rubber dam was removed. The patient was scheduled for follow-up every 2 weeks to assess and repeat the internal bleaching procedure until no further whitening was observed.

Clinical photographs were taken after each application using a Vita Classical Shade Guide. Postoperative radiographs were also taken to monitor for adverse effects, such as cervical resorption. Permanent adhesive restoration was completed during the final visit of the bleaching procedure.

Inside-Outside Bleaching Technique

The inside-outside bleaching method involves applying a bleaching agent to both the inner and outer surfaces of the tooth. Unlike the walking bleach technique, the access cavity remains open during treatment. The patient wears a vacuum-formed splint over the area being bleached. An impermeable base is used to seal the root canal filling. A small amount (pea-sized) of 10% carbamide peroxide is applied to the access cavity and the corresponding area of the splint using a syringe.[3] The patient is instructed to wear the splint overnight to protect the exposed tooth and follow up with the dentist every 3 days to monitor color changes. Once the target color or desired shade is achieved, the access cavity is cleaned and sealed with temporary materials such as glass ionomer cement. A permanent restoration is placed a week later.

The benefits of this technique include a low risk of cervical root resorption due to the low concentration of bleaching material and the absence of temporary restoration. However, it necessitates patients using bleaching trays, which can pose a risk of bacterial invasion if the patient neglects to return for access closure. Furthermore, an additional cost is associated with tray fabrication. 

In-Office Bleaching Technique

In-office bleaching is a widely used method for whitening vital teeth and can also be applied to nonvital teeth. The initial steps of the procedure are identical to those of the walking bleach technique, including isolation, accessing the tooth, and sealing the root canal. After applying 35% hydrogen peroxide, the material is rinsed off 20 minutes later, and the process is repeated. This technique involves a more concentrated application compared to other methods, necessitating definitive access closure during a subsequent appointment.[3]

Clinical Significance

The walking bleach technique using hydrogen peroxide offers a promising and aesthetically pleasing solution for treating nonvital tooth discoloration. In addition, its conservative approach and economic advantages make it appealing to patients seeking satisfying results without removing additional tooth structure and at a fraction of the cost of a fixed restoration. This technique is effective for managing discoloration in teeth that have undergone endodontic treatment.

Case Report

A 28-year-old man with a medical history of controlled hypertension presented with the chief concern, "A previous dentist told me that I need a crown to fix my dark tooth." The patient underwent endodontic treatment on the upper right central incisor in July 2021 (see Image. Periapical x-ray), with discoloration reported 1 month after root canal therapy. The patient had previously undergone endodontic treatment on the upper right lateral incisor and received a porcelain fused metal (PFM) crown to improve discoloration after root canal therapy. Dissatisfied with the visible discoloration of his central incisor, the patient expressed motivation to pursue a crown, influenced by his positive experience with the treatment of the lateral incisor.

Crowns necessitate the loss of tooth structure, reducing the life cycle of teeth for future treatments, and are costly compared to noninvasive treatments.[10] Internal bleaching using the walking bleach technique was suggested as an alternative to a fixed prosthetic restoration, offering a more conservative and economical approach.

The discoloration on the upper right central incisor corresponded to a C4 VITA shade at the initial visit (see Image. Initial Discoloration). Hydrogen peroxide 40% was placed intracoronally in 2-week increments. Significant esthetic outcomes were observed after the second application. Tooth color was monitored regularly using a VITA shade guide, with the initial shade at C4 VITA progressing to a final shade of C1 VITA.

The initial discoloration corresponded to a C3 VITA shade after the first internal bleaching (see Image. Initial Bleaching), progressed to a C1 VITA shade after the second internal bleaching (see Image. Second Bleaching), and remained at a C1 VITA shade after the third internal bleaching (see Image. Third Bleaching). No discomfort or cervical resorption was reported during the initial visit, and the same C1 VITA shade was maintained at a 6-month follow-up visit (see Images. Follow-Up at 6 Months, VITA Shade Comparison, and Occlusial View at 6 Months). The patient expressed satisfaction with the treatment outcome.

Enhancing Healthcare Team Outcomes

Internal bleaching is a practical choice for managing intrinsic discoloration in nonvital root-filled teeth. This procedure offers a cost-effective, noninvasive alternative that avoids further loss of tooth structure, making it an economical and attractive option to restorative alternatives such as crowns and veneers.

Managing discolored endodontically treated teeth necessitates a multidisciplinary approach involving diverse healthcare professionals to ensure patient-centered care, optimal outcomes, safety, and efficient team performance. Interprofessional collaboration among dental professionals is essential for developing effective treatment plans, considering the integrity of the clinical crown and the type of discoloration. Ethical considerations in internal bleaching encompass informed consent, patient autonomy, and confidentiality. Dentists should offer comprehensive information about the procedure, potential risks, and alternative treatments, enabling patients to make informed decisions about their dental care.