Introduction

Teeth bleaching is the most conservative attempt to restore standard tooth color and has clear advantages over other procedures such as avoiding tooth structure wear. It provides proven long-term satisfactory aesthetic results and is efficient, relatively simple, and inexpensive compared to prosthetics treatment^1-5. Even if it fails, more invasive additional therapies can still be performed, such as veneers or full crowns⁶.

Factors such as trauma, pulp stones, inadequate therapeutic techniques, and failed endodontic treatment (obturation materials such as gutta-percha cones and endodontic cement when left in the pulp chamber after endodontic treatment) can lead to chromatic changes^5,7-10.

The first reports in the literature on the use of bleaching agents date back to 1860, as well as the use of various substances: calcium chloride, chlorine, aluminum chloride, oxalic acid, sulfur dioxide, sodium hypochlorite, among others¹. The market offers 30% to 35% hydrogen-peroxide bleaching agents that can be used separately or with sodium perborate^3,5,11.

Potential external cervical resorption is one of the main concerns regarding tooth bleaching in endodontically treated teeth^10,12. Other possible undesired effects are reduction of fracture resistance and dentine microhardness on account of tooth overexposure to these substances in high concentrations and/or for prolonged periods¹³.

This paper presents two clinical cases describing the techniques used for tooth bleaching to address darkened endodontically treated teeth in individuals attending Hospital de Reabilitação de Anomalias Craniofaciais, University of São Paulo given patients’ aesthetic requirements.

Background

Darkened teeth break a smile’s color harmony, leading patients to seek therapies to restore natural tooth color. There are several treatments for endodontically treated teeth with chromatic change. However, tooth bleaching is presented as a first option⁶.

Non-vital tooth bleaching should be indicated cautiously. The following factors should be evaluated: extensive restorations or insufficient remains, enamel fracture lines, tetracycline staining, quality of endodontic treatment, periapical lesions, external and internal resorptions, cause and time of chromatic change, and degree of darkening^7,9,14.

Pulp removal is a dental intervention that causes bleeding in the dentin, where blood enters the dentinal tubules and then breaks down. Discoloration may occur when the pulp tissue is not entirely removed during endodontic treatment. When sodium hypochlorite and chlorhexidine are mixed, reddish-brown precipitates are formed, which can cause chromatic change. So, it is necessary to neutralize them with physiological saline or saline solution between irrigant uses. Although highly biocompatible, white, or grey mineral trioxide aggregate (MTA) can cause undesired discoloration⁸.

The most commonly used bleaching agents in pulpless teeth are hydrogen peroxide, carbamide peroxide and sodium perborate associated with distilled water, saline solution or 35% hydrogen peroxide. However, using sodium perborate with distilled water or physiological serum is more effective and safer when compared to hydrogen peroxide, which is considered caustic^5,15-16.

Bleaching must meet some conditions to be safe: correct, complete, and total isolation of soft tissues (gingival tissues, lips, cheeks) to protect them from possible burns^17-20.

One of the main concerns regarding the bleaching of endodontically treated teeth is pH level and the high permeability of bleaching agents. When these agents reach the periodontal tissues through the dentinal tubules, they can alter the cementoenamel junction. This can trigger an inflammatory reaction caused by the denaturation of dentin. Said dentin can be considered a different tissue and thus be detected as a foreign body. This can lead to external cervical resorption^{1,12,14,19,21}. This resorption is asymptomatic and is usually diagnosed through routine radiography or clinical examination that reveals swollen papilla and a positive response to percussion²².

Therefore, it is essential to create a barrier in the cervical region, at the cementoenamel junction, between the obturating material (gutta-percha) and the pulp chamber space. This prevents the penetration of bacteria and the extrusion of the bleaching agent towards the apical periodontium, which could cause cervical resorption. Glass ionomer cement is the most widely used material to make this barrier because it is more cost-effective, among other advantages^(6,14,19.

Several tooth bleaching techniques are described in the literature. They can be classified into two groups: according to the area (internal or external) or to the time the bleaching agent remains in place (immediate, walking bleach, and mixed)⁽¹⁵. The main difference is the method applied by bleaching chemicals to release active oxygen. The bleaching agent is placed inside the pulp chamber in the walking bleach technique and remains there for three to seven days. It must be changed until the desired color is obtained, with a maximum of four sessions. This technique is considered the least risky regarding external cervical resorption. In the immediate technique, the bleaching agent is applied to the pulp chamber and the outer surface and left for approximately 45 minutes. Bleaching materials are potent oxidizing agents that react with the pigment compounds formed by carbon macromolecules. These molecules become compounds of lower molecular weight (carbon dioxide and water) through oxidation, and thus pigments diffuse through mineralized tissues, resulting in an oxidation bleaching action ^9-10,12,19.

After achieving the desired whitening effect, calcium hydroxide medication should be applied before the final restoration for 7-14 days to alkalize the medium and wait for the residual oxygen release time. This time is necessary to promote effective sealing and avoid microfiltration, as such residues may inhibit adhesive material polymerization^{5,10,14-15,19}.

Below we present two clinical cases, the relevant considerations, and the results obtained.

Clinical case 1 report: 23-year-old male with Treacher Collins Syndrome attending Hospital de Reabilitação de Anomalias Craniofaciais, University of São Paulo (HRAC/USP). He reports a chromatic change in the lower left canine (33) (Fig. 1, A). This was verified on clinical examination, as well as absence of painful symptoms. Satisfactory endodontic treatment was observed on radiographic examination (Fig. 1, B). Internal bleaching was performed with the mixed technique. The color (A4) was selected using the VITA scale (Wilcos do Brasil, Petrópolis RJ, Brazil). There followed an intraoral photo (Fig. 1, C), absolute isolation (Fig. 1, D), followed by access to the pulp chamber using diamond bur No. 1012 (KG Sorensen Ind. Com. Ltda, Barueri, Brazil). Endodontic obturation was removed at approximately 3 mm deep with No. 2 condensers heated at the root canal entry, the cavity was cleaned, and the cervical barrier was prepared (Figure, E) with glass ionomer cement (FGM, Joinville, SC, Brazil). Acid etching of the pulp chamber was then performed with 37% phosphoric acid (Biodynamics, Ibiporã, PR, Brazil) for 30 seconds, then washed with plenty of water for 60 seconds and dried with an air jet. This is done to remove the smear layer, open the dentinal tubules and therefore increase the dentin's permeability to the bleaching agent. We handled 35% hydrogen peroxide gel (Whiteness HP, FGM, Joinville, SC, Brazil) following the manufacturer’s guidelines and placed it inside the pulp chamber and on the buccal face with a medium-sized microbrush (KG Sorensen Ind. Com. Ltda, Barueri, Brazil) for 45 minutes (Fig. 1, F and G). The gel was removed by washing with water for 1 minute, and then a granular sodium perborate paste (Pharmacy Specific, Bauru, SP, Brazil) was handled with sterile saline solution in a sterile Dappen glass. The paste was placed inside the pulp chamber with an insertion spatula and evenly spread (Fig. 1, H). The tooth was sealed with glass ionomer cement (FGM, Joinville, SC, Brazil). A satisfactory result was observed after seven days (Figs. 1, I and J) when comparing the tooth to its past appearance. Calcium hydroxide paste (Calen) (SSWhite Duflex, São Cristovão, RJ, Brazil) was applied. The temporary restoration with glass ionomer cement (FGM, Joinville, SC, Brazil) was placed. The patient reported the yellowing of the other teeth and was then referred to the Aesthetic Dentistry sector of HRAC/USP for external whitening and for the final restoration.

Fig. 1: Clinical and radiographic sequence of clinical case 1 

Clinical case 2 report: 30-year-old male with Apert syndrome attending HRAC/USP. He reports chromatic change in the lower left canine (22) (Fig. 2, A and B). This was verified on clinical examination, as well as the absence of painful symptoms. Unsatisfactory endodontic treatment was observed on the radiograph (Fig. 2, C). Endodontic retreatment (Fig. 2, D, and E) was performed. It was necessary to prepare an apical barrier with MTA (Fig. 2, F) (Angelus Ind. De Productos Odontológicos S/A, Londrina, PR, Brazil). Immediate internal tooth bleaching was started six months after retreatment. The color was recorded with the intraoral photo (Fig. 2, B) because the tooth color was not identified on the VITA scale (Wilcos do Brasil, Petrópolis, RJ, Brazil) as it was darker. Absolute insulation was then placed, followed by access to the pulp chamber using diamond bur No. 1012 (KG Sorensen Ind. Com. Ltda, Barueri, Brazil), endodontic obturation removal with No. 2 condensers, root canal entry. The cavity was cleaned, and the cervical barrier was prepared with SureFil SDR flow light-curing resin (Dentsply Ind. Com. Ltda, Petrópolis, RJ, Brazil) (Fig. 2, G). Acid etching of the pulp chamber was then performed with 37% phosphoric acid (Biodynamics, Ibiporã, PR, Brazil) for 30 seconds, then removed with plenty of water for 60 seconds and dried with an air jet. We handled 35% hydrogen peroxide gel (Whiteness HP, FGM, Joinville, SC, Brazil) following the manufacturer’s instructions and placed it inside the pulp chamber and on the buccal face (Fig. 2, H and I) with a medium-sized microbrush (KG Sorensen Ind. Com. Ltda, Barueri, Brazil) with a 45-minute application. The gel was removed after washing with water for 1 minute. A second application was performed for 25 minutes and sealed with SureFil SDR flow resin (Dentsply Ind. Com. Ltda, Petrópolis, RJ, Brazil). The second session included absolute isolation, cervical barrier with Top Dam (FGM, Joinville, SC, Brazil), acid etching, washing and drying in the same way, 35% hydrogen peroxide gel (Whiteness HP, FGM, Joinville, SC, Brazil) was handled following the manufacturer’s guidelines and inserted inside the pulp chamber and on the vestibular face with a medium-sized microbrush (KG Sorensen Ind. Com. Ltda, Barueri, Brazil). The first application lasted 15 minutes. After removing the gel, the second application was performed for 15 more minutes but only externally limited to the cervical region. Satisfactory results (Fig. 2, J and K) were achieved compared to the appearance before bleaching and temporary restoration with SureFil SDR flow resin (Dentsply Ind. Com. Ltda, Petrópolis, RJ, Brazil). On his return, the patient was referred to the Aesthetic Dentistry sector, where the final restoration was performed.

Fig. 2: Clinical and radiographic sequence of clinical case 2 

Discussion

Aesthetic dissatisfaction appears most clearly when one or more teeth change color, leading patients to search for a treatment to restore the smile’s natural characteristics and harmony^19,23. However, dental professionals must diagnose and determine the etiology of chromatic change for clinical planning, material selection, and the clinical success of the bleaching treatment²⁴.

As several materials are often used for endodontic obturation of the pulp chamber, considerable discoloration is promoted, which intensifies in the cervical third. This is caused by cutting the obturation incorrectly, which should be done at or below the cementoenamel junction^6,11. This was the leading cause of tooth darkening in the clinical cases described above.

Non-vital teeth bleaching is contraindicated in teeth with a widely restored or decayed buccal surface, tooth cracks, poor restorations, and unsatisfactory endodontic treatment. Teeth that have been intensely darkened for many years have a slight chance of restoring color successfully. In some situations, it is necessary to suggest prosthetic or restorative alternatives¹³. The clinical conditions in case 1 were favorable for bleaching without any endodontic intervention; in case 2, endodontic retreatment was first indicated, and then bleaching was performed.

Hydrogen peroxide (H₂O₂) is the primary bleaching agent used. It is a cytotoxic, thermally unstable free radical with a low molecular weight that penetrates enamel and dentin through diffusion and reaches the periodontium^6-7,25. Hydrogen peroxide penetration was significantly higher in teeth with cement defects and/or a gap between the cement and the enamel at the cementoenamel junction^1,14.

The use of heat (thermocatalytic technique) should be avoided to prevent external cervical resorption cases, which can be caused by internal bleaching of non-vital teeth. Additionally, proper cervical sealing is essential.

Cervical sealing consists of a mechanical barrier placed at the cementoenamel junction between the obturation material (gutta-percha) and the pulp chamber space, where the bleaching agent will be placed. Its function is to prevent bacteria penetration or the diffusion of bleaching agent molecules towards the apical periodontium via the dentinal tubules⁶. Given the above, we chose glass ionomer cement to prepare the cervical barrier in case 1, and SureFil SDR flow resin in case 2.

Different techniques were selected for these cases since the patient in case 1 was available and could return periodically to perform the bleaching; therefore, the mixed technique was selected. In addition to applying the bleaching gel during the endodontic session, both in the pulp chamber and externally on the buccal surface, a whitening paste was used internally in the pulp chamber and left for seven days. According to the literature, the bleaching agent should be changed or reassessed every seven days. As the patient in clinical case 2 could not return for these weekly changes, the immediate technique was applied in two consecutive sessions. This prevented the patient from returning to their home city with the bleaching agent inside the tooth.

The most commonly used bleaching agents are hydrogen peroxide, carbamide peroxide, and sodium perborate. The latter can be associated with distilled water, saline solution, or 35% hydrogen peroxide. However, using sodium perborate with distilled water or saline solution is more effective and safer when compared to hydrogen peroxide, which is highly caustic^7,26. This was why sodium perborate was associated with saline solution in paste form in case 1, in which the mixed technique was performed.

The effectiveness of the bleaching paste also depends on the material used to seal the cavity. This material aims to prevent fluid infiltration into the pulp chamber, preventing dentin contamination and tooth recoloration²⁴. The temporary material-glass ionomer cement-was placed to provide mechanical and displacement resistance due to the pressure exerted by the oxygen released by the bleaching paste (sodium perborate + saline solution). Patients were advised to be careful about the consistency of the food ingested and chewing with the bleached tooth throughout the bleaching period to avoid tooth fracture.

Fourteen days must elapse without adhesive alterations after bleaching to perform adhesive restorative procedures on the enamel. During this period, the pulp chamber must be filled with calcium hydroxide paste to neutralize the effect of bleaching agents, given the paste’s ability to permeate the dental tissues¹. In the two clinical cases reported, we used Calen calcium hydroxide paste for the 14-day period and then referred the patient for the final restoration.

The duration of the bleaching treatment cannot be predicted. The longer the time and degree of tooth darkening, the more clinical sessions will be needed and the lower the likelihood of success. In addition to external resorption, which can occur up to seven years after the internal bleaching treatment, it is essential to perform clinical and X-ray evaluations²³. Another limitation is maintaining the long-term outcome, as many cases might present recurring darkness caused by poor sealing between the tooth and the restoration^23,15.

Conclusion

Internal bleaching of endodontically treated teeth with chromatic changes has several advantages: minimal wear of tooth surface, low cost and effectiveness in a short time. The use of mixed and immediate techniques-when correctly indicated-restores the smile’s harmony with a simple, effective, fast and satisfactory method. These techniques made it possible to restore patients’ self-esteem and provided a solution for the clinical cases presented.