Abstract
Noticeable discoloration of permanent teeth can impact on a person’s self-image, self-confidence, physical attractiveness and employability. Success in bleaching a non-vital discolored tooth varies by depending on the etiology appearance, localization, severity, and adhesion to tooth structure. It can be defined as being extrinsic or intrinsic on the basis of localization and etiology. Moreover, the success of bleaching depends on several factors, where the most important are the cause of the discoloration of the tooth, the adequate diagnosis of the problem and the proper choice of the bleaching technique. Different phenomena can ensure that endodontically treated teeth become darker. Although there is a deficiency of evidence-based science in the literature that addresses the prognosis of bleached non-vital teeth, it is important to always be aware of the possible complications and risks that are associated with the different bleaching techniques and agents. This present article aims to emphasize on the different procedures to bleach a non-vital tooth in order to get the best results.
Key Words
Devitalized tooth, Tooth discoloration, Bleaching agents, Tooth bleaching techniques
Introduction
Bleaching discolored non-vital teeth has been described for the first time in 1864 [1]. A variety of bleaching agents were then used, such as chlorite, sodium hypochlorite, sodium perborate and hydrogen peroxide, alone or in combination, with or without heat activation[2]. Different techniques were described such as the walking bleach technique, the thermocatalytic and in-office techniques. Each one of these procedures has its own positive and negative points. Before proposing any treatment to the patient in a way to correct the discoloration of his or her devitalized tooth, it is essential to determine the exact cause of the color change. Discoloration of a tooth can occur during or after the formation of dentin and enamel, and can be associated with the patient himself or with a treatment performed by the dentist. Discolorations associated with the patient himself may be superficial or incorporated within tooth structure. Regarding the discolorations associated with the dentist, they are usually predictable and should be avoided[3] [4]. Tooth discoloration varies in etiology, appearance, location, severity, and affinity to tooth structure. It can be classified as intrinsic, extrinsic, or a combination of both, according to its location and etiology [5](Table 1).
Bleaching Agents for whitening Devitalized Teeth
The most commonly products used for bleaching are carbamide peroxide, sodium perborate and hydrogen peroxide[1]. The teeth whitening is now based on the use of hydrogen peroxide as an active agent. Hydrogen peroxide can be applied alone or produced by a chemical reaction of the sodium perborate or carbamide peroxide. Regarding the carbamide peroxide (CH6N2O2), upon reaction, it dissociates into hydrogen peroxide (H2O2) and urea (CH4N2O)[2]. Other whitening products use rather sodium perborate as the active ingredient. In the reaction, complex oxygen is created during removal of the sodium perborate. A peroxide gel is then released. This gel interacts with the tooth structure and becomes activated. Oxygen complex interacts with the tooth, saturates and modifies the amino acids. Double bonds of the oxygen are responsible for the discoloration of the tooth. Hydrogen peroxide, in turn, is used in different proportions in most bleaching products and dissociates in water and long chain molecules of dark colored chromophores[3]. The tooth thus finds its original color or at least a lighter color. It should also be noted that the success of bleaching depends primarily on the ability of the agent to penetrate deeply into the dentinal tubules. The success of the treatment also depends on the concentration of the whitening agent and on the period during which the agent is in contact with the molecules. The bleaching agents are available in several concentrations, but different studies do not agree on the ideal concentration in terms of whitening power and preservation of oral tissues[4]. Carrasco and al. found that the ideal product for whitening is carbamide peroxide 37%[5]. According to Lim and al, carbamide peroxide 35% and hydrogen peroxide 35% are most effective for whitening, but the first one is preferable to the second, because it is less offensive to the tissues[6]. The reason which hydrogen peroxide is harmful to tissues is that it releases free radicals toxic anions (perhydroxyl). While for Kinomoto and al, the sodium perborate 2 grams/ml is preferable to hydrogen peroxide 30%[7]. In short, the authors conclude that hydrogen peroxide is too harmful to tissues and it is recommended to use an alternative product, preferably peroxide carbamide, otherwise sodium perborate. However, we know that sodium perborate contains hydrogen peroxide because it is a by-product of the dissociation of sodium perborate, as is also the case of carbamide peroxide as mentioned above. Hydrogen peroxide is the main constituent of either bleaching agent or the product of dissociation of carbamide peroxide or perborate sodium and it acts as an oxidizing agent by causing the formation of free radicals. Other studies (Weiger 1992) found that sodium perborate mixed with distilled water in a ratio of 2: 1 (g/ml) is a bleaching agent and prevents or at least minimizes the external cervical resorption of the root, an important consequence, although rare in internal bleaching, compared with a bleaching agent not combined with water[8]. In cases of severe discoloration, hydrogen peroxide (H2O2) 3% can replace water. The use of 30% H2O2 is not recommended, always due to the risk of external resorption. Other authors have focused their research on the comparison between the hydrogen peroxide and carbamide peroxide. They concluded that in fact, as previously mentioned, these two products contain hydrogen peroxide and both work well. It appears, however, that H2O2 gives the desired results faster and requires a shorter treatment and a less exposure time than solutions of carbamide peroxide. In addition, there is less chance that dehydration occurs in hard tissues of the tooth treated with H2O2 as this system is based on aqueous gel, unlike carbamide peroxide gel based on anhydride. Carbamide peroxide seems to be softer on tissues, possibly due to the fact that the concentration of hydroxyl ion, acid, urea ammonium or carbonic acid is lower. In all whitening products, you can find other substances such agent thickener like Carbopol. This substance allows a slower reaction, but a longer period by altering the rate of release of oxygen. In addition, the urea produced by salivary glands can also be found in the whitening agents. The urea dissociates to ammonia and carbon dioxide. In addition to stabilizing the hydrogen peroxide, it has properties such as anticariogenic raising the pH of the solution and stimulating salivation. The high pH also facilitates whitening procedures[9]. This is explained by the fact that in basic solution, a smaller amount of energy is required for the formation of free radicals from hydrogen peroxide and level of reaction is higher, which leads to a better performance, in comparison with a bleach acid environment. It also contains glycerin due to its properties to increase the viscosity of the product and to facilitate handling thereof. However, it can cause tooth dehydration. A surfactant is also used to allow the hydrogen peroxide to diffuse into the tooth. Pigment dispersants, meanwhile, have the function to keep the pigments in suspension[10].
Techniques and tips to follow to ensure the success of treatment
he most commonly methods used to whiten endodontically treated teeth are the walking bleach technique and the thermocatalytic technique. The thermo / photo and internal / external techniques are also used for whitening devitalized teeth. The walking bleach is preferable because this technique requires less time in the office and is safer and more comfortable for the patient[11].
Walking Bleach Technique
The first description of the walking bleach technique with a mixture of sodium perborate and distilled water was mentioned in a congress report by Marsh and published by Salvas[12] .In this procedure, the mixture was left in the pulp cavity for a few days, and the access cavity was sealed with provisional cement. The mixture of sodium perborate and water was reconsidered by Spasser[13] and modified by Nutting and Poe[14], who advocated the use of 30% hydrogen peroxide instead of water to improve the bleaching effectiveness of the mixture. A mixture of sodium perborate and water or hydrogen peroxide continues to be used today and has been described many times as a successful technique for intracoronal bleaching. There are numerous studies that have reported the successful use of the walking bleach technique for correction of severely discolored teeth caused by incorporation of tetracycline [15].This procedure starts with intentional devitalization and root canal treatment of the tooth to enable application of the bleaching agent into the pulp chamber. Because the methods of intentional devitalization and root canal treatment have risks, the advantages and disadvantages of this therapy should be assessed. Restorative treatment options such as ceramic veneers should be considered as an alternative procedure. Furthermore, there is now evidence that prolonged bleaching with carbamide peroxide can also reach the desired results[16]. (Figure 1)
Before starting the treatment, the patient should be informed about the technique, the expected results and the possibility of a recurrence of the coloration.
1. Periapical radiographs should be taken to assess the status of periapical tissues and the quality of endodontic obturation. If it is unsatisfactory or questionable, it is imperative to retreat the tooth prior to the bleaching treatment.
2. Evaluate the quality and color of the restorations on the discolored tooth and replace if defective, because the discoloration of the tooth is often the result of a leak. In such cases, you only have to clean the pulp chamber and replace the defective restoration.
3. Evaluate the tooth shade with a shade guide, if possible, take photographs at the beginning and during the treatment, as this will be a reference point for any comparison. Clean and polish the tooth to be treated to remove any extrinsic stains[1].
Preparation of the Pulp Cavity
Before preparation of the access cavity, rubber dam should be applied to protect the adjacent structures. After that, restorative materials closing the access to the pulp cavity should be removed. Then, check that the entire pulp chamber is adequately accessible and cleaned. All remnants of restorative materials and necrotic pulp tissue must be removed completely.
Cervical Seal
Regarding the root canal filling material ending up inside the pulp chamber, it must be removed to a depth of 1-2 mm (a periodontal probe can be used to be sure of the length) below the CEJ with a Gates-Glidden or a Largo bur. A pulp chamber completely sealed with aesthetic material presents technical difficulties because the composite is difficult to distinguish from the tooth itself.
A root filling does not adequately prevent diffusion of bleaching agents from the pulpal chamber to the apical foramen[2]. Hansen- Bayless and Davis[3] indicated that a base is required to prevent radicular penetration of bleaching agents. Therefore, sealing the root filling with a base is essential, for which a variety of dental materials such as glass-ionomer cements, intermediate restorative material (IRM), hydraulic filling materials (Cavit®, Coltosol®), resin composites, photo-activated temporary resin materials (Fermit®), zinc oxide– eugenol cement, and zinc phosphate cement have been suggested as an interim sealing agent during bleaching techniques. McInerney and Zillich[4] found that Cavit® and IRM provided better internal sealing of the dentin than did zinc phosphate cement, whereas Hansen-Bayless and Davis[5] reported that Cavit® was a more effective barrier to leakage than IRM. Furthermore, hydraulic filling materials (Cavit® and Coltosol®) provided the most favorable cavosurface seal when they were firmly packed into the cavity space to prevent microleakage, when compared with a photoactivated temporary resin material (Fermit®), zinc oxide– eugenol cement, and a zinc oxide phosphate cement[6]. Temporary sealing materials need to be removed before providing the final restoration of the access cavity. Rotstein et al[7] demonstrated that a 2-mm layer of glass-ionomer cement was effective in preventing penetration of 30% hydrogen peroxide solution into the root canal. Thus, the use of this material as a base during bleaching presents the additional advantage that it can be left in place after bleaching and can serve as a base for the final restoration. The sealing material should reach the level of the epithelial attachment or the CEJ, respectively, to avoid leakage of bleaching agents into the periodontium. The shape of the cervical seal should be similar to the external anatomic landmarks, thus reproducing CEJ position and interproximal bone level. A flat barrier, leveled with the labial CEJ, leaves a large portion of the proximal dentinal tubules unprotected. Therefore, the barrier should be determined by probing the level of the epithelial attachment at the mesial, distal, and labial aspects of the tooth. The intracoronal level of the barrier is placed 1 mm incisal to the corresponding external probing of the attachment. With this method the coronal outline of the attachment defines an internal pattern of the shape and location of the barrier. However, the impact of the bleaching agents on the discolored dentin should not be hampered by the cervical seal. Dentin tubules at the coronal third of the root run in an oblique direction from the apex to the crown, so that the tubules at the CEJ are originating more apically inside the root canal. If bleaching of the cervical region of the tooth is required, a stepwise reduction of the labial part of the seal and use of a mild bleaching agent are recommended for the final dressings. The placement of a piece of rubber dam has been suggested to act as a further barrier to isolate filling material from the bleaching agent. However, Hosoya et al[8] reported no significant differences between the groups with and without the placement of this barrier.
Application of the Bleaching Agent
The bleaching agent can be applied with an amalgam carrier or plugger or with the syringe and should be changed every 3–7 days. Successful bleaching becomes apparent after 2– 4 visits, depending on the severity of the discoloration. The patients should be instructed to evaluate the tooth color on a daily basis and return when the bleaching is acceptable to avoid “over-bleaching”.
Temporary Filling
A temporary filling ( Cavit®, Coltosol®) will be applied to the outer periphery of the cavity Then the access of the cavity will be sealed with composite. The patient should be informed that the bleaching works slowly and that the results should be visible a few days later. Every week the patient must show up to the clinic to repeat the procedure[9].
Restoration of the Access Cavity and Postoperative Radiographs
When the devitalized tooth reaches the desired color, the access cavity will be sealed with a composite.
To obtain optimal adhesive bond between the restorative material and hard tissues of the tooth, it is advisable to proceed with the establishment of the permanent restoration after a period of approximately 10 days after the last bleaching therapy. Whitening the tooth leaves supersaturated oxygen, which inhibits the polymerization of the resins. A radiograph of the bleached tooth will be taken on all annual appointments to diagnose the earliest possible cervical resorption[10].
Thermocatalytic Technique
It is a technique where the hydrogen peroxide 30-35% is placed in the pulp chamber and activated by a heating source, either with an electric heating devices (Touch’ n Heat, System B) or especially designed lamps. The steps for placing the bleaching agent and sealing the pulp chamber are similar to the walking bleach technique. Heat application is repeated 3 or 4 times at every appointment. When heat is applied, a reaction produces foam and releases the oxygen present in the preparation[11]. The major risk of this technique is the external root resorption due to the excessive heat applied on the tooth[xii].
Combined Technique
When an agent fails to remove a stain completely or when multiple patches of different origins are present on the same tooth, a combination of whitening techniques can be used. The technique combines external / internal bleaching, so the patient can do it at home. This technique is both simple and effective. It consists of putting the whitening gel in a tray especially customized for the patient and placed directly on the tooth. There are certain risks with this technique, in that an unsealed access opening enables bacteria and stains to penetrate into dentin. Therefore, a restorative material such as glass-ionomer cement or resin composite should be used to seal the root filling at the orifice[13].
Discussion
Despite many clinical reports, there are few scientific evidence based studies on devitalized tooth whitening[14]. Most reports present optimal initial results after bleaching, with complete color matching of the bleached tooth (teeth) with the adjacent one(s). However, occasionally darkening after internal bleaching can be observed[15], which is presumably caused by diffusion of staining substances and penetration of bacteria through marginal gaps between the filling and the tooth. It is worth noting that the opinion of the patient regarding the success of the therapy is often more positive than the opinion of the dentist. One study reported an 80% rate of success after 1 year and 45% after 6 years of 20 cases that were chemically bleached by using the thermocatalytic technique[16]. Some authors have suggested that teeth that have been discolored for several years do not respond as well to bleaching as teeth that are stained for a short period of time. Furthermore, it is uncertain whether darkening after bleaching is more likely when the tooth is heavily or mildly discolored [17].Discoloration caused by restorative materials has a dubious prognosis. Certain metallic ions (mercury, silver, copper, iodine) are extremely difficult to remove or alter by bleaching. Brown[18] reported that trauma- or necrosis-induced discoloration can be successfully bleached in about 95% of the cases, compared with lower percentages for teeth discolored as a result of medicaments or restorations. There is a difference in opinion as to whether teeth that respond rapidly to bleaching have a better long-term color stability prognosis. Some studies have reported that stained teeth in young patients are easier to bleach than discoloration in older patients, presumably because the wide open dentinal tubules in young teeth enable a better diffusion of the bleaching agent. However, not all studies are in agreement with age related success of bleaching. Teeth with internal discoloration caused by root canal medicaments, root-filling materials, or metallic restorations such as amalgam have a poor prognosis, because this type of discoloration is difficult to bleach and tends to reappear over time because of the tenacity of the oxidizing products to dental tissues. Anterior teeth with interproximal restorations occasionally show less optimum results than teeth with a palatal access cavity only. This might be attributed to the fact that resin composites cannot be bleached[19]. In these cases, replacement of existing restorations after the whitening treatment is recommended to get optimal results.
Conclusion
oday, the causes of discoloration of endodontically treated teeth are well recognized, and techniques of bleaching that have proved their efficacy over the years, yield optimal results if the cases have been selected appropriately and if the dentist and the patient are aware of the remote risks of dental bleaching. Therefore, we can successfully treat tooth discoloration that has undergone a root canal using the walking bleach technique. Bleaching is done by temporarily placing a mixture of perborate (tetrahydrate) of sodium and water in the pulp chamber. This releases the mixture H2O2 which is capable of reacting with the coloring substances. The use of thermocatalytic method by heating a solution of 30% H2O2 is not recommended as this method increases the risk of external cervical resorption. For the same reason, the dentist should not use either 30% H2O2 for the walking bleach technique. To avoid leakage of the bleaching agent into the dentine, it is necessary to place a compact filling material, that is to say, gutta percha, and an additional cervical barrier, before beginning the bleaching technique. For a long-term success, it seems important to restore the access cavity with an adhesive filling material, which prevents the infiltration of bacteria and stains. The fact of following these procedures provides a much safer bleaching technique in the course of maintaining the integrity of the tooth and above the surrounding tissue, while maintaining an optimum result goal. Nevertheless, this treatment involves minimal risk. It is therefore desirable to have a product providing the benefits of effective bleaching agent while eliminating the associated risks.