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Bleaching of Non-vital Discolored Teeth: Keys of Success.

Abstract

Teeth discoloration is a fundamental aesthetic problem. It has a social impact on children, adolescents and adults. It is necessary for dentists to identify the etiology of teeth discoloration to establish an accurate and proper diagnosis. There are different options to treat discolored teeth such as restorative procedures, veneers, crowns... Actually, bleaching of non-vital teeth is a routine conservative approach to have a suitable esthetic result for endodontically treated teeth.

Various methods to bleach non-vital teeth have been proposed. Three techniques were described through the literature: the walking bleach technique, the inside/outside bleach technique and the in-office bleaching procedure. The most recommended one is the walking bleach technique since it is simple, safe, with lower risks and suitable for patients and dentists.

Different bleaching agents were used such as sodium perborate, hydrogen peroxide and carbamide peroxide with various concentrations. Some side effects were reported like external root resorption, diminution of tooth resistance (fracture...), morphological alteration of dental hard tissues and alteration of the characteristics of dental materials.

The objectives of this article:

- To describe the causes of discolored non-vital teeth,

- To explain the protocol of the different bleaching procedures and the agents used for,

To report different clinical cases of discolored non-vital teeth treated in our service of Dental Medicine with internal bleaching procedures.

Key words

Non-vital teeth, Discoloration, Bleaching, Carbamide peroxide, Hydrogen peroxide, Sodium perborate, Cervical root resorption.

Introduction

In our daily dental practice, we observe the increasing demand for esthetics in all fields of dentistry. Esthetic procedures can vary from restorative techniques such as conventional crowns, veneers, or bonding to bleaching treatments. 26 Despite different methods that can improve esthetics; bleaching procedures are safe, minimally invasive, conservative, low cost and effective to treat discolored teeth. 11

Referring to Zarow et al. 2014, even the esthetic treatment plan is based on conservative or prosthodontic procedure; dentist should start with teeth bleaching.

Referring to Rona et al. 2009, the discolored teeth can have an incidence on the self-confidence, self-image, attractiveness and employability of every one. 6

Actually, bleaching of non-vital teeth is considered as a popular procedure because of the continuous need for white teeth and good looks. 1

The internal tooth-bleaching is used to lighten a discolored tooth that was endodontically treated and the procedure consists of the placement of a chemical oxidizing agent within the cavity access chamber to remove discoloration. 25

The first reports concerning bleaching of discolored non-vital teeth were published in the middle of the 19th century. 2, 3

Different chemical agents were used to bleach discolored teeth such as chlorinated lime, oxalic acid, acetic acid, chlorine compounds and solutions, sodium peroxide, sodium hypochlorite, different concentrations of hydrogen peroxide, carbamide peroxide and sodium perborate. 1, 2, 3, 4, 23

The mechanism of action of the different bleaching products is the same. The hydrogen peroxide will decompose into oxygen and water. Then, the oxygen will cause the oxidation and reduction of the organic pigments that are mainly concentrated in the dentin structure. As a result, we obtain the bleaching impact. 7 Referring to literature, we can use light, heat and even electric currents to activate the bleaching agents and to have a rapid result. 2

Clinical examination and radiographic exploration are important before establishing the treatment plan of bleaching. In case of discolored tooth, a periapical radiograph is necessary to evaluate the quality of endodontic filling, the periapex region and a possible alteration of a resorption process. 24 Dentist must define the etiology of the dental discoloration that will have a deep impact on the success of the bleaching treatment. 3

Various procedures are available for non-vital tooth bleaching: In-office bleach technique, Inside/outside bleach technique and Walking bleach technique. Some side effects have been reported in non-vital tooth bleaching including external root resorption, alteration of morphology of dental tissues, modification of the properties of restorative materials and reduction of tooth resistance and adhesion. 7

Different causes of intrinsic discolorations

It is important that clinicians understand the etiology of tooth discoloration to establish the appropriate diagnosis and to define which treatment to apply. 2, 3

Referring to Zimmerli et al. 2010, the intrinsic discoloration is a discoloration that originates from the pulp chamber. Dental trauma or removal of the pulp tissue are the most common causes of intrinsic discoloration. 19

The optical properties and interaction with light of both enamel and dentin help to define the intrinsic color. 2

The modifications of enamel or dentine structures and the induction of different chromatogenic materials into the dental tissues during odontogenesis or in post eruption lead to the intrinsic tooth discoloration. 2, 5

The intrinsic discoloration can be brown, grey, red or yellow. 5 The regular prophylactic techniques cannot remove the intrinsic discoloration and the best treatment is bleaching using

various penetrating agents into enamel and dentin to oxidize the chromogens. 8

- Pulp necrosis:

Pulp necrosis can be caused by mechanical, bacterial or chemical irritations. Chromogenic degradation products such as protein degradation products of the pulp tissues can be generated by pulp necrosis leading to tooth discoloration. 1

The degree and the severity of the intrinsic discoloration is proportional to the period that pulp tissues has been necrotic. 2, 3 The treatment of choice for this discoloration is the intracoronal bleaching. 2, 3

- Intrapulpal hemorrhage:

After dental trauma, the intrapulpal bleeding is the most common etiology of tooth discoloration. 1 After rupture of blood vessels, the blood will penetrate the tubules of dentin and its consecutive break down will lead to different chromogenic degradation products like hematoidin, hemine, hemosiderin and hematin. 1, 5 Added to that, pulp extirpation can generate hemorrhage in the pulp chamber. 1, 2, 3, 26

At first, a pink coloration of the crown can be noticed. 2, 3 The iron (Fe) formed by the combination of heme and the putrefying tissue of the pulp will be turned into dark colored iron sulfates by hydrogen sulfates causing a grey staining of the tooth 2 Referring to Umar et al. 2014, the modification of tooth color is related to the degree of disintegrated hemoglobin.

- Calcification of the pulp:

In case of calcification of the pulp, there is an obliteration of the dentinal tubules and accumulation of reactionary tertiary dentin. 1

Referring to Fearon et al. 2007, we observe a yellow discoloration in case of accumulation of tertiary dentin in the canal and the pulp chamber. This yellow discoloration is not only due to the important volume of additional dentin in the pulp chamber but also due to the translucent enamel.

Generally, the treatment of calcified and discolored tooth is invasive and not conserving the vitality of the pulp (direct or indirect veneers, or ceramic crowns). However, according to Ramos et al. 2013, when respecting the concepts of minimally invasive dentistry and preserving tooth vitality, performing an in- office external bleaching combined with supervised home bleaching is the recommended treatment especially when there is no indication for endodontic treatment.

- Endodontic materials:

The incomplete removal of filling materials, sealer residues and medicaments with tetracycline in endodontically treated tooth can cause coronal discoloration. 2, 3 , 26

Referring to Zimmerli et al. 2010, the combination of some irrigants like sodium hypochlorite and chlorhexidine will cause brownish-red precipitates. That is why a separate rinse between the two different solutions with distilled water or Ringer's solution is recommended. Despite intracoronal bleaching is the best treatment; the prognosis is related to the type of materials and the contact period. 2, 3

- Incomplete removal of pulp tissue:

The incomplete removal of the pulp tissue especially in the pulp horn area during endodontic treatment can cause discoloration by the persistent residual tissue. 1, 5, 26

The residual tissues will disintegrate progressively, and blood components will infiltrate into the dentinal tubules, causing discoloration. 2, 3 The elimination of the remaining tissue and the intra-coronal bleaching is the recommended treatment. 3

- Coronal restorative materials:

Ancient composite restorations can lead to dark discoloration of margins and even discoloration of dental tissues due to the microleakage formed in resin composite. 2, 3

The amalgam can produce a dark grey coloration of dentin when it is used after endodontic treatment because of the black metallic compounds. 2, 3 The use of metal posts for realizing a core can cause discoloration of the crown because of the metallic ion release and transparent enamel. 2, 3

Bleaching agents of Root-filled Teeth

Referring to Carey et al. 2014, bleaching procedure is determined as the chemical degradation of the chromogens. The most used bleaching agents are hydrogen peroxide, carbamide peroxide and sodium perborate. Other ingredients may be present in the different bleaching products like thickening agents, surfactant, carrier and pigment dispersant, preservative, and flavoring. 8

- Hydrogen peroxide HP (H2O2): 2, 4, 9, 26

Nowadays, it is the active and most commonly used ingredient in whitening products. It is used directly or resulting from a reaction involving sodium perborate or cabamide peroxide. Referring to Bahuguna et al. 2013, the commonly used bleaching chemical agents are oxidizers since they degrade the organic structures of the tooth into shorter lighter in color molecules.

- Carbamide peroxide CP (CH4N2O * H2O2): 1, 2, 9, 19, 25

It is also called urea peroxide. An organic white crystalline compound formed by hydrogen peroxide and urea. Bleaching agents with 10% carbamide peroxide will release 3.5% hydrogen. The stable complex will decompose in contact with water to release hydrogen peroxide.

Most of the time, carbamide peroxide is used in a 37% concentration for internal bleaching.

Referring to Douglas et al. 2016, the use of carbamide peroxide for non-vital bleaching is a safe and secure alternative since the diffusion of the hydrogen peroxide to the external root surface is lower and the pH in the external root surface is higher. Added to that, the use of 37% carbamide peroxide generates less structural weakening of the bleached structure compared with sodium perborate.

- Sodium perborate: 1, 2, 25, 26

It is also called perboric acid. Different forms: mono-, tri- (NaBO2 * H2O2 * 3H2O) or tetrahydrate. It is an oxidizing agent presented as a powder.

Sodium perborate will decompose to form sodium metaborate, hydrogen peroxide and nascent oxygen when it is in contact with water, acid or even warm air.

It is often used for internal bleaching since it has excellent results and it respects the periodontal tissues.

Different authors recommend the use of a mixture of sodium perborate and distilled water. However, Kwon et al. 2011 suggested that when we use 30% of hydrogen peroxide mixed with sodium perborate (ratio 2:1 g/mL), we obtain an alkaline pH and the bleaching agent will be more effective.

Importance of the Initial Examination 26, 27

The initial examination is very important in the treatment plan. It includes the evaluation of the color of teeth and the adjacent gingiva.

Added to that, the vitality of teeth must be tested and a radiographic examination is recommended. Dentists must question patients that are presenting a discolored tooth about any history of traumatic injury.

Referring to Van B. Haywood et al. 2010, pulpal problems can happen from 1 to 20 years after dental trauma. Dentists should evaluate the color of the gingival tissues, their thickness and their level. In addition, the color of the root must be taken into consideration.

The discolorations of the gingival tissues may lead to a tooth with a not harmonious color match. Referring to Kwon et al. 2011, the root dentin is different from the dentin in the crown and does not bleach well if at all, nevertheless internal or external bleaching is done. In case that the patient suffers from a gummy smile or hyperactive lip, these problems will be more evident.

The different bleaching techniques

- The walking bleach technique:

In this therapy, clinician applies a bleaching agent into the empty pulp chamber of an endodontically treated and discolored tooth. 5

This technique was first described using a mixture of sodium perborate and distilled water. Later, some authors suggested replacing water by 30% hydrogen peroxide to ameliorate the bleaching efficiency. 1, 2

However, referring to Zimmerli et al. 2010, there is no difference in efficiency between the two methods and that using carbamide peroxide in concentrations of 10% or 35% mixed with sodium perborate will improve the bleaching effectiveness.

Treatment steps referring to Kwon et al, 2011:

* Make a radiographic exam to evaluate the presence or not of a root canal filling and to assess the quality of the endodontic filling.

* Isolate the tooth by means of a rubber dam.

* Clean the pulp chamber and the pulp horns of any debris or pulpal remnants to have the entire pulpal cavity visible and cleanable.

* Eliminate the gutta percha with a heated instrument or a low-speed small round bur to 2 mm below the cementoenamel junction CEJ. We can also use Gates-Glidden or Largo burs. This step can be controlled with a periodontal probe.

* Place a cervical barrier of 2mm thickness with a glass-ionomer cement or a flowable resin to seal the endodontic filling material from the pulp chamber. It is important that the shape of the cervical barrier should be like to the external anatomic landmarks replicating the CEJ level and the interproximal bone level.

* Mix sodium perborate with water or hydrogen peroxide in a ratio of 2:1 (g/mL) to a thick mix.

* Insert the mixture into the pulp chamber with an amalgam carrier or an applicator.

* Use a damp cotton pellet to eliminate the excess.

* Seal the access cavity with a provisional filling material like Cavit, glass-ionomer cement or IRM.

Referring to Fearon et al 2007, the bleaching agent should be covered with cotton pellet and sealed with an adhesive temporary restoration. 5

The provisional adhesive restoration is recommended because it ameliorates the seal against the penetration of bacteria. 1

In the next appointment (after 3 to 5 days), the bleaching result is evaluated and, if necessary, the walking bleach procedure is repeated (3 to 5 times) until the color becomes similar to the adjacent teeth. 26

The final step after the last walking bleach technique is the restoration of the access cavity with resin composite. This procedure is achieved 2 to 3 weeks later when the desired color change is obtained and the bond strength to the tooth has returned to normal. 26 The resin composite used for final restoration should have a light color. 5

The walking bleach technique is not recommended only for adults but also for children with colored non-vital tooth. A case report of a 12-year-old female patient treated with internal bleaching and with 6 years follow-up showed good prognosis and no reversal of tooth discoloration. 21

The walking bleach technique using sodium perborate mixed with distilled water is recommended as a secure alternative in whitening non-vital primary teeth with intrinsic discoloration. 28

- The inside/outside bleach technique:

The principle of this technique is to apply the bleaching agent in the same time on the facial enamel (outside) and the sealed cavity access (inside) of the discolored endodontically treated tooth. 1, 5

For this technique, we use a vacuum-processed plastic mouthguard that is cut to the facial and lingual margins after taking an alginate impression of the whole arch. 5 The preparation of the cavity access and the achievement of the cervical barrier were performed as previously described for the walking bleach technique.

The bleaching agent used is 10% to 20% carbamide peroxide gel (syringe) that the patient inserts in the access cavity and the marked tooth of the vacuum-drawn splint. 1, 5, 26, 27

Some instructions to give to the patient: To eliminate the excess of the bleaching agent after inserting the splint with a fingertip or a cotton swab and to place a cotton wool plug in the cavity access to prevent accumulation of food particles. 1, 5

In the control visits, when the non-vital tooth has been bleached, the steps followed are as previously described for the walking bleach technique. The major drawback of this technique is the lack of bacterial control affecting the result and the endodontic treatment longevity. 1

The risk of this technique is stopping the bleaching by the patient himself and not returning to the dental office in time to seal the cavity access. 27

- In-office bleaching technique:

For this technique, a high concentration of hydrogen peroxide 35% is used like in-office bleaching of vital teeth. 26

The hydrogen peroxide will be applied in the external and/ or the internal surface of the discolored tooth and it can be activated with light and/or heat to increase the chemical reaction. 27

The major risk of this technique is resorption and loss of the tooth because of the history of trauma, the high concentration of hydrogen peroxide used, the high heat used to activate the bleaching agent, the absence of seal over the gutta-percha and the absence of connection between enamel and cementum. 27 For this technique, it is recommended to isolate the tooth with a rubber-dam. [1, 26]

The application time of the bleaching agent is 15--20 minutes. Then, the gel is eliminated and rinsed off. The application is repeated until the desired shade is obtained. [1]

Side effects of bleaching of non-vital teeth

- Cervical root resorption:

Referring to Bahuguna et al. 2013, it is defined as an inflammatory mediated external resorption affecting the root, occurring after trauma and after internal bleaching. The bleaching agent will diffuse via dentinal tubules and reaches the cervical cementum and the periodontal ligament initiating an inflammatory reaction. 4, 6

The use of an important concentration of hydrogen peroxide activated with heating can lead to cervical root resorption. 4, 5, 6

This complication of bleaching can develop when a thermo-catalytic bleaching technique is employed in teeth presenting cervical defects of the cementum. 4

The use of 30% hydrogen peroxide alone or mixed to sodium perborate is more toxic and dangerous for the periodontal ligament cells than the mixture of sodium perborate and water. 5

Most of the times, the diagnosis of the cervical root resorption is done after several years. 4

This complication is observed through routine radiographs. However, in some cases we can note the presence of papillary swelling and tenderness to percussion. [5] Referring to Leith et al. 2009, there is no evidence that cervical resorption can occur after using a low concentration of hydrogen peroxide associated with heat like in inside/outside bleaching procedure.

A clinical case treated by Kim et al. 2012 showed an invasive cervical resorption. The explanation of the authors was the damage of the cervical cementum resulting from avulsion (after trauma) and from intra-coronal walking bleach technique (sodium perborate and distilled water).

- Effects on enamel:

Bleaching of non-vital teeth can lead to substantial alteration of the enamel surface topography. The amount of alteration depends on concentration of peroxide used and the period of exposure. 5 The considerable alterations affecting the enamel after bleaching described in literature are: 8

* Augmentation of porosity of the superficial enamel structure.

* Demineralization.

* Reduction of protein concentration.

* Degradation of organic matrix.

* Changing in the calcium: phosphate ratio, calcium loss.

Other morphological alterations that can affect enamel surface are shallow depressions and slight erosion. 8

After bleaching, the surface roughness will be increased and the bleached teeth will be more vulnerable to extrinsic discoloration. 5

Added to that, the use of 35% hydrogen peroxide increase the diminution of hardness and the histomorphologic changes of the enamel surfaces exposing the tooth to risk of caries. 8 Reducing the contact time of 35% hydrogen peroxide or its concentration will produce a progressive color change of the tooth and will minimize the diffusion of hydrogen peroxide through both enamel and dentin. 12

The diminution of bond strength of enamel and dentin treated with HP is caused by residual oxygen existent in enamel and dentin pores after bleaching treatment. 10

- Effects on dentin:

Referring to Berger et al. 2014, the presence of calcium in the composition of bleaching products will influence the flexural strength of bovine dentin after bleaching procedure (office bleaching 35% HP and home bleaching 7.5% HP).

A study of Pessarello et al. 2012 that evaluated the bond strength of adhesive systems and composite resin to bleached dentin concluded that the association with fluoridated adhesive and flowable resin ameliorates the shear bond strength of dentin submitted to internal bleaching.

- Effects on restorative materials:

The oxygen released into the tooth structure after bleaching will inhibit the polymerization of resin. 5

The use of 10--16% carbamide peroxide will lead to an increase in surface roughness and numbers of porosities of microfilled and hybrid composite resins. 8

Referring to Bahannan et al. 2015, the influence of bleaching agents on surface roughness can be considered concentration dependent.

Carbamide peroxide with different concentrations did not produce a prejudicial effect on the fracture toughness and flexural strength of composite resin. Added to that, in-office bleaching agents (35% CP and HP) did not

affect the tensile strength of composite resin. 13 The microhardness of nano composite resin and resin modified glass ionomer is reduced significantly with 20% and 35% carbamide peroxide. 11

Clinicians have to inform their patients concerning possible modifications that may affect their existing restorations by bleaching agents and the possibility of replacing them after the treatment due to color difference and surface or subsurface alteration. 8, 13 Concerning the glass ionomer cement, the setting of cement is inhibited by the residual oxygen. 10

It is necessary to wait at least 2 weeks before placement any adhesive restorative material after completion of bleaching. 13

Referring to Vohra et al. 2013, bleaching procedure using 10% carbamide peroxide reduce importantly the microtensile bond strength of resin composite to enamel. Moreover, it is recommended to use 10% sodium ascorbate when resin composite restoration will be placed instantly after bleaching.

The application of 10% sodium ascorbate for 10 min is enough to have a reversal effect. 14

Referring to Feiz et al. 2017, the use of antioxidant agents, regardless of their type, form, concentration and duration of application, can improve the shear bond strength after bleaching. To dissolve the remnants of peroxide, dentists can clean the cavities with catalase or 10% sodium- ascorbate. However, their applications can be time-consuming or expensive. 10

The placement of a protective varnish on the surface of restoration can be advantageous to reduce the adverse bleaching effects on restorations. 13

When the duration of application of sodium perborate --hydrogen peroxide mixture is increased, the rate of microleakage of the restored access cavities will be more important. For this reason, it is recommended to use intracoronal medication of calcium hydroxide (7 days) after walking bleach technique. 10

- Fracture resistance of bleached teeth:

A study of Azevedo et al. 2011, evaluated the fracture resistance of teeth treated with internal bleaching and restored with various procedures. The conclusion was that bleached teeth can be restored with composite resin alone and the use of posts in these teeth did not ameliorate their resistance.

Another study of Leonardo et al. 2014, evaluated the fracture resistance of teeth exposed to several internal bleaching protocols using 35% hydrogen peroxide, 37% carbamide peroxide, 15% hydrogen peroxide with titanium dioxide nanoparticles photo activated by LED-laser or sodium perborate. The conclusion was that all these protocols reduce, in equal values, the fracture resistance of endodontically treated teeth.

Clinical cases:

Case report NA1:

A 17-year old patient was unsatisfied with the discoloration of the tooth 21. History: trauma. The treatment proposed was the endodontic retreatment of the 21 and walking bleach technique using Endoperox kit (100 % carbamide peroxide

Case report NA2:

A 29-year old patient was unsatisfied with the discoloration of the tooth 21. History: trauma. The treatment proposed was the endodontic treatment of the tooth 21 and walking bleach technique using Endoperox kit (100 % carbamide peroxide).

Case report NA3:

A 64-year old patient was unsatisfied with the discoloration of the tooth 11 caused by trauma. The treatment proposed was the walking bleach technique using sodium perborate with distilled water.

Case report NA4:

A 32-year-old patient was unsatisfied with the discoloration of the tooth 11 caused by trauma. The treatment proposed was the walking bleach technique using sodium perborate with distilled

Conclusion

Bleaching of non-vital teeth can be achieved by either walking bleach technique, inside/outside bleach technique or in-office bleaching procedure. The bleaching agents used are sodium perborate, hydrogen peroxide and carbamide peroxide.

The above clinical cases highlight the effectiveness of the walking bleach technique in producing successful esthetic results and patients showed satisfaction with the outcome. Referring to literature, bleaching of non-vital teeth is an effective and safe technique to manage discoloration. However, clinicians must inform their patients about the potential risk of cervical resorption.

After termination of bleaching, it is recommended to delay resin composite restoration for at least 1--3 weeks. Each year follow-up visits are advisable to control the outcome and to repeat the bleaching treatment when clinician detects a regression of the initial result to preserve the desired esthetic color.

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