Summary

Tooth discolouration caused by endodontic procedures can be an important aesthetic concern to the patient. The literature reveals a number of different approaches for the management of coronal discolouration. In this chapter, we discuss aetiological factors for coronal discolouration, its prevention, and management guidelines including patient preparation, intracoronal bleaching procedures, and their prognosis. The chapter also covers possible complications following bleaching, ways to prevent them, and current recommendations for restoration of teeth following bleaching. The potential for tooth discolouration following regenerative endodontic procedures together with a suggested management protocol is discussed.

23.1 Introduction

The appearance of teeth is of particular cosmetic importance with ever-increasing interest amongst the public and dental practitioners [1–3]. Tooth discolouration creates a range of aesthetic problems, and considerable amounts of time and money are invested in attempts to improve the appearance of discoloured teeth.

Tooth discolouration describes a broad array of clinical manifestations that can result from an equally broad list of aetiological factors [4–6]. Therefore, it is important for dental professionals to have a thorough knowledge and understanding of the aetiology and clinical features of tooth discolouration in order to prevent its occurrence and also to select the most appropriate treatment for each case [7, 8]. In this chapter, we will discuss aetiological factors, methods of prevention, and guidelines for the management of coronal discolouration and their prognosis. In addition, potential complications following bleaching procedures, ways to prevent them, and current recommendations for restoration of teeth following bleaching with a final section on the discolouration potential of regenerative endodontic procedures (REPs) are discussed.

23.2 Aetiology

The ability to assess and diagnose the cause of coronal discolouration accurately allows clinicians to execute the appropriate treatment modality and avoid disappointing outcomes [4–6].

Tooth discolouration can be intrinsic, extrinsic, or a combination of both. Internalised tooth discolouration is another category that describes the changes in normal tooth colour because of cracks, dentinal caries, and dental restorations [2, 3, 8]. Table 23.1 summarises aetiological factors for tooth discolouration.

A wide range of endodontic procedures can discolour teeth and/or the gingiva such as direct pulp capping [9], pulpotomy procedures [10], repair of perforation and resorption defects [11, 12], root canal treatment procedures [8], and regenerative endodontic procedures (REPs) [13], in addition to inappropriate application of root-end filling materials in root-end surgical procedures [14]. This chapter focuses on coronal discolouration caused by vital pulp treatments (direct pulp capping and pulpotomy), root canal treatment, and REPs.

Direct pulp capping and pulpotomy procedures require the direct application of a suitable material onto dentine and pulp tissues, which creates a wide range of interactions with body fluids and blood. One systematic review concluded that pulp capping materials such as grey and tooth-coloured (white) ProRoot MTA (WMTA) (Dentsply, Tulsa, OK, USA), grey and white MTA Angelus (Londrina, PR, Brazil) have a strong discolouration potential compared to other materials such as calcium hydroxide, Biodentine (Septodont, Saint Maur des Fosses, France), and EndoSequence Root Repair Material (Brasseler USA, Savannah, GA, USA) [15], mainly because of heavy metal oxides such as iron and/or bismuth oxides that interact with collagen and blood as well as NaOCl [15, 16] that is often used in pulpotomy procedures before application of the capping material [10].

Following root canal treatment, loss of moisture from the tooth is expected, and this may alter the light-transmitting properties of root filled teeth. Although usually not reported, if also associated with unsatisfactory endodontic procedures, then discolouration ranging from mild to severe may occur [8]. Coronal tooth discolouration may be the result of intra- and/or post-root canal procedural errors, mainly because of inadequate removal of coronal pulp tissues and subsequent degradation of erythrocytes into iron pigments and insufficient knowledge of the discolouration potential of intra- and post-endodontic materials including irrigants, medicaments, and root canal sealers [8, 17–35]. Tables 23.2 and 23.3 and Figure 23.1 summarise the discolouration potential of endodontic materials.

23.3 Prevention of Coronal Discolouration Related to Endodontic Procedures

For direct pulp capping and pulpotomy procedures in aesthetic areas, the selection of capping materials with no or minimal discolouration potential is essential. Indeed, the use of biocompatible pulp capping materials that can induce hard tissue formation is of prime importance; however, the operator should be aware of the chemical composition of capping materials and their discolouration potential, especially for anterior teeth.

During root canal treatment, a well-designed and appropriately extended access cavity is essential in the anterior dentition. Successful detection, with the aid of a contra-angled probe, and removal of any “catch” from the roof of the pulp chamber will ensure complete removal of pulp tissue, particularly from the mesial and distal pulp horns [8] (Figure 23.2). Thorough irrigation of the access cavity will also help to ensure that all pulp tissue has been removed from the pulp chamber [8]. Notably, Clark and Khademi [36, 37] introduced conservative designs for access cavity preparations in molar teeth to minimise tooth structure removal, especially the pulp chamber roof and pericervical dentine, which has been a subject of recent research. However, there is no evidence to support this conservative approach in the anterior dentition. The authors believe that the potential benefits for leaving the pulp roof in the anterior teeth is not justified and may compromise aesthetics because of the possibility of retaining pulp tissue (usually infected) in the narrow pulp horns, which can be a location for sealer remnants that can also add to the discolouration. In addition, the adaptation of the final tooth-coloured restoration to this area could be compromised.

During root canal treatment, all intracanal medicaments should be confined to the root portion of the canal system (or apical of gingival margin in instances of gingival recession) [8] (Figure 23.2). They should not be placed in the crown of the tooth or in the pulp chamber in order to avoid coronal discolouration particularly since they have no therapeutic effect in that situation. Most medicaments are pastes, and they should be placed in the root canal in a manner that does not leave remnants in the pulp chamber. This can be achieved using either delivery needles with suitable gauges (such as a NaviTip, Ultradent, UT, USA) or a spiral paste filler in a low speed handpiece. The use of magnification (such as dental loupes or microscope) is helpful. The operator should remove all paste residue from the pulp chamber walls with an excavator and then wipe the pulp chamber clean with one or more (as required) wet cotton pellets [8]. The use of sandblasting can be beneficial for cleaning the access cavity [38]. After root canal filling, excess material should be removed completely from the pulp chamber to a level that is at least 2 mm apical to the gingival margin/cemento-enamel junction (CEJ).

23.4 Management Guidelines

23.4.1 History

Before management, a detailed and systematic history is essential to aid in the diagnosis of coronal discolouration. A focused exploration of the nature of the staining will help to identify the cause of the discolouration and thus define the most appropriate treatment approach [4]. Gathering information from patients related to the duration and progression of discolouration as well as a history of trauma, pain, previous treatment, and habits (such as smoking) are essential [5, 6].

23.4.2 Evaluation and Preparation

A thorough clinical examination, augmented by an appropriate radiographic examination, is mandatory for proper evaluation of a discoloured tooth [5, 6, 8]. Improper adaptation and/or discoloured margins of coronal restorations, the presence of carious lesions and extrinsic stains, the quality and coronal extension of the root filling, as well as periodontal diseases should all be identified initially. It is essential to treat caries, remove calculus and extrinsic stains (if present), and polish the external crown surface to facilitate the proper identification of the final tooth shade before starting any bleaching procedure, if needed [6, 39, 40]. Detailed discussion with the patient including the risks and benefits of each treatment option is essential.

23.4.3 Selection of the Appropriate Treatment Approach

23.4.3.1 Removal of the Cause

In discoloured teeth following vital pulp treatments using MTA formulations, a radiographic confirmation for dentine bridge formation is necessary before intervention to prevent traumatic exposures. Under magnification, a small access can be performed to reach the discoloured MTA, which can be removed using a small round bur [10] (Figure 23.3). This step usually results in considerable improvement in the colour of the tooth [10] (Figure 23.3). Intracoronal bleaching can be performed if necessary.

In root canal treated teeth, adequate extension of the access cavity and removal of remaining pulp tissue (if present) and root canal filling material coronal to the level of cemento-enamel junction (CEJ) or gingival margin (based on which is in a more apical location) is required before internal bleaching [8, 41]. Indeed, the quality of previous root fillings should also be evaluated carefully, and retreatment procedures should be scheduled before bleaching, if indicated. The tooth should then be re-evaluated since the colour may be satisfactory once the cause has been removed. This is typically the case when the discolouring agent only acts as a dark background and has not yet penetrated into dentinal tubules [8].

23.4.3.2 Intracoronal Bleaching

Intracoronal (internal) bleaching is a simple, inexpensive, and reliable treatment approach for most coronal discolouration caused by endodontic procedures [42] (Figures 23.4–23.6).

23.4.3.2.1 Materials Used for Intracoronal Bleaching

Hydrogen peroxide (H₂O₂) and hydrogen peroxide-releasing agents, such as sodium perborate (NaBO₃.nH₂O – where “n” represents the available formulations in monohydrate, trihydrate, and tetrahydrate) and carbamide peroxide (CH₆N₂O₃), are the most commonly used bleaching agents [39, 43]. In addition, sodium percarbonate has been suggested as a possible substitute for sodium perborate because of its high bleaching effectiveness at a low temperature [42]. Despite its comparable in vitro cytotoxicity and genotoxicity to other bleaching agents, more in vivo investigations are required to validate its safety for clinical applications [44].

Various concentrations, formulations (liquid or gel), combinations (sodium perborate/hydrogen peroxide, and sodium perborate/carbamide peroxide), and application of heat or light have been suggested in an attempt to accelerate and optimise the bleaching process [39, 40, 43]. However, it should be noted that the use of bleaching agents at high concentrations (such as 30% of hydrogen peroxide) with the aid of heat (thermo-catalytic technique) increases the risk for external invasive root resorption [45], especially in traumatised teeth or those with infected root canals [40, 46]. In addition, these bleaching agents should be handled with care to avoid contact with the oral tissues, which can lead to chemical burns and scar tissue formation.

23.4.3.2.2 Patient Preparation for Intracoronal Bleaching

In general, there are no specific guidelines for patient preparation. However, the American Dental Association (ADA) recommends that application of bleaching materials should be deferred during pregnancy [47]. The American Academy of Pediatric Dentistry has developed guidelines for bleaching procedures in the primary dentition [48]; however, intracoronal bleaching of primary teeth is generally not recommended because of a lack of research and potential risks of root resorption. In addition, the permanent successor teeth can also be at risk of developmental disturbance from intramedullary inflammatory changes [48].

A preoperative photograph should be taken with a colour reference for documentation before bleaching a tooth. Furthermore, a preoperative radiographic view is important to evaluate the periapical status of the tooth and the quality of the root filling. If the quality of the root filling is questionable and there is a likelihood of canal infection, root canal retreatment should be performed before commencing the bleaching procedure. It is preferred that the operator plans with the patient for the estimated time frame of the bleaching process. The literature reveals evidence for the effect of bleaching time on the fracture resistance of teeth [49]; however, it must be remembered that this association is limited to experimental studies and requires further research.

23.4.3.2.3 Placement of the Coronal Barrier

A protective barrier may help to prevent leakage of bleaching agents between the gutta-percha (GP) and the root canal walls that may reach the periodontal ligament via dentinal tubules, lateral canals, or the apical foramen [6, 8]. The root canal filling material should be 2–3 mm apical to the CEJ/gingival margin. It is important that all root canal filling material is removed carefully from the pulp chamber (without removing dentine unnecessarily) to allow proper diffusion of the bleaching material into the discoloured dentine.

The coronal portion of the canal should be sealed with a dental cement such as Cavit or IRM [4, 5]. Preferably, the barrier should be manipulated to match the contour of the epithelial attachment [8]; however, evidence is lacking for its effectiveness compared to placing the barrier horizontally at the level of CEJ or gingival margin (the one which is more apical). The use of adhesive materials as coronal barriers has been advocated; however, there are concerns that such materials may block the dentinal tubules thus compromising the penetration of the bleaching material if it is necessary to apply it more apically in subsequent visits. Cavit or IRM is easier to remove when stepwise reduction is indicated in cases with resistant cervical discolouration and the bleaching has to be applied more apically [8] (Figure 23.5).

23.4.4 Types of Intracoronal Bleaching

23.4.4.1 Walking-Bleach Technique

This technique was first described by Spasser [50] (Figure 23.4). The bleaching material is introduced into the access cavity after placing the coronal barrier (Figure 23.4a–d). Sodium perborate is usually mixed with distilled water [51, 52] (Figure 23.4e, f) rather than with hydrogen peroxide to reduce the risk of post-bleaching external root resorption [51]. Sodium perborate can be mixed with carbamide peroxide to enhance the bleaching effect, regardless of the concentration of carbamide peroxide (10% or 35%) [53]. It has been shown that carbamide peroxide has a greater capacity for penetration into dentine compared to sodium perborate [54]. Previous etching of dentine with phosphoric acid before placing the bleaching agent will enlarge dentinal tubules but has no effect on the results of bleaching [55].

After placing the bleaching material, a provisional restoration with a good seal must be placed (Figure 23.4g). One study reported that Cavit (Premier Dental, Philadelphia, PA, USA) and Coltosol (Coltene, Altstätten, Switzerland) had a better marginal seal to the access cavity for 1 week compared to Fermit (Ivoclar Vivadent, Schaan, Liechtenstein), and zinc oxide-based cements [56]. According to previous recommendations, the bleaching agent can remain for 3 to 7 days, then it should be removed or replaced with fresh bleaching agent, if needed [40]. However, there is evidence that sodium perborate tetrahydrate can still be active for more than 7 days; thus, the bleaching interval may be increased up to 3–4 weeks in order to reduce the number of clinical appointments, particularly in cases with severe discolouration [57].

It is recommended to take a photo at every recall and compare it with the previous session. At the end of the bleaching therapy, a photo should be taken for the patient’s record and for documentation of the long-term success of the treatment (Figure 23.4h, i). It has been recommended that a calcium hydroxide suspension should be inserted coronal to the root filling to reduce the polymerisation inhibition of the final restoration as a consequence of remaining oxygen and to reduce the permeability of dentine [58]. Furthermore, the low pH in the pulp chamber is increased by the calcium hydroxide [59]. Instead of placing a calcium hydroxide suspension, the adhesion of resin composite restorations can be improved by rinsing the cavity with 10% ascorbic acid [60].

23.4.4.2 Inside-Outside Bleaching

The technique was first described by Settembrini et al. [61], and presented as a modified walking-bleach in another report [62]. In this technique, the bleaching agent is placed in the access cavity of the root filled tooth (after the protective barrier) and on the outer enamel surface. The access cavity remains open with no provisional restoration. The mouth guard (bleaching tray) made for bleaching has a reservoir on the buccal and palatal/lingual surfaces of the tooth. The patient is taught how to place the bleaching agent (usually 10% carbamide peroxide) into the mouth guard and access cavity, which should usually occur at 2-hour intervals. The recall is usually set every 2–3 days to evaluate the outcome. Good patient compliance is mandatory for the success of this technique, which would be difficult when the treatment duration is longer [63]. It is also possible to combine this technique with bleaching other teeth in the arch. In this case, the design of the mouth guard should be adapted to include all the teeth scheduled for bleaching [64]. Within the first few days, the efficacy of the inside-outside bleaching technique could be greater compared to the walking-bleach technique; however, it has been shown that after 6 months the success rate of both techniques is similar [65]. The increased risk for microbial invasion into the open access cavity is a concern, even with the presence of the protective barrier, which explains why this technique is not usually practised or taught in dental schools.

23.4.4.3 In-Office Bleaching

This technique (also associated with bleaching of teeth with vital pulps) can be used in root filled teeth. A rubber dam or the application of a resin material (liquid dental dam such as Opaldam, Ultradent, South Jordan, UT, USA) is required to avoid bleaching of the gingival tissue. The tooth is prepared in the same way as described for the inside-outside technique. However, the bleaching tray is not used because the highly concentrated bleaching agent (30% hydrogen peroxide) is placed directly in the pulp chamber and on the outer surface the tooth. After 15–20 minutes, the bleaching agent is rinsed off and the procedure can be repeated if needed. It is important that the patient wears protective glasses to avoid contamination of the eyes with the highly concentrated bleaching agent. Similar to bleaching of teeth with vital pulps, home bleaching with lower concentration, but for a longer period, can be more successful than in-office bleaching for long-term success [66]. The final restoration should be placed in the next appointment. Bleaching with hydrogen peroxide-releasing agents may result in significant decrease of enamel calcium and phosphate content and alteration in the dentine organic matrix, which may not allow formation of a strong and stable bond between the resin composite applied and the superficial etched enamel layer [67]. Furthermore, the residual oxygen present in enamel and dentine pores after completion of the bleaching treatment can inhibit polymerisation of resins that cure via a free-radical mechanism [67]. However, the oxygen can be removed by applying an antioxidant (such as ascorbic acid) for 3 minutes [60].

Table 23.4 provides a summary for the advantages and disadvantages of the bleaching techniques mentioned previously.

23.5 Bleaching of Teeth with Calcified Pulp Chambers and Root Canals

Pulp canal calcification (PCC), a gradual narrowing of the pulp space because of accelerated deposition of hard tissue within the pulp chamber and along the root canal walls is a common sequela of luxation injuries [68, 69]. Likewise, orthodontic treatment may initiate the accelerated deposition of secondary dentine [70, 71]. Furthermore, the incidence of PCC is increased in teeth of older patients [72] or in restored teeth [73]. PCC is considered a sign of pulp vitality, and unless there is clinical and radiographic evidence of pulp necrosis, root canal treatment is not indicated [74–78]. Due to decreased translucency, teeth with PCC often have a yellow discolouration of the crown [76, 79].

Intracoronal bleaching of calcified teeth is one indication for elective root canal treatment [80], which is likely to provide a good aesthetic result. However, some practitioners may consider root canal treatment not justifiable in teeth with vital pulps, which might be associated with an increased risk of perforation [81], especially when an operating dental microscope and options for guided access cavity preparations are not available. A less invasive method has been suggested in which an access cavity is prepared without exposure of the pulp [82]. After application of a protective base, intracoronal bleaching can be performed as described previously [82]. However, concerns have been raised because of the increased risk of pulp exposure and root canal infection associated with this approach [78]. Therefore, this treatment option remains questionable.

As a simple and noninvasive treatment option, a home bleaching gel can be used for extracoronal bleaching in a specially designed bleaching tray with a reservoir on the labial surface of the affected tooth [83–85] (Figure 23.7). To restrict the bleaching effect to a single tooth, windows can be cut out on either sides of the tray adjacent to the discoloured tooth [78, 86