Summary

Maintaining healthy pulp tissue and preventing apical periodontitis form the basis of minimally invasive, biologically based vital pulp treatment (VPT). Although the dental pulp has the ability to both protect itself against irritation and repair itself afterwards, treatment of deep caries and pulpal exposure has traditionally been regarded as unpredictable. Developments in biomaterial science and an increased understanding of the role of dentine and molecular influences on pulpal repair have led to the promotion of new treatment strategies for pulpitis. Caries remains the principle challenge to the dental pulp and if untreated will progressively stimulate pulpitis, pulp infection, and necrosis. If the carious process is deep or extremely deep, even the symptomatic pulp has the capacity to recover if managed correctly. Selective-caries (i.e. partial) removal strategies reduce the chance of pulp exposure and are generally preferred in responsive sensible teeth with symptoms no worse than reversible pulpitis. This treatment can be carried out as a one-visit or two-visit stepwise approach. Conservative strategies for carious pulp exposure, including pulp capping and pulpotomy are also re-emerging as definitive treatment choices in permanent teeth even with signs/symptoms indicative of (partial) irreversible pulpitis. This chapter gives an overview of current trends in VPT for both the exposed and unexposed pulp.

16.1 Introduction

VPT encompasses a range of techniques aimed at preserving all or part of the dental pulp [1]. The pulp can be challenged by trauma, mechanical or microbiological irritants, with dental caries and micro-leakage around restorations the most common causes of pulpitis, highlighting the essential role of microbial infection in causing pulpal disease [2, 3]. Pulpal disease starts as an inflammatory process (pulpitis), which is often painful and only becomes severe when the irritation such as caries nears the pulp [4]. If the challenge is allowed to proceed without intervention, pulp necrosis will ensue and the tooth will require root canal treatment (RCT) or extraction [5]. Notably, if the disease process is managed and the tooth suitably restored, then there is growing evidence to suggest that RCT can be avoided and the tooth managed conservatively even with advanced pulp disease [1, 6]. However, if carried out well root canal treatment (RCT) is a successful procedure, why is there a need to preserve pulp vitality in cases of deep caries and pulpal disease? The main advantages of VPTs are:

• It maintains the pulp’s developmental, defensive, and proprioceptive functions [7–9],
• It is often technically easier to carry out than pulpectomy [10], and
• It preserves tooth substance and improves the cost-effectiveness of treatment [11].

Therefore, VPTs should be encouraged as an efficacious alternative to RCT for the management of pulps that can be saved and remain functional.

VPTs are biologically based minimal intervention strategies that include the management of deep caries to avoid pulp exposure, using either one-visit selective caries removal techniques or two-visit stepwise excavation techniques [12]. The conservative management of pulp exposure by pulp capping and pulpotomy techniques is also considered part of VPT [1]. In general, there is good clinical trial evidence to support selective caries removal and the avoidance of pulp exposure in cases of deep caries as long as the pulp responds to sensibility tests and there is an absence of symptoms indicating more than reversible pulpitis [13–17]. It is accepted, however, that signs and symptoms may necessitate exposing or removing the pulp and that the caries may be so deep in certain cases that exposure becomes inevitable. In order to assist practitioners faced with advanced disease, a division between ‘deep’ and ‘extremely deep’ caries has now been introduced [1]. In deep carious lesions, there is ‘radiographic evidence of caries reaching the inner third or quarter of dentine, but with a visible zone of dentine between the caries and the pulp’ [1]. Treatment of deep caries carries a risk of pulp exposure. Notably, in extremely deep carious lesions, there is ‘radiographic evidence of caries penetrating the entire thickness of the dentine with certain pulp exposure’ [1]. Therefore, selective caries removal techniques are unlikely to be of assistance in extremely deep caries cases [1].

The overall aim of this chapter is to analyse current evidence on VPT, including the defensive response of the dentine-pulp complex to irritation and the diagnosis and management of teeth with deep carious lesions and pulp exposures.

16.2 Caries: Current Thinking and Radiographic Classification

It is tempting to ask whether caries is still a problem? If we address this question from a global perspective, caries clearly remains a huge burden [18]; however, a focus on prevention and reducing the speed of disease progression represents a clear trend in Western society. In 2004, the reasons for performing RCTs was investigated over a 25-year period in Denmark, during which it was hypothesized that caries would not be the principal reason for RCT [19]. Notably, the data revealed that over half the cases were related to caries (55%), followed by traumatic infractions (14%). The results were influenced by age with 80% of younger patients, ages 20–28 years, having RCT due to caries. In the oldest group (70–79 years), this declined below 50% [19]. This highlights that operative intervention for carious disease remains a major issue, even in countries with a low prevalence of caries such as those in Scandinavia. In countries with a low caries rate, there is a marked decrease in the number of extractions; however, the number of RCTs are increasing, as RCT in molars becomes more common.

When researchers analysed the frequency of VPTs (pulpotomies, direct pulp capping, and stepwise excavation) over several decades in Denmark, a relatively low proportion was observed compared with RCTs. In the 1970s, only 12 of 1000 patients received a pulpotomy, with this number reducing almost to zero by the start of the century [20]. In terms of other VPT procedures, fewer than 10 of 1000 patients received direct pulp capping and stepwise excavation by the year 2000 (Figure 16.1). Accepting the limitations of these findings, one could speculate that the previous pulpotomies were used as an alternative to challenging RCT and that the integration of rotary nickel-titanium instrumentation has reduced the concern about carrying out technically challenging RCT. However, this is just speculation.

In 2015, a consensus group gathered in order to update and clarify the nomenclature for carious disease and specify the clinical meaning of carious tissue removal [21, 22], which included a radiographic focus on deep lesions being two thirds to three fourths through the dentine thickness. For teeth with deep carious lesions, there is a diagnostic problem as we are not able to noninvasively or objectively measure the degree of pulp inflammation. As a result, the dentist is forced to apply other subjective measures to establish a diagnosis, including subjective patient information, tooth sensibility, and radiographic interpretation. Within VPT and deep carious lesions, clinically, there is strong rationale to identify a radiographic threshold indicating when exposure should be prevented and when it is inevitable. Within the limitations of the two-dimensional radiographic view, a clinically relevant radiographic classification is proposed, deep and extremely deep, which guides the operator’s choice between avoiding pulp exposure and managing the exposed pulp. The deep lesion is defined as being into the pulpal quarter of the dentine but still with radiodense dentine separating the lesion from the pulp, whereas extremely deep lesion will have the demineralized/translucent lesion in radiographic contact with the pulp [1, 23]. The biological rationale supporting the deep/extremely deep classification is that microorganisms are not expected if there remains a radiopaque barrier separating the carious lesion from the pulp cavity. In contrast, when the carious lesion has reached the pulp radiographically, the risk of microbial invasion is inevitable, making clinical attempts to avoid exposure unrealistic [1, 23].

Core Points

• Caries remains a worldwide oral health problem and preserving pulp vitality is crucial to prevent further infection.
• A radiographic subdivision of caries penetration enables the selection of treatments, either avoiding exposure or recommending pulp capping or pulpotomy.
• In well-defined deep lesions, the risk of pulp infection is considered low.
• In extremely deep lesions, the risk of pulp infection is considered high.

16.3 Role of Pulp and Dentine in Repair

In health, the pulp is encased in dentine with the odontoblast cells lining the periphery of the pulp in contact with dentine; this forms a functional unit known as the dentine-pulp complex [24]. This ‘complex’ reacts to challenge (e.g. caries) by a combination of pulpal inflammation and the promotion of mineralisation processes, a balance that is essential if pulp vitality is to be maintained [25]. From an immunological perspective, microbial presence is first recognised by odontoblasts; however, later other pulpal cells including fibroblasts, stem cells (SCs), and immune cells are involved during the activation of a series of antibacterial, immune, vascular, and localised inflammatory responses [5, 26]. The odontoblast acts as part of the early pathogen recognition system [27]; however, its principle function is to secrete mineralised tissue, forming primary dentine during tooth development and the production of secondary dentine throughout life, as well as tertiary dentine production in response to irritation [28]. Tertiary dentine forms in the inflamed pulpal region below the dentinal tubules affected by the challenge [29, 30]. There are two types of tertiary dentine, with a mild/low-grade irritation inducing an upregulation of existing odontoblast activity and forming reactionary dentine, while stronger stimuli cause odontoblast death and the initiation of a complex cascade of cellular processes involving the recruitment of dental pulp progenitor cells by the release of endogenous bioactive molecules from dentine and pulp tissue. These bioactive molecules promote differentiation of the progenitor cells into odontoblast-like cells, forming the second tertiary dentine, reparative dentine [30]. Other cells, including fibroblast and circulating mesenchymal progenitor cells (i.e. fibrocytes) have been proposed to at least contribute to the mineralised process or perhaps even cyto-differentiate to become secretory cells themselves [30, 31]. From a clinical perspective, the most advanced/aggressive parts of the lesion are likely to display reparative dentinogenesis, and the new or slowly advancing parts of the lesion are likely to exhibit reactionary dentinogenesis [32] with the likelihood that both processes will be ongoing in a tooth with deep caries.

The cellular events associated with tertiary dentine formation are orchestrated and regulated by a range of bioactive molecules, including growth factors (GFs), chemokines, cytokines, and proteases, which are stored in the dentine matrix during development, prior to being released by advancing caries [9, 33–35]. The carious process will demineralise dentine, releasing dentine matrix components (DMCs), with the assistance of matrix metalloproteinases (MMPs). These MMPs are contained within the DMCs and propagate the breakdown of dentine matrix [36], releasing other bioactive molecules that migrate down the dentinal tubules and stimulate tertiary dentine formation and associated reparative processes [37–39]. Therapeutic intervention using the irrigant ethylenediaminetetraacetic acid (EDTA) [40], ultrasonics [41], and dental materials including calcium hydroxide and mineral trioxide aggregate (MTA) [42] can also induce the release of bound DMCs from the extracellular matrix. The multiple bioactive constituents of DMCs modulate a range of reparative processes other than mineralisation, including chemotaxis [43, 44], angiogenesis [45], SC recruitment [46], and neurogenesis [47]. GFs, in particular, modulate pulpal regeneration processes with members of the transforming-GF superfamily [34, 48] and insulin-like GFs [37] present in relatively high quantity in DMC extracts. Other angiogenic GFs, such as fibroblast GF 2 (FGF-2), vascular endothelial GF (VEGF), and placental GF (PlGF) [45, 49] as well as the neurogenic factors brain-derived neurotrophic factor (BDNF) and growth/differentiation factor 15 (GDF-15) [50] have also been identified in dentine extracts.

In addition to DMCs, the pulp cells themselves also respond dynamically to the microbial or other challenge by the expression of both inflammatory and reparative genes and proteins; this will promote defensive cellular processes including cell migration, proliferation, and differentiation [5]. Although the bulk of attention has focused on the role of odontoblasts [27, 51] or SC populations in repair [52], fibroblasts, which are the major cell component of the pulp, are also able to secrete GFs and complement fragments that promote mineralisation and SC recruitment [53]. In addition, fibrocytes have been reported to be present at the pulpal wound interface after injury and have been linked to the early establishment of new blood vessels [31]. Progenitor cells migrate and differentiate to form odontoblast-like cells during reparative dentinogenesis replacing dead odontoblasts. Several progenitor cell populations may contribute to this process including DPSCs [54], undifferentiated mesenchymal cells from cell-rich and central pulp perivascular regions (i.e. pericytes [55, 56]) as well as SCs migrating from outside the tooth [52, 57].

Core Points

• A balance between inflammation and repair is essential to preserve pulp vitality.
• There are two forms of tertiary dentine: reactionary and reparative.
• Dentine matrix contains a rich reservoir of bioactive components, which are released during injury to aid reparative processes.
• These bioactive molecules (GFs, chemokines, cytokines) can be utilised during operative procedures.

16.4 What Does Vital Pulp Treatment Encompass?

The task of accurately assessing if the pulp is irreversibly inflamed remains a significant clinical challenge [58]. Clinicians require a device that can (a) accurately establish the point at which the pulp becomes irreversibly damaged and necrosis ensues, and (b) can aid a decision as to whether exposing the pulp is necessary or should be avoided. Furthermore, if the pulp is cariously exposed, can VPT procedures such as pulp capping or partial pulpotomy provide predictable outcomes or is more aggressive tissue removal (pulpotomy) or pulpectomy necessary?

The diagnostic challenge of accurately estimating the level of pulp inflammation has led to different treatment concepts emerging within general dental practice. Questionnaire-based surveys in which dentists study radiographs of ‘deep carious lesions’ have analyzed whether the respondents believed a tooth should be treated conservatively by avoiding pulp exposure or alternatively managed by exposing the pulp and VPT. The results have highlighted that there is substantial variation between respondents [59–61] with no consensus on management options for when to avoid carious pulp exposures and when it is inevitable. In clinical practice, the decision on whether to maintain the pulp also varies [62], even when important objective and subjective diagnostic data are considered as part of the scenario. Notably, the majority of dentists adopt an invasive approach choosing either a VPT or a pulpectomy, rather than avoiding pulp exposure [59–61], but what is the reason for the observed variations in treatment choice? The fluctuation in the chosen therapy could be the result of a paucity of high-quality clinical evidence, or simply an unclear definition and understanding of the nature of a deep carious lesion. Finally, as indicated in the treatment statistics (Figure 16.1), dental practitioners may prefer pulpectomy over capping/VPT simply because it works predictably in their hands (i.e. tooth retention, absence of signs and symptoms), even if it is performed poorly and asymptomatic periapical disease emerges. For a pulpectomy to fail usually takes ‘two to three years’ as an apical infection and pain must develop. In contrast, if VPT fails, this usually occurs within a shorter time frame (1–12 months) and often because of severe pain [13]. Economics may also affect the treatment choice, as remuneration for a RCT in a molar tooth is radically different from a direct pulp cap on the same tooth. Unfortunately, at present from a patient perspective, the critical factor in the treatment chosen by the dentist probably relates to whether the dentist prefers retaining pulp tissue. In the future, treatment variation needs to be reduced, and therapeutic solutions should be cohesive and biological, based on a clear definition of a deep/extremely carious lesion as well as valid clinical evidence. In addition, dentistry perhaps needs to embrace and develop next-generation diagnostic devices to accurately determine the inflammatory state and threshold of the pulp.

A relevant question should be, are general practitioners or endodontists the best people to treat and maintain pulp vitality? Established borders of a dental specialty may create traditions or obstacles for providing the best possible pathway for optimal pulpal care. Clearly, endodontists have the expertise on aseptic strategies that are fundamental to optimal maintenance of pulp vitality. This includes preparation of an aseptic working field using dental dam isolation, cleaned with a disinfectant. Unfortunately, due to the nature of secondary care, it is unusual for the endodontist to make a decision on whether the pulp should be saved or removed, as these decisions are carried out in primary dental care by general dental practitioners. Indeed, even the endodontic tradition of an aseptic working field using rubber dam is not widespread in general practice [63–66]; this of course compromises the VPT procedure from the very onset. Clear guidelines are required, both for treatment and referral, which should include underlining the importance of referral for perceived simpler treatments such as VPT to a specialist environment [67]. This may result in more standardized treatment and RCTs for teeth in which the pulp could be maintained. At the very least, improved education for general practitioners and endodontists on the best way to handle deep caries and exposed pulp tissue should be considered a priority.

Core Points

• Lack of objective tools for assessing inflammation may help to explain the wide range in decision making with regard to VPT.
• Clarifying objective signs of the deep lesion is also important to reduce aspect on treatment variation.
• The endodontic tradition of an aseptic working field using dental dam is not widespread in general practice and jeopardizes the outcome of VPT.
• Dental practitioners and endodontists need to communicate better together to manage deep caries lesions and the exposed pulp.

16.5 How Do We Classify and Diagnose Pulpal Disease?

The American Association of Endodontists (AAE) endorsed the currently accepted classification of pulpal disease in 2013 [68], describing pulpitis as either reversible or irreversible depending on clinical signs and symptoms. The classic symptoms of reversible pulpitis are described as ranging from no complaint to a short sharp pain sensation to hot/cold stimuli; notably, the symptoms should resolve after removal of the stimulus. Pain described as spontaneous, radiating, nocturnal, and lingering after removal of the stimulus tends to indicate irreversible pulpitis [69]. Notably, symptoms cannot be the only tool used to establish a diagnosis, as irreversible pulpitis has been shown to be symptomless in 14–60 % of cases [70, 71]. In contrast to earlier research [69, 72], it has been reported that reversible and irreversible pulpitis correlate well with histological features of pulp damage [73]; however, the decision to diagnose the pulp as reversibly or irreversibly inflamed does not actually indicate whether it is able to be successfully maintained. With the interest in pulpotomies as a definitive intervention in teeth with signs and symptoms of irreversible pulpitis [6, 74, 75], there have been proposals to extend the current classification of pulpal disease [15] or indeed introduce a new classification linking diagnosis to treatment and removing the term irreversible altogether [76].

Pulp testing should follow a detailed pain history and examination and although thermal and electric pulp testing remains the appropriate clinical tests to use, they are crude and subject to false positive and negative readings [76, 78]. Current methods of assessing pulp status actually assess the response of nerve receptors in the pulp rather than other techniques such as pulse oximetry and Doppler flowmetry [79] that measure blood supply; therefore, pulp sensibility testers is a more appropriate description. Notably, pulp sensibility is relatively effective in carrying out a yes or no response; however, they are not accurate in quantifying the severity or extent of pulpitis [58]. It has been reported that a painful response to cold stimuli, classic of acute forms of pulpitis, remains the principle reason for emergency dental treatment [80]. Therefore, it is logical when testing the tooth that these symptoms are mirrored with cold testing, with colder stimuli such as carbon dioxide, tetrafluoroethane, and other commercial products diagnostically superior to ice or ethyl chloride in determining pulpal status [81, 82]. Heat can be used to mimic the patient’s symptoms and may remain useful in the diagnosis of painful pulpitis; however, the heat test has low accuracy [79]. It should be stressed that even in combination with a thorough history and examination, these diagnostic tests are subjective and only provide further clinical guidance towards making a diagnosis.

All currently used methods are limited in their ability to accurately quantify the severity and extent of pulpitis, and as a result VPT procedures may have traditionally been considered unpredictable due in part to the diagnostic difficulty of accurately assessing the severity of pulpitis [73, 83]. New diagnostics are being developed and trialled, designed to discriminately assess the inflammatory state of the pulp at chairside using blood or another tissue fluid to assess quantitatively various biomarkers of disease [84]. At present, several inflammatory cytokines and tissue proteases have been preliminarily investigated, but identifying a reliable, stable indicator of pulpitis has thus far not proved possible [85]. The development of novel diagnostic chairside assays of disease biomarkers has been identified as a focus for translational development [86, 87]. This need not necessarily be cytokine-based, but could be a protease, marker of cell death, or other inflammatory marker such as noncoding ribonucleic acids (ncRNAs), which are detectable and stable in body fluids and have been successfully employed to discriminately assess inflammation at other sites of the body [88, 89].

Until reliable and effective chairside molecular tests are developed, other available information should be used to supplement the history, examination, and tests including the ‘clues’ gained by direct visualisation and handling of exposed pulp tissue. The presence of necrosis and the colour and intensity of pulp bleeding can provide a crude measure or surrogate marker of inflammation [90] and indeed can lead to a change in treatment if the pulpal bleeding is profuse and cannot be arrested. However, pulpal bleeding is altered by variables such as trauma and the use of a vasoconstrictor [91] and can only be weakly recommended to supplement other information in cases of pulp exposure [1].

Core Points

• Current diagnostic ability to determine the level of pulp inflammation is limited.
• Symptoms, although useful, cannot be used alone to determine the severity of pulpitis.
• The currently accepted diagnostic terms of reversible and irreversible pulpitis are becoming outdated and will need revision.
• In teeth exhibiting signs and symptoms indicative of irreversible pulpitis, the pulp tissue in the root canal is generally uninflamed in the initial stages.

16.6 How Do We Treat Pulpal Disease? Techniques to Avoid Pulpal Exposure

16.6.1 Indirect Pulp Capping

An indirect pulp therapy addresses the excavation of deep carious dentine aiming to avoid pulp exposure. A biomaterial is thereafter applied onto the thin dentine barrier in one visit after a carious-tissue removal technique, generally to hard dentine [1]. Indirect pulp capping was originally described as leaving only residual caries, suggesting that further carious tissue removal would result in pulpal exposure [92]. A considerable volume of research over the last 50 years has modified the original concept of excavation close to the pulp as it is open to misinterpretation. Indirect pulp capping can be difficult to establish clinically as in reality the dentist either avoids a pulp exposure or manages the pulp after exposure. With the promotion of less invasive treatment concepts, indirect pulp capping has been superseded by other therapies, as evidence does not support the maintenance of a central nonselective carious removal procedure to hard dentine. Other studies have introduced less invasive carious removal techniques such as selective carious-tissue removal in one visit and stepwise excavation, which leave more carious dentine and have a good prognosis [13, 14]. Indirect pulp therapy is considered an aggressive approach because it leaves neither soft nor firm carious dentine behind [22]. For example, invasive techniques run the risk of pulpal exposure when it could have been avoided with more conservative techniques.

16.6.2 Selective Carious-tissue Removal in One Visit

Selective carious-tissue removal is defined as the application of a biomaterial onto a thin dentine barrier in a one-stage technique. The removal should be to soft or firm dentine with a permanent restoration generally placed immediately. What do these terms actually mean? Selective removal to firm dentine leaves leathery dentine at the deepest pulpal aspect of the carious lesion, which means clinical resistance to a hand excavator [22]. Notably, the peripheral dentine is nonselectively removed to hard dentine. Although selective removal to firm dentine is the treatment of choice for both dentitions, it is more established in the primary dentition – even in shallow or moderately deep cavities in dentine (i.e. lesions radiographically extending less than the pulpal third or quarter of dentine). The evidence for using this one-stage approach in well-defined deep lesion is weak and should not be used as selective removal to firm dentine increases risks of pulp exposure. Selective removal to soft dentine is recommended in deep cavitated lesions (i.e. extending into the pulpal third or quarter of the dentine). Soft carious tissue is left over the pulpal aspect of the cavity to avoid exposure, thereby promoting pulpal health, while peripheral enamel and dentine are prepared nonselectively to hard dentine to allow a tight seal and placement of a durable restoration. Selective removal to soft dentine reduces the risk of pulpal exposure significantly as compared with nonselective removal to hard or selective removal to firm dentine; however, the evidence on permanent teeth with lesion depth larger than three fourths is sparse. One point of concern could be the longevity of the restoration placed on the top of soft dentine, as the residual carious tissue will shrink over time forming a gap between the carious dentine and the restoration.

One-visit selective carious removal has been reported to be successful in the primary dentition [93, 94]. In addition, the concept of sealing the entire carious lesion with a stainless steel crown in the ‘Hall technique’, has also been successful [21]. Permanently leaving carious dentine in a one-visit selective approach using the pulpal third of dentine as a threshold has shown comparable results with a stepwise excavation approach [95]. There is less evidence for one-visit selective removal of deep carious lesions using the pulpal quarter as a threshold. If residual carious dentine remains in situ, the dentine may shrink and potentially impair the coronal restoration, which could potentially lead to pulpal complications [23]. It is accepted that a suboptimal temporary restoration and lack of a permanent coronal seal during the less invasive carious removal strategies will lead to failure including pulpal and apical pathosis [14, 32]. Therefore, a general approach of using this concept requires (i) an immediate permanent restoration; (ii) careful documentation indicating that this is the final treatment and no further intervention is required. This is particularly relevant from a medical-legal standpoint. Notably, a clear definition of lesion depth is lacking in many studies and the available evidence on well-defined deep carious lesions as well in adult teeth remains limited.

16.6.3 Stepwise Excavation

Stepwise excavation is defined as the application of a biomaterial onto a thin dentine barrier in a two-stage selective carious removal technique. Temporary restoration placement is performed between visits and re-entry after 6–12 months. The first stage involves selective carious removal to soft dentine to an extent that allows proper placement of a calcium hydroxide or calcium silicate base and a temporary restoration (glass ionomer cement). At the second stage, further removal of caries to firm dentine is followed by placement of a permanent restoration (Figure 16.2).

Stepwise removal aims to maintain pulp vitality and avoid pulp exposure but also to ensure restoration longevity. The two-stage approach provides the clinician with the opportunity to confirm that the residual carious tissue has arrested during the treatment interval (i.e. dryer, darker, harder dentine remaining after the interval [96, 97]). When leaving soft dentine behind during the first stage, it can shrink and a gap will be formed between the deep carious tissue and the temporary restoration. So is the two-stage approach necessary? The second-stage