migrate, and form new collagen in contact with the necrotic zone [71]. Although the process is similar with HCSC, the pulpal irritation is less than that with calcium hydroxide (Figure 2.2) [9]. Tertiary reparative dentinogenesis is then initiated, odontoblast cells are formed, and mineralized matrix is secreted [72]. This matrix forms the so called ‘hard tissue’ bridge, which walls off the pulp and offers further protection to the soft tissue adjacent to the wound site.
Figure 2.2 Histological response to pulp capping. (a) Macrophotographic view of the mesial half of a human maxillary third molar demonstrating the remnants of the restorative material (A) and ProRoot MTA capping material (B) at one month. Note the distinct hard tissue bridge (arrow). Original magnification ×8. (b) Photomicrograph of histological section of the specimen in (a) of an MTA pulp cap at one month. Note that the mineralized barrier (arrow) stretches across the entire width of the exposed pulp (C). Original magnification ×16. (c) Higher‐magnification photomicrograph from (a) and (b). Cuboidal cells (arrows) line the hard tissue barrier (D). Note the absence of inflammatory cells in the pulp (E). Original magnification ×85. (d) Photomicrograph of a selected serial section of hard‐setting calcium hydroxide cement (Dycal) at one month. Engorged blood vessels are prominent and inflammatory cells are present. Note the presence of Dycal particles (arrows) in the pulp (F). Original magnification ×16.
Source: Images adapted from Nair, P.N., Duncan, H.F., Pitt Ford, T.R., Luder, H.U. Histological, ultrastructural and quantitative investigations on the response of healthy human pulps to experimental capping with mineral trioxide aggregate: a randomized controlled trial. Int. Endod. J. 2008; 41(2):128–50.
2.3 Clinical Procedures for Maintaining Pulp Vitality
2.3.1 Managing the Unexposed Pulp
Regardless of the many years spent researching the ideal restorative material, there is no such thing as a permanent restoration: all have a limited lifetime [73]. As soon as the integrity of a tooth is broken, it must be replaced, setting it on a ‘restorative cycle’ [74]. And each time a restoration is placed, the pulp is made vulnerable and put under threat.
Clinicians carrying out an operative procedure on a vitaI tooth should be mindful of the heat generated by dental handpieces, the potential damage caused by overdehydrating dentine, and the use of caustic agents in tooth restoration, all of which can result in unnecessary iatrogenic pulp damage. Often, prevention is better than cure, so care and attention should be taken when removing tooth tissue and selecting materials to prevent injury to the pulp. The most influential variables in terms of causing injury to the unexposed pulp are considered the cavity's RDT and preparation of the cavity in the absence of coolant [75]. This confirms the observation that excessive heat is the most injurious event to pulp tissue [76]. Other potential sources of pulp injury during restoration of a cavity include etching of the dentin [77] and the choice of restorative material [78].
Any therapeutic process for the benefit of pulp survival that is adopted during the restoration of a tooth with a deep cavity, but unexposed pulp is an indirect pulp cap. Classically, this procedure is carried out when dentine is lost due to caries, trauma, or a previous iatrogenic intervention, and when a cavity exists close to the pulp but dentine remains over the pulp tissue. Indirect pulp capping can be defined as an application of a material on to a thin layer of dentine located close to the pulp with the aim of producing a positive biological response so that the pulp can protect itself.
2.3.2 Tooth Preparation to Avoid Exposure
The tooth should be isolated with a rubber dam and asepsis should be maintained throughout cavity preparation. The cavity should be disinfected using cotton pellets soaked with sodium hypochlorite (0.5–5%). Less invasive carious tissue‐removal techniques are generally carried out using sterile round burs and excavators [79], but other self‐limiting chemomechanical methods (e.g. Carisolv gel) have also been advocated for the management of deep carious lesions [80]. Regardless of the technique employed, carious tissue should be removed from the periphery of the cavity to hard dentine (i.e. nonselective removal), leaving soft or leathery dentine only on the pulpal aspect of the cavity. As RDT over the pulp cannot be accurately assessed clinically, the use of a biologically based biomaterial is recommended. Ideally, an HCSC or a glass ionomer cement (GIC) should be routinely applied to the dentine barrier prior to definitive restoration (Figure 2.3) [1, 27].
2.3.3 Managing the Exposed Pulp
If there is a suspicion that the pulp is exposed, the tooth should be immediately isolated with a rubber dam to ensure an aseptic environment and prevent any of the consequences that would result if the pulp were to become infected [12]. Magnification should ideally be used throughout the procedure to ensure removal of all softened dentine and to allow visual inspection of the pulp tissue in order to determine the degree of inflammation. The dentine should be carefully manipulated using sterile burs and sharp instruments. A high‐speed bur and water coolant should be used for pulp tissue removal [81], followed by disinfection and control of pulpal bleeding. Haemostasis and disinfection should be achieved using cotton pellets soaked ideally with sodium hypochlorite (0.5–5%) or chlorhexidine (0.2–2%) [64, 82, 83]. If haemostasis cannot be controlled after five minutes, further pulp tissue should be removed (partial or full pulpotomy). In cases with signs and symptoms indicative of irreversible pulpitis (i.e. partial irreversible pulpitis confined to the coronal pulp tissue), a full coronal pulpotomy can be carried out to the level of the root canal orifices, with bleeding arrested as detailed previously [84]. This procedure may be easier for general dental practitioners without access to magnification than either partial pulpotomy or even direct pulp capping. Ideally, an HCSC should be placed directly on to the pulp tissue and the tooth immediately definitively restored to prevent further microleakage [61, 83, 85]. If bleeding cannot be controlled after full pulpotomy, a pulpectomy and RCT should be carried out, provided the tooth is restorable. Four different VPTs can be carried out: direct pulp capping, partial pulpotomy, full pulpotomy, and pulpectomy.
Figure 2.3 Intraoral photographs of an indirect pulp‐capping procedure. (a) Preoperative image of a grossly broken‐down upper right first premolar, showing a deep lesion with unexposed pulp. (b) Indirect pulp cap with a thin layer of Biodentine interfacing with dentine overlying the pulp, leaving
