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Although the pulp can be challenged by microbial, mechanical, and chemical stimuli, necrosis will not result without the presence of microorganisms [12]. Caries has traditionally been considered the principal cause of pulpal damage, and although falling in prevalence, it is now manifesting more commonly in disadvantaged and elderly populations [13–15]. Whilst inflammation of the pulp is evident even in shallow carious lesions [16, 17], it is not until the carious process is deep and comes within 0.5 mm of the pulp that the pulpitic response significantly intensifies [18]. As a result, before it reaches this stage, the damage is likely to be reversible. This forms the basis of predictable operative dentistry, in that the pulp should recover after removal of carious dentine and insertion of a suitable dental restorative material [19]. Microbial challenge, however, is not limited to caries, as bacterial microleakage is also a common cause of pulpitis and subsequent necrosis due to oral microorganisms colonizing the ‘gap’ between the restoration and the tooth [20]. Prevention of microleakage using lining material is no longer considered good practice [21], but dentine bonding agents and incremental placement of resin‐based composites will reduce the risk of bacterial colonization [22], particularly if there is sufficient residual dentine thickness (RDT).

Views on the irritant effect of dental materials on the pulp have changed over the last 50 years. The idea that their toxicity to pulp tissue leads to pulpal necrosis has been questioned by several operators [20, 23, 24], who point to microbial contamination and leakage as the decisive factor in sustained pulpal inflammation. That said, there is also good evidence to suggest that some materials are more biocompatible and ‘pulp‐friendly’ than others, with the adverse toxic effects of dental resins on pulp cells being repeatedly highlighted [25, 26]. Alternatively, the positive biological responses of HCSC [9] have led to recent suggestions that deep carious lesions should be lined with HCSC after deep caries removal [27]. Other nonmicrobial irritants such as bleaching procedures, particularly chairside ‘power’ techniques, can lead to rises in pulpal temperature and pulpitis [28]; however, whilst these are increasingly common as treatment strategies, the pulpal changes seen are generally reversible and are not catastrophic in nature [29, 30].