pulp (tooth) pulp (tooth) the pulp is the connective tissue, nerves, blood vessels, and odontoblasts that comprise the innermost layer of a tooth. the pulp's activity and signalling processes regulate its behaviour. pulpsection of a human molardetailsidentifierslatinpulpa dentismeshd003782ta98a05.1.03.051ta2934fma55631anatomical terminology diagram showing pulp histology:odontoblast layer;cell-free zone of weil;cell-rich zone;pulp core anatomy the pulp is the neurovascular bundle central to each tooth, permanent or primary. it is composed of a central pulp chamber, pulp horns, and radicular canals. the large mass of the pulp is contained within the pulp chamber, which is contained in and mimics the overall shape of the crown of the tooth. because of the continuous deposition of the dentine, the pulp chamber becomes smaller with the age. this is not uniform throughout the coronal pulp but progresses faster on the floor than on the roof or sidewalls. radicular pulp canals extend down from the cervical region of the crown to the root apex. they are not always straight but vary in shape, size, and number. they are continuous with the periapical tissues through the apical foramen or foramina. the total volume of all the permanent teeth organs is 0.38cc, and the mean volume of a single adult human pulp is 0.02cc. accessory canals are pathways from the radicular pulp. these canals, which extend laterally through the dentin to the periodontal tissue, are seen especially in the apical third of the root. accessory canals are also called lateral canals because they are usually located on the lateral surface of the roots of the teeth. development the pulp has a background similar to that of dentin because both are derived from the dental papilla of the tooth germ. during odontogenesis, when the dentin forms around the dental papilla, the innermost tissue is considered pulp. sdeo: dental pulp of a stained and decalcified tooth. there are 4 main stages of tooth development: bud stage cap stage bell stage crown stage the first sign of tooth development is known to be as early as the 6th week of intrauterine life. the oral epithelium begins to multiply and invaginates into ectomesenchyme cells, which gives rise to dental lamina. the dental lamina is the origin of the tooth bud. the bud stage progresses to the cap stage when the epithelium forms the enamel organ. the ectomesenchyme cells condense further and become dental papilla. together the epithelial enamel organ and ectomesenchymal dental papilla and follicle form the tooth germ. the dental papilla is the origin of dental pulp. cells at the periphery of the dental papilla undergo cell division and differentiation to become odontoblasts. pulpoblasts form in the middle of the pulp. this completes the formation of the pulp. the dental pulp is essentially a mature dental papilla. the development of dental pulp can also be split into two stages: coronal pulp development (near the crown of the tooth) and root pulp development (apex of the tooth). the pulp develops in four regions from the periphery to the central pulp: odontoblast layer cell-free zone – likely to be an artefact cell-rich zone pulp core internal structure pulpal dentin junction.outside tooth/enameldentin tubuledentinodontoblastic processpredentinodontoblastcapillariesfibroblastsnerveartery/veincell-rich zonecell-poor zonepulp chamber the central region of the coronal and radicular pulp contains large nerve trunks and blood vessels. this area is lined peripherally by a specialized odontogenic area which has four layers (from innermost to outermost): pulpal core, which is in the center of the pulp chamber, with many cells and an extensive vascular supply; except for its location, it is very similar to the cell-rich zone. cell-rich zone, which contains fibroblasts and undifferentiated mesenchymal cells. cell-free zone (zone of weil, which is rich in both capillaries and nerve networks. odontoblastic layer, the outermost layer which contains odontoblasts and lies next to the predentin and mature dentin. cells found in the dental pulp include fibroblasts (the principal cell), odontoblasts, defence cells like histiocytes, macrophages, granulocytes, mast cells, and plasma cells. the nerve plexus of raschkow is located central to the cell-rich zone. the plexus of raschkow the plexus of raschkow monitors painful sensations. by virtue of their peptide content, they also play important functions in inflammatory events and subsequent tissue repair. there are two types of nerve fibers that mediate the sensation of pain: a-fibres conduct rapid and sharp pain sensations and belong to the myelinated group, whereas c-fibres are involved in dull aching pain and are thinner and unmyelinated. the a-fibres, mainly of the a-delta type, are preferentially located in the periphery of the pulp, where they are in close association with the odontoblasts and extend fibers to many but not all dentinal tubules. the c-fibres typically terminate in the pulp tissue proper, either as free nerve endings or as branches around blood vessels. sensory nerve fibers that originate from inferior and superior alveolar nerves innervate the odontoblastic layer of the pulp cavity. these nerves enter the tooth through the apical foramen as myelinated nerve bundles. they branch to form the subodontoblastic nerve plexus of raschkow, which is separated from the odontoblasts by a cell-free zone of weil. this plexus lies between the cell-free and cell-rich zones of the pulp. plexus of raschkow:odontoblast layer;cell-free zone of weil;cell-rich zone;pulp core pulp innervation as the dental pulp is a highly vascularised and innervated region of the tooth, it is the site of origin for most pain-related sensations. the dental pulp nerve is innervated by one of the trigeminal nerves, otherwise known as the fifth cranial nerve. the neurons enter the pulp cavity through the apical foramen and branch off to form the nerve plexus of raschkow. nerves from the plexus of raschkow provide branches to form a marginal plexus around the odontoblasts, with some nerves penetrating the dentinal tubules. the dental pulp is also innervated by the sympathetic division of the autonomic nervous system. these sympathetic axons project into the radicular pulp, where they form a plexus along the blood vessels. their function is mainly related to blood vessel constriction within the dental pulp. a sharp fall in pulpal blood flow may be caused by stimulation of these nerves. there is no evidence for a parasympathetic pulpal innervation. there are two main types of sensory nerve fibres in the pulp, each densely placed at different locations. the differing structural features of the two sensory nerve fibres also result in different types of sensory stimulation. myelinated a-fibres: the a-fibres present in the pulp can be further classified into 2 different types. a-delta fibres make up 90% of the a-fibres, while the rest are a-beta fibres. have a relatively low-threshold sensory apparatus. mainly located at the pulp-dentine border at the top of the pulp, and more specifically concentrated in the pulp horn. have a relatively small diameter with a relatively slow conduction velocity. they are is still faster than c-fibres. a-fibres transmit signals to the brainstem and then to the contralateral thalamus. able to respond to stimuli through a shell of calcified tissue due to the stimulus-induced fluid flow in dentinal tubules. this is known as the hydrodynamic theory. stimuli that displaces the fluid within the dentinal tubules will trigger the intradental myelinated a-fibres, leading to the sharp pain sensation commonly associated with dentine hypersensitivity unmyelinated c-fibres: they are mainly located at the core of the pulp and extend underneath the odontoblastic layer. c-fibres have higher pain thresholds, responsible for detecting inflammatory threats. they are heavily influenced by modulating interneurons before they reach the thalamus. c-fibre stimulation often results in a "slow pain", normally characterised as a dull and aching pain. functions the primary function of the dental pulp is to form dentin (by the odontoblasts). other functions include: nutritive: the pulp keeps the organic components of the surrounding mineralized tissue supplied with moisture and nutrients; protective/sensory: extremes in temperature, pressure, or trauma to the dentin or pulp are perceived as pain; defensive/reparative: the formation of reparative or tertiary dentin (by the odontoblasts); formative: cells of the pulp produce dentin which surrounds and protects the pulpal tissue. pulp testing main article: dental pulp test the health of the dental pulp can be established by a variety of diagnostic aids which test either the blood supply to a tooth (vitality test) or the sensory response of the nerves within the root canal to specific stimuli (sensitivity test). although less accurate, sensitivity tests, such as electric pulp tests or thermal tests, are more routinely used in clinical practice than vitality testing, which requires specialised equipment. a healthy tooth is expected to respond to sensitivity testing with a short, sharp burst of pain which subsides when the stimulus is removed. an exaggerated or prolonged response to sensitivity testing indicates that the tooth has some degree of symptomatic pulpitis. a tooth that does not respond at all to sensitivity testing may have become necrotic. pulp diagnoses normal pulp in a healthy tooth, enamel and dentin layers protect the pulp from infection. reversible pulpitis reversible pulpitis is a mild to moderate inflammation caused by any momentary irritation or stimulant whereby no pain is felt upon the stimulants' removal. the pulp swells when the protective layers of enamel and dentine are compromised. unlike irreversible pulpitis, the pulp gives a regular response to sensibility tests and inflammation resolves with management of the cause. no significant radiographic changes are present in the periapical region. further examination is required to ensure that the dental pulp has returned to its normal state. common causes bacterial infection from caries thermal shock trauma excessive dehydration of a cavity during restoration irritation of exposed dentine repetitive trauma caused by bruxism or jaw misalignment fractured tooth exposing pulp symptoms temporary post-restoration sensitivity non-spontaneous and milder pain compared to irreversible pulpitis short sharp pain caused by a stimulant differential diagnosis x-rays to determine extent of decay and inflammation sensitivity tests to see if pain/discomfort is experienced when tooth is in contact with hot, cold or sweet stimuli tooth tap test (lightweight, blunt instrument gently tapped onto affected tooth to determine extent of inflammation) electric pulp test treatment treatment should resolve reversible pulpitis; early treating may help prevent irreversible pulpitis follow-up required to determine whether the reversible pulpitis has returned to a normal status prevention regular check-ups when preparing cavities, dehydrate with sufficient alcohol/chloroform and apply sufficient varnish to protect the pulp irreversible pulpitis pulpitis is established when the pulp chamber is compromised by bacterial infection. irreversible pulpitis is diagnosed when the pulp is inflamed and infected beyond healing. removal of the aetiological agent does not permit healing, and a root canal is often indicated. irreversible pulpitis follows reversible pulpitis absent early intervention. while the pulp is still vital and vascularised, it is not classified as 'dead pulp'. irreversible and reversible pulpitis are distinguished by the pain responses to thermal stimulation. if the condition is reversible, the pulp's pain response lasts a few seconds upon exposure to cold or hot. if the pain lingers from minutes to hours, the condition is classified as irreversible. this is a common presenting complaint that facilitates initial diagnosis. irreversible puplitis may be symptomatic or asymptomatic. asymptomatic irreversible pulpitis results from transition of symptomatic irreversible pulpitis into an inactive/quiescent state. this is due to its aetiology; inflammatory exudate can be quickly removed, e.g. through a large carious cavity or previous trauma that caused painless pulp exposure. the build-up of pressure in a confined pulp space initiates pain reflexes. when this pressure is relieved, pain subsides. as the names imply, these diseases are largely characterised by their symptoms: pain duration and location, and exacerbating and relieving factors. inputs include clinical tests (cold ethyl chloride, ept, hot-gutta percha, palpation), radiographic analysis (peri-apical and/or cone-beam computed tomography) and others. thermal tests are subjective, and are therefore performed the compromised tooth and the adjacent and contralateral teeth, allowing the patient to compare them. normal healthy teeth are used as a baseline for diagnoses. key characteristics of symptomatic irreversible pulpitis include: spontaneous and unpredictable pain at any time, and specific causal factors cannot be identified patient may complain of sharp lingering pains that last longer than 30 seconds, even after removal of stimulus possible referred pain pain may increase with changes of posture, e.g. from lying down to standing. analgesics tend to be ineffective. no pain on percussion because the bacteria are not present in the peri-apical region. key characteristics of asymptomatic irreversible pulpitis include: no clinical symptoms. pulp