![Pulp Histology](https://upload.wikimedia.org/wikipedia/commons/e/ed/Pulp_Histology_.png)
The pulp is the
connective tissue
Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...
,
nerves
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
,
blood vessels
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
, and
odontoblast
In vertebrates, an odontoblast is a cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the formation of dentin, the substance beneath the tooth enamel on t ...
s that comprise the innermost layer of a
tooth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
. The pulp's activity and signalling processes regulate its behaviour.
Anatomy
The pulp is the
neurovascular bundle central to each tooth,
permanent
Permanent may refer to:
Art and entertainment
* ''Permanent'' (film), a 2017 American film
* ''Permanent'' (Joy Division album)
* "Permanent" (song), by David Cook
Other uses
* Permanent (mathematics), a concept in linear algebra
* Permanent (cy ...
or
primary
Primary or primaries may refer to:
Arts, entertainment, and media Music Groups and labels
* Primary (band), from Australia
* Primary (musician), hip hop musician and record producer from South Korea
* Primary Music, Israeli record label
Works
* ...
. 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.
[Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 164.] Because of the continuous deposition of the
dentine
Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...
, 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
In dental anatomy, the apical foramen, literally translated "small opening of the apex," is the tooth's natural opening, found at the root's very tip—that is, the root's apex—whereby an artery, vein, and nerve enter the tooth and commingle w ...
or foramina.
The total volume of all the
permanent teeth
Permanent teeth or adult teeth are the second set of teeth formed in diphyodont mammals. In humans and old world simians, there are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mandibul ...
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
Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate sta ...
, when the dentin forms around the dental papilla, the innermost tissue is considered pulp.
![SDEO- Dental Pulp](https://upload.wikimedia.org/wikipedia/commons/b/b6/SDEO-_Dental_Pulp.png)
There are 4 main stages of
tooth development
Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stag ...
:
# 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
The dental lamina is a band of epithelial tissue seen in histologic sections of a developing tooth. The dental lamina is first evidence of tooth development and begins (in humans) at the sixth week in utero or three weeks after the rupture of th ...
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
In embryology and prenatal development, the dental papilla is a condensation of ectomesenchymal cells called odontoblasts, seen in histologic sections of a developing tooth. It lies below a cellular aggregation known as the enamel organ. The ...
. 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
odontoblast
In vertebrates, an odontoblast is a cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the formation of dentin, the substance beneath the tooth enamel on t ...
s. 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](https://upload.wikimedia.org/wikipedia/commons/c/cf/Pulpal_dentin_junction.png)
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
Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every o ...
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
A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells o ...
(the principal cell),
odontoblasts
In vertebrates, an odontoblast is a cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the formation of dentin, the substance beneath the tooth enamel on the ...
, defence cells like
histiocytes
A histiocyte is a vertebrate cell that is part of the mononuclear phagocyte system (also known as the reticuloendothelial system or lymphoreticular system). The mononuclear phagocytic system is part of the organism's immune system. The histiocyt ...
,
macrophages
Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
,
granulocytes
Granulocytes are
cells in the innate immune system characterized by the presence of specific granules in their cytoplasm. Such granules distinguish them from the various agranulocytes. All myeloblastic granulocytes are polymorphonuclear. They hav ...
,
mast cells
A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a par ...
, and
plasma cells
Plasma cells, also called plasma B cells or effector B cells, are white blood cells that originate in the lymphoid organs as B lymphocytes and secrete large quantities of proteins called antibodies in response to being presented specific substan ...
. The nerve plexus of Raschkow is located central to the cell-rich zone.
[Antonio Nanci, Ten Cate's Oral Histology, Elsevier, 2007, page 91]
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
myelin
Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be ...
ated 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.
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
Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...
(by the
odontoblast
In vertebrates, an odontoblast is a cell of neural crest origin that is part of the outer surface of the dental pulp, and whose biological function is dentinogenesis, which is the formation of dentin, the substance beneath the tooth enamel on t ...
s).
Other functions include:
* Nutritive: the pulp keeps the organic components of the surrounding
mineralized tissue
Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Typically these tissues form a protective shield or structural support. Bone, mollusc shells, deep sea sponge ''Euplectella'' species, radiolarians, diato ...
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 Tertiary dentin (including reparative dentin or sclerotic dentin) forms as a reaction to stimulation, including caries, wear and fractures. Tertiary dentin is therefore a mechanism for a tooth to ‘heal’, with new material formation protecting th ...
(by the odontoblasts);
* Formative: cells of the pulp produce
dentin
Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...
which surrounds and protects the pulpal tissue.
Pulp testing
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
Pulpitis is inflammation of dental pulp tissue. The pulp contains the blood vessels, the nerves, and connective tissue inside a tooth and provides the tooth’s blood and nutrients. Pulpitis is mainly caused by bacterial infection which itself is ...
. A tooth that does not respond at all to sensitivity testing may have become
necrotic
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
.
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
Bruxism is excessive teeth grinding or jaw clenching. It is an oral parafunctional activity; i.e., it is unrelated to normal function such as eating or talking. Bruxism is a common behavior; reports of prevalence range from 8% to 31% in the gene ...
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
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
/
chloroform
Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...
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
Chloroethane, commonly known as ethyl chloride, is a chemical compound with chemical formula CH3CH2Cl, once widely used in producing tetraethyllead, a gasoline additive. It is a colorless, flammable gas or refrigerated liquid with a faintly sweet ...
, EPT, hot-
gutta percha
Gutta-percha is a tree of the genus ''Palaquium'' in the family Sapotaceae. The name also refers to the rigid, naturally biologically inert, resilient, electrically nonconductive, thermoplastic latex derived from the tree, particularly from ' ...
, 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 will respond to sensitiviity tests as a healthy pulp would.
Treatments include root canal or tooth extraction. In endodontic therapy, removal of the inflamed pulp relieves the pain. The empty root canal system is then obturated with gutta-percha (rubber material that acts as a pressure/pain reliever).
Pulp necrosis
Pulp
necrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
is when the pulp has died/dying. Causes include untreated caries, trauma or bacterial infection. It is often subsequent to chronic pulpitis. Teeth with pulp necrosis undergo a root canal or extraction to prevent further spread of the infection, which may lead to an abscess.
Symptoms
Necrosis may be symptomatic or asymptomatic. Symptomatic necrosis involves lingering pain response to hot and cold stimuli, spontaneous pain that may cause a patient to awaken during sleep, difficulty eating and senstivity to percussion.
Asymptomatic necrosis is non-responsive to thermal stimuli or electric pulp tests, leaving the patient unaware of the pathology.
Diagnosis
Asymptomatic necrosis is may go unnoticed by the patient and so a diagnosis may not be attempted. Diagnosis may involve X-rays and sensitivity testing with. hot or cold stimuli (using warm gutta-percha or ethyl chloride), or an electric pulp tester. Tooth vitality (blood supply) may be assessed using doppler flowmetry. Sequelae of a necrotic pulp include acute
apical periodontitis, dental abscess, or
radicular cyst
Radicular pain, or radiculitis, is pain "radiated" along the dermatome (sensory distribution) of a nerve due to inflammation or other irritation of the nerve root ( radiculopathy) at its connection to the spinal column. A common form of radic ...
and tooth discolouration.
Prognosis and treatment
Untreated necrotic pulp may result in further complications, such as infection, fever, swelling, abscesses and bone loss. Two treatment options are available for pulpal necrosis.
Pulp response to caries
Pulpal response to caries can be divided into two stages – pre- and post-infection. In caries-affected human teeth, odontoblast-like cells appear at the dentine-pulp interface along with specialized pulp immune cells to combat caries. Once they identify specific bacterial components, these cells activate innate and adaptive immunity.
In uninfected pulp,
leukocytes
White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...
can sample and respond to the environment, involving macrophages,
dendritic cells
Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. The ...
(DCs),
T cells
A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell re ...
and
B cells
B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or ...
.
This sampling process is part of the normal immune response, as it triggers leukocytes from the circulatory system to adhere to
endothelial
The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...
cells lining blood vessels and then migrates to the site of infection for defence. Macrophages can
phagocytose
Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...
bacteria and activate T cells, triggering the adaptive immune response that occurs in association with DCs.
In the pulp, DCs secrete a range of cytokines that influence immune responses, and are key regulators of the infection defence.
A comparatively small number of B cells are present in healthy pulp tissue, and pulpitis and caries progression increase their numbers.
When bacteria get closer to the pulp but are still confined to primary or secondary dentine, acid demineralization of dentine occurs, producing tertiary dentine to help protect the pulp from further injury.
After a pulp exposure, pulp cells are recruited and differentiate into odontoblast-like cells, contributing to the formation of a dentine bridge, increasing dentin thickness. The odontoblast-like cell is a mineralized structure formed by a new population of pulp-derived cells that can be expressed as
Toll-like receptors
Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane-spanning receptors usually expressed on sentinel cells such as macrophages and dendritic cells, that recognize st ...
. They are responsible for the upregulation of innate immunity effectors, including antimicrobial agents and
chemokines
Chemokines (), or chemotactic cytokines, are a family of small cytokines or signaling proteins secreted by cells that induce directional movement of leukocytes, as well as other cell types, including endothelial and epithelial cells. In addition ...
. One important antimicrobial agent produced by odontoblasts is
beta-defensins (BDs). BDs kill microorganisms by forming micropores that destroy membrane integrity and cause leakage of the cell content.
Another is
nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
(NO), a highly diffusible
free radical
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing.
Ageing
Ailments of unknown cause
Biogerontology
Biological processes
Causes of death
Cellular processes
Gerontology
Life extension
Metabo ...
that stimulates chemokine production to attract immune cells to the affected areas and neutralize bacterial by-products in pulp cells ''
in vitro
''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
''.
Pulp stones
Pulp stones are calcified masses that occur in the pulp, either in the apical or coronal portions. They are classified according to their structure or location. According to their location, pulp stones can be classed either as free (completely surrounded by pulp), embedded (surrounded by dentine tissue) or adherent (attached to pulp wall continuous with dentine, but not fully enclosed).
Depending on the structure, they are either true (dentine lined by odontoblasts), false (formed from degenerating cells that mineralise) or diffuse (more irregular in shape to false stones). The aetiology of pulp stones is little understood. It has been recorded that pulpal calcifications can occur due to:
* Pulp degeneration
* Increasing age
* Orthodontic treatment
* Traumatic occlusion
* Dental caries
Pulp stones usually consist of circular layers of mineralised tissues. These layers are made up of blood clots, dead cells and collagen fibres. Occasionally, pulp stones appear surrounded by odontoblast-like cells that contain tubules.
Pulp stones can reach as high as 50% in surveyed samples. Pulp stones are estimated to typically range from 8–9%.
Pulpal calcifications are more common in females and more frequent in maxillary teeth compared to mandibular teeth. The reason is uncertain. They are more common in molar teeth, especially first molars compared to second molars and premolars.
A review suggested this was because the first molars are the first teeth to be located in the mandible (lower jaw) and have longer exposure to degenerative changes. They also have a larger blood supply.
In general, pulp stones do not require treatment. Depending on the stones' size and location, they may interfere with endodontic treatment and should be removed.
Complications
Pulp acts as a security and alarm system. Slight decay in tooth structure not extending to the dentin may not alarm the pulp, but as the dentin gets exposed, due either to dental caries or trauma, sensitivity starts. The
dentinal tubules
Bone canaliculi are microscopic canals between the lacunae of ossified bone. The radiating processes of the osteocytes (called filopodia) project into these canals. These cytoplasmic processes are joined together by gap junctions. Osteocytes do ...
pass the
stimulus
A stimulus is something that causes a physiological response. It may refer to:
*Stimulation
**Stimulus (physiology), something external that influences an activity
**Stimulus (psychology), a concept in behaviorism and perception
*Stimulus (economi ...
to the pulp's odontoblastic layer, triggering the response. This mainly responds to cold. At this stage, simple restoration can be performed. As the decay progresses near the pulp, the response magnifies. Sensation to heat and cold increases. At this stage, indirect
pulp capping
Pulp capping is a technique used in dental restorations to prevent the dental pulp from necrosis, after being exposed, or nearly exposed during a cavity preparation, from a traumatic injury, or by a deep cavity that reaches the center of the toot ...
may be adviseable. At this stage it may be impossible to clinically diagnose the extent of decay. Carious dentin by dental decay progressing to the pulp may get fractured during
mastication
Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, th ...
, traumatizing the pulp, resulting in pulpitis.
Pulpitis can be painful and may call for
root canal therapy
Root canal treatment (also known as endodontic therapy, endodontic treatment, or root canal therapy) is a treatment sequence for the infected pulp of a tooth which is intended to result in the elimination of infection and the protection of ...
or endodontic therapy.
Traumatized pulp starts an inflammatory response. The hard and closed surroundings builds pressure inside the pulp chamber, compressing the
nerve fibres
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...
and eliciting pain. At this stage, the pulp starts to die, progressing to periapical abscess formation (chronic pulpitis).
Pulp horns recede with age. The pulp undergoes a decrease in intercellular substance, water, and cells as it fills with
collagen fibers
Type I collagen is the most abundant collagen of the human body. It forms large, eosinophilic fibers known as collagen fibers.
It is present in scar tissue, the end product when tissue heals by repair, as well as tendons, ligaments, the endomys ...
. This decrease in cells is evident in the reduced number of undifferentiated
mesenchymal cells. The pulp becomes more fibrotic, reducing the regenerative capacity of the pulp due to the loss of these cells. The overall pulp cavity may become smaller by the addition of secondary or tertiary dentin and cause pulp recession. The lack of sensitivity associated with older teeth is due to receded pulp horns, pulp fibrosis, the addition of dentin, or all these changes. Restorative treatment can be performed without local anaesthesia on older dentitions.
See also
*
Dental pulp stem cells
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Dental pulp test Dental pulpal testing is a clinical and diagnostic aid used in dentistry to help establish the health of the dental pulp within the pulp chamber and root canals of a tooth. Such investigations are important in aiding dentists in devising a treatment ...
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Parts of tooth
Tissues (biology)