Dental Pulp
Introduction
Soft tissue of mesenchymal origin (dental papilla)
Forms core of the tooth & occupies the space that approximates the external contour of tooth
Loose connective tissue, but unique
Specialised cells: odontoblasts, which lay down dentine
Acts as a sensory organs
Enclosed by hard tissue: Low compliant system
Enclosed within rigid structure of dentine and enamel
Ability of pulp volume to expand when inflammed is restricted
Leads to pain during inflammation
Structural Organisation
Odontoblastic Layer
Cell-free zone of Weil
Cell-rich zome/ Subodontoblastic layer
Plexus of Raschkow
Pulp Core
Adjacent to predentine
Pseudostratified layer of columnar (@ coronal region) or cuboidal (@ root region) cells with a single long process extending into predentine and dentine
Responsible for dentine formation
Provides a controlled barrier between pulp and dentine
Protects pulp from external irritants
below odontoblastic layer
Contains most number of cells in the pulp
Undifferentiated progenitor cells
Consists of network of blood vessels known as subodontiblastic capilary plexus
Formed when blood vessels entering via apical foramen up through the central root portion branch laterally
Sensory and autonomic nerves + blood vessels enter via apical foramen and branch extensively below cell-rich zone
Forms the Plexus of Raschkow
Predominantly fibroblasts
Large arteries (veins + nerve trunks) enter apical canal and proceed to the coronal pulp chamber
Composition
75% water, 25% organic materials
Dental pulp is a loose connective tissue made up of a combination of cells embedded in an ECM of fibres in a semi-fluid gel, the ground substance
Cells of Dental Pulp
Odontoblasts
Specialised cells responsible for the formation of dentine
Continues to lay down secondary dentine throughout life (or for as long as the tooth remains vital)
Highly-polarized post-mitotic secretory cells
Post-mitotic --> cannot divide and will die if subject to injury
Coronal odontoblasts are columnar
Radicular odontoblasts are cuboidal
Cell body has a single cytoplasmic process (with lateral branches) that extends into predentine and dentine within dentinal tubules
Lateral branches link the cell to adjacent odontoblasts and other pulp cells
Amount or RER, golgi apparatus & secretory granules depends on life cycle
Cell body form a pseuostratified layer of cells (single layer) attached to predentine surface
Higher density in crown that in root
Highest in region of pulp horns
Junctions found between adjacent odontoblasts
Tight Junction
Gap Junction
Desmosomes
Limit permeability and maintain integrity of odontoblast layer
Openings for communication of electrical impulses and small molecules directly between adjacent cells
Responible for mechanical union of cells
Functions
Lay down dentine throughout the life of the tooth
Cell body: synthesis and control of the amount of proteins
Cell process: secretion of calcium and dentine phosphoprotein
Rate of dentine formation
Primary: 4µm/ day
Secondary: 0.4µm/ day
Fibroblasts
Function
Production of extracellular fibres and ground substance
Note; they do NOT contribute to the production of dentine
They are the most common type of cell in the pulp, and are abundant in the cell-rich zone
Stellate appearance with large, multiple protoplasmic processes that extend outwards and contact adjacent cells through gap junctions
Become smaller, narrower and spindle shaped with age
Slow turnover rate (compared to high turnover rate in PDL)
Can differentiate into odontoblast-like cells as replacement
Defence Cells
Dendritic Cells
Macrophages
B and T Lymphocytes
initiate primary immune response
migrate with trapped antigen to regional lymph nodes and induce T lymphocyte division and differetiation
An immunosurveillance cell
Found in dentine border and pulp core
Function
Initate primary immune response
When memory T lymphocytes recognise antigen presented by dendritic or macrophages, T cell activation triggers T cell dependant immunity
B lymphocytes are activated by T helper cells
Derived from monocytes from blood
Found in proximity of blood vessels
Function
Scavanger cells, phagocytose and lysosomal enzymes destroy dead cells and foreign bodies
Antigen presenting cells
Undifferentiated Mesenchymal cells
Stellate shaped cells
Mainly in cell-rich zone and pulp core
Difficult to distinguish from fibroblasts using LM
Function
Induced Pluripotent stem cells (iPS) has the potential to differentiate into fibroblasts or odontoblasts
Produced tertiary dentine
Components of Extracellular Matrix
Collagen Fibres
Principle component of dental pulp
Radicular pulp is more fibrous than coronal pulp
Mainly Type I (60%) and Type III (40%)
Type V and Type VI in small amount
Fibres are grouped into fibrils thingy and irregularly scattered
Arranged irregularly, except at periphery where alignment is approximately parallel to forming predentine surface
Surrounded by ground substance of pulp
Type I
Synthesized by odontoblasts and fibroblasts
Provides consistency and strength
Type III
Synthesised by pulp fibroblasts
Provides elasticity
Abundant in cell free zone
Usually co-distributed with Type I collagen
Elastin Fibres
Found around arterioles and not in ECM
Fibronectin
Glycoprotein found in fibrous form throughout the pulp
Binds to membrane receptor proteins (e.g. integrins)
Mediator for cell-cell and cell-matrix adhesion
Glycosaminoglycans
unbranched polysaccharide chains composed of repeating dissacharide units
4 GAGs
Chondroitin sulphate
Dermatan sulphate
Heparan sulphate
Hyaluronic Acid
Covalently bound to a core protein to form proteglycans which fill most of the ECM
Function
Allow movement of water and ions
Ground substance acts as a binder, providing anchorage and support to the cels
Act as a resevoir for growth factors and bioactive molecules
Acts as mechanical barrier against bacteria
Supporting Structures
Blood Vessels
Extensive vasculature; pulp is a micro-circulatory system
Regulates local interstitial environment by absorbing low molecular weight solutes
Not all capillaries are continuously perfused; they are controlled by pre-capillary sphincters
Atriovenous shunt controls blood flow
AVA shunt becomes active during inflammation and repair to permit regional control of pulpal blood flow so that the effect is compartmentalized
Filtration takes place at the arteriole end (Pc= 35mmHg), and absoprtion takes place at the venous end (Pc=19mmHg)
Pathway
- Enters the apical canal and up the root pulp into coronal area
- Anastomosis with arterioles of other branches entering from other root canals
- Gives off side branches to periphery
- Branches profusely within coronal pulp
- Capillary loops towards dentine
- Forms sub-odontoblastic capillary plexus below odontoblast layer
Capillaries are present both within and below odontoblast layer, and between the odontoblast and predentine
they DO NOT enter the dentinal tubules
Lymphatics
Similar to capillaries but has discontinuous basement membrane
Nerves
Two types of sensory fibres
Unmyelinated C fibres
Myelinated A fibres
One of the last major structures to appear in developing teeth
in the core and extend to the cell-free zone
mainly in the pulp-dentine border
Dominant mechanism for the removal of high m.w. solutes from the intersitial fluid
Transport antigens directly to regional lymph nodes as part of immune response
Sympathetic efferent fibres from the trigeminal nerve modulate blood flow
Function of Pulp
Inductive
Initiates tooth formation and probs induced the dental organ to develop into a particular type of tooth
Participates in the initiation and development of dentine
Formative
Primary Dentine
Secondary Dentine
Tertiary Dentine
Consists of regular S shaped tubular dentine formed before tooth eruption
Convexity of primary curvature nearest the pulp faces towards the root
Regular circumpulpla tubular dentine formed in continuity with primary dentine but at a slower rate, throughout life
Produced by downregulated odontoblasts after completion of root formation or tooth goes into occlusion
Greater deposition on roof and floor of pulp chamber
Nutritive
Provides nutrients essential for dentine formation and maintaining the integrity of the pulp
Protective
Pulpodentine complex is one of the most highly innervated tissues in the body
Nerve endings mediate sense of pain from heat, cold, pressure, trauma, infection and decat
Brannstrom's Hydrodynamic Theory
Stimulus causes inward or outward fluid movement within dentinal tubules that excite the nerve endings, interpreted as pain
A fibres are responsible for sensitivity to hot, cold etc.
C fibres are responsible for toothache symptoms
non-myelinated, found throughout pulp, high stimulation threshold
myelinated, found at PDJ and has low stimulation threshold
Odontoblasts and Mechanoreceptors
acts as a sensory cell
may act as mechano-transducer between dentinal fluid and nerve endings
Shear forces in dentinal fluid stimulates odontoblast cell membrane
They have primary cilium that helps to convert mechanical fluid movement into an electrical signal
Contain
High conductance Ca- activated K+ channels
Stretch-activated TREK-1 K+ channels
N-ty[e Ca2+ channels at the base of cilia
Transient receptor potential (TRP) channels
Activated in response to temperature changes
Modulate warm/ cold
Defensive
Pulp provides defence againt, caries, attrition, erosion, abrasian, leakage etc.
How:
Dentinal fluid
Outward flow of dentinal fluid makes it difficult for bacteria to reach the pulp
Contains immunoglobulins
Intratubular fibres in dentinal tubules can trap bacteria
Inflammatory Response
Immunocompetent cells mount inflammatory response to bacteria attack
Inflammation is compartmentalised to area of pulp corresponding to breach of dentine
Achieved through AVA shunt-- fluid (blood) perfusion increases in those areas
Inflammation spreads apically
Usually fluid capacity is not at maximum.
However, during an inflammation, if fluids entering the pulp is faster than drainage pressure builds up --> causes pain
Odontoblasts synthesise tertiary dentine to reduce dentine permeability
Dissolution of dentine matrix protein fossilised in dentine stimulates celllar activity to repair dentine
Odontoblasts are upregulated or destroyed
Age Changes
Pulp Volume Decreases
Cells decrease
Fibres increase
Pulpal calcifications
Secondary dentine formation throughout life reduces the size of the pulp
Greater deposition on floor and roof of pulp chamber
Clinical Implications
More leeway in cutting tooth tissue before the dental pulp is exposed
Harder to locate root canals
Gradual reduction in all pulp cells, nerves and blood vessels
Cell density reduced by ~50% between 20 and 70 years of age
Clinical Implications
Inherent healing ability of aged pulp is reduced
Increase in number and thickness of collagen fibres, forming bundles
Discrete physiological calcifications in the pulp
Free/ attached/ embedded
More often in the coronal region
May increase in number or size due to local of systemic pathosis