Sign In Endodontium comprises of dentine and pulp both of which derive from the dental papilla.
Cells of the endodontium are located in the pulp. Therefore, tissue reactions in dentine are dependant on pulpal response.
Tissue changes in the dentine will modify pulpal response.
Cells of the pulp
- Odontoblast
- Fibroblasts
- Macrophages
- Lymphocytes
- Dendritic Cells
- Mesenchymal cells
- Mast cells
Pulp also contains a matrix of ground substances in which connective tissue and fibres are embedded. Ground substances contain proteoglycans and glycoproteins. Fibres are collagen and elastin.
Laying down of dentine
- During tooth germ development, the first layer of dentine is laid down by newly differentiated odontoblasts originating from the dental papilla (mantle dentine).
- Odontoblasts then form primary dentine during development.
- After development, secondary dentine is laid down throughout the life of the tooth.
- Tertiary dentine is laid down in response to wear or disease.
- Odontoblastic processes (extensions of the odontoblast), afferent nerve terminals and immunocompetent cells all extend into dentinal tubules which are found in the inner dentine.
Layers of the pulp
- Odontoblast Layer – The outermost layer of the pulp, immediately adjacent to predentine. Contains odontoblast cell bodies, capillaries and nerve fibres. Tight junctions between odontoblasts make it selectively permeable to fluids and solutes between pulp and dentinal tubules.
- Cell Poor zone – Immediately below the odontoblastic layer and is relatively cell free containing capillaries, nerve fibres, and fibroblast processes.
- Cell Rich Zone – Next layer down containing fibroblasts, macrophages and lymphocytes.
- Pulp Proper – The central mass of the pulp containing nerves, blood vessels and connective tissue cells.
Pulpal innervation consists of both afferent and autonomic innervation.
- Autonomic fibres regulate micro-circulation of the pulp
- Afferent fibres conduct sensory impulses
- Sympathetic fibres also appear around arterioles forming plexuses, modulating blood flow
Afferent fibres are both myelinated and unmyelinated. the principle fibres are Aδ fibres (A-delta), C fibres with a lesser number of Aβ fibres (A-beta).
- Aδ fibres have a relatively low threshold with myelinated fast acting pain fibres responding to transient pain
- C fibres are unmyelinated slow acting pain fibres causing a burning aching pain which is more diffuse
- C fibre stimulation is indicative of more pronounced inflammation
Afferent fibres ramify in subodontoblastic plexus – unmyelinated branches pass through to odontoblasts and dentine. Dentine under cusps have a greater number of nerves (~50%) as opposed to midcoronal dentine (~5%) in cervical and root dentine.
- Arterioles enter via the apical foramen.
- Capillary loops pass between odontoblastic processes.
- Lymphatic vessels are also present involved in draining interstitial fluid.
- Pulpal arteriole pressures is between 40 – 45mm/Hg (very low) – lower than in most other systemic arterioles.
- Interstitial fluid pressure is around 10mm/Hg (very high) – higher than in most other tissues.
- This reflects the low compliance of the pulp, as it is confined within rigid dentine, and any change in pulpal volume will affect pulpal pressure.
- Blood flow in pulp is greater in the periphery than the central areas.
- Tubular fluid contains extracellular ions and plasma proteins from pulpal capillaries.
- Dentine permeability is dependent on the number & diameter of the tubules.
- Permeability is higher in deeper dentine than in peripheral dentine.
The movement of fluid in tubules stimulates nerves:
- Brännström (Hydrodynamic Theory) – Movement of fluid is in response to thermal, mechanical and chemical stimuli.
- Recent studies suggest that outward fluid flow excites nerves more readily than inward flow.
| OUTWARD FLUID FLOW CAUSES: | INWARD FLUID FLOW CAUSES: |
|---|---|
| Cooling – Evaporation | Heating |
| Hypertonic solutions | Mechanical |
| Decreased hydrostatic pressure | Increased hydrostatic pressure |
| Drying |
Berggreen E, Bletsa A, Heyeraas K. Circulation in normal and inflamed dental pulp. Endodontic Topics 2010; 17: 2-11 https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1601-1546.2010.00249.x
Orchardson R, Cadden S. An update on the Physiology of the Dentine- Pulp Complex. Dental Update 2001;28:200-209 https://www.magonlinelibrary.com/doi/abs/10.12968/denu.2001.28.4.200
See also Dental Pulp And Periapical Pathology
