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

  1. Enters the apical canal and up the root pulp into coronal area
  1. Anastomosis with arterioles of other branches entering from other root canals
  1. Gives off side branches to periphery
  1. Branches profusely within coronal pulp
  1. Capillary loops towards dentine
  1. 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