The Dentino-Pulp Complex Flashcards
What are the physical properties of Dentine?
- Fresh dentine is pale yellow
- Harder than bone and cementum
- Softer than enamel
- Tubular nature renders it strong (high compressive, tensile and flexural strength)
- Permeable, depending on the patency of the tubules (decreases with ageing)
What are the key features of Dentine?
- Forms the bulk of the teeth
- Large number of parallel tubules in a mineralised collagen matrix
- Tubules contain the processes of odontoblasts
- Formed constantly throughout life
- Sensitive tissue
What’s the chemical composition of Dentine?
- 70% inorganic
- 20% organic
- 10% water by weight
What’s the inorganic composition of Dentine?
- Calcium hydroxyapatite crystals (smaller than enamel crystals)
- Calcium poor and carbonate rich (bad for erosion)
- Crystals are found between and on the collagen fibrils
Whats’s the organic composition of Dentine?
- 90% collagen (mainly type I)
- Dentine phospho-proteins
(Phosphorphoryn - most acidic protein known - can bind to calcium - aids mineralisation of dentine)
- Proteoglycans
(Biglycan & decorin - important role in collagen assembly, cell adhesion. migration, differentiation and proliferation) - More like a modified CT
Dentine Tubules: How far do the tubules extend?
Extend from the pulp surface to the amelo-dentinal & cemento-dential junctions
- Have a curved sigmoid path (primary and secondary)
What is the dentine between tubules called?
Intertubular dentine
How do dentine tubules appear in cross-section?
Circular
How do dentine tubules change over time?
- Walls of newly formed tubules at the pulp surface are made of mineralised type I collagen
- Maturation of tubules is associated with deposition of another type of collagen
- Followed by reduction in size of lumen or complete obliteration = PERITUBULAR OR INTRATUBULAR DENTINE
What is a benefit and drawback of Peritubular dentine?
+ Teeth become less sensitive
- Teeth become more brittle
What are the characteristics of Peritubular dentine?
- Lacks collagen matrix
- Increased radiographic and electron density (more mineralised)
- Main protein isn’t phosphophoryn
- Inorganic component is mainly carbonated apatite with different crystal structure
What’s the content of Dentinal tubules?
1) Odontoblastic processes
2) Afferent nerve terminals
3) Antigen presenting cells processes
4) Extracellular dentinal fluid
What are Odontoblastic processes?
- Extensions of the Odontoblasts (produce dentine) which are found in the pulp
- Odontoblastic process branches which extend into the enamel = Enamel spindles
- Contain organelles - predominantly at the perdentine area
- In the inner layers of the dentine; the processes occupy almost the full width
Dentinal Tubules: What are Afferent nerve terminals and what are they associated with?
- Sensory nerve fibres of the dental pulp; afferent endings of the trigeminal cranial nerve
- Mainly present in the inner layers of dentine
- Intimate relationship with odontoblastic processes
- Related to tooth sensitivity & mostly un-myelinated
Dentine tubules: What’s the purpose of Antigen presenting cells processes?
- Immune response to infection
- Appear as small processes in the tubules near the pulp
- Within and beneath odontoblasts
- Limited to pre-dentine area and below
- In carious dentine (bacterial) they extender deeper in the tubules
Dentine tubules: Whats Extracellular dentinal fluid?
- Unknown composition: Know it has higher potassium and lower sodium ion levels that other fluids
- Positive force from pulpal tissure pressure
What’s Mantle dentine?
- Most peripheral (1st to be formed) layer of dentine (outermost layer next to enamel)
- 20-150μm in width
- Different orientation of collagen fibres (perpendicular)
- Less mineralised then circumpulpal dentine
When are the contour lines of Owen found?
Mantle dentine
What’s interglobular dentine?
- Minerals deposited as globules (calcospheres) which fuse to form a uniform calcified tissue
- Hypomineralised
- Found beneath mantle detine
- Uncalcified interglobular area appear DARK
What’s the granular layer of Tome?
- Peripheral root dentine has a dark granular zone
- Dentinal tubules branch and loop back on themselves which creates air spaces
- “tree top” appearance of tubules
- Hypomineralised granular layer
What’s the Hyaline layer?
- Outside layer of granular layer
- Atubular and structureless
- Helps bonding of tentine to cementum
What’s Cirumpulpal dentine?
- Forms the bulk of the dentine
- Uniform in structure except at the peripheries
What’s Predentine?
- Initially laid dentine matrix prior to mineralisation
- Mineralisation front may show a globular or a linear appearance
- 10-40μm in width & thicker in young teeth
What lines are associated with the primary curvatures of dentinal tubules?
Schreger lines - follow a sinusoidal path called the primary curvature (S-shape)
What lines are associated with the secondary curvature of dentinal tubules?
Contour lines of Owen
- Exaggerated line on the boarder of primary and secondary dentine
- Neonatal line
What are the dentine incremental lines?
Changes in collagen fibres orientation
- Short term = Von Ebner’s lines
- Long term = Andresen lines (go across the prisms) & exaggerated neonatal line
What are the 2 Physiological age changes to dentine are (1)?
Secondary dentine:
- Normal change in dentine (just change in tubular direction)
- Nearer the pulp as it forms later
- Forms once the root is completed and the tooth comes into occlusion
- Similar to primary dentine
- Sudden change in tubules direction
- Slower deposition thus less regular
- Closer incremental lines
What are the 2 Physiological age changes to dentine are (2)?
Translucent dentine:
- Intratubular dentine
What are the 3 changes associated with dentinal responses to stimuli (1)?
Tertiary dentine:
- External stimuli can induce the pulp to produce more calcified material
- NOT A CONTINUATION OF PRIMARY AND SECONDARY DENTINE
- Cells in the pulp differentiate into odontoblasts (produce dentine) – production of type I collagen and dintine sialoprotein
What are the 3 changes associated with dentinal responses to stimuli (2)?
Sclerotic dentine:
- Stimuli induces the deposition of material inside the dentine tubules
- Similar appearance to transparent dentine but it has a different composition to intratubular dentine
- Spindles are observable - appear as continuations of the dentine
What are the 3 changes associated with dentinal responses to stimuli (3)?
Dead Tracts of Fish:
- Primary odontoblasts which have been kidded by external stimuli and results in empty tubules
- Might be sealed at their pulpal end by tertiary dentine
- Air filled
- Caused by cavity and acid-wear
Dentine Sensitivity: What’s the theory behind dental sensitivity?
Hydrodynamic theory (Fluid movement within the tubules):
- Stimuli applied to dentine causes fluid movement; can be sufficient to depolarise the nerve endings and cause them to fire
- In the tubules
- at the dentine-pulp junction
- in the plexus of Raschkow (innovate the odontoblastic layer in pulp)
What types of stimuli can cause fluid movement within tubules?
- Heat
- Osmotic pressure
Drying - Cold stimuli causes inward movement of fluids
- Inward/outwards movement mechanically affect nerve terminals
- Tubular branching near DEJ explain the higher sensitivity
- A- group fibres – responsible for the sensitivity of dentine and thus for the mediation of the sharp induced by dentine sensitivity
What is dental pulp?
- Innermost part of the tooth
- Unmineralised tissue
- Composed of 2 parts: Pulp chamber and root canals
- Highly innervated tissue with no space for movement
What’s the general organisation of dental pulp?
1) Pulp chamber
2) Root (at least 1 canal)
2b) Accessory canals in the apical 3rd
What’s the composition of dental pulp?
- Cells are in a extracellular matrix
- 75% water by weight
- 25% organic material: polysaccharides/proteins/etc
- Non-fibrous matrix
- Fibres (mainly collagen)
What fibres are present in dental pulp?
Collagen type I
- Fibrils thinly scattered through the pulp
- Randomly organised
- At peripheries - parallel to the predentine surface
- Right angles to the amelo-dentine junction in mantle dentine (Von Korff’s)
- More crosslinking with age
Collagen type III
- Present in large amounts (41% pulpal collagen)
- Only alpha1 chains
- Collagen type V + VI present in small amounts
What are the components of the non-fibrous matrix?
- Glycosaminoglycans
- Proteoglycans
- Fibronectin
- Laminin
What’s the significance of Glycosaminoglycans in the matrix?
- Bulky hydrophillic molecules that form gels
What’s the significance of Proteoglycans?
- Core protein’s surrounded by glycosaminoglycans
- Decorin: Bind collagen and TGF-beta (regulates cell proliferation/differentiation and reparative dentiogenesis) (aids dentine production)
What’s the role of Fibronectin?
- Glycoprotein which aids cell attachment to extracellular matrix
- Widely distributed in the pulp
- Cell adhesion molecule
What’s the role of Laminin?
- Cell adhesion molecule
- Forms part of the basement membranes and bind epithelial cells to the ECM
- Important for blood vessels
Whats the role of Odontoblasts in the dental pulp?
- Produce Dentine
- Found at the periphery in dental pulp
- Form a layer of single cells attached to the predentine by a single process
- Coronal odontoblasts are columnar in the outline BUT cuboidal in the root
How does the single layer of Odontoblasts communicate?
- Interact via cell junctions
- Tight junctions = limit permeability and provides mechanical integrity
- Gap junctions: Allows synchronisation of cells
What’s the role of Fibroblasts in dental pulp?
- Responsible for matrix turnover (produce collagenase/protease etc)
- Scattered all around the pulp
- Slowly produce fibres and ground substance
What’s the role of undifferentiated cells?
- Located beneath the odontoblastic layer - capable of differentiating into Odontoblasts
- Pluripotent primitive mesenchymal cells (can differentiate into a variety of cell types)
Blood vessels: what’s their relationship with nerves in the dental pulp?
- Close relationship
How do blood vessels enter the pulp?
- Arterioles and venules enter via the apical foramen and lateral canals
- Once in the canal they branch to the peripheries and branch profusely in the coronal pulp chamber
Is there a subodontoblastic capillary plexus?
YES
- Technically, within and beneath odontoblasts
- 4-5% are fenestrated with only a basement membrane at their wall
- High fluid pressure
Is there a rich supply of nerve fibres within teeth?
YES
- 2500 axons enter a mature premolar
- 25% are myelinated afferents
- 90% are Alpha fibres - these are associated with acute pain and with sensations of temperature pressure
What’s the predominant nerve fibre within the pulp?
- Unmyelinated C fibres
- Afferent or autonomic (sympathetic fibres associated with blood vessels)
- C fibres have a slow conduction velocity and are associated with chronic or dull pain + with sensations of warmth/mechanical/chemical stimuli
- Most fibres are nociceptors
How do nerves enter the pulp?
- Part of neuro-vascular bundle
- Branch into coronal part of pulp
- Branches end in and around odontoblastic layer : plexus of nerves beneath the odontoblasts= PLEXUS OF RASCHKOW
Do branches from the Plexus of Raschkow enter dentinal tubules?
YES
- Lots of axons are present in the tubules and the peripheries of dentine - devioid of Schwann cells
- Lack of Schwann cells facilitates their response to stimuli from the immediate environment
What’s the function of the neuropeptide: Calcitonin gene-related peptide (CGRP)?
- CGRP is a potent vasodilator which controls pulpal blood flow
- Synthesised by neurons and transported by axons
- May contribute to the control of hard tissue formation
- Function of nerves in the pulp is maintaining the local environment
What are the regions of the Dental pulp?
- Supraodontoblastic region
- Odontoblastic layer
- Subodontoblastic
3a: Cell free zone of Weil
3b: Cell rich zone - Bulk of the pulp
What’s the Supraodontoblastic region?
- Between the odontoblastic cell bodies and the predentine
- Unsheathed axons are present (predentinal plexus of Bradlaw)
- Dendritic antigen presenting cells present
- 1st region in the pulp where changes in the tubules could be detected
What’s the Cell Free Zone of Weil?
- Cell free zone/Anuclear zone
- Cell processes of fibroblasts, odontoblasts, axons and capillaries are found across this region
- Only in the coronal pulp of erupted teeth
- Might be considered an artefact
What’s the Cell Rich Zone?
- Potentially an artefact layer again
- Subodontoblastic capillary and neural plexus
- Cells associated with these plei could result in the richness of this zone
What’s the Bulk of the Pulp?
- Central area of pulp
- Loose CT
- Rich blood and nerve supply
What happens to the pulp as it ages?
- Size decreases
- Decrease in vascularity
- More fibrous
- Reduced innervation
- Calcification: Pulp stones or snow storm calcification
What are Pulp stones?
- Either single or in a group
- Either true or false denticles:
+ T = resemble dentine (tubular)
+ F = resemble bone (trapped cells) - Some are attached to dentine
- Case complications when carrying out root canal therapy
What are the clinical considerations regarding pulp?
- Defects in dental tissue are mediated through the pulp
- Sense organ of the tooth so it requires anaesthesia
- Possess defence mechanisms against caries and trauma (stimulating tertiary dentine)
