The Pulpodentine Complex 2 Flashcards
Is the pulp necessary for the function of the tooth?
Yes
What is the function of the pulp?
Functional (produces dentine)
Nutritive (Nourishes the avascular dentine)
Protective (Carries nerves that give dentine its sensitivity as well as forming barriers, inflammation and an immune response)
Reparative (Capable of producing new dentine when required)
What initiates dentine development in the pulp?
An epithelial-mesenchymal interaction (enamel epithelium induces the differentiation of odontoblasts. Odontoblasts and dentine induce the formation of enamel)
Dentine formation (odontoblasts form primary and secondaryt dentine)
What is the nutritive role of the pulp?
Supplies nutrients and moisture to the tooth which is essential for dentine formation as well as maintaining integrity of the pulp itself.
What is the protective function of the pulp?
Carries nerves that provide sensory function and proprioception
Acts as an immune system organ:
Makes fluid flow outwards which forms a barrier
Odontoblast process in tubules behave as positively charged electrogel which arrest bacterial ingress
Antigen recognition (Odontoblast TLRs, dendritic cells, and macrophages)
Cytokines, chemokines, and complements.
Innate and acquired immunity (vascular and neural involvement)
What is the reparative function of the pulp?
Continued formation of dentine. (Reactionary, reactive, and sclerotic dentine.)
What are the functions of dentine?
Protection: Forms hard tissue case surrounding the pulp together with enamel and cementum to preserve the integrity of pulp tissue. Dentine mineralization provides a reaction to external trauma (such as wear and caries), regulates the inflammatory response in the pulp (non-collagenous proteins and growth factors)
Support: Provides elasticity, strength and toughness to the tooth
Which part of dentine withstands the load?
The inorganic component
Which part of the dentine provides the soft wrap around the mineral platelets and protects them from peak stresses caused by external load?
The organic component
What part of dentine provides stiffness/strength?
Inorganic component
Which part of dentine provides toughness?
Organic component
Which part of dentine homogenizes stress distribution within the composite structure?
The organic component
How is the function of each component of the dentine distributed?
Most is carried by the mineral platelets.
Protein transfers load
How does collagen provide structural support?
It incorporates water of hydration into the triple helix of the collagen structure (2 water molecules fr each tripeptide making it swell up laterally. Water acts as a plasticizer)
How is the collagen matrix of dentine affected by hydration?
Hydrated dentine forms interpeptide hydrogen bonds preferentially with water. This fill sup interfibrillar spaces with water, expanding the overall fibril diameter and increasing the toughness.
In the absence of water interpeptide hydrogen bonds form causing loss of interfibrillar spaces and shrinkage of overall diameter of the fibrils and the stiffness.
When water is absent dentine becomes brittle and more stiff.
What blood vessels supply the teeth?
Maxillary side is supplied by the maxillary artery which is a branch of the external carotid artery.
The maxillary artery gives a superior alveolar artery which divides into posterior, middle, and anterior branches.
The maxillary artery also gives a inferior alveolar artery which supplies the mandible side.
What nerve supplies the sensory afferent innervation of the teeth?
Maxillary and inferior alveolar nerve comes from the trigeminal ganglion.
What nerve provides the sympathetic innervation of the teeth?
The superior cervical ganglion (less numerous)
What structure does the neurovascular bundle pass through to enter teeth?
The apical foramen.
How does the pulp get the microcirculation?
Arteriole - Capillary - Venule system in place which courses up through the central portion, gives off 90 degree branches laterally towards odontoblast layer, ramifies to form a capillary plexus near root dentine.
How does the coronal area of the tooth receive microvascular supply?
ACV system fans out towards the dentine. It gives rise to a dense terminal capillary network TCN in the subodontoblast region, capillaries extend into the odontoblast layer which provides a rich source of nutrients.
What efferent vessels are present in the microcirculation?
Postcapillary venules (thin walled)
Larger venules (progressively larger as they pass through the central region og the pulp)
Exit at apical foramen to drain maxillary vein posteriorly and the facial vein anteriorly
How does lymphatic drainage travel through the teeth?
Lymphatic vessels arise as small, blind, thin-walled vessels in the periphery of the pulp (not in odontoblast layer)
Travel from central coronal pulp to the root
Extensive anastomoses between lymph vessels of the pulp PDL and the alveolar bone.
Drain into regional lymph gland (submental, submandibular, and cervical)
Empty into the subclavian and internal jugular veins.
What does lymphatic drainage do to the teeth?
Drains fluids/proteins and inflammatory exudates/transudates and cellular debris
It is also important for immune defence.
What determines pulp lymph flow?
The pulp interstitial fluid pressure.
What are the components of the terminal capillary network in the pulp?
The precaillary arteriole
The calillaries
The postcapillary venule
How is blood flow to the pulp controlled?
Pre-capillary sphincter is under local cellular and sympathetic neuronal control
The local factors that control the flow include cellular metabolic demands; dentinogenesis, neuropeptide Y, Neuropeptide (symp) vasoconstriction, and nitric oxide vasodilation.
The pulp is compartmentalised so adjacent regions can have substantially different circulatory conditions.
What types of anastomoses are present in the pulpodentine complex?
Arteriovenous anastomosis connects arteriole directly to a venule
Venous-venous anastomosis connects venule directly to a venule
U-turn loop arteriole is more frequent in the radicular pulp, shunts blood away from the area of injury/inflammation especially during initial stage of inflammation
What are the characteristics of microvasculature?
They are true isolated microcirculatory networks (depend on relatively few arterioles, lack collateral, alternative blood supply, and make the apical region a critical point)
Heterogeneity within the pulp (Dense capillary networks in the periphery; peripheral vs central core areas, coronal vs apical areas)
U-turn loop arterioles
Anastomoses
What are the requirements of the microcirculation to the dental pulp?
Relatively high blood volume (3% of pulp wet weight)
Relatively high capillary density (1400/mm2 which is greater than most other tissues)
Relatively high resting pulp blood flow (Very similar blood flow rate to that of the brain and 40 - 100% of the pulp blood volume is replaced each minute)
Relatively high pulp tissue pressure (6 - 10 mmHg)
Which part of the tooth gets a higher blood flow?
The coronal part of the tooth gets nearly twice the flow of the radicular part.
What is the function of the blood supply to the dental tissue?
Homeostasis: Nutrients + O2, metabolic wastes removal, Distribute extracellular fluid and maintaining pulp blood pressure in harmony with the pulp tissue pressure.
Inflammation: Altering local capillary filtration rates, angiogenesis, and recruiting immune cells.
How do nerves enter the pulp?
through the apical foramen in bundles.
Bundles are in close proximity to pulp blood flow (neurovascular bundle)
How does the radicular region get its nerve supply differently to the coronal region?
Nerve fibers arborize peripherally as they move coronally
Few branches along the root (lack plexus of Raschkow) whereas in the coronal region the plexus of raschkow has formed.
Coronal region has dense branching (densest in the pulp horn)
What is the contribution of individual myelinated axons to the overall innervation of the pulp?
Each individual myelinated axon sends at least 8 branches to the plexus
Within plexus there is further prolific branches innervating more than a hundred dentinal tubules. There is a tremendous overlap of receptor fields.
Where is the sympathetic innervation from?
Less numerous than sensory afferent innervation. Arrives from the superior cervical ganglion.
Where in the pulp is sympathetic innervation seen?
In the deeper parts of the pulp proper it forms plexuses around the pulp arterioles
Less numerous in the radicular part of the pulp compared to the pulp proper.
How does sympathetic innervation control the pulp microenvironment?
Vascular control via neurotransmitters:
Norepinephrine is produced locally in nerve terminals
Neuropeptide Y is produced in neurons and supplied to nerve terminals
There is an interplay between nerves, blood vessels, and immunocompetent cells (A functional unit in pulp homeostasis and defense mechanisms)
What is the function of terminal axons of sensory nerves?
Nociception
Neurogenic modulation (Microcirculation, vasodilation, neurogenic inflammation and immune response)
Regulation of dentinogenesis
What is the function of terminal axons of sympathetic nerves?
Neurogenic modulation (Microcirculation, vasoconstriction, neurogenic inflammation, and immune response)
Regulation of dentinogenesis
What factors affect the rate of solute permeation into the pulp through dentine?
Molecular size, charge
Dentine surface area
Remaining dentine thickness
Proximity of the pulp
What factors affect the rate of solute removal by the pulp?
Capillary number
Capillary flow rate
Perfusion pressure
Colloid osmotic pressure
Pre vs postcapillary resistance
What affects filtration of dentine?
Pressure difference across the dentine (osmotic and hydrostatic)
Number, length and diameter of the tubules
Hydraulic conductance of dentine
What is the single most important factor in protecting the pulp from insults?
The remaining dentine thickness (RDT)
Deeper cavity = Greater permeability
Which part of the tooth is dentine permeability lower?
The radicular dentine due to decrease in density of dentinal tubules.
What causes dead tracts?
Bacteria may cause early death of odontoblasts leaving empty tubules leading directly to the pulp.
What is located at the pulp end of dentinal tubules?
Cellular processes of odontoblasts
Nerve terminals
Cells of the immune system
Immunoglobulins
Intraluminal collagen
Outward flow of dentine fluid
Why are bacteria seldom found in the tubules at the extreme front of a carious attack?
Dentinal fluid flows outwards
Outward flux of immunoglobulins and fibrinogen.
What affects the types of tertiary dentine produced in response to an injury?
If the stimulus is mild it injures the primary odontoblasts leading to formation of reactionary dentine.
Is there is a strong stimulus that kills the primary odontoblasts then the newly differentiated replacement odontoblasts produce reparative dentine.
What are the features of reparative dentine?
It results in newly formed odontoblasts and the new tertiary dentine does not line up with the original primary dentine.
The new odontoblasts lack a process so they form a layer of atubular dentine.
What are the features of reactionary dentine?
More dentine is produced at a fast rate increasing the dentine thicknes.
Intraluminal crystaline deposits are formed in the tubules.
What are the factors that affect how tertiary dentine is formed?
Extent and duration of the stimulus (Attrition or slow progression vs a cavity prep which is an immediate crisis)
Dentine permeability (Tubules containing a process, dentine sclerosis, tertiary dentine)
Age of the tooth (Dentine forms throughout life, decreased volume of pulp chamber/root canal)
Why does age have an effect on how tertiary dentine is formed?
Decreased volume of pulp chamber / root canal
Decreased cellularity
Increased collagens
Diminished neurovascular supply
What chemical messengers are produced during dentine matrix breakdown?
TGF-beta
BMPs
What receptors in the teeth respond to thermal stimuli?
TRPV1 to >43 degree heat
TRPM8 to cold
What do mechanical receptors in the pulp respond to?
Excess pressure or deformation
What are the types of pain that can be sensed by nociceptors in the dental pulp?
Prepain (low intensity electrical stimulation)
Sharp, stabbing pain
Dull, aching, throbbing pain
What affects the pain perceived in the pulp?
Stimulus: Type, intensity, and frequency
Nerve fiber sensing the pain: Type A or C
Condition of the pulp: Normal or inflamed
What are the main differences between type A fibers and type C fibers?
Type A fibers:
Myelinated (Type C are unmyelinated)
Large in diameter (Type C are small in diameter)
Fast in conduction velocity (Type C are slow in conduction velocity)
Located in the pulp periphery (pulp-dentine border) whereas type C fibers are located in the pulp proper along the blood vessels and extend into the cell-free zone under the odontoblasts.
Located mainly in the coronal portion of the pulp, in particular the pulp horns penetrating inner dentine
Where are cell bodies located in both type A and type C fibers?
Cell bodies in trigeminal ganglion
What activates myelinated A fibers?
Mechanical nociceptors activated by hydrodynamic stimulants.
Overlapping receptive fields of individual fibers (stimulation of a small area of dentine can activate multiple nerve fibers)
What neurotransmitters are most often used by myelinated Aδ fibers?
Neuropeptide CGRP (most abundant, 3 - 4x more than SP)
They also express receptors for NGF
Where are myelinated Aβ Fibres located?
Close to odontoblasts near the pulp horn tip (in the predentine portion of dentinal tubules)
What are the features of the myelinated Aβ Fibres?
They are low threshold fibers with less receptors for NGF (Low affinity for NGF and more sensitive to hydrodynamic stimuli)
What kind of receptors do C fibers have?
Polymodal nociceptors (activated by thermal, mechanical, chemical etc factors)
What do C fibers do?
They are silent in normal healthy pulp and start to activate when the pulp tissue is exposed.
What neuropeptides do unmyelinated C fibers use?
Mainly substance P
What direction is dentinal fluid flow a trigger for nociceptor firing?
Outward flow
What stimuli is dentine particularly sensitive to that can be tested?
Cold/heat
Probing
Air blasts
Hyper-osmotic sweet solutions
Does direct application of local anaesthetics decrease the intensity of pain from dentine?
No
What is the hydrodynamic theory?
Movement of dentinal fluid through the tubules stimulates the pulp nerve which elicits pain.
Direct exposure of dentine to stimuli does not cause pain for this reason.
What causes the rapid dentinal tubule flow?
Physical properties of capillarity
Strong capillary forces cause rapid fluid flow in the tubules
Stimuli affect rate of flow of fluid through the tubules
What is the trigeminal pain system?
A dedicated pain system where nerve fibers only carry information related to pain.
How is pain detected, processed, and perceived?
Afferent nociceptive nerves in the pulp detect painful stimuli.
First order neurons in trigeminal ganglion to second order neurons in trigeminal spinal tract to third order neurons in the thalamus.
Pain is then perceived in the cerebral cortex.
How is pain arising from a molar (fast pain) localised?
Nociception Aδ fibre arising from a molar - fast pain - localised:
Carried by the first order neurons in the trigeminal ganglion Via trigeminal tract into the trigeminal spinal tract nucleus.
It then synapses at the subnucleus caudalis region, with nociceptive-specific neurons (NS, the second order neurons)
Via the Neospinothalamic tract - directly and quickly - into the thalamus
(the third order neurons)
Onto the cortex for interpretation
How do air blasts trigger the pain response in dentine?
It dehydrates the outer end of the exposed dentinal tubules induces a greater loss of fluid via rapid outflow of fluid through tubules causing deformation of mechanoreceptors of the pulpodentine border.
How do hyperosmotic solutions trigger pain?
They extract fluid from the outer end of the exposed dentinal tubules due to high osmotic pressure.
This leads to a rapid fluid flow and deformation of the mechanoreceptor at the pulp.
How does probing dentine lead to pain?
The light pressure produces strong local compressive forces creating shallow grooves lined by smear layers which mechanically compresses dentine and partially occludes the tubules with the smear layer.
Why does the cervical dentine seem to be especially sensitive?
The time course of dentine tubule exposure (Much faster in cervical area due to gingival recession)
Different responses of the pulp-dentine complex (To irritation in the coronal dentine compared with cervical dentine)
Pulp inflammation due to persistent dentinal tubule exposure. (Sensitization of intradental A nociceptors)
How is the nociceptive reflex activated when accidentally biting on a hard object?
Biting on a hard object unexpectedly activates the nociceptive reflex.
This occurs in response to elastic deformation of dentine to occlusal overloading. (rapid fluid movement through dentinal tubules, strong capillary force, deformation of mechanoreceptor at the pulp-dentine border and rapid reflex withdrawal)
Occlusal overloading response:
Primary afferent nerve in pulp activated by mechanoreceptors triggered by deforming dentine pushing fluid outwards.
Trigeminal spinal tract nucleus contains the interneurons which trigger jaw depressing muscles and inhibitory fibers inhibit the muscles that elecate the jaw.
Which fibers are triggered by flow of fluid through dentinal tubules?
The A fibers which are important for sharp pain.
What are the types of tests used to measure pulp sensibility?
Electric
Cold
Heat
How does pulp cold testing work?
Thermal stimuli applied to the intact enamel surface cause rapid movement of fluid through the dentinal tubules causing pain.
Temperature change must be rapid enough to cause sufficient fluid flow
Cold is more effective than heat.
Are newly erupted teeth different in pain sensation compared with normal teeth?
Newly erupting teeth are less sensitive than older teeth
