Pulp D Flashcards
What factors of the dentine tubules control dentine permeability?
1) remaining dentine thickness -> deep or shallow cavity prep
- deeper cavity prep = greater permeability, b/c Increase no., increase diameter & decrease length.
2) location of exposed area -> coronal vs radicular
- radicular = less permeability, b/c decrease density of tubules
3) total surface area exposed -> full crown vs exposed dentine
4) diameter/ radius of the tubules -> small changes in radius can have large effect on fluid flow.
all these influence the number, length & diameter of dentinal tubules.
Explain what happens to dentine tubules as we go further down to the pulp.
- increase permeability, b/c
- increase no., increase diameter & decrease length
- the dentin tubules converge
What are the benefits of thick dentin?
- better insulator -> to temperature increases during cavity prep
- better buffering -> protect pulp from insults
What are dead tracts?
- Dentinal tubules that have no odontoblast processes; may result from injury caused by caries, attrition, erosion, or cavity preparation
- occurs mostly in young teeth.
Describe ways we can reduce dentine permeability.
1) Function vs anatomical tubular diameter
- most tubules have things inside that reduces permeability
- ie. processes of odontoblast, nerve terminals, cells of the immune system, immunoglobulin, outward flow of dentine fluid.
2) outward flow of dentinal fluid
- tubules have an outward flow of fluid & outward flux of Ig & fibrinogen.
3) dentin sclerosis
- physiological peritubular dentin deposition of intraluminal crystalline deposits.
4) tertiary dentine
a) Reactionary -> produced by injured primary odontoblasts, when injured by a mild stimulus
b) Reparative -> produced by newly differentiated replacement odontoblasts, occurs when strong stimulus causes death or primary odontoblasts
List the types of pain.
- prepain
- sharp, stabbing
- dull, aching, throbbing
What determines the type of pain felt?
- stimulus -> type of intensity & frequency
- nerve fibre -> Type A or C
- condition of pulp -> inflamed or normal
What types of nerve fibres register pain in the teeth?
- Type A fibres
- Type C fibres
What is the difference in dentin permeability in the coronal area and radicular area.
1) Coronal area -> remaining dentin thickness (RDT)
- the deeper we go into the dentin, the higher the permeability
2) Radicular area
- lower permeability, because of decrease in density of dentinal tubules
- relatively impermeable to bacterial toxins
What is the difference between A fibres and C fibres?
1) A fibres
- myelinated
- large in diameter
- fast in conduction velocity
- located in the pulp periphery -> pulp-dentine border, mainly in coronal portion of pulp, esp at the pulp horns
2) C fibres (majority - 70-80%)
- unmyelinated
- small in diameter
- slow in conduction velocity
- located in the pulp proper, along blood vessel and extend into the cell free zone
What are the functions of the A and C fibres?
1) A fibres
- mechanical nociceptors, which are activated by hydrodynamic stimulants
- stimulation of a small area can activate multiple nerve fibres -> increased intensity of pain response.
2) C fibres
- polymodal nociceptors, which are activated by different stimuli: thermal, mechanical, chemical
- pulp tissue has to be exposed for their activation
- silent in normal healthy pulp
What are the different types of A fibres?
1) Myelinated Ab fibres (faster)
- close to odontoblasts near the pulp horn tip
- lack receptors -> low threashold
- most sensitive to hydrodynamic
2) Myelinated Ad fibres (slower)
- heterogeneity in distribution -> concentrated near the pulp horn tip and sparse in root.
Which nerve fibre responds most to the outward flow of the dentinal fluid?
- A fibres
What conditions are necessary for the teeth to perceive pain?
- requires the absence of enamel and cementum to expose the dentinal tubules.
What is the hydrodynamic theory?
- when dentin is exposed, the pressure from the pulp causes and outward flow of fluid, which activates mechanoreceptors.
- however, hydrodynamic stimuli displaces in the tubules -> pain.
- movement of fluid through dentin tubules stimulate pulp nerve.
Explain the process of the trigeminal pain system.
1) detection
- afferent nerves in the pulp detect the displaced fluid
2) Processing
- 1st order = neuron in trigeminal ganglion
- 2nd order = neuron in trigeminal spinal tract nucleus, mainly nucleus caudalis
- 3rd order = neurons in thalamus
3) Perception
- cerebral cortex
What factors cause pain and how do they cause pain?
1) Air blasts
- dehydrating the outer end of dentinal tubules -> induces loss of fluid
- causes rapid outward flow of fluid through tubules -> strong capillary force -> deforms mechanoreceptors at the pulp dentin border.
2) Sweet: hyper-osmotic solutions
- solution extracts fluid from the outer end of the exposed dentinal tubules due to high osmotic pressure -> causing rapid outward fluid flow.
- causes rapid outward flow of fluid through tubules -> strong capillary force -> deforms mechanoreceptors at the pulp dentin border.
3) Probing dentin
- light pressure on tooth -> produces strong local compressive force
- creates shallow grooves lined by smear layers in the dentin -> causes rapid fluid displacement in the exposed dentinal tubules and activates A fibres (mechanoreceptors.)
What factors affect dentin hypersensitivity?
a) Time course of dentin tubule exposure
b) different responses of the pulp-dentin complex
c) pulp inflammation due to persistent dentinal tubule exposure
What is occlusal overloading and what reflex does it activate?
- Occlusal overloading = biting on a hard object unexpectedly
- Activates -> nociceptive reflex
How it happens
1) Occlusal overloading -> elastic deformation of dentin -> causes rapid fluid movement through tubules
2) Strong capillary force causes deformation of mechanoreceptors -> activates nociceptive reflex -> jaw opens, due to sharp transient pain
How do we test pulp sensibility?
- use electric, cold & heat on an intact tooth that doesn’t have exposed dentinal tubules
- don’t do this on tooth with exposed dentinal tubules -> causes severe pain
what is the difference between sensitivity and sensibility?
1) Sensitivity
- condition of being very responsive to a stimulus
2) Sensibility
- ability to respond to stimulus
Name some tests to measure sensibility
1) pulp cold testing
- brief application on intact tooth with enamel, evokes a rapid painful response in 1-2 seconds.
2) Electric pulp testing
- low intensity -> stimulates Ab fibres -> prepain
- low intensity, but with increase frequency -> stimulates Ad fibres -> pain
Note: C fibres are not activated as you need significantly more current.
How doe cold evoke pain?
- rapid movement of fluid through dentin tubules causes volumetric changes in the dentinal fluid
- leads to contraction of fluid in the tubules -> activate mechanoreceptors -> sharp transient pain.
What is the difference between the process of cold vs heat evoked pain?
1) cold causes fluid contraction: Fluid > dentine
- outward flow away from pulp
2) Heat causes fluid expansion: Fluid > dentine
- inward flow toward pulp
