Pulp D

Question 1

What factors of the dentine tubules control dentine permeability?

Answer 1

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.

Question 2

Explain what happens to dentine tubules as we go further down to the pulp.

Answer 2

• increase permeability, b/c
• increase no., increase diameter & decrease length
• the dentin tubules converge

Question 3

What are the benefits of thick dentin?

Answer 3

• better insulator -> to temperature increases during cavity prep
• better buffering -> protect pulp from insults

Question 4

What are dead tracts?

Answer 4

• Dentinal tubules that have no odontoblast processes; may result from injury caused by caries, attrition, erosion, or cavity preparation
• occurs mostly in young teeth.

Question 5

Describe ways we can reduce dentine permeability.

Answer 5

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

Question 6

List the types of pain.

Answer 6

• prepain
• sharp, stabbing
• dull, aching, throbbing

Question 7

What determines the type of pain felt?

Answer 7

• stimulus -> type of intensity & frequency
• nerve fibre -> Type A or C
• condition of pulp -> inflamed or normal

Question 8

What types of nerve fibres register pain in the teeth?

Answer 8

• Type A fibres

- Type C fibres

Question 9

What is the difference in dentin permeability in the coronal area and radicular area.

Answer 9

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

Question 10

What is the difference between A fibres and C fibres?

Answer 10

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

Question 11

What are the functions of the A and C fibres?

Answer 11

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

Question 12

What are the different types of A fibres?

Answer 12

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.

Question 13

Which nerve fibre responds most to the outward flow of the dentinal fluid?

Answer 13

• A fibres

Question 14

What conditions are necessary for the teeth to perceive pain?

Answer 14

• requires the absence of enamel and cementum to expose the dentinal tubules.

Question 15

What is the hydrodynamic theory?

Answer 15

• 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.

Question 16

Explain the process of the trigeminal pain system.

Answer 16

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

Question 17

What factors cause pain and how do they cause pain?

Answer 17

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.)

Question 18

What factors affect dentin hypersensitivity?

Answer 18

a) Time course of dentin tubule exposure
b) different responses of the pulp-dentin complex
c) pulp inflammation due to persistent dentinal tubule exposure

Question 19

What is occlusal overloading and what reflex does it activate?

Answer 19

• 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

Question 20

How do we test pulp sensibility?

Answer 20

• 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

Question 21

what is the difference between sensitivity and sensibility?

Answer 21

1) Sensitivity
- condition of being very responsive to a stimulus
2) Sensibility
- ability to respond to stimulus

Question 22

Name some tests to measure sensibility

Answer 22

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.

Question 23

How doe cold evoke pain?

Answer 23

• 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.

Question 24

What is the difference between the process of cold vs heat evoked pain?

Answer 24

1) cold causes fluid contraction: Fluid > dentine
- outward flow away from pulp
2) Heat causes fluid expansion: Fluid > dentine
- inward flow toward pulp