Pulp & Periapical Biology

Question 1

Q1: Difference between peritubular dentin and inter-tubular dentin?

Answer 1

Peritubular: is highly mineralized 95% with no or little collagen
Inter-tubular: is primarily formed of dense collagen matrix with collagen fibers and it forms the major bulk of the dentin.

Question 2

Q2: Why are there differences in the % of reported prevalence of cyst and granulomas?

Answer 2

Granulomas and cyst represent different stages of chronic periradicular pathosis. (Liapatas et al, IEJ 2003)
Accurate histopathological diagnosis of radicular cyst can only be achieved through serial sectioning or step-serial sectioning of the lesions removed in toto (Nair et al, OOOE – 1996) and only few studies in which either one of those essential techniques were used (Nair, IEJ 1998, Simon, JOE 1980) while most of the others studies analyzed specimens obtained from wide sources for routine histopathological reports.

Question 3

Q3 : Does the increase in pulpal pressure due to inflammation result in strangulation of the pulp and pulp necrosis?

Answer 3

NO
The strangulation theory has been disproven by Van Hassel (OOO – 1971) He showed that the increase in pulpal blood pressure is localized at the area of inflammation and the blood pressure is less 1-2mm away from area of inflammation. This is made possible by 3 main features:
Low compliance environment (pulp is housed by hard dentin) which does not allow further increase in net fluid filtration (tissue pressure) (Heyeraas & Berggreen, Crit Rev Oral Biol Med -1999)
Flow of blood vessel to adjacent tissues: Increase in the pulpal pressure to the critical level (16-20mm/Hg) will open the arterio-venous and venous-venous anastomosis resulting in shunting of the blood.
Lymphatics:
Which collect tissue fluid and tissue protein back to the blood stream.

Question 4

Q4 : What are the functions of the dental pulp?

Answer 4

1) Formation of dentin
2) Repair of dentin (tertiary)
3) Nutrition to avascular dentin
4) Protection (defense)
5) Sensory (pressure & temperature)
6) Hydrates dentin (prevent fracture)

Question 5

Q5 : Which of the following neuropeptides have the highest concentration in a healthy pulp?

NKA / SP / CGRP / VIP

Answer 5

Awawdeh et al (EJ - 2002) investigated the concentration of substance P (SP), neurokinin A (NKA) and calcitonin gene related peptide (CGRP) in painful and healthy human dental pulps. They found that Substance P and CGRP were present in all samples and NKA was detected in 96% of the pulps. They also found that CGRP was present in much higher concentrations than SP and NKA in both painful and non-painful teeth.

Question 6

Q6 : What is the role of Dendritic cells in the pulp?

Answer 6

• They are Accessory cells of the immune system
• They are antigen presenting cells (phagocytose antigens, present peptides to the T cells) - They provide necessary signals to activate T-lymphocytes
  (Jontell et al, Crit Rev Oral Biol Med - 1998)

Question 7

Q7 : Which method can accurately allow proper diagnosis of radicular cysts?

Answer 7

Accurate histopathological diagnosis of radicular cysts can only be achieved through serial sectioning or step-serial sectioning of the lesions removed in toto (Nair et al, 000OE – 1996)
Only few studies in which either one of those essential techniques were used** (Nair, IEJ - 1998, Simon, JOE - 1980)**. While most of the others studies analyzed specimens obtained from wide sources for routine histopathological reports.

Question 8

Q8 : What is the prevalence of periapical cysts compared to granuloma?

Answer 8

Lalonde & Luebke (000 - 1968) showed that out of 800 specimens the results showed the following incidence:
Periapical granulomas (45.2%)
Radicular cysts (43.8%)
Such histopathological diagnostic specimens, however, were derived through apical curettage do not represent lesions removed in-toto. Therefore, the diagnosis may not be accurate
Nair et al (OOOE 1996) showed that out of 256 specimens:
- 35% were periapical abscesses
- 50% were periapical granulomas
- 15% were periapical cysts: a) 9% were true cysts b) 6% were pseudocysts

Question 9

Q9 : What is the intra-pulpal hydrostatics pressure of a healthy pulp?

Answer 9

10-28mmHg

Question 10

Q10 : Describe the role of neuropeptides in the dental pulp?

Answer 10

Neuropeptides are signaling molecules released by stimulated sensory or autonomic (sympathetic or parasympathetic) nerves.
They modulate neural activity as well as vascular and immunological activity within the dental pulp. This all plays a role in the function and repair of the dental pulp. Neuropeptides form the communication between the nerve fibers and the pulpal blood flow. Inflammation will lead to nerve sprouting resulting in increased production of neuropeptide
There are 3 types of neuropeptides:
Sensory derived neuropeptides
1) Substance P (SP)
2) Calcitonin gene related peptide (CGRP)
3) Neurokinine A (NKA) & Neurokinine B (NKB)
They result in vasodilation and increase in capillary permeability and they can also activate inflammatory cell migration.
Sympathetic derived neuropeptides: Neuropeptide Y (NPY)
Which result in vasoconstriction and modulation of the sensory neuropeptides.
Parasympathetic derived neuropeptides: Vasoactive intestinal peptide (VIP)
Result in vasodilatation and can modulate the sympathetic neuropeptides

Question 11

Q11 : What does the term “proton pump” mean?

Answer 11

Proton pump is the pumping of hydrogen ions to make the area more acidic to initiate resorption, this results in dissolution of the hydroxyapatite (inorganic structure). This occurs at the Ruffled border of osteoclasts/dentinoclasts/cementoclasts

Question 12

Q12 : What are the cells present in the dental pulp?

Answer 12

1) Odontoblast (responsible for dentin formation and repair as well as the pro-inflammatory responses)
2) Fibroblast Plays role in the production of the extra-cellular matrix
3) Stem/progenitor cells
4) Defensive cells (macrophages and T cells)
5) Dendritic cells

Question 13

Q13 : Explain the difference between primary dentin, secondary dentin and tertiary dentin?

Answer 13

Primary dentin: formed by odontoblast previous to tooth eruption
Secondary dentin: formed by odontoblast after tooth eruption (at a slower rate).
Tertiary dentin: formed in response to a localized stimulus of any sort

Question 14

Q14 : What is the composition of the Dentin organic Matrix?

Answer 14

Type I collagen
Type V collagen
5 types of Dentin Noncollagenous protein (NCP):
1- Dentin Sialo Phosphoprotein (DSPP), DSP (5-8%) and DPP which represent 50% of ECM
2 - NCP with Calcium binding properties (found in dentin and bone) :
a) Osteocalcin (OC)
b) Dentin Metalo Protein (DMP1)
c) Bone Sialoprotein (BSP)
3- NCP synthesized by odontobolast but also present in soft tissue and organs)

a) Osteonectin
b) Osteopontin
4- NCP not expressed by odontobolast (2HS glycoprotein) ).
5 - Growth factors sequestered in the dentin matrix (BMP, TGFβ)

Question 15

Q15: Describe the hydrodynamic theory and the evidence supporting it?

Answer 15

The hydrodynamic theory refers to the rapid outward flow of fluid in the dentinal tubules that is initiated by strong capillary forces resulting in pain stimulation. (Brannstrom, JOE - 1986)
Early work by Brännstrom & Astrom (JDR-1964) hypothesized that fluid movement within the dentinal tubules can be responsible for pain responses. Later Brannström et al. (Caries Res-1967) showed that heat can cause inward fluid movement, while cold can cause outward fluid movement resulting in distortion of odontoblastic processes and stimulation of nerve responses. Olgart et al. (Acta Odontologica Scandinavica-1974) showed that there is an out fluid movement in the dentinal tubules which prevent bacteria from invading the dentinal tubules. Later Narhi et al. (Arch Oral Biol-1982) in a dog model supported the hydrodynamic hypothesis by showing that various stimuli (such as air blast, acid etch and several solutions) would induce fluid flow in dentinal tubules which can result in sensitivity.

Question 16

Q16 : Which of the following inflammatory cells have the highest representation in a periapical granuloma?

Answer 16

Macrophages were the predominant inflammatory cell, followed in descending numerical order by lymphocytes, plasma cells, and neutrophils (Stern et al, JOE-1981)
% of inflammatory cell :
- Macrophages (24%)
- lymphocytes (16%)
- Plasma cells (7%)
- Neutrophils (4%)
Majority of inflammatory cells were macrophages, T and B lymphocytes (Liapatas et al, IEJ-2003)

Question 17

Q17 : What are the types of terminal nerves present in the pulp-dentin complex?

Answer 17

Gunji (Arch Histol Jpn - 1982) classified the terminal nerves in the pulp and dentin into :
1- Marginal pulpal nerve fibers: Runs from the sub-odontoblastic nerve plexus (Plexus of Rashkow) towards the odontoblastic layer but do not reach the predentin (most common fibers).
2- Simple predentin nerve fiber: Reaches or penetrates the predentin border.
3- Complex predentin nerve fiber : Penetrate the predentin border and shows very complicated terminal ramifications.
4- Dentinal nerve fiber: they enter the dentin through dentinal tubules. They can extend up to 200µm (50-100 µm average).

Question 18

Q18 : What is the compositional differences between a granuloma and a cyst?

Answer 18

Granulomas and cysts are structurally very similar. Periapical cyst, however, contain nearly 5 times more epithelial cells than granulomas. In all other cellular parameters, the cysts and granulomas were quantitatively similar (Stern et al, JOE - 1981)

Question 19

Q19 : Which of the following fibers is the smallest in size?
A-Beta, A-Delta, C-fibers

Answer 19

C Fibers size ranges from 0.4-1.2µm in size and their velocity is 0.5-2 m/sec. They are located in the core of the pulp. C fibers have high threshold to stimulus and their response will result in a dull aching pain. Activation of the C fibers indicates a later stage of inflammation (given its location).

Question 20

Q20 : Describe the role of cytokines in regulating bone resorption?

Answer 20

Kawashima & Stashenko (Arch of Oral Bio-1999) evaluate the expression of bone-resorptive and regulatory cytokines in the development of periapical lesions in mice. They showed that:
Th1 cell cytokines (IL-1 a, IL-12, TNFα and INF Y) seem to up-regulate inflammatory bone resorption. Th2 cells cytokines (IL-4, 6, 10, 13) appears down-regulate bone resorption.

Question 21

Q21: Explain how the microvasculature of the pulp help regulating pulpal inflammation?

Answer 21

Through the extensive arterio-venous and venous-venous anastomosis which allow regulation of blood flow during inflammation by passing blood from region of inflammation to region of viable cells. This shunting mechanism will regulate the pulp blood flow during injury (Kim, JDR 1985)

Question 22

Q22 : What is neural sprouting and how does it participate in dental pain?

Answer 22

Neural sprouting is an increase in the density of innervation in inflamed tissue that leads to increase in pain sensitivity.
Taylor et al. (Brain research - 1988) showed extensive increases in the number of calcitonin gene-related peptide immunoreactive(CGRP-IR) nerve fibers subjacent to injured root dentin of rat molars suggesting that rapid reversible sprouting of sensory nerve fibers may be an integral part of dentin reaction to injury.

Question 23

Q23 : How far do the odontoblastic processes extend into the dentinal tubules?

Answer 23

The odontoblastic process extend around 1/3 the length of the dentinal tubule. This has been shown by several studies (Holland, J Anat- 1976; Thomas, JDR-1985; Weber & Zaki, JDR-1986). LaFleche et al. (J Biol Buccal - 1985) proposed that dentinal tubules extend only about one-third the distance from the tubule due to a retraction of the process during extraction. The formers, however, believe that LeFleche et al may have been confused by fixation and tissue reparation artefacts.
A more read on this as well as the pulp dentin complex can be viewed in the review by Pashley (Crit Rev Oral Biol Med - 1996)

Question 24

Q24 : Which of the following sensory fibers are not stimulated by EPT?
A-beta, A-delta, C-fibers

Answer 24

C - Fibers
The unmyelinated C-Fibers of the pulp do not respond during conventional electric pulp testing because they have higher threshold and only intense thermal stimuli that are able to proceed tissue injury can activate them (Trowbridge, JOE 1986).
Narhi et al. (Scand J Dent Res-1979) investigated electrical stimulation of teeth with pulp testers on cats. They found that EPT stimulates only A-beta and A-delta fibers, not C-fibers.

Question 25

Q25 : What is the difference between A-delta fibers and A-Beta fibers?

Answer 25

A fibers are myelinated, fast conduction fibers with low stimulation threshold. They are superficially located in the pulp/dentin junction. They transmit pain directly to the thalamus and generate a sharp and stabbing pain that is easily localized. (Narhi et al, Proc Finn Dent Soc-1992). They are usually the first to react & transmit the pain impulse.

According to Gomes (J Endod Rosario-2011), A-delta fibers represents more than 90% of the A fibers in the pulp. Their diameter range from 2-5 μm and their velocity 12-30 m/sec is activated by hydrodynamic stimuli which lead to rapid fluid movement within the tubules resulting in sharp, piercing pain. The arousal thresholds vary among the A-Delta fiber population.
Low-threshold fibers: cooling & vibration
Higher-threshold fibers: mechanical instrumentation
A-beta fibers is functionally similar to the A-delta fibers but they respond differently to vibration. They are stimulated at a lower electrical threshold and involved in detecting non-noxious stimuli such as vibration and proprioception (pressure and touch); found in the periodontal ligament & oral mucosa. The A-beta fibers represent 7% of the myelinated fibers entering premolar pulp.
(Figdor, Ann R Australas Coll Dent Surg 1994)

Question 26

Q26 : Which of the following sensory fibers can maintain their functional integrity in a hypoxic situation?
A-Delta Fibers // A-Beta Fibers // B-Fibers // C-Fibers

Answer 26

Oxygen consumption is higher in the thick A fibers than in the thin C fibers, C fibers function for a longer time compared to A fibers in events of injury (Narhi, J Dent Res-1985)

Question 27

Q27 : What is the difference between reactionary dentine & reparative dentine?

Answer 27

Reparative dentin is formed in response to a strong stimulus where the original odontoblasts were destroyed and a newly formed odontoblast-like cells are formed by fibroblasts, that starts forming dentin, which is poorly mineralized and has less tubules. It is also often referred to as “osteo-dentin “due to lack of tubules.
Reactionary dentin is formed in response to decay where the original odontoblast has not been destroyed. Tubules formed are usually not continuous with those of secondary dentin.

Question 28

Q28 : What is “condensing Osteitis”? and why it develops?

Answer 28

It’s a radiopacity at the root apex because of a proliferative bone response to a low-grade chronic irritant.
Green et al (JOE-2013) showed that the histologic changes of condensing osteitis consisted of the replacement of cancellous bone with compact bone. All teeth exhibiting condensing osteitis had an identifiable etiology that likely resulted in degenerative pulp disease.

Question 29

Q29 : Describe the hydrodynamic theory and the evidence supporting it?

Answer 29

The hydrodynamic theory refers to the rapid outward flow of fluid in the dentinal tubules that is initiated by strong capillary forces resulting in pain stimulation. (Brannstrom, JOE-1986)
Early work by Brannstrom & Astrom (JDR-1964) hypothesized that fluid movement within the dentinal tubules can be responsible for pain reponses. Later Brännström et al (Caries Res- 1967) showed that heat can cause inward fluid movement while cold can cause outward fluid movement resulting in distortion of odontoblastic processes and stimulation of nerve responses. Olgart et al. (Acta Odontologica Scandinavica-1974) showed that there is outward fluid movement in the dentinal tubules to prevent caries from invading the dentinal tubules. Later Narhi et al. (Arch Oral Biol-1982) in a dog model supported the hydrodynamic hypothesis by showing that various stimuli (such as air blast, acid etch and several solutions) would induce fluid flow in dentinal tubules which can result in sensitivity.

Question 30

Q30 : What is the function of the sub-odontoblastic plexus in the pulp-dentin complex?

Answer 30

Exchange of nutrients and waste products between the pulp and the odontoblastic cells

Question 31

Q31 : Give examples of neuropeptides normally present in the dental pulp?

Answer 31

1) Substance P
2) Calcitonin gene-related peptide (CGRP)
3) Neurokinin A
4) Neuropeptide Y
5) Vasoactive intestinal polypeptide (VIP)

Question 32

Q31 : Describe the basic pulpal protective mechanisms against caries?

Answer 32

• Decrease in dentin permeability: by increasing the deposition of intra-tubular dentine and tubule occlusion by precipitated crystals (Dentin sclerosis) (Pashley, JOPD - 1991)
  Tertiary dentin formation: Acidic by-products of the carious process act indirectly by degrading the dentin matrix and liberating bioactive molecules to stimulate tertiary dentinogenesis. (Smith et al, Adv Dent Res - 2001)
• Inflammatory and immune reactions. Accumulation of inflammatory cells (accumulation of lymphocytes, leukocytes and exudates) Macrophages are usually the most dominating cells (Brannstrom & Lind, JDR-1965)

Question 33

Q32 : What are the structural compositional differences between plasma and dentinal fluids?

Answer 33

Protein concentration is 10% greater in plasma than dentinal fluid
Calcium concentration is 2-3 times higher in dentinal fluids than plasma

Question 34

Q33 : Which of the following cells represent the highest percentage in a periapical cysts?
Vascular elements // Fibroblasts // Inflammatory cells // Epithelial cells

Answer 34

Inflammatory cells comprised slightly more than half the formed elements in periapical cysts or granulomas the others were connective tissue elements. (Stern et al, JOE - 1981)

The % cells is as follows:
a) Inflammatory cells (52 %)
b) Fibroblasts (40%)
c) Vascular elements (6%)
d) Epithelial cells (5%)

Question 35

Q34 : Why are there differences in the % of reported prevalence of cysts & granulomas?

Answer 35

-Granulomas and cysts represent two different stages in the development of chronic periradicular pathosis (Liapatas et al, IEJ 2003)
- Accurate histopathological diagnosis of radicular cysts can only be achieved through serial sectioning or step-serial sectioning of the lesions removed in toto (Nair et al, 0000E-1996) and only in few studies in which either one of those essential techniques were used (Nair, IEJ - 1998, Simon, JOE-1980), while most of the others studies analyzed specimens obtained from wide sources for routine histopathological reports.

Question 36

Q35 : Describe the distribution of the A and C fibers within the dental pulp?

Answer 36

A Fibers are located in the pulp-dentin border in the coronal portion of the pulp and concentrated in the pulp horns
C fibers are located in the core of the pulp

Question 37

Q36 : Which of the following sensory fibers are not stimulated by EPT?
A - Delta Fibers / A - Beta Fibers / C - Fibers

Answer 37

The unmyelinated C-Fibers of the pulp do not respond during conventional electric pulp testing because they have higher threshold and only intense thermal stimuli that are able to proceed tissue injury can activate them (Trowbridge, JOE 1986).
Narhi et al. (Scand J Dent Res-1979) investigated electrical stimulation of teeth with pulp testers on cats. They found that EPT stimulates only A-beta and A-delta fibers, not C-fibers.