Endo: Dentine-Pulp Complex Flashcards
What is formed from the ectoderm?
Enamel
What is formed from the Neural crest derived ectomesenchyme?
Dentine-pulp complex
Name the 3 stages of tooth development
- Bud stage
- Cap stage
- Bell stage
What happens in the bud stage?
Assumes shape of a bud from the folding of of the epithelium from the dental lamina proliferating into the ectomesenchyme
What happens in the cap stage?
Assumes the shape of a cap
Further epithelial proliferation gives rise to enamel organ
What happens in the bell stage?
Shape of a bell
Invagination/folding deepens - dental papilla contained within this leads to formation of dentine-pulp complex
2 cell layers facing each other have different fates - inner layer = ameloblasts
outer layer = odontoblasts; initiate dentine deposition
What induces and controls differentiation of odontoblasts and cementoblasts?
Hertwig’s epithelial sheath
What does Hertwig’s epithelial sheath do? (3)
Guides and initiates root formation
Signals odontoblasts and cementoblasts to differentiate
Further differentiation = perio support structure forms
What happens following the bell stage of tooth formation?
cells of inner and outer enamel epithelium merge to form cervical loop = root formation begins at CEJ
How does the cementum attach to the perio support structure?
through Sharpey’s fibres
What allows the bone to anchor to the periodontal fibres?
The outer layer of the dental sac
What is the composition of dentine (& percentages)?
70% hydroxyapatite (mineral)
20% organic matrix (collagen - mostly type 1, some type 5)
10% water
What type of collagen mostly makes up the organic matrix of dentine?
type 1
type 5 is minor
Give examples of growth factors or enzymes that are present and embedded in the dentine (5)
TGF-B: transforming growth factor PDGF: Platelet-derived growth factor IGF: insulin-like growth factor BMPs: bone morphogenic proteins MMPs: matrix-metalloproteinases
When are the enzymes and growth factors released from the dentine?
They are released during demineralisation and triggers dentinal reparative events
What constitutes the largest part of tooth structure?
Primary dentine
Primary dentine is deposited by what and at what rate per day?
Deposited by odontoblasts
at 4 micrometres per day
What are the 2 sub-categories of primary dentine?
Mantle
Predentine
Which subcategory of primary dentine is formed first and is closest to the enamel/cementum?
Mantle
Describe the subcategory of primary dentine: predentine
10-40 micrometre layer of dentine undergoing completion of it’s mineralisation.
Located between odontoblast layer and mineralised dentine; and moves towards centre during secondary dentine deposition
Describe secondary dentine
deposited by odontoblasts AFTER root formation and throughout the life of the tooth (explains progressive reduction of the root canal space)
What type of dentine is laid down in response to an external stimuli?
tertiary
Name the 2 types of tertiary dentine
Reactionary
Reparative
Outline reactionary tertiary dentine
Odontoblast insult not severe and odontoblast layer survives.
Still has continuous tubular structure (like primary and secondary dentine)
Outline reparative tertiary dentine
Severe insult to odontoblast layer
Pulpal stem cells recruited and differentiate into odontoblast-like cells.
Tubules NOT present or continuous
What type of dentine is characterised by enhanced mineralisation of the intratubular/peritubular dentine?
Sclerotic dentine
How are dentine tubules formed?
During primary and secondary dentinogenesis.
Odontoblast mineralisation front moves towards centre
Describe odontoblasts and how they interact with the tubules
They are columnar cells with polarised processes that leave imprints on newly formed dentine
> cytoplasmic processes projected into dentinal tubules
Which dentine is more calcified - intra tubular dentine or inter tubular dentine?
Intratubular
Where would you find intratubular dentine and intertubular dentine?
Intra/peritubular dentine - inner part of tubule
Intertubular - between dentine tubules
Which type of dentine makes up the most of the dentinal structure?
Intertubular dentine
What is the diameter(s) of the dentine tubules?
2.5 microm by the pulp
1 micro m by the enamel/cementum
Is the dentine more or less dense near the pulp?
More dense
higher density
What is contained within dentinal tubules? (5)
- Dentinal fluid
- Odontoblastic processes
- Nerve fibres
- Type 1 collagen
- Ground substance (glycoproteins, proteoglycans, glycosaminoglycans)
What are the 2 important structures that the tubular structure provides to dentine?
Permeability
Sensitivity
Dentine permeability varies in different areas - does this increase or decrease towards the pulp chamber?
Increases progressively
How does dentine sclerosis affect the permeability of dentine tubules?
It makes them less permeable
What is considered as the main mechanism for dentinal sensitivity and hypersensitivity?
Hydrodynamic theory
What is the mechanism behind the hydrodynamic theory of dentine sensitivity?
Rapid displacement of dentinal fluid in tubules deforms odontoblast processes and activates A-delta fibres, leading to transfer of nociceptive signal
What can trigger dentinal fluid movement?
Temperature (hot and cold)
Osmolarity (e.g. sweet)
Mechanical pressure (e.g. chewing, probing)
What are the 4 functions of the pulp?
- Nociception (painful,injury) : sense harmful stimuli
- Proprioception (ability to sense movement, action, and location) & sensitivity: sense own position related to pressure = warning mechanism
- Defence: prevents systemic spread of dental infection by inducing foreign body response. Immunocompetent - can induce dentine formation
- Formative: produces dentine > forms coronal & radicular structure during odontogenesis
What are the components of the pulp? (4)
It is a connective tissue composed of different type of cells, extracellular connective matrix (fibres and ground substance), blood vessels and nerves
What are the main cell lineages in the pulp? (5)
Odontoblasts, mesenchymal stem cells, fibroblasts, Schwann cells, defence cells (antigen presenting cells, macrophages, lymphocytes)
Describe the shape of the odontoblasts at:
- The crown
- The root
- Columnar
2. Cuboidal
How are odontoblasts organised?
They are organised into a single layer of cells (odontoblastic layer) facing predentine.
Odontoblast cells are polarised - what does this mean?
The nuclei are localised towards the pulp.
Mitochondria-rich area is closer to predentine and localised at formative (developing) end before the cytoplasmic/odontoblastic projection
Where are the pulpal stem cells?
They are scattered amongst the pulp but are mostly localised in cell-rich area
Which cell lineage is the most abundant in the pulp?
Fibroblasts
What do the fibroblasts produce?
They produce the extracellular matrix (glycosaminoglycan, proteoglycans, glycoprotein), representing the medium of signals and nutritive substance
The pulpal blood supply is provided by vessels that enter from where?
The apical foramen and lateral canals
What vessels are involved in the vascularisation of pulp?
arterioles, capillaries, venules, arteriovenous shunts, lymph vessels
Which blood vessels enter the root canal and follow the long axis of the root?
Arterioles
What branch off the arterioles towards the odontoblastic layer (which represents the vascular zone adjacent to the cell-rich zone)?
Capillaries
Where are venules present?
Venules are present towards the centre of the pulp
What is the purpose of the arteriovenous and venous-venous shunts in the vascularisation of pulp?
They control the microcirculation
Pulpal blood flow is relatively high compared to other cranial tissues - what may this favour?
It may favour a wash out effect of irritants
What is the self-strangulation theory of the pulp?
The hard case around the pulp, in the case of inflammation, can lead to pulpal hypoxia
What nerve innervates the pulp?
Maxillary and mandibular branches of the trigeminal nerve
Is an autonomic (involuntary) component present in the pulp?
Yes
Among the nerve fibres reaching the pulp - what percentage are unmyelinated and myelinated, and what type are they?
80% unmyelinated C fibres
20% myelinated A fibres
