Development Flashcards
Stages of tooth germ development
- Initiation
- Morphogenesis
- Histogenesis (Differentiation)
What do interactions between epithelium (ectoderm) give rise to? (x2)
Enamel and Hyaline layer of the root
What do interactions between mesenchyme (ectomesenchyme) give rise to? (x4)
- Dentine
- Pulp
- Cementum
- Periodontium (PDL & Bone)
When does initiation (1st sign) of tooth development begin?
6 weeks i.u.l
Which tissue initiates tooth development?
(Dental) epithelium has the odontogenic potential, then ECTOMESENCHYME
What does the primary epithelial band give rise to?
Dental lamina
Vestibular lamina
What happens with the vestibular lamina?
Grows then break down (undergoes apoptosis)
What does the vestibular lamina form?
Vestibule between teeth and lips/cheeks
List the stages of tooth development
Bud
Cap
Bell
Crown
List the components of the tooth germ (x3)
- Enamel organ
- Dental papilla
- Dental follicle
Which week is the bud stage in?
Week 8
Describe the bud stage
Week 8
- spherical/ovoid epithelial condensation
- cell proliferation
- no histodifferentiation/morphogenesis
Describe the cap stage
Week 11
- Cap shaped enamel organ
- Poorly histodifferentiated
- Little morphogenesis
Which week is the cap stage in?
Week 11
What does the enamel organ give?
(from outer to inner)
- Outer enamel epithelium
- Stellate Reticulum
- Stratum Intermedium
- Inner enamel epithelium
What is the role of the outer enamel epithelium?
Maintenance of shape and exchange
What is the role of the stellate reticulum?
Maintenance of shape and protection
What is the role of the stratum intermedium?
Synthesis and transport to and from inner enamel epithelium
What is the role of the inner enamel epithelium?
Forms ameloblasts –> enamel
At which stage does the enamel organ break down into its specific components? List the components.
Bell stage (Early-14weeks) OEE, SR, SI, IEE
What does the ectomesenchyme differentiate into? What structures do each form?
Ectomesenchyme differentiates into dental follicle and dental papilla.
Dental follicle gives: cementum, PDL, bone
Dental papilla gives: odontoblasts (dentine) & pulp
At which stage does the ectomesenchyme differentiate?
Bell stage (Early-14 weeks)
When does the dental lamina breakdown? At what stage is this?
Week 17; Bell stage
What is the cervical loop with respects to the enamel organ?
It is where the outer enamel epithelium meets the inner enamel epithelium
What is the enamel knot?
A localisation of cells on an enamel organ that appears thickened in the centre of the inner enamel epithelium
When is the enamel knot formed and what happens in the next stage?
Formed in the cap stage
Undergoes apoptosis in the bell stage
Function of the enamel knot
Signalling centre of the tooth that provides:
- positional information for tooth morphogenesis
- patterning of tooth cusps
Molecular signals produced by the enamel knot (x3)
- SHh (Sonic Hedgehog)
- FGF (Fibroblast growth factor)
- BMP (Bone morphogenetic proteins)
Composition of Dentine
Mineral - 70%
Organic Matrix - 20%
Water - 10%
Properties of dentine (x4)
Hard (KHN: 75)
Strong and resilient
Tubular/porous
Vital
What forms dentine
Odontoblasts
What is odontoblast derived from?
Cells of dental papilla (ectomesenchymal - specialised cells from neural crest)
When does dentine formation begin?
At the end of bell stage
Stages of dentine formation (x3)
- Cytodifferentiation
- Matrix formation
- Mineralisation
What is the organic matrix of dentine made up of?
Collagen (mainly type I); Ground substance (ECM) - dentine phosphoproteins, proteoglycans, lipids
Direction of dentine formation
Inwards (i.e. from enamel to pulp)
What is the first formed dentine called?
Mantle dentine
Compare mantle dentine vs circumpulpal dentine (x4)
- Mantle dentine is the first formed dentine; Circumpulpal dentine is the rest of it
- Mantle dentine has large collagen fibrils that run perpendicular to the ADJ; Circumpulpal dentine has small collagen fibrils that run parallel to the ADJ
- Ground substance of mantle dentine is not solely of odontoblast origin; Ground substance of circumpulpal dentine is formed from odontoblasts
- Matrix vesicles required for mineralisation of mantle dentine, whereas circumpulpal dentine involves the use of heterogenous nucleation
Composition of enamel
- 96% mineral
- 1-2% matrix
- 2% water
What makes up the enamel matrix?
Enamel proteins (NOT COLLAGEN) Enzymes (present to break down enamel proteins via a self-destruct process)
Name the enamel proteins (x3)
- Enamelins (2%)
- Tuftelins
- Amelogenins (90%)
What is the main mineral of enamel/dentine?
Hydroxyapatite
Name the 3 theories of mineralisation
- Alkaline phosphatase hypothesis
- Nucleation (homogenous / heterogenous)
- Matrix vesicles
What is Tomes process responsible for?
Prismatic structure of enamel;
1st and last formed enamel does not have the Tomes process and hence are aprismatic
When are epithelial cells at their longest?
Just before they produce enamel / before the basal lamina disintegrates
Direction that ameloblasts go
upwards and outwards
Which enamel protein is removed and which remains?
Amelogenin is removed; Enamelin remains
Which feature of amelogenin allows it to be removed during enamel mineralisation?
It is thixotropic - flows/changes their properties under pressure
Final secretion of ameloblasts
Enamel cuticle
Functions of the reduced enamel epithelium (x3)
- Provides an epithelial lined pathway for eruption of teeth
- Forms the initial junctional epithelium, which attaches mouth epithelium to teeth
- Protection of enamel surface from resorption and prevention of cementum formation
Fate of the reduced enamel epithelium (x2)
- Fusion with basal lamina to become junctional epithelium
2. Cell death
What must happen for mineralisation to occur?
Crystal growth and protein removal
Role of enamel proteins (x3)
- Aid nucleation of hydroxyapatite
- Orientate and stabilise crystal growth
- Broken down and lost during maturation
Compare enamel mineralisation VS dentine mineralisation (x2)
no pre-enamel for enamel mineralisation
no MVs for enamel mineralisation
What is the basic unit of enamel?
Enamel prism / rod
What are the 2 components of the enamel prism?
Prism core
Prism sheath
What does the prism core comprise?
Tightly packed hydroxyapatite crystals
What governs the prismatic shape of the enamel prism?
Tomes process
Name the regions of the enamel found without Tomes process
First formed (innermost) - 5um Last formed (outermost) - 30um
What are incremental growth lines of enamel termed?
Striae of Retzius
What does the Striae of Retzius represent?
incremental growth line - represent where the ameloblasts were at each different stage
What can result in accentuated incremental enamel growth lines? (x2)
- Systemic disturbance e.g. illness
2. Birth - neonatal line
What is perikymata?
Shallow furrow where the striae meets the surface
What are dentinal tubules that project into enamel termed?
Enamel spindles
What are the incremental lines of dentine termed?
Incremental lines of von Ebner
What is the shallow furrow where the striae meets the surface
Perikymata
Where mantle dentine meets the circumpulpal dentine
Interglobular dentine
What does interglobular dentine result from
Failure of calcospherites to fuse
What are the two types of tertiary dentine
- Reactionary
2. Reparative
What is the difference between the two types of tertiary dentine
Reactionary dentine employs the use of existing odontoblasts whereas reparative dentine recruits “newly” differentiated “odontoblasts”.
Reactionary - slow formation VS Reparative - fast formation
Function of tertiary dentine
Removes pulp from stimulus in response to injury/insult
