CTB Theme 2 Flashcards
what are the 3 phases of tooth development
initiation
morphogenesis
histogenesis
what is determined in initiation and how is it characterised
the tooth position
appearance of tooth germs
what is determined in morphogenesis and how is it characterised
tooth shape
cell proliferation and movement
what is formed in histogenesis and how is it characterised
dental tissues
cell differentiation and specialisation (e.g. odontoblasts and ameloblasts)
what occurs firstly in tooth initiation
primary epithelial band forms
thickening of oral epithelium
condensation of mesenchymal cells
when is the primary epithelial band formed
6 weeks in utero
what causes the thickening of the oral epithelium
the cells divide downwards thickening the epithelial band
what are the 2 types of lamina formed in tooth initiation
dental and vestibular lamina
in what direction do dental and vestibular lamina form
dental - lingually
vestibular- buccally
how is vestibular lamina formed
epithelial cells proliferate and the central cells subsequently enlarge and degenerate to produce the sulcus of the vestibule
what occurs in tooth morphogenesis
formation of the tooth bud
when is the tooth bud formed
8 weeks in utero
what occurs in the bus stage of tooth morphogenesis
elongation of dental lamina
formation of localised swellings
condensation of mesenchymal cells surrounding the tooth bud
what occurs in the early cap stage
enamel organ develops
cap not completely formed
when does the early cap stage occur
11 weeks in utero
when does the late cap stage occur
12 weeks in utero
how does the enamel organ form
dental epithelium forms a cap shaped structure, the enamel organ
what forms the enamel knot
a group of non-dividing epithelial cells
what is the function of the enamel knot
a transient molecular signalling centre. can send instructions to surrounding cells to induce changes in shape
what forms the dental papilla
condensed mesenchymal cells underlying the enamel organ
what forms dental follicle
mesenchymal cells surrounding the enamel organ
what does the dental papilla form
pulp
what does the dental follicle form
periodontal tissue
when does the early bell stage form
14 weeks in utero
what is the enamel organ distinguished by
outer enamel epithelium
with cuboidal epithelial cells
what is the stellate reticulum
group of star shaped cells in the centre of the enamel organ and synthesise glycosaminoglycans
what are the intracellular spaces filled with when epithelial cells get separated in morphogenesis
glycosaminoglycans and collagens I, II, III (ECM)
what are the characteristics of inner enamel epithelium
columnar
the epithelial cells differentiate into ameloblasts later
what happens to the mesenchymal cells of the dental papilla and dental follicle in morphogenesis
they continue proliferating
what is the stratum intermedium
2-3 layers of flat epithelial cells that form between inner enamel epithelium and stellate reticulum
what does the stratum intermedium produce
alkaline phosphatase
- mineralisation of enamel matrix
what is the stratum intermedium involved in
protein synthesis, transport of substances to and from inner enamel epithelium (epithelium)
-ameloblasts supporting function
what happens to the dental papilla in tooth morphogenesis
generates fibroblasts and mesenchymal stem cells of the pulp, and odontoblasts
what happens to the dental follicle in tooth morphogenesis
it supports the enamel organ with nutrients and generates tooth supporting tissues
when does the late bell stage occur
18 weeks in utero
what happens to the tooth in the late bell stage
its acquired its future shape
what happens to the stellate reticulum in the late bell stage
it moves downwards which helps protect the cellular area of the developing tooth
what is the cervical loop
the growing end of the enamel organ (cell interactions)
where is the cervical loop located
where the IEE and OEE meet and is later involved in root formation
what happens when the dental lamina breaks down in the late bell stage
enamel organ loses contact with oral epithelium
what are odontoblasts and what do they do
they’re dental papilla cells and secrete predentine that mineralises and forms dentine
what are ameloblasts and what do they do
they’re inner enamel epithelial cells that secrete preenamel that mineralises and forms enamel
what does the stratum intermedium produce
alkaline phosphate and support the enamel
what does the stellate reticulum do
protects and maintains tooth shape
what does outer enamel epithelium do
maintains tooth shape and exchanges substances with dental follicle
what are the reciprocal tissue interactions in crown formation
- inner enamel epithelium (IEE) separated from dental papilla cells by a cell-free zone
- IEE cells become elongated and secrete signalling molecules to induce odontoblast differentiation from dental papilla cells.
- odontoblasts align and produce predentine
- Signals from odontoblasts (in the predentine) induce differentiation of pre-ameloblasts into ameloblasts that start producing pre-enamel.
Dentine produced first and enamel later due to this interaction
how is the IEE separated from the dental papilla cells
by a cell free zone
how is odontoblast differentiation induced from dental papilla cells
IEE cells become elongated and secrete signalling molecules to induce odontoblast differentiation from dental papilla cells
how is differentiation of pre-ameloblasts into ameloblasts induced
by signals from the odontoblasts in the predentine
what do ameloblasts do
produce pre-enamel
is dentine or enamel produced first? why?
dentine, as signals from odontoblasts are what cause ameloblast formation
how is the crown protected after completion
root formation begins
reduced enamel epithelium(REE)
how is REE formed
from flattened ameloblasts and remnants of the enamel organ
how does REE protect the tooth crown after completion
protects enamel of erupting tooth from being attacked by osteoclasts which remodel the jaw bone once the tooth erupts
how is enamel space caused
by demineralisation of enamel during tissue processing
pre-enamel is only partially mineralised, what does this mean for the enamel proteins after demineralisation
they remain afterwards
in which direction do successional tooth germs of the permanent teeth bud off from the dental lamina, and what happens to them
lingually (not molars)
they stay dormant until further tooth development is initiated
how are permanent molars formed since they have no primary predecessors
they are formed by posterior growth of the dental lamina
what does the backward extension of dental lamina give off in the formation of permanent molars
gives off epithelial buds which form the molars
when are the first molars formed
4 months in utero
when are the second molars formed
6 months in utero
when are the third molars formed
4-5 years after birth
what are the components of the tooth germ
enamel organ
dental papilla
dental follicle
what are the cells of the enamel organ
cervical loop outer enamel epithelium stellate reticulum stratum intermedium inner enamel epithelium
what are the cells of the dental papilla
odontoblasts
undiff. mesenchymal cells
fibroblasts
what are the cells of the dental follicle
cementoblasts
fibroblasts
osteoblasts
what are ex of ectodermal appendages
mammary glands salivary glands teeth hair tongue papillae
what is the function of the enamel knot
signalling centre determining the shape of the tooth
what does the number of enamel knots correspond to
the number of cusps
how can an experiment be carried out to determine the odontogenic potential
- dissection of mandibular arch
- enzymatic digestion to isolate epithelial and mesenchyme
- recombination of epithelium and mesenchyme followed by in vitro culture
- transplantation of tooth germ into kidney capsule and in vivo culture for 2-3 weeks
- tissue analysis
what is meant by the odontogenic potential
capability of a tissue to induce gene expression in an adjacent tissue and to initiate tooth development
where is the odontogenic potential at the initiation stage
its on the epithelium (epithelial signalling)
where is the odontogenic potential at the bud stage
is on the mesenchyme
mesenchymal signalling
how do we know that the odontogenic potential for the initiation stage is on the epithelium
because after 11 days there is no tooth formation when dental mesenchyme instructs non-dental epithelium, however there is tooth formation when the dental epithelium instructs the non-dental mesenchyme
how do we know that the odontogenic potential for the bud stage is on the mesenchyme
because after the 13 days, when the bud has formed, the dental epithelium cannot instruct the non-dental mesenchyme to form a tooth, however after 13 days the dental mesenchyme can instruct the non-dental epithelium
how is a transcriptional response induced in the dental mesenchyme
by overlapping gradients of the morphogens: FGF, BMP in the dental epithelium
what does the initiation stage signalling determine
tooth position
which cells will form a tooth
only those that express PAX 9
what does mesenchymal signalling by the dental mesenchyme in the bud stage secrete and induce
secretes signalling molecules (FGF, BMP) and induces the formation of the enamel knot in the dental epithelium
what signalling occurs in the cap stage
enamel-knot signalling
what does enamel knot signalling induce
cell cycle arrest within the enamel knot but induces cell proliferation in surrounding cells
which signalling molecules induce cell cycle arrest & proliferation (2 separate molecules)
BMP- cell cycle arrest
FGF- cell proliferation in surrounding cells
where does FGF bind in the cap stage
to epithelial cells bordering the enamel inducing cell proliferation directed downwards
in which key genetic regulator would tooth development be arrested at an early stage to give rise to Ectodermal dysplasia
EDA1/EDAR
in which key genetic regulator would tooth development be arrested at an early stage to give rise to hypodontia
PAX9 and MSX1
what is the odontogenic homeobox code tell
a hypothesis for specification of tooth identity
what is the evidence for an odontogenic homeobox code
mandibular molars will still form if you remove the DLX gene for maxillary molars as they have different genes which can compensate for the loss of DLX 1 and 2
Also an expressed molar gene Barx 1 in the incisor region will transform the incisor into a molar as it overrides the Msx1 incisor gene
what do defects during initiation affect
tooth number and identity
what are examples of defects that have occurred during initiation
ectodermal dysplasia, hyperdontia
what do defects during morphogenesis affect
tooth number, shape and size
what are examples of defects that have occurred during morphogenesis
hypodontia, hyperdontia
what do defects during cell differentiation and histogenesis affect
hard tissue formation
what are examples of defects that have occurred during cell differentiation and histogenesis
amelogenesis imperfecta, dentinogenesis imperfecta
what other dental anomalies can various cellular defects cause
eruption
replacement
tumours
what are examples of defects that have occurred as a result of various cellular defects
osteopetrosis
eruption cysts
odontomes
what are characteristics of early defects (development)
missing teeth
supernumerary teeth
abnormalities of tooth shape and size
what are examples of late defects (cell differentiation)
anomalies in structure of teeth-dentine
anomalies in structure of teeth- enamel
anomalies of teeth eruption and/or resorption
what are syndromic defects
dental defects seen in combination with other anomalies
what are non-syndromic defects
dental defects are not associated with other anomalies (only the dental tissue is affected
what is associated with non-syndromic hypodontia and oligodontia
missing teeth e.g.
premolars, lateral incisors, peg shaped tooth
what is associated with syndromic oligodontia
Hypohidrotic ectodermal dysplasia (→ Eda1) Rieger syndrome(→ Pitx2) Oligodontia-colorectal cancer syndrome (→ Axin2)
which teeth are most likely to be missing caused by MSX1 mutation
5s and 8s
which teeth are most likely to be missing caused by PAX9 mutation
7s and 8s
what is the multidisciplinary team approach to manage hypodontia
Orthodontist Child Dental Health dentist Restorative dentist Maxillofacial Surgeon Psychologist Geneticist
what are treatment options for hypodontia
open spaces for bridges or implants
close spaces using orthodontic devices
what gene mutation causes hyperdontia (supernumerary teeth)
RUNX2
what occurs in hyperdontia
bone defects and craniofacial malformations
enamel hypoplasia, delayed eruption, malocclusion
Dentigerous cysts
normally, what happens to the dental lamina at the bell stage
it breaks down
what happens if there is incomplete removal of epithelial remnants
supernumerary teeth
eruptions cysts
odontomes (bening tumours)
what do eruption cysts do
they block the eruption pathway
what happens if remnants of dental lamina are not removed
they can receive signals from the dental follicle and abnormal cysts can form
what is an odontome composed of
bone, dentine, soft tissue
what is hypoplasia
affects enamel matrix formation- reduced enamel thickness
what is hypomineralisation
normal enamel thickness but decreased enamel thickness
what is hypomaturation
normal enamel thickness but mottled and softer
what are the inheritance patterns for amelogenesis imperfecta
autosomal dominant
autosomal recessive
x-linked forms
what are the gene mutations in amelogenesis imperfecta
AMELX, ENAM, MMP20, KLK4, DLX3, FAM83H, WDR72
what is dentinogenesis imperfecta
defects in dentine formation (odontoblasts)
what do teeth look like in dentinogenesis imperfecta
Blue-gray or amber brown, opalescent teeth
Bulbous crowns and short narrow roots; obliterated pulp chambers
what is the dentine like in dentinogenesis imperfecta
Soft dentine => Enamel chipping => Teeth wear down rapidly
what are the inheritance patterns for dentinogenesis imperfecta
autosomal dominant
what are the gene mutations in dentinogenesis imperfecta
DSPP (DSP, DGP, DPP)
how can dentine be classified
by time of development or by anatomical location/histology
what are the types of dentine that develop over time
pre-dentine
primary dentine
secondary dentine
tertiary dentine
what is pre-dentine
an unmineralised dentine matrix secreted by odontoblasts
what is primary dentine
all dentine until the completion of root formation
when does secondary dentine form and what is it associated with
after root completion/eruption
ageing- in time it will reduce the pulp chamber and root canal size
when is tertiary dentine produced
in response to an external stimuli (attrition, caries, cavity preparation etc).
what is tertiary reactionary dentine
when original odontoblasts function in dentine deposition , produce few tubules (slow response=weak stimuli/injury)
what is tertiary reparative dentine
when odontoblasts die and are replaced by newly recruited odontoblast-like cells induced from pulp stem cells. deposit dentine with very little structure (rapid response=severe injury)
what are the types of dentine that can be classified by anatomical location/histology
coronal dentine
root dentine
what are the types of dentine classified by anatomical location
coronal dentine (in crown) root dentine
what are the types of coronal dentine
mantle dentine
circumpulpal dentine
what is mantle dentine
outermost layer of crown dentine, forms first
what is circumpulpal dentine and what are its 4 types
forms the bulk of the crown
- interglobular dentine
- intertubular dentine
- intratubular/peritubular dentine
- sclerotic dentine
what is interglobular dentine
a type of circumpulpal dentine- it forms when dentine is mineralised rapidly
what is intertubular dentine
a type of circumpulpal OR root dentine - it forms between dentinal tubules
what is intratubular/peritubular dentine
a type of circumpulpal OR root dentine- forms inside dentinal tubules
what is sclerotic dentine
a type of circumpulpal OR root dentine - caused by complete obliteration of dentinal tubules
what are the layers of root dentine
Hyaline layer
Granular layer of Tomes
what is the Hyaline layer
the outermost layer of root dentine
what are the chemical properties of dentine (by weight)
70% inorganic: calcium hydroxyapatite crystals
20% organic: mainly collagen fibrils
10% water
its less mineralised than enamel
where do hydroxyapatite crystals form and how do they appear (inorganic matter)
form between type 1 collagen fibrils
appear as uniform small plates (smaller than those in enamel)
what type of collagen forms in the organic matrix
mainly type 1 collagen (90%) and some type III- rest are traces of type V and VI
how do type I and type III collagen form a network
type I are linear and type III are reticular which link them together
what makes up the organic matrix
collagen fibrils proteoglycans glycoproteins phosphoproteins growth factors
what are the glycoproteins involved in the mineralisation process of dentine
osteonectin, osteopontin and dentine sialoprotein (DSP)
what are the phosphoproteins in the organic matrix of dentine
dentsialoprotein
dentoglyco protein
dentphospho protein
what gene makes the 3 phosphoproteins in the dentine organic matrix and how
dentine phosphoprotein gene (DPP) via proteolytic cleavage
what are the growth factors in the dentine organic matrix and what is their function
transforming growth factors (TGF)
bone morphogenic proteins (BMP)
released and travel down tubules and stimulate repair in caries
what are the properties of dentine
softer than enamel higher tensile strength than enamel more resilient (elastic) than enamel (supports brittle enamel) porous (dentinal tubules) sensitive (pulp innervation) reactive to damage (tertiary dentine)
how can pulp dentine respond to structure and physical properties especially changes with age
its a living organ
how does dentine appear on a radiograph compared to enamel
its less radiopaque
how does the dental pulp appear on a radiograph
radiolucent
when does dentine formation begin
at the late bell stage at the cusp tip
what are odontoblasts
mesenchymal cells derived from dental papilla (form dental pulp), they differentiate when receiving molecular signals from pre-ameloblasts
what is a sub odontoblast cell
a daughter cell from the division of ectomesenchymal which HAS NOT been exposed to epithelial influence to differentiate into an odontoblast
what is the first step in the formation of pre-dentine
formation of large von Koff’s fibres (type III collagen) at 90 degrees angle to the EDJ
what occurs after the formation of von Koff’s fibres in dentinogenesis
odontoblasts odontoblast secrete smaller type 1 collagen fibres parallel to the EDJ
what occurs after smaller type 1 collagen fibres are secreted in dentinogenesis
the odontoblasts secrete matrix vesicles (mv) than contain highly concentrated calcium phosphate ions (mineralisation)
what is the unmineralised area between the odontoblast layer and mineralising front termed
pre-dentine
what do odontoblasts develop in dentinogenesis
cell processes
where does initiation of mineralisation in dentinogenesis occur
within the matrix vesicle
how is the mineralising front formed in dentinogenesis
mineralisation occurs within the matrix vesicle secreted by odontoblasts, causing crystallites to burst out and form the mineralising front
what are matrix vesicles and where are they secreted
small (25-250nm) membrane bound vesicles produced by odontoblasts, its secreted into the dentine matrix surrounding odontoblasts
what do matrix vesicles contain
phospholipids that bind to calcium
alkaline phosphates
what do the alkaline phosphates from matrix vesicles do
increase phosphate concentration and destroys the inhibitor of mineralisation (pyrophosphate)
are matrix vesicles involved in the mineralisation of circumpulpal dentine
they have only been observed during mineralisation of mantle dentine. Therefore, they may or may not be involved with mineralisation of circumpulpal dentine
what suggests that collagen is not responsible for initiating mineralisation
there is no mineralisation in or near the collagen fibres
why does the thickness of predentine remain constant
because the amount that calcifies is balanced by the addition of new unmineralised matrix
what are the 2 patterns of dentine mineralisation
linear or globular depending on the speed of dentine formation
where is globular calcification found
in the mantle dentine, where the mineralisation occurs by the matrix vesicles
what type of calcification is found in the circumpulpal dentine
linear and globular calcification both occur depending on the rate of dentine deposition
when dentine deposition is fast, what mineralisation occurs in circumpulpal dentine
globular
when dentine deposition is slow, what mineralisation occurs in circumpulpal dentine
linear
what forms within the collagen matrix in globular calcification
calcospherites (globular masses of mineralised dentine)
they form within collagen matrix and increase in size until they fuse to form a single calcified mass
what happens if globular calcification proceeds fast
incomplete fusion of calcospherites results in formation (of the hypomineralised) interglobular dentine
where can interglobular dentine be found
in the upper third of circumpulpal dentine
what are enamel spindles
formed from an odontoblast process that has intercalated between two ameloblasts and extends into the enamel (it doesnt follow the path of enamel prisms)
what is enamel tuft
hypomineralised region in the enamel which follwos he
what does the scalloping of dentine allow for
increased surface area of the EDJ which enables a tighter interlocking between enamel and dentine
what does the excessive branching of dentinal tubules at the EDJ allow for
increased sensitivity as the odontoblast processes are involved in sensation of whats going on outside of the tooth
what are the types primary curvature of dentinal tubules
s-shaped
linear
where do s-shaped dentinal tubules occur and why
in coronal dentine due to the crowding of the odontoblasts because they are pushed apically as dentine grows inwards towards the pulp
where do linear dentinal tubules occur and why
in the cervical dentine of the crown and in root dentine because little or no crowded results from decrease the surface areas, and tubules run in a straight course
what is the secondary curvature of dentinal tubules
slight changes in tubule direction during dentine deposition creating wavy tubules
what are the 2 types of dentine incremental growth lines
von Ebner lines -short period/daily
Adresen lines - long period
what are the characteristics of von Ebner lines
daily equivalent to cross striations in enamel weakiler defines with a closer spacing dentine deposited daily each line is 3-4 microm
what are the characteristics of Andresen lines
long period equivalent to striae of Retzius in enamel more sharply defined with wider spacing each line 20 micrometers 6-10 short period lines
when does a contour line of Owen form in dentinal tubules
when secondary curvature is pronounced and coincides in adjacent tubules
what causes a contour line of Owen form
metabolic stress during dentine formation
what are owen lines
accentuated incremental growth lines (von Ebner lines) and are hypomineralised
what is the most prominent incremental growth line
the neonatal line due to the disturbances of dentine formation by the birth process
what do the accentuated owen lines correspond to
accentuated lines in enamel
where is secondary dentine found
mostly on roof and floor of pulp chamber
what is intratubular dentine (peritubular)
forms within the dentinal tubule and lines the inner surface as a hyper mineralised layer of dentine (40% more mineralised than the surrounding dentine)
what is intertubular dentine
can be any primary or secondary dentine
dentine between the dental tubules
contains a dense network of type I collagen fibrils in which HA are deposited
less mineral than intratubular dentine
what is sclerotic dentine
continued formation of intratubular dentine leads to obliteration of the dentinal tubules. if complete the dentine is termed sclerotic dentine
why does sclerotic dentine appear transparent in ground sections
due to increased mineralisation
what are dead tracts
when dentinal tubules have lost their odontoblast processes following death of odontoblasts or retraction of processes, the tubules become empty and air-filled, and appear as a dark lines in ground sections
why does sclerotic dentine increase with age
in areas of attrition & caries of the enamel => Protection of the pulp against invading microorganisms.
what are the two explanations for Tomes’ granular layer
- extensive branching and backward looping of odontoblast processes
- incomplete fusion of calcospherites
when does amelogenesis occur
at the late bell stage, morphological changes occur in the enamel organ
how do Inner enamel epithelium cells differentiate into ameloblasts
receive signals from odontoblasts (in the predentine)
once ameloblasts are formed what do thy do
secrete enamel matrix which forms the aprismatic initial enamel layer
what 2 events can amelogenesis be characterised by
enamel secretion
enamel maturation
what occurs in enamel secretion in ameolgenesis
enamel matrix secreted by ameloblasts is partially mineralised (30%)
what occurs in enamel maturation in amelogenesis
When enamel is fully formed, the mineral content increases to about 96%. Enamel crystals grow wider & thicker at the expense of the organic content and water which is gradually removed
wha are the 3 stages for the life cycle of ameloblasts
presecretory
secretory
maturation
what can the presecretory stage be divided into in amelogenesis
morphogenetic stage
histodifferentiation stage
what can the secretory stage be divided into in amelogenesis
Initial secretory stage without Tomes’ process
Secretory stage with Tomes’ process
what can the maturation stage be divided into in amelogenesis
Ruffle-ended ameloblasts
Smooth ended ameloblast
Protective stage
what occurs in the morphogenetic phase in amelogenesis
IEE cells have a cuboidal shape
basal lamina produced by IEE separates IEE from the dental papilla
late bell stage: predentine produced by odontoblasts, ameloblast differentiation
what occurs in the differentiation phase
in amelogenesis
IEE cells differentiate into ameloblasts
what happens to the pre-ameloblasts in the differentiation phase of amelogenesis
Preameloblasts elongate and become columnar; cell nuclei are located proximally towards the stratum intermedium (→ establishment of polarity)
when ameloblasts are fully differentiated what do they do
synthesise enamel proteins
what happens to the basal lamina in the differentiation phase of amelogenesis
Basal lamina between ameloblasts and odontoblasts is removed as its where dentine and enamel have formed
what occurs in the initial secretory stage of amelogenesis
Ameloblasts elongate and secrete enamel matrix, form an (aprismatic) initial layer of enamel
Enamel has lines, not enamel prisms (as its produced by ameloblasts without tomes process)
what occurs in the secretory stage of amelogenesis
the ameloblasts form tomes’ process (proximal and distal portion)
what does the proximal portion produce in the secretory stage of amelogenesis
interprismatic enamel (‘interrod’ enamel)
what does the distal portion produce in the secretory stage of amelogenesis
produces prismatic enamel (‘rod’ enamel)
what happens when the outermost layer of enamel is formed in the secretory stage of amelogenesis
Ameloblasts become shorter, lose the distal portion of Tomes’ process → form a thin aprismatic enamel layer (similar to the initial enamel layer)
what happens as the enamel thickness increases in the secretory stage of amelogenesis
Distal portion of Tomes’ process develops from proximal portion. It elongates, becomes thinner and is located between prismatic & interprismatic enamel
what are the enamel matrix components
amelogenins
non-amelogenin proteins
what are the characteristics of amelogenins
90% matrix component
Low molecular weight
roles in regulating growth and thickness of enamel crystals
Form nanospheres
Selectively removed by proteolytic enzymes
provides scaffolding allowing controlled mineralisation of enamel
what proteolytic enzymes are amelogenins removed by
enamelysin (MMP20) and kallikrein 4
what are the characteristics of non-amelogenin proteins
secreted first but rapidly processed by proteolytic enzymes
10% of matrix content
Form the enamel sheath
Larger proteins: Ameloblastin (70 kDa), Enamelin
amelotin
what is the function of ameloblastin
facilitates adhesion of ameloblasts to enamel matrix
what is the function of enamelin
promotes and guides formation of enamel crystals; least abundant protein
what is amelotin
basal lamina protein; involved in adhesion of junctional epithelium to enamel
how is the maturation stage of ameolgenesis characterised
by growth in width and thickness of pre-existing crystals (hardening of enamel)
what are the phases of the maturation phase in amelogenesis
transitional phase
maturation proper (phase)
cyclic modulation of ameloblasts
what occurs in the transitional phase of maturation
After the enamel layer has been fully formed:
- Decrease in height & volume of ameloblasts
- 50% ameloblasts die by apoptosis
what occurs in the maturation proper phase of maturation
Removal of water and proteins from the enamel matrix
Transport of ions is required for the increase in mineral content
what occurs in the cyclic modulation of ameloblasts in maturation
ruffle-end and smooth-ends alternate
this increases mineral content (ruffle ended) and removal of organic matrix (smooth-ended)
how do ruffle ended (80%) ameloblasts allow selective transfer of calcium ions into the enamel and prevent material in interstitial space
there leaky junctions between ameloblasts at proximal (basal) end; tight junctions at distal (enamel) end;
what are the characteristics of smooth ended ameloblasts
20%
leaky junctions at distal end
enamel protein fragments and water leave the maturing enamel
trace elements
where does the ISF travel in smooth ended ameloblasts
leaks into enamel layer – when cells pump positive ions into a place this is accompanied by H+ which decrease the pH
what do the trace elements in the ISF do (smooth ended ameloblasts)
e.g. strontium and fluoride enter the enamel layer and increase hardness
where is the enamel layer most mineralised
at the occlusal surface
mineralisation decreases towards the EDJ
why are primary teeth less mineralised than permanent
because the maturation phase is shorter
what contributes to the dynamic cycle of enamel demineralisation and remineralisation
acid (from food, stomach or of bacterial origin) causes mineral loss
bicarbonate ions from saliva cause remineralisation (pH buffering), allows other ions like fluoride to incorporate into the tissue
what occurs in the protective stage of amelogenesis
reduced enamel epithelium(REE) forms inactive (cuboidal) ameloblasts and remnants of the enamel organ (‘papillary layer’)
what does the REE do
it covers the tooth crown and protects the enamel from being resorbed by osteoclasts that resorb bone as part of the eruption process or from abnormal cementum deposition
what is the additional function REE has in tooth eruption
forms the junctional epithelium
what are the clinical issues of fluoridation? how is this seen histologically
excessive consumption- “fluorosis”
- faint white opacities/severe pitting and discolouration
- histologically, high porosity in the outer third of the enamel
what are the benefits of water fluoridation
incorporation of fluoride ions into enamel crystals
enamel becomes more resistant to acid so reduction of dental caries
what is etching the enamel surface with acid beneficial for
adhesive dental restorative materials when removing plaque or a thin layer of enamel which would increase the surface area and create a better bonding surface for adhesive materials
what are white spot lesions due to
localised demineralisation of the enamel surface near the gingival margin or fissures
(can be arrested or progress to cavity formation)
when would abnormal enamel formation affect all teeth
ameogenesis imperfect, fluorosis
when would abnormal enamel formation affect individual teeth
- local (non-systemic) causes e.g. trauma or unknown aetiology.
- systemic causes affecting the teeth developing at time of this disturbance e.g. chronological /linear enamel hypoplasia, molar-incisor hypoplasia
how does enamel hypoplasia appear
as a groove or pit on the enamel surface
what does enamel hypomineralisation appear as
smooth surface but abnormal colour (less mineral; abnormal maturation)
what enamel defects affect all teeth caused by enviro/systemic factors
febrile disease
treatments with tetracycline
a chronic ingestion of fluoride ions
how does treatment with tetracycline cause enamel defects
it can be incorporated into mineralising tissues resulting in band or total brown pigmentation
what are enamel defects that affect all teeth caused by genetic factors
syndromic vs non-syndromic
pattern of inheritance: autosomal or x-liked, dominant or recessive
what is molar hypomineralisation (MIH)
associated with opacities and loss of enamel affecting teeth in the first year of life, the molars are fragile and can develop caries easily
when MIH more common
in children who have taken amoxicillin in the first year of life , usually for otis media
how does amoxicillin interfere with enamel
amoxicillin interferes with ameloblast function at the secretory stage and the temporal sequence of amelogenesis events.
what is linear enamel hypoplasia
It is a disruption to enamel formation that causes deep grooves forming on the surface of the tooth. Generally caused by poor nutrition during tooth development
what is the general structure of enamel
highly mineralised
96% inorganic contain
4% organic content and water
what origin is enamel
epithelial
what are the 2 steps in amelogenesis
1st formed enamel is only partially mineralised (30%)
the crystals grow whilst the organic matrix and water are lost
how does the thickness of enamel vary
it varies in thickness over different locations (thickest in . cusps, thinnest over cervical margin)
it varies in thickness between different teeth (increase from 1st to 3rd)
enamel is thicker in primary vs permanent
what are the properties of enamel
translucent extremely hard lacks resilience brittle resistant to abrasion resistant to sharing and impact forces low tensile strength
what are the components of enamel
96% mineral- calcium hydroxyapatite (HA)
3% organic - proteins
1% water
what do the HA crystallites combine to form
prisms separated by the inter-prismatic region
why is it clinically important to be aware that enamel is brittle and it is supported by the underlying dentine
when considering caries and cavity preparation
what is the orientation of the crystals in enamel like
not entirely uniform and differ for the prism and interprismatic region
wha are enamel prisms
the structural unit of enamel, millions in enamel (each prism=1 ameloblast)
where do enamel prisms grow from
the EDJ to the crown surface in layers
what are the three enamel prism patterns in cross section
- prisms circular
- prisms stacked
- keyhole pattern
which enamel prism pattern predominates in humans
3- keyhole
what is pattern 1 of enamel prisms
form with discrete rods surrounded by interprismatic enamel
what is pattern 2 of enamel prisms
discontinuities- rods in vertical rows with interrow sheets of interprismatic enamel
what is pattern 3 of enamel prisms
horseshoe shaped (keyhole); interprismatic attached to the tail below the head of the prism when seen in cross section
what does the keyhole pattern look like in cross section
a wide head towards coronal/occlusal surface
a narrow tail towards cervical
how many ameloblasts is each keyhole rod formed by
4
1- head
3- tail
what is the orientation of the crystals within the prism
parallel to the long axis of prism in head
oblique to the long axis of prism in tail (angled)
what does the prism sheath form
the boundary between rod and interprismatic enamel
what does the prism sheath contain
organic material
what is the prison direction (except from in cervical region)
from the EDJ to the surface like spokes of a wheel but with a 3D curve
what is the prism direction in cervical enamel in primary teeth
obliquely oriented towards the oral cavity
what is the prism direction in the cervical enamel in permanent teeth
obliquely oriented toward the alveolar crest
why is the direction of the rods important in cavity preparation
cavity prep must be done in the same direction as the rods
what is prisms decussation
bundles of enamel rods cross eachother as they travel from EDJ to the surface
what path do groups of enamel rods follow
sinusoidal
what is the benefit of prism decussation
it strengthens the enamel structure, prevents propagation of cracks into deeper areas of the enamel, and improves the resistance to fracture
what are Hunter-Schreger Bands
an optical phenomenon occurs in the inner two-thirds of enamel, as an alternating light and dark bands
what is the underlying mechanism responsible for Hunter-Schreger Bands
prism decussation
what are parazones
prism bands that are cut longitudinally (light zones)- reflective zones
what are diazones
prism bands that are cut transversely (dark zones)- transparent zones
what is gnarled enamel
an area with exaggerated prism decussation (extremely angular) over cusp tips
what causes gnarled enamel
the ameloblasts adapt to the rapidly expanding enamel surface and as the crown becomes larger, cohorts of ameloblasts are displaced apically by their own enamel production
where does scalloping occur
on the EDJ
what does scalloping do
increases the surface area for accommodating more ameloblasts where there is a large difference between EDJ area and crown surfaces area
what is the benefit of a scalloped enamel dentine junction
strengthens the attachment of enamel to dentine
prevents the shearing of enamel during function
less scalloped in primary vs permanent
what does prism decussation result in
hunter-schreger bands and gnarled enamel
what is the neonatal line
an incremental line that occurs at birth resulting from stress
how can the neonatal line be identified
its darker than other incremental lines
how does daily enamel secretion rate vary
it increases from the EDJ to the enamel surface in both permanent and primary teeth
how many micrometers is the inner, mid and outer enamel in permanent cuspal
2-3 inner
3-4 mid
4-5 outer
how many micrometers is the enamel from the EDJ to the surface in lateral primary enamel
2.5 to 4.5
by how much do daily enamel secretion rates drop by per day across the neonatal line in primary teeth
0.5 microns per day
what are cross striations (short daily lines)
DAILY secretion of enamel
how do cross striations form
they are the result of a daily variation in ameloblast secretion rate and mineralisation
what are cross striations (short daily lines) equivalent to in dentine
von Ebner lines however they are weaklier defined with a closer spacing
what are the Striae of Retzius (long period lines )
WEEKLY, wider lines, more defined and result from the ameloblast position at various points of time during development
what are the striae of retzius (long period lines) equivalent to in dentine
Anderson lines
how many short period lines are between 2 long period lines
7-10
what are accentuated striae
neonatal line also produced due to systematic disturbance
what is perikymata
- Perikymata is the outward aspect of internal growth increments
- Visible on teeth to naked eye
- The normal transverse wavelike grooves or lines on the external surface of the tooth
what are the enamel incremental growth lines
cross striations - short daily lines
striae of retzius- long period lines
perikymata
what do the striae of retzius represent
the growth of all the prisms at that increment
what are perikymata surface manifestations of
striae of retzius
what are hunter schreger bands related to
prism orientation
what are the structural defects of enamel
enamel tufts
enamel lamellae
enamel spindles
what are enamel tufts
hypomineralised voids following the direction of decussation
where are enamel tufts and what do they contain
inner third of enamel, start at the EDJ and project outwards
they contain organic material (mainly tuftelin)
how do enamel tufts appear
like lines and only travel for a short distance
what are enamel lamellae
when enamel tufts pass through the entire thickness of enamel (contain organic material)
enamel lamellae appear visually as cracks, how are they different
cracks are still mineralised enamel where as lamellae enamel is hypomineralised and they contain organic material
what are enamel spindles
formed from an odontoblast process embedded into the first zone of enamel, mainly in the cusp tips
why do enamel spindles not follow prism direction
Tomes’ process produces enamel at and an angle
what is enamel erosion
the chemical dissolution of dental hard tissues from acid that does NOT originate from bacteria (extrinsic or intrinsic acid) , resulting in irreversible tooth surface loss
what is the process by which enamel erosion occurs
- hydrogen ions dissociate from the acids & interact with the HA crystal causing dissolution (combine with carbonate/phosphate)
- this releases all ions from that region of the crystals creating the typical honey comb etched surface
- the core of the enamel prisms has been dissolved by the acid and the adjacent interprismatic areas appear more prominent
what is the connective tissue from the dental pulp derived from
mesenchymal cells of the dental papilla
what are the 2 types of pulp
coronal pulp and radicular pulp
what does the pulp open into through the apical foramen
the periodontal ligament
what does the dental pulp provide entry for
blood vessels- nourishment
nerves- sensation
lymphatic vessels- lymph drainage
why may there be 3 roots present instead of 2 and what problems can this cause
accessory canals present- they are the source of infection and inflammation
what is the dental pulp and whats it made up off
loose connective tissue made up of:
- ECM
- different cell types
- blood and lymphatic vessels
- nerves
what does the dental pulp contain
75% water
25% organic material
is there hard tissues in the dental pulp
usually no but calcifications and pulp stones can be found in the pulp of aged teeth
what are the histological zones of the dental pulp
odontoblast cell layer
cell free zone
cell rich zone
pulp core
where do nerve endings terminate
cell free zone
what is the shape and structure of odontoblasts
coronal are columnar
cellular processes reaching into the dentinal tubule
cuboidal in root
what happens to the odontoblast layer as the tooth matures
it becomes flatter and the number of cells is reduced by apoptosis
what does secondary dentine do
its laid at a slower rate after root completion and reduces the size of the space occupied by the dental pulp
how can tertiary dentine be produced
in response to external stimuli, odontoblast-like cells can differentiate from progenitor cells in the pulp
what are the types of junctions between odontoblasts
- tight junctions
- desmosomes
- gap junctions
what are tight junctions and desmosomes , what is there function
mechanical union between 2 cells
maintain spatial relationship
restrict substances in the pulp from entering the dentine
what do gap junctions allow for
openings allowing exchange of small molecules and cell-to-cell communication
