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tooth development Flashcards

1
Q

Ectoderm lining stomodeum gives rise to oral epithelium

on the

A

1st branchial arch.

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2
Q

when is primary epithelial band formed

A

6th week of prenatal development

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3
Q

Primary epithelial band origin

A

oral epithelium

thickens and invaginate into the ectomesenchyme

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4
Q

Primary epithelial band

A

These bands are roughly
horseshoe shaped and
correspond to the future dental
arches of the upper & lower jaws

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5
Q

what happen by the 7th week

A

primary epithelial band
will divide to form:
(1) vestibular lamina
(2) dental lamina

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6
Q

Vestibular lamina

A

form vestibule

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7
Q

Vestibular lamina process

A

Cells of the vestibular lamina will proliferate,
and then the central epithelial cells
degenerate to form the sulcus of the vestibule
between the cheek and the tooth bearing
area.

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8
Q

Dental lamina

A

-Dental lamina contributes to the development of teeth.
• Dental lamina is not a strand but a sheet.
• Is divided into General lamina & Lateral lamina

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9
Q

dentall lamina process

A

Within the dental lamina continued & localized proliferative
activity leads to the formation of a series of epithelial
outgrowths into the ectomesenchyme,
the outgrowth occurs at sites corresponding to future deciduous teeth

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10
Q

What controls the initiation of tooth

development?

A

earliest msenchymal markers = Lhx 6 & 7 (expressed at ncc)
lhx induced by fgf8
fgf expressed at 1st branchial arch

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11
Q

What controls the position & number of tooth

germs?

A

pax 9 - define location of tooth germs

fgf8 induce pax 9

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12
Q

TOOTH TYPE DETERMINATION

A

PATTERNING , homodont and heterodont

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13
Q

Hypothetical Models Explaining How Different

Tooth Shapes Are Determined

A

field model and clone model

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14
Q

field model

A 
Genes responsible for tooth
shape reside within the
ectomesenchyme in distinct
BUT graded fields for each
tooth family.
Each of the fields express differing patterning homeobox
genes.
However, genes in the oral epithelium provides the
signalling.
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15
Q

clone model

A

Each tooth class is derived from a clone of
ectomesenchymal cells programmes by
epithelium to produce tooth of a given pattern.
A: The molar clone has induced the dental lamina to begin tooth development. At its
posterior border the clone and dental lamina grow posteriorly by means of the
progress zone.
B: When a clone reaches the critical size, a tooth bud is initiated at its center.
C: The next tooth bud is initiated until the progress zone of the clone has escaped
its influence

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16
Q

when is bud stage

A

8th week of prenatal development

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17
Q

what happen during bud stage

A 
A series of epithelial
outgrowth develops on the
surface of the dental lamina..
Forming tooth bud
maxillary arch : 10 buds
mandibular arch : 10 buds
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18
Q

when is early cap stage

A

Forming tooth bud
maxillary arch : 10 buds
mandibular arch : 10 buds

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19
Q

what happen during early cap stage (1)

A

Each of the tooth buds
Will invaginate into the
ectomesenchyme to form a capshaped structure.
tooth germ

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20
Q

what happen during early cap stage (2)

A

Nerve fibres & blood vessels are NOT present
in the enamel organ at any time.
• Blood vessels enters the dental papilla during
cap stage.
• Blood vessels are also found around the tooth
germ in the dental follicle

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21
Q

tooth germ

A

enamel organ, dental papilla, dental follicle

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22
Q

late cap stage

A 
histodifferentiation
Epithelial cells in the enamel organ will
differentiate to form Stellate reticulum
(SR) during late cap stage.
However, the development of SR will
continues until early bell stage
formation of transitory structures.
formation of permanent dentition
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23
Q

stellate reticulum

A

Cells in the center of the enamel organ synthesize &
secrete glycosaminoglycans into the extracellular
components between the epithelial cells
Glycosaminoglycans are hydrophilic, and so pull
water into the enamel organ
Volume of the extracellular compartment of the enamel
organ increases, forcing the central cells to separate.
The cells retained connections through desmosomal
contacts, and thus become star shape & is termed
Stellate Reticulum (SR)

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24
Q

TRANSITORY STRUCTURES

A
  • Enamel knot
  • Enamel cord
  • Enamel niche
  • Enamel navel
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25
enamel knot
``` - Is a localised mass of cells in the centre of the enamel organ - visible in sections of molar cap stage tooth germs. ```
26
Enamel cord
Enamel knot which extends between the IEE & EEE
27
Enamel navel
A small invagination situated at the EEE where the enamel cord terminates.
28
Enamel niche
It is seen where the tooth germ appears to have a double attachment on the dental lamina. The enamel niche area contains connective tissue.
29
when is formation of permanent dentition
At the 10th wk of prenatal development | during the late cap stage for each primary dentition
30
formation of permanent dentition
Tooth bud for permanent dentition forms on the | lingual of the deciduous tooth germ
31
Succedaneous
Permanent teeth formed with primary predecessors. - include anterior teeth & premolars - replace primary anterior teeth & molars, respectively. - permanent succedaneous tooth crown will erupt lingual to its primary predecessors root
32
Nonsuccedaneous
- Permanent molars. - Have no primary predecessors. - Develop from a posterior extension of the dental lamina. (distal to the primary second molar’s dental lamina)
33
when is early bell stage
11th – 12th wk of prenatal development
34
early bell stage
``` Enamel organ resembles a bell as the undersurface of the epithelial cap deepens. During this stage, the tooth crown assumes its final SHAPE (morphodifferentiation). breakup of dental lamina crown pattern determination ```
35
morphodifferentation in early bell stage
cells in enamel organ into : | eee,iee, sr, si
36
iee
``` is having columnar cell shape. - is adjacent to SI (IEE is connected to SI by desmosomes & gap junction) - will differentiate into ameloblasts ```
37
eee
``` - are the outer cuboidal cells of the enamel organ. - will serve as a protective barrier for the rest of the enamel organ during enamel production. ```
38
si
``` - consists of 2 or 3 layers of flattened cells lying over the IEE - SI helps to support the production of enamel. ```
39
sr
``` - are star-shaped cells, forming a network. - cells are connected to one another by desmosomes. - SR helps to support the production of enamel ```
40
Break Up of the Dental Lamina
``` Epithelial cells of the dental lamina undergo lysis Dental lamina disappears The developing tooth & the oral epithelium is separated ```
41
Crown Pattern Determination
The intrinsic growth by differential rates of mitotic division within IEE. Resulted in the folding of the IEE The point at which IEE cell differentiation 1st occurs represents the site of future cusp development The occurrence of a 2nd zone of cell differentiation within the IEE leads to the formation of a 2nd cusp.
42
when BELL STAGE (late)
13th -18th wk of prenatal development
43
BELL STAGE (late)
``` Is associated with the formation of the hard tissues : • Dentin • Enamel ree root formattion ```
44
BELL STAGE (late) process
``` (1)Ectomesenchymal cells of the dental papilla facing IEE will differentiate into odontoblasts to form dentin (dentinogenesis). (2) The increase in size of the papillary cells eliminates the acellular zone (basement membrane) between odontoblasts and IEE. (3) The columnar cells of IEE facing the odontoblasts will then differentiate into ameloblasts to form enamel (amelogenesis) ```
45
Odontoblasts :
- will deposit organic matrix of dentin. | - will then move towards the center of dental papilla.
46
Ameloblasts
- will secrete organic matrix against the newly formed dentinal surface (mantel dentin). - will then move away from the dentin, giving the thickness to the enamel
47
nutrient suppy of late bell stage
- will secrete organic matrix against the newly formed dentinal surface (mantel dentin). - will then move away from the dentin, giving the thickness to the enamel When dentin is formed: -It cuts off the nutrient sources from the blood vessels of the dental papilla. -Causing a drastic reduction of nutrients reaching the enamel organ (occurs when the cells of the IEE are about to secrete enamel, and thus, the demand for nutrients increases)
48
demand of nutrient supply satisfied by (late bell)
(i) the collapse of SR (ii) Invagination of EEE by blood vessels lying outside the enamel organ
49
ree what
Also known as reduced dental epithelium. | Overlies a developing tooth.
50
ree formed by
(1) a layer of ameloblasts (differentiated IEE) (2) the adjacent layer to IEE (SI, SR, EEE)
51
As REE degenerate
the tooth is revealed by | erupting into the oral cavity.
52
root formation
when crown is completed, process of root formation will start. and when 1/3 root formed, tooth erupt
53
component for root formation
cervical loop, hers
54
cervical loop
``` Cervical loop (CL) is responsible for root development. CL is the most cervical portion of the enamel organ. CL consist of only IEE and EEE. Cervical Loop Epithelial cells of the cervical loops will proliferate & forms a double layer of cells known as Hertwig’s Epithelial Root Sheath (HERS) ```
55
fx of hers
- to determine the shape of the root. - to determine the number of roots. - to induce the formation of root dentine.
56
hers
``` HERS induce the outer cells of dental papilla (cells facing the HERS) to undergo differentiation & form odontoblasts. The odontoblasts will then undergo dentinogenesis and begin to secrete predentin. HERS will extend downwards & the tip of HERS will bend slightly to form epithelial diaphragm enclosing dental papilla, except for an opening at base (primary apical foramen). When root dentin formation is completed, HERS will disintegrate & the cells may become the epithelial cell rests of Malassez (located in the periodontal ligament area). Some epithelial cell rests of Malassez may become calcified in the periodontal ligament, and known as cementicles ```
57
multirooted tooth
horizontal ‘tonguelike’ epithelial extensions occurs within the root trunk The single cervical opening (primary apical foramen) will be divided into 2 or 3 openings at the bifurcation or trifurcation of the root by these horizontal extensions
58
disturbances during root development
accessory root canal, enamel pearl, dilaceration, supernumerarry roots
59
Accessory Root Canal
``` • occurs due to a break in the continuation of the HERS, eg.: (i) HERS encircles a blood vessel (ii) lack of fusion of the epithelial diaphragms.  causes no deposition of dentine  is usually at the apical 1/3 of the root. ```
60
Enamel Pearl
Is a small spherical enamel formed on the root surface. Caused by HERS which accidentally contained SI & SR Induce the formation of ameloblasts at the root area
61
Dilaceration
``` • is due to distortion of HERS caused by injury or pressure during root development • causes root (or roots) to be distorted • can occur in any tooth or group of teeth Assoc Prof Dr Wan Himratul Aznita Wan Harun Dilaceration • can cause problems during extraction and endodontic treatment. ```
62
Supernumerary Roots (accessory root)
occurrence could be due to trauma, pressure or metabolic disease that affects HERS could occur in any teeth, but mainly in the permanent 3rd molars (occurrence are rare in the incisors). can cause problems during tooth extraction and endodontic treatment.

Integration finals (19 decks)

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