Initiation and crown development Flashcards
1
Q
Name the different stages of tooth development n
A
- Primary epithelial band splits into vestibule lamina and dental lamina
- Dental lamina progresses into BUD stage
- Cap stage
- Early bell stage
- Late bell stage
- Root development
2
Q
What does the dental lamina dictate
A
It maps out where the upper and lower dental arches form
3
Q
While the tooth is developing what other changes are happening
A
- A plate of bone is forming below the tooth germ- the lateral plate of the mandible
- . Bone of the jaw form denovo within the mesenchyme- intramembranous bone
- second, medial, plate of bone will develop to form a trough in which the tooth germs are contained
4
Q
Name the cartilage found in the mandible
A
Meckels cartilage
5
Q
Where us the tooth germ contained
A
A trough of bone
6
Q
What happens to the trough of bone where the tooth germ sits during development
A
The trough will become subdivided by cross plates of bone to form individual sockets
7
Q
As the jaw is developing what is happening to the tooth
A
The enamel organ has started to grow in to the beginnings of a cap shape marking out where the primary cusps of the toot will from
8
Q
Has histogenesis started in the cap stage
A
Yes
9
Q
What is hostogeneisis
A
More than one cell type making up the enamel organ
10
Q
Describe the ectomesenchyme in the cap stage
A
It has proliferated to form a dose condensation in and around the enamel organ
11
Q
What is the dental papilla
A
The part enclosed by the enamel organ
12
Q
What is the dental follicle
A
The part surrounding the enamel organ
13
Q
What does the dental papilla eventually form
A
The dentine and pulp
14
Q
What does the dental follicle eventually form
A
The periodontal ligament and cementum
15
Q
Where does the enamel organ proliferate as it develops
A
Proliferates downwards to enclose more of the mesenchyme
16
Q
Describe the later cap stage
A
- Beginnings of the socket are evident
- Bone surrounds tooth germ
- Further histogenesis
- Enamel organ has grown
17
Q
Describe the histogenesis of the later cap stage
A
Distinct inner layer of columnar cells- inner enamel epithelium
Cuboidal cells forming the ‘outer’ envelope termed -outer enamel epithelium
18
Q
What is the inner enamel epithelium
A
Distinct inner later of columnar cells
19
Q
What is the outer enamel epithelium
A
Cuboidal cells forming the outer envelope
20
Q
What is the bulk of the enamel organ made up of in the later cap stage
A
Stellate reticulum
21
Q
What is the stellate reticulum
A
Loose stellate cells
22
Q
Name the 2 transitionary structures found in the enamel organ during the late cap stage
A
- Enamel knot
2. Enamel septum
23
Q
What is the significance of the name knot
A
Recent studies show it may have a important role in interacting with the mesenchyme in cuspal initiation and initial control
24
Q
What is the significance of her enamel septum
A
May be site where cell diction is occurring to proceed more cells fro the stellate reticulum as it enlarges
25
name the most significant development of the later cap stage
The down growth lingually of a branch of the dental lamina
26
What is the significance of the downward growth of the dental lamina
It develops the bud of the permanent tooth
27
What happens to the enamel organ as tooth developing continues into the bell stage
The enamel organ develops such that the inner enamel epithelium is more pronounced and has a shape that resembles a bell
Shape of the incisal edge or cusp of teeth are clearly outlines
28
What does the junction between the inner enamel epithelium and the adjacent papilla map out?
The future amelo-dentinal junction (ADJ).
29
Describe the cells of the inner enamel epithelium in the bell stage
They are more elongates especially at the top of the cusps
30
Which part of a developing tooth is the most mature
The cusps
31
What is happening to the outer cells of the papilla during the bell stage
They are beginning got differentiate into odontoblasts
32
What do odontoblasts do
They produce dentine
33
Name the least mature part of a developing tooth
The cervical loop
34
How do we know the cervical loop is the least mature area of a developing tooth
As the inner enamel epithelium cells are still cuboidal
35
Describe the stellate reticulum in the bell sage
They have grown and become more uniform
36
What is the part surrounding the enamel organ called?
Dental follicle
37
What is the part enclosed by the enamel organ called
Dental papilla
38
What is the bulk of the tooth made up of in the bell stage
A matrix rich in glycosaminiglycans (GAGs)
39
Wha too glycosaminiglycans (GAGs) attract
Attracts hate and makes the enamel organ relatively turgid
40
What new layer of cells develops in the early bell stage
A single or double layer of cells lying adjacent to the base of the inner enamel epithelium cells called the ‘stratum intermedium’.
41
What is the stratum intermedium
A single or double layer of cells lying adjacent to the base of the inner enamel epithelium cells
42
What is the significance of the stratum intermedium
Appear to be important in the final differentiation of the inner enamel epithelium cell into ameloblasts
43
What do ameloblasts do
They produce enamel
44
Describe the jaw as the tooth forms into the early bell stage
Both lateral and medial plates are present alongside a considerable amount of the body of the mandible
45
Describe Meckel’s cartilage as the tooth is in the early bell stage
Meckel’s cartilage has been reduced in size and displaced by the bone.
46
What significant event has occurred in the later bell stage
Dentine matrix has been secreted at the cusp/incisal edge
47
What differentiates the late bell stage from the early bell stage
The secretion of dentine matrix
48
How does mineralised dentine appear on a radiograph
As snow capped peaks
49
Describe the cells that secrete dentine
they are dull elongates functional odontoblasts
50
What is triggered by the production of dentine
The cells of the inner enamel epithelium are triggered to terminally differentiate into ameloblasts
51
What happens to the stellate reticulum during the later bell stage
They collapse to markedly reduce the distance between the inner enamel epithelium and the outer enamel epithelium
52
Where did the inner enamel epithelium initially receive its nutrients from
The vasculature in the papilla
53
What happens to the vasculature in the papilla during the later bell stage
The mineralising dentine matrix cuts it off so it can no longer provide nutrients to the inner enamel epithelium
54
Where does the inner enamel epithiun receive its nutrients from during the LATER bell stage
Capillaries invaginate the outer enamel epithelium to provide an alternative supply (The papillary layer)
55
What is the papillary layer
The capillaries that invaginate the outer enamel epithelium
56
What does the bell stage represent in terms of crown formation
It represents the very earliest stage in crown formation
57
In terms of cell development what pattern do we see in developing teeth
There is gradient from cusp tip to cervical loop
| Most mature teeth are at the cusp tip and least mature at the cervical loop
58
What controls the differentiation of ameolblasts and odontoblasts
The conversation between the inner enamel epithelium and the papilla
59
What is the inner enamel epithelium derived from
The ectoderm
60
What is the papilla derived from
The ectomesenchyme
61
What controls cell morphology in a developing tooth
The papilla
62
What brings about mitotic changes in pre ameloblastic and pre odontblastc cells
A change in the receptiveness of the papilla cell to signals from the IEE that brings about this change in its mitotic status
63
What events occur when the odotnblasts become full developed
They begin to secrete extra cellular matrix long the basal lamina
The basal lamina then subsequent degenerates
64
What does the degeneration of the basal lamina intimate
signals the pre amelobalsts to withdraw from the cell cycle
65
What is required for enamel production to occur
Dentine production
66
Until when do the ameloblasts secrete enamel matrix
Unti the full thickness of the enamel has been secreted
67
What is a cereal parameter in deterring crown morphology
Enamel thickness
68
Until when do the odontoblasts secrete dentine
They produce dentine throughout the life of the tooth
69
What happens to the basal lamina
The position of the basal lamina will be ‘fossilised’ as the amelodentinal junction.
70
What do ectodermal/mesenchymal interactions and tooth development involve
Temporary and spatially regulated production of growth factors, their receptors and hox genes
71
Give some examples of growth factors
BMP
TGF beta
FGF
72
What are hox genes
homeobox GENES
73
What is responsible for controlling tooth type and shape
The dental papilla
74
How does the dental papilla determine tooth type and shape
By controlling proliferation within the inner enamel epithelium
75
What happens to the enamel matrix once fun thickness has been reached
The matrix at the ADJ will begin to mineralise
76
Is the mineralisation of the matrix at the ADJ uniform
no there are variations in rate of deposition at any given moment in tim
77
What forms due to the variation in the rate of matrix mineralisation
growth line within the enamel
78
Give an example of a growth line found in enamel
striae of Retzius.
79
What are the striae of Retzius.
Growth lines found oblique to the ADJ and surface
80
what is mature enamel made up of
Hydroxyapatite crystals
81
what does the development of enamel start with
The secretion of a dense protein matrix
82
What is the initial protein matrix that makes up enamel made up of
A protein called amelogenin
| Other enamel specific proteins are present in much smaller amounts (<10%)eg enamelin and ameloblastin.
83
Is amelogenin found in mature enamel
NO
84
What are diseases involving tooth enamel usually caused by
Mutations in the genes coding for the matrix proteins eg amelogenin, enamelin and ameloblastin
85
What happens to the protein matrix of enamel once full thickness has been secreted by ameloblasts
The protein matrix is degraded and removed from the tissue (proteolysis)
86
Which cell is responsible for the process of producing enamel, degrading it and then adding mineral to mature it
Ameloblasts
87
What are Ameloblasts derived from
They are the terminally differentiated form of the cells of the inner enamel epithelium.
88
What changes do the ameloblasts undergo ro preform their function
newly differentiated cells are a short columnar shape, approximately 5μm wide and 30μm long with significant amounts of rough endoplasmic reticulum, mitochondria and golgi, Their nucleus is displaced towards the basal end of the cell, away from the AD
89
How are neighbouring ameloblasts cells joined together
By desmosomes and gap junctions
90
Where is the matrix secreted from in the amelobalsts
Secreted at the apex of the cell towards the ADJ
91
As the ameloblasts migrate what do they do
They leave matrix behind
92
What changes do the ameloblsats undergo as they migrate
They elongate and their apical ends develop the Tomes process
93
What is the significance of the tomes process
Its shape dictates the orientation of the secreted matrix to the ADJ
94
For the bulk of matrix secretion the cells will have what?
A tomes process
95
Having a tomes process means what for enamel
Means bulk of enamel thickness will be prismatic
96
What stage follows the late bell stage?
Transition stage
97
What happens to ameloblasts in the transition stage
They decrease in length and become less active
Their tomes processes disappear
20% of cells die from apoptosis
98
What does the loss of tomes process mean for amelobalsts in the transition stage
Results in a second thin layer of prismatic enamel being deposited at the surface.
99
Which stage follows the transition phase
Maturation phase
100
What happens in the maturation phases
The matrix will be totally degraded, removed and replaced by mineral so that hydroxapatite crystals can grow
101
What she does hydroxyapatite start at and what does it end up as
Starts as long thin ribbons and ends as large hexagonal crystals
102
How would you describe the process of amturation
It is cyclical
103
Why is the process of maturation described as cyclical
As cells oscillate between so-called smooth-ended and ruffle-ended forms
With each cycle a little bit more matrix is removed and more mineral is added
104
What happens simultaneously with maturation of cells
The pH of the underlying mineralising matrix also changes in acidity
105
Why is a regal change in acidity important during maturation
As it is needed for sustained crystal growth
106
What happens to the ameloblsats and other elements of the enamel Organ once maturation of enamel is complete
They collapse down to form a layer 2-3 cels thick which covers the surface of the enamel-reduced enamel epithelium
107
what does the collapsing of the ameloblsars following maturation of enamel lead to
the reduced enamel epithelium
108
What is the reduced enamel epithelium involved in
Tooth eruption and the shedding of deciduous teeth.
109
What is the final act int the formation of enamel
The secretion of a thin layer of protein at the enamel surface called the primary enamel cuticle
110
What is the primary enamel cuticle
The outermost thin layer of protein found on the enamel surface
