Tooth Development Flashcards
1
Q
What is the basic repeating structure of hydroxyapatite?
A
OH- ion surrounded by 3 Ca2+ ions, surrounded by 3 PO43- ions, enclosed by 6 Ca2+ ions
2
Q
What is the result of F- substituting OH- in hydroxyapatite?
A
- stabilises the lattice
- makes it more acid resistant
- F- and prevention
3
Q
What is the critical pH of hydroxyapatite and fluorapatite?
A
Hydroxyapatite: 5.5
Fluorapatite: 4.5
4
Q
what are the three theories of mineralisation?
A
- Alkaline phosphotase hypothesis
- Nucleation ( homogeneous and heterogeneous)
- Matrix vesicles
5
Q
What is the alkaline phosphatase hypothesis of mineralisation?
A
Alkaline phosphatase, an enzyme present in developing teeth and bones, drives the formation of apatite.
6
Q
What is the homogeneous nucleation theory of mineralisation?
A
The formation of a 1st solid from a solution of ions in which no solid previously existed
7
Q
Can homogeneous nucleation occur for hydroxyapatite?
A
No, hydroxyapatite crystals do not form spontaneously in a supersaturated solution
8
Q
what is heterogenous nucleation?
A
A foreign solid will assist nucleation of a crystal
9
Q
What may act as an epitactic agent in heterogeneous nucleation, promoting formation of crystals?
A
Organic matrix
10
Q
what are possible nucleators of heterogenous nucleation?
A
Collagen
Proteoglycans
Lipids
Phosphoproteins
11
Q
Where do crystals form in collagen structures?
A
In the gaps
12
Q
what are the accepted theories of mineralisation?
A
- heterogeneous nucleation
- matrix vesicles
13
Q
What is the first central tissue to form?
A
Dentine
14
Q
What are matrix vesicles?
A
Membrane packages produced by cells, that contain high concentrations of Ca2+ and PO43- ions
15
Q
What is the main benefit of matrix vesicles in mineralisation?
A
They provide an ideal micro environment for crystal formation and growth (mineralisation)
16
Q
What is the function of matrix vesicles?
A
They help to initiate mineralisation in a tissue
17
Q
What is the sequence of hard tissue mineralisation for a tooth?
A
- Dentine
- Enamel
- Cementum
18
Q
Matrix vesicles are involved in the formation of what hard tissue?
A
Mantle dentine
19
Q
What type of cells is dentine derived from?
A
Ectomesenchymal cells
20
Q
What are the 4 stages of a tooth germ?
A
- Bud stage
- Cap stage
- Bell stage
- Crown stage
21
Q
In what stage of tooth germ do hard tissues start to appear?
A
End of bell stage, start of crown stage
22
Q
what cells form dentine?
A
Odontoblasts
23
Q
Where are odontoblasts derived from?
A
From the cells of the dental papilla
24
Q
At what part of the developing tooth does dentine formation begin?
A
At the cusp tip
25
What are the three stages of dentine formation?
- cytodifferentiation
- matrix formation
- mineralisation
26
what happens during the cytodifferentiation stage of dentine formation?
Cells change from papilla cells to odontoblasts. This requires instruction from epithelial cells.
27
what happens during the matrix formation stage of dentine formation?
Odontoblasts produce matrix and promote mineralisation
28
What type of cells are found in the enamel organ, and what does it form?
Cell type: epithelial cells
Forms: enamel
29
What type of cells are found in the dental papilla, and what does it form?
Cell type: ectomesenchymal cells
Forms: odontoblasts
30
What type of cells are found in the dental follicle, and what does it form?
Cell type: ectomesenchymal cells
Forms: supporting tissues ( PDL, bone, socket and cementum)
31
what are the five components of the enamel organ?
1. Outer enamel epithelium
2. Stellate reticulum
3. Stratum intermedium
4. Inner enamel epithelium
5. Cervical loop
32
Give the 6 steps involved in the formation of dentine from the dental papilla
1. Dental papilla cells divide
2. Cells enlarge and cross acellular space
3. Increased synthetic/ secretory organelles
4. The organic matrix is secreted = predentine
5. Odontoblasts retreat secreting predentine
6. Predentine mineralises forming dentine
33
What process signals the start of enamel formation?
Disintegration of the basal lamina
34
What are the two initial types of dentine?
1. Mantle dentine
2. Circumpulpal dentine
35
What is the first formed dentine?
Mantle dentine
36
What is the mantle dentine characterised by?
- large collagen fibrils at 90 degrees to the ADJ
- matrix vesicles are involved in it’s formation
37
What will the inner enamel epithelium cells mature into?
Ameloblasts
38
what happens to epithelial cells as they mature?
They elongate
39
What direction do ameloblast’s move during enamel formation?
Upwards and outwards
40
What process has allowed for enamel prisms to crucially exist?
Tomes process
41
What governs the shape of enamel prisms?
- tomes process
- direction of retreat of ameloblasts
42
What is the final cue for onset of amelogenesis?
1. Dentine formation
2. Breakdown of basal lamina
43
What is the enamel organic matrix made up of?
Amorphous gel containing enamel proteins and enzymes
44
What are the three enamel proteins within the amorphous gel organic matrix?
- amelogenins (90%)
- enamelins (2%)
- tuftelin (confined to ADJ)
45
what are amelogenins rich in?
Proline and glutamine
46
What two features characterise amelogenins?
- hydrophobic
- thixotropic (changes in properties depending on conditions)
47
What are the three main roles of enamel proteins?
- aid nucleation of hydroxyapatite
- orientate and stabilise crystal growth
- broken down and lost during maturation
48
What does enamel require to mature?
Mineral ions to move IN and enamel matrix to move OUT
49
What proteins are contained in the enamel matrix that flows out?
Amelogenins
50
What proteins are contained in the enamel matrix that remains once mineral ions start to flow into enamel?
Enamelin
51
when is the tomes process lost?
When most of the enamel thickness is laid down
52
Why is the last formed enamel aprismatic?
Because there is no Tomes process present, it is lost once most of enamel thickness is laid down.
53
What is the protein layer, formed when maturation of enamel is complete and is the final ameloblast secretion, called?
Enamel cuticle or reduced enamel epithelium
54
When does the ‘reduced enamel epithelium’ form?
When enamel formation is complete
55
What are the three functions of reduced enamel epithelium?
1. Protection of enamel surface from resorption or prevention of cementum formation
2. Provide an epithelial lined pathway for eruption
3. Forms initial junctional epithelium
56
Define:
The differentiation of cells into specialised tissues and organs during growth
Histogenesis
57
Define:
First stage of tooth development
Initiation stage
58
what is the vestibular lamina?
Contributes to the vestibule of the mouth, delineating the lips and cheeks from the teeth. Involved in formation of sulcus.
59
Define:
The second stage of tooth germ development
Bud stage
60
Define:
The third stage of tooth germ development
Cap stage
61
Define:
The fourth stage of tooth germ development
Bell stage
62
Define:
The last stage of tooth germ development
Crown stage or late bell stage
63
Define:
Outer layer of cuboidal cells that limits the enamel organ
External enamel epithelium
64
Define:
Two or three layers of cells sitting above the inner enamel epithelium
Stratum intermedium
65
Define:
A group of star-shaped cells located in the centre of the enamel organ
Stellate reticulum
66
Define:
Columnar shaped cells rich in RNA, connected by desmosomes to each other. Part of the enamel organ.
Inner enamel epithelium
67
Define:
A form of mesenchyme, in the embryo, consisting of neural crest cells and forms he tissues of the neck and cranium.
Ectomesenchyme
68
What growth factor does ectomesenchyme have receptors for which allows its condensation to occur?
FGF8
69
What does the primary epithelial band give rise to?
- dental lamina
- vestibular lamina
70
What process does the vestibular lamina undergo to form the vestibule between teeth and lips/cheeks?
Apoptosis
71
What week in tooth development does differentiation between dental and vestibular lamina occur?
Week 7
72
What week in tooth development does apoptosis of the vestibular lamina begin?
Week 9
73
What week in tooth development is apoptosis of vestibular lamina complete, leaving a sulcus ?
Week 12
74
what are the three overlapping phases of tooth development?
1. Initiation
2. Morphogenesis
3. Histogenesis
75
What does epithelium (ectoderm) give rise to?
- enamel
- hyaline layer of root
76
what does mesenchyme (ectomesenchyme) give rise to?
- dentine
- pulp
- cementum
- periodontium
77
which tissue is thought to have odontogenic potential so initiates tooth development?
Epithelium
78
what are the three components of a tooth germ?
- enamel organ
- dental papilla
- dental follicle
79
What stage of tooth development is described here?:
- spherical/ovoid epithelial condensation
- cell proliferation
- no histodifferentiation or morphogenesis
Bud stage
80
What stage of tooth development is described here?:
- enamel organ formation
- histodifferentiation and morphogenesis
Bell stage
81
What stage of tooth development is described here?:
- cap shaped enamel organ
- little morphogenesis
- poorly histodifferentiatied
Cap stage
82
what is the role of inner enamel epithelium?
Forms ameloblasts which from enamel
83
what is the role of the stratum intermedium?
Synthesis and transport to and from the inner enamel epithelium
84
what is the role of the Stellate reticulum?
Maintenance of shape and protection
85
what is the role of outer enamel epithelium?
Maintenance of shape and exchange
86
What are the three transitory (temporary) structures of a developing tooth germ?
1. Enamel knot
2. Enamel niche
3. Enamel septum
87
which transitory structure aids change in shape from cap to bell stage?
Enamel septum
88
Give examples of important genes involved in the initiation stage of tooth development
- Bmp2
- EGF
- MSX1
- msx2
-Shh
89
why does the basement membrane have to be intact in a developing tooth?
So that differentiation of mesenchyme to odontoblast can occur
90
What week of tooth development is initiation stage?
Week 6/7
91
What week of tooth development is bud stage?
Week 8
92
What week of tooth development is cap stage?
Week 9/10
93
What week of tooth development is bell stage?
Week 11/12
94
In bell and crown stages, when dental papilla cells signal to IEE cells, what happens to the IEE cells?
They elongate and polarise
95
What happens to the cervical loop during bell and crown stages?
Cells divide
96
During bell and crown stage, which cells invade acellular zone ( what will become the dental pulp in the long term)?
Mature Dental papilla cells
97
what do dental papilla cells mature into?
Odontoblasts
98
What do inner enamel epithelial cells develop into?
Ameloblasts
99
Where OEE cells and IEE cells meet, what is this called?
Cervical loop
100
What, in the long-term, is the cervical loop responsible for?
Root development
101
How does the odontoblast process form?
Pre-odontoblasts start to differentiate upon signalling from the ameloblasts, synthetic organelles are made and the nucleus retreats basally.
102
what happens to the basement membrane as odontoblast process forms?
It breaks down and is replaced by predentine
103
What are the stages of life for an ameloblast?
1. Pre-secretory
2. Secretory
3. Transition
4. Maturation
5. Postmaturation
104
What stage of an ameloblast’s life is described:
Undergoes cytodifferentiation, morphodifferentiation, resorption of basal lamina and epithelial-mesenchymal interactions
Pre-secretory
105
What stage of an ameloblast’s life is described:
Ameloblasts shorten and 50% die
Transition
106
What stage of an ameloblast’s life is described:
Final degradation and withdrawal of matrix
Maturation
107
What stage of an ameloblast’s life is described:
Initial layer of aprismatic enamel formed, tomes process develops, matrix secretion to final thickness and development of prismatic structure
Secretory
108
What stage of an ameloblast’s life is described:
Enamel organ degenerates, eruption and exposure of enamel to oral cavity
Postmaturation
109
what is pre-dentine?
The organic matrix that makes up dentine before it is calcified
110
During what stage of an ameloblasts life cycle is BMP4 expressed?
Secretory
111
At what stage of tooth development does tooth shape determination occur?
Late cap stage and early bell stage
112
What determines tooth shape?
Differential rates of cell division/maturation
113
What feature of the developing tooth signals for tooth shape?
Dental papilla
114
What feature of the enamel organ determines the tooth shape and type?
Inner enamel epithelial cell maturation
115
What is the key transcription factor, found in the dental epithelium, that MUST be switched on in order for any tooth development to occur?
PITX2
116
Expression of what transcription factor drives incisive development?
MSX-1
117
Expression of what transcription factor drives molar development?
Barx-1 and Dlx1/2
118
What would happen to development of teeth if Dlx1/2 expression was switched off?
There will be no maxillary molars present
119
What would happen to teeth development if Barx-1 is over expressed?
The whole jaw would be covered in molars
120
What enzyme does the reduced enamel epithelium secrete to facilitate the breakdown of connective tissue to form am eruption pathway?
Protease
121
Which features of the developing tooth germ play a key role in bone resorption as the tooth erupts?
Reduced enamel epithelium and dental follicle
122
what two layers form the reduced enamel epithelium?
A layer of ameloblasts and the adjacent layer of cuboidal cells (outer enamel epithelium) from the dental lamina
123
what epithelium does the reduced enamel epithelium form?
Junctional epithelium
124
What common dental developments disturbances can occur in the initiation stage?
- hypodontia
- oligodontia
- anodontia
- supernumerary tooth or teeth
125
What common dental developments disturbances can occur in the bud stage?
Microdontia and macrodontia
126
What common dental developments disturbances can occur in the cap stage?
- dens in dente
- fusion
- gemination
127
What is dens in dente?
A rare developmental tooth anomaly characterised by invagination of the enamel organ into the dental papilla
128
What three components interact to from the root of a tooth?
- dental follicle
- Hertwig’s epithelial root sheath (HERS)
- dental papilla
129
Where do HERS cells originate from?
The apical region of the enamel organ (cervical loop)
130
what two cell layers does the enamel organ consist of?
The inner and outer enamel epithelium
131
What direction does HERS proliferate?
Apically
132
What direction does HERS disintegrate?
Cervically
133
what two processes do HERS cells influence?
- root dentinogenesis
- cementogenesis
134
What cells of tooth support does the dental follicle give rise to?
- Cementoblasts
- fibroblasts
- osteoblasts
135
What do Cementoblasts form?
Cementum
136
what do fibroblasts form?
PDL collagen fibres
137
What do osteoblasts form?
Alveolar bone
138
What are the three layers of the dental follicle?
1. Inner investing layer ( becomes cementoblasts)
2. loose connective tissue layer ( mainly fibroblasts)
3. Outer layer (lines alveolar bone)
139
how do hyaline layers of Hopewell Smith form?
Enamel matrix proteins bind to dentine and predentine
140
What is the hyaline layer of Hopewell Smith?
The most peripheral layer of initially unmineralised dentin that forms immediately below the cementodentinal junction.
141
HERS produces what growth factors?
BMP4
EGF
TGF beta family
Transcription factor Shh
142
What process does HERS induce?
Odontoblast formation
143
what shape are fully differentiated odontoblasts in the coronal site (crown) of the tooth?
Columnar
144
what shape are fully differentiated odontoblasts in the root of the tooth?
Cuboidal
145
What enamel matrix proteins do HERS cells secrete on pre-dentine surface?
Amelogenins
146
What does HERS stand for?
Hertwig’s epithelial root sheath
147
How are cementoblasts formed?
By the induction of follicle cells that migrate to root surface of tooth and differentiate into cementoblasts
148
What happens when the cementum matrix mineralises?
Entraps PDL fibres (mainly type 1 collagen)
149
After disintegration of HERS, remnants are left over. What do they form?
Cell rests of Malassez in PDL
150
What are cell rests of Malassez in PDL?
Represent a group of cells in the PDL that have cystic potential
151
What two structures is the hyaline layer found between?
Dentine and cementum
152
What are the two main roles of the hyaline layer?
1. Induces cementoblast formation
2. Cements cementum to the tooth
153
What are the two types of cementogenesis?
1. Acellular (primary)
2. Cellular (secondary)
154
Where does the alveolar bone originate from?
The outer layer of condensed mesenchyme
155
Through what process to HERS cells form bone cells?
Osteogenic differentiation
156
what is the gubernacular canal?
An anatomical structure, which carries the gubernacular cord within it, that starts in the dental follicle and goes through to the alveolar bone crest behind the deciduous tooth
157
What is the main cell type found in the PDL?
Spindle-shaped fibroblasts
158
What two structures is the PDL found between?
Cementum and alveolar bone
159
In crown formation:
What does the epithelium form?
Enamel organ
160
In crown formation:
What cells does the enamel organ produce?
Ameloblasts
161
In crown formation:
What do ameloblasts form?
Enamel
162
In crown formation:
What does the ectomesenchyme form?
- dental papilla
- dental follicle
163
In crown formation:
What cells does the dental papilla produce?
Odontoblasts
164
In crown formation:
What do the odontoblasts form?
Dentine
165
In root formation:
What does the epithelium form?
Hertwig’s epithelial root sheath (HERS)
166
In root formation:
What does HERS form?
Hyaline layer of Hopewell Smith
167
In root formation:
What does the ectomesenchyme form?
-dental papilla
-dental follicle
168
In root formation:
What cells does the dental follicle produce?
- cementoblasts
- fibroblasts
- osteoblasts
169
Where does the permanent successor tend to sit in comparison to the primary predecessor tooth?
Lingually (lower) /palatally (upper)
170
What does ‘active’ eruption mean?
Bodily movement of the tooth
171
what does ‘passive’ eruption mean?
Uncovering of the tooth by apical gingival migration
172
What is the term used to describe the primary tooth eruptive movement?
Bloodless eruption
173
How could early loss of primary teeth delay the eruption of permanent teeth?
The cortical bone will heal fully, which is thick and more difficult for permanent teeth to erupt through
174
What are the 3 “PUSH’ eruption theories ?
- root formation
- bone formation
- fluid pressure
175
What are the 3 ‘PULL” theories of eruption, involving the PDL?
- collagen contraction
- fibroblast contraction
- fibroblast migration
176
What two theories of eruption are most likely to be correct?
Pull: by PDL fibroblasts
Push: hydrostatic pressure
177
In what direction do fibroblasts in the PDL move on eruption?
Cervically
178
What is bloodless eruption?
When a primary tooth passes through an epithelial-lined channel/pathway to erupt
179
What cells resorb primary teeth?
Odontoclasts
180
What can cementum be classed into?
Acellular and cellular cementum
181
what type of cementum is thin and covers the cervical root?
Acellular cementum
182
What type of cementum is thick and covers the apical root?
Cellular cementum
183
What percentages of cementum make up mineral, matrix and water?
Mineral: 65%
Matrix: 23%
Water: 12%
184
What role does HERS play in root formation?
Guides root formation and determines size, shape and number of tooth roots
185
When HERS cells secrete enamel matrix proteins onto dentine, what forms when they mineralise?
Hyaline layer of Hopewell Smith
186
What is the role of the hyaline layer?
1. Induces cementoblast formation
2. Cements cementum to the tooth
187
what is the traditional view of how cementum forms?
Cementum formed by cementoblasts derived from the dental follicle
188
What has new evidence found in regard to cementum formation?
At least some cementoblasts may be derived from HERS cells, undergoing EMT.
189
What happens upon cementum matrix mineralising?
PDL collagen fibres become trapped
190
What do remnants of HERS form, which have cystic potential?
Cells rests of Mallassez in PDL
191
Proteins in enamel can induce cementogensis. True or false?
True
192
What enamel matrix derivative us used clinically to induce cementogenesis?
Emdogain
193
What four layers make up the enamel organ?
1. Inner enamel epithelium
2. Outer enamel epithelium
3. Stellate reticulum
4. Stratum intermedium
194
What happens to the shape of maturing inner enamel epithelial cells?
They become more columnar and the nuclei polarise to basal end
195
What is the earliest week in utero that initiation stage of tooth development can occur?
6th week
196
What is the week in utero that bud stage of tooth development can occur?
8th week
197
What is the earliest week in utero that cap stage of tooth development can occur?
11th week
198
What week in utero can bell stage of tooth development occur?
14th week
199
What is the earliest week in utero that late bell/crown/appositional stage of tooth development can occur?
18th week
200
What genes cause selective tooth agenesis in humans?
PAX9 and MSX1
