Tooth development Flashcards
(97 cards)
1
Q
When do deciduous teeth start to develop?
A
Between 6-8 weeks in utero
2
Q
When do successional teeth begin to develop?
A
20 weeks in utero to 10 months after birth
3
Q
Which teeth are not successional?
A
Permanent molars
4
Q
When does the 1st molar begin to develop?
A
20 weeks in utero
5
Q
When does the 2nd molar begin to develop?
A
After birth
6
Q
When does the 3rd molar begin to develop?
A
4-5 y/o
7
Q
What are the 3 phases of tooth development?
A
- initiation
- morphogenesis
- histogenesis
8
Q
What is initiation?
A
The first initial events of tooth development
9
Q
What is morphogenesis?
A
The change in shape of the tooth as the tooth develops (how become an incisor or molar etc.)
10
Q
What is histogenesis?
A
Differentiation of the cells responsible for making the tissue of the tooth e.g. into ameloblasts
11
Q
Interactions between which two types of cells does tooth development heavily rely upon?
A
Epithelial cells and ectomesenchymal (derived from neural crest) cells
12
Q
What type of cells are neural crest cells?
A
Pluripotent
13
Q
Where are ameloblasts derived from?
A
Epithelial derived
14
Q
What is the fate of an individual cells determined by?
A
The environment into which it migrates and a combination of homeobox gene expression
15
Q
What is the role of epithelium and mesenchyme in tooth development?
A
Epithelium is instructive in very early events (type of tissue), then mesenchyme takes over (tooth specificity)
16
Q
Skin mesenchyme + dental epithelium forms:
A
skin
17
Q
Dental mesenchyme + skin epithelium forms:
A
tooth
18
Q
Incisor germ mesenchyme + molar epithelium forms:
A
incisor
19
Q
Molar germ mesenchyme + incisors epithelium forms:
A
molar
20
Q
What does the dental follicle become in a fully developed tooth?
A
The periodontal ligament
21
Q
What does the dental papilla become in a fully developed tooth?
A
The dental pulp
22
Q
Which transcription factors/ signalling molecules are involved in tooth development?
A
Pitx-2 = initiates tooth development, Sonic hedgehog (Wnt) = increases cell proliferation, Pax9 & Msx1 = needed for the early tooth genre ti progress from the bud stage
23
Q
What are the homeobox genes?
A
The different gene expressions needed to form different types of teeth
24
Q
What are the homeobox genes for incisors?
A
Msx1, Msx2 & Alx3
25
What are the homeobox genes for molars?
Dlx1, Dlx2 & Barx 1
26
What was shown by experiments removing 1 or other of the genes Dlx1 or Dlx2?
Absence of maxillary molars
27
What happens by the 6-7th week of development?
A thickening of the oral epithelium occurs = invaginate into mesenchyme and divides into the buccal vestibular lamina (hollows out to form buccal vestibule) and the lingual dental lamina (tooth)
28
What is a placode?
A swelling within which teeth develop
29
Where are successional placodes placed?
Lingual to developing tooth buds (except tooth that dont have predecessors = molars)
30
What are the 3 tooth germ stages of development?
Bud, Cap and Bell (early and late)
| n.b. = a continuum
31
At what time is the tooth in cap stage?
By 11th-12th week
32
By what time is the tooth in early bell stage?
By the 14th week
33
What does the inner epithelial layer do in the early bell stage?
Maps out the occlusal pattern of the tooth crown
34
How do we protect the tooth germ?
The stellate reticulum produces glycosaminoglycans = jelly like ECM in the cap stage = protects against pressure which would change the shape of the tooth
35
What are remnants of the dental lamina in the early bell stage called and what can they cause?
Epithelial pearls of serres -> may be involved in aetiology of cysts and tumours
36
Which occurs first, dentine or enamel formation?
Dentine formation always just precedes enamel formation
37
Where does dentine and enamel formation start?
Future cusp tip or incisal edge (proceeds apically)
38
What is an enamel knot?
A little accumulation of cells usually in the centre of where an incisal tip or cusp is developing (may have >1 in a tooth germ) = thought to be a centre for production of signalling molecules (disappears in early bell stage)
39
What is an enamel cord?
A line of cells appearing to divide the stellate reticulum into two, not know where they come from or function (may be remnants of enamel knot)
40
When an enamel cord stretches from stratum intermedium out to the outer enamel what is it called?
An enamel septum
41
Which end of the ameloblasts is the secretory end?
The distal end
42
At what stage does formation of enamel and dentine start?
Late bell stage
43
What is the early sequence of events for formation of dentine and enamel?
Cells of internal epithelium begin to differentiate (pre-ameloblasts), dental papilla cells induced by ameloblasts = osteoblasts, basal lamina breaks down, odontoblasts produce first layer of dentine matrix and then ameloblasts are initiated to produce enamel
44
Where does enamel and dentine formations start?
At the ADJ then moves outwards
45
What are the 5 stages of amelogenesis?
1. pre-secretory stage
2. secretory stage
3. transition stage
4. maturation stage
5. post-maturation stage
46
What is the pre-secretory stage?
Anything up to when the amelogenins (all lost) and non-amelogenins (e.g. enamelling, ameloblastin, tuftelin, amelotin) are secreted by the ameloblasts
47
What is the secretory stage?
Laying down of amelogenins and non-amelogenis (proteins) which are immediately mineralised to form enamel
48
How does the enamel from the secretory stage differ to mature enamel?
Very thin and ribbon like hydroxyapatite with lots of protein and water in between
49
What is the maturation stage?
Ameloblast controlling the mineralisation of the enamel matrix itself (majority of proteins removed and full mineralisation occurs)
50
What is the post-maturation stage?
Forms protective lining over newly formed lining of tooth -> cells are either lost or some are involved in forming the junctional epithelium
51
What % of proteins secreted in the secretory stage are amelogenins?
90-95%
52
What type of enamel is the initial layer formed?
A-prismatic (randomly formed)
53
What is responsible for the formation of prismatic structures?
Tomes process
54
What are the consequences of distal webs forming?
Controls the environment where mineralisation occurs
55
The central core of a prism is produced by how many tomes processes?
1
56
The prism boundary is produced by how many tomes processes
Multiple
57
What % of weight of early developing enamel do enamel proteins make up?
25%
58
What % of weight of mature enamel do enamel proteins make up?
59
What are the roles of enamel proteins thought to be>
Initiating and controlling development of enamel (individual roles unknown but mutations in their genes associated with disturbances of enamel structure)
60
What is the striae of retzius?
Weekly incremental lines
61
What is the neonatal line?
A line that forms within dentine and enamel at birth (disruption causing exaggerated striae of retzius)
62
What is different between prisms?
The angles of hydroxyapatite crystals only
63
What happens to ameloblasts during the transition stage?
Shorten (become less columnar) and 50% die
64
During maturation stage which forms do ameloblasts switch between?
"ruffle ended" borer (moves ions in) and "smooth ended" border (removing degrade proteins and water)
n.b. switches approx 7 times during maturation stage
65
What is the dentine matrix composed of?
Collagens (type 1), proteoglycans, glycoproteins (e.g. dentine sialoproteins), phosphoprotein (dentine phosphoprotein DPP)
66
What happens if we dont have dentine phosphoprotein (DPP)?
We dont get accurate dentinogenesis occuring
67
What is mantle dentine?
The first dentine laid down (in crown of tooth), has a different structure and compsotiiton to bulk of the matrix (type 1 collagen fibres laid down at right angles to future ADJ)
68
What is circumpulpal dentine?
The majority of the dentine, laid down in a regular incremental pattern with collagen fibres parallel to dentine-pulp border
69
What is pre-dentine layer?
Non mineralised layer = adjacent to pulp
70
What is intertubular dentine?
Between he tubules, all the dentine laid down initially
71
What is intratubular dentine?
Begins almost immediately and is continuous with intertubular dentine but different composition (other plasma proteins mineralised), physiological (happens with age) = translucent dentine
72
What is translucent dentine?
When the tubule is occluded (can be used to age teeth)
73
When is tertiary dentine laid down?
In response to injury
74
When does root formation begin?
Once tooth starts to erupt
75
Which interactions are involved in root formation?
Dental follicle, hertwigs epithelial root sheath and dental papilla/pulp
76
What is the role of hertwigs epithelial root sheath (HERS)?
To map out the root shape and induces odontoblasts (dentine formation), then breaks foes allowqing contact with dental follicle cells = cementogenesis
77
What is hertwigs epithelial root sheath (HERS) developed from?
Layers of inner and outer enamel epithelium from the cervical loop
78
What are the remnants of hertwigs epithelial root sheath (HERS) called? and what can they cause?
Rests of mallassez = potential to develop into cysts or tumours at a later stage
79
What is the consequence of having a stellate reticulum or stratum intermedium in the root (n.b. we normally don't!)?
Forms enamel pearls = spherical mineralised spheres with no clinical significance but if become exposed i.e. due to recession can be difficult for pt. to keep clean
80
What is acellular cementum?
Contains the collagen fibres from the principle bundles of the PDL and embeds them in the cementum
81
What is the granular layer of tomes?
A layer of dark granules in root dentine = transverse sections of highly coiled dentinal tubules
82
What is the hyaline layer?
A hybrid layer between cementum and granular layer of tomes = layer of dentine/cementum/intermingled layer of both (not mineralised immediately, waits until cementum laid down = type 1 collagen of cementum is intermingled = bonds to cementum to dentine)
83
What is secondary dentine?
Dentine formed after root formation is complete (slows down and slight change of direction but continuous with primary tubules)
= physiological and age related
84
What is tertiary dentine?
Dentine laid down in response to injury (inc. dental caries)
85
What are the two structures of tertiary dentine?
Reactionary dentine (for mild stimulus) and reparative dentine (for strong stimulus)
86
What is the structure of reparative dentine?
Tubular, laid down by new odontoblasts served from pulpal stem cells
87
What determines the length of a tooth root?
Genetics
88
When does cementogenesis occur in comparison to dentinogenesis in the root?
Simultaneous
89
When does cementinogenesis of the root start?
When HERS breaks down
90
What is acellular cementum?
Thin layer immediately adjacent to dentine of root (laid down slower so cementoblast not trapped and become cementocytes)
91
What is cellular cementum?
Found apically and inter-raddicular areas (laid down faster = embedded cementoblasts and incremental lines of salter farther apart ), thought it could cause the extra eruption to maintain occlusion after tooth loss but doesn't explain why its present between the roots
92
What is acellular extrinsic fibre cementum?
Contains no cementocytes and contains extrinsic fibres (collage from the PDL = continuity)
93
What is cellular intrinsic fibre cementum?
Contains cementocytes and contains collagen fibres derived from cementoblasts, has a precementum layer
94
What are the different congenital abnormalities of teeth?
- disturbance of epithelial-mesenchymal interactions
- splitting/joining of tooth germs
- trauma/infection of deciduous tooth causing malformations in permanent tooth (turner tooth)
- Variations in number/size/shape of tooth crown and or roots (e.g. root dilacerations -> bends in root forming)
- Odontoma formation
95
What is germination?
Splitting of a tooth germ
96
What is fusion?
Joining of two tooth germs
97
What are the two types of odontoma (benign tumour) formation?
Compound - made up of lots of little tiny teeth;
| Complex - mineralised tissues you get within teeth but no real tooth like structure
