2 - Evolution and Development of Teeth Flashcards
What are the 4 layers that make up a tooth?
1) Enamel
2) Dentine
3) Dental pulp
4) Cementum
What is contained within the pulp chamber?
Dental pulp
Blood vessels
Nerves
Where do vessels and nerves enter / leave the tooth?
Apical foramina
What forms the wall of the pulp chamber?
Dentine
What two components make up the dentine structure?
1) Collagen
2) Calcium hydroxyapatite
What % are both components of dentine present in?
Collagen = 25%
Ca-Hydroxyapatite = 75%
What is the function of collagen in dentine?
Strength in tension
What is the function of calcium hydroxyapatite in dentine?
Strength in compression
What are the two regions for every erupted tooth?
1) Crown (above gingiva)
2) Root (below gingiva)
Where does the root of the tooth sit?
In the alveolus
What is the outer-most layer of the root region of a tooth?
Cementum
What is the outer-most layer of the crown region of a tooth?
Enamel
The composition of cementum is like which other tooth layer?
Dentine
i.e. 75-80% mineralised
What is the composition of enamel?
99% mineralised.
very brittle
Tooth development occurs from which developmental origins?
1) Ectoderm
2) Neural crest tissue
3) Mesoderm
What cell produces dentine and where is it found?
Odontoblasts
In the pulp chamber
What cell produces enamel?
Ameloblasts
Where do odontoblasts and ameloblasts initially meet?
Enamel-dentine junction (EDJ)
What happens to ameloblasts before tooth eruption?
They disappear.
What cell produces cementum?
Cementoblasts
How many stages are there to tooth development?
6
What are the names of tooth development stages from early to late?
1) Placode stage
2) Bud stage
3) Cap stage
4) Bell stage
5) Crown stage
6) Eruption
The jaw is formed from what embryological structure?
First pharyngeal arch
The lower jaw arises from what structure within the first pharyngeal arch?
Mandibular prominence
The upper is formed from two developmental parts. Firstly, how are these split?
Mesially (4 incisors)
Distally (canine-> m3)
The mesial section of the upper jaw arises from what prominence?
Frontonasal prominence
The distal section of the upper jaw arises from which prominence?
Maxillary prominence
Teeth form as a result of the interaction between which two developmental layers?
1) Dental lamina (neural crest)
2) Mesenchyme
Which developmental layer invades the other, to form U shaped arches for each tooth?
Dental lamina invades the mesenchyme
In the bud stage, which developmental tissue is responsible for expressing signals?
Dental lamina
Signals from the dental lamina result in the expression / inhibition of what transcription factor within the mesenchyme?
Pax-9
Pax-9 is expressed and inhibited in various areas. What structures result from these differences?
Pax-9 expression:
- Tooth development
Pax-9 inhibition:
- Gaps between teeth
Where pax-9 is not expressed, another protein is expressed - what is it?
Bone morphogenic proteins (BMPs)
In the bud stage, what layer forms between the dental lamina and the mesenchyme?
Enamel epithelium
What two structures form the enamel organ?
Enamel epithelium
Dental lamina
Within the cap stage, the horizontal side of the enamel epithelium is the site of which cell? To form what structure?
Ameloblasts
Forming enamel.
What structure is responsible for forming a tooth’s cusp?
Enamel knots.
At the cap stage, what tissue becomes the primary signalling centre?
Mesenchyme
What studies have shown the mesenchyme to be the primary signalling centre?
Transplant studies of mesenchyme.
The mesenchyme can be described as what at the cap stage?
Dental papilla
What cells does the dental papilla give rise to? What tissue do they go on to make?
Odontoblasts
Make dentine.
Enamel knots begin acting as signalling centres at the bell stage. What factors are produced WITHIN the knot to stimulate what change?
Fibroblast growth factors (FGFs).
Stimulates growth and division.
What factor is expressed around the knot and inhibits growth?
BMP-4
Tooth and jaw growth involves epigenetic interactions between which two structures?
Alveolar bone
Tooth roots
What effect do tooth roots have on alveolar bone?
Stimulate alveolar ossification.
What 2 phenotypes occur in MSx-1 k/o mice?
What paper?
Normal mandibles
No teeth + no alveolar processes (= undeveloped alveolar bone)
(Satokata and Maas, 1994)
In senescence, tooth loss has what effect on the jaw?
Reduced demand for alveolar bone to buttress teeth, as a result of lower strain on the jaw, particularly at muscle attachment sites.
ALVEOLAR BONE resorption occurs.
Why is alveolar bone resorption particularly bad for ageing individuals?
Coupled with osteoporosis, much more likely to fracture.
In evolutionary terms, where did teeth most likely arise from?
Dermal denticles
What evidence supports this, in the context of developmental layers?
Both dermal denticles and teeth arise from ectoderm/mesoderm/neural crest contributions.
DON’T contain endoderm.
Why might endoderm be thought to be involved in teeth? Contributing to the confirmation that teeth arose from dermal denticles?
Oral cavity is a structure that is derived from the bucco-pharyngeal membrane, which degenerates early in development.
Therefore part of GI tract.
GI tract is lined by endoderm.
What are the 2 hypotheses for teeth and denticle relationship?
Outside-in hypothesis
Inside-out hypothesis
What are the 3 reasons for why the outside-in hypothesis is more likely?
1) Endoderm labelling shows NO contribution from ENDODERM in mice.
2) Fossil developmental stages support tooth/dermal denticle homology.
3) Fossil basal gnathostomes show dermal denticles are modified as they approach the oral cavity.
What are the 3 specialisations of mammalian dentition?
1) Mastication - specific to mammals
2) Differentiated dentition (of which there are 4 types)
3) Delayed eruption
4) Fewer sets of teeth
What is different about molars in regards to deciduous / adult teeth?
Humans ONLY have adult molars - no deciduous versons.
Define: monophyodont
Give an example
One set of teeth
e.g. Marsupialia
Define: diphyodont
Give an example
Two sets of teeth
e.g. humans
Define: polyphyodont
Given an example
Multiple sets of teeth
e.g. Reptilia
What occurs to the dental lamina in diphydonts that doesn’t occur in polyphyodonts?
Dental lamina fragments and regresses following formation of permanent dentition.
(maintained throughout life in polyphyodonts)
What two features characterise the typical mammalian growth pattern?
Rapid juvenile growth
Growth cessation at maturity
What does the typical mammalian growth pattern allow for?
Diphyodonty
How do we get around the disadvantages of diphyodonty in early stages of life?
Ability to suckle - reduces teeth exposure time, so more likely to stay around for longer.
What structure attaches the cementum to the alveolar bone in human adults?
Periodontal ligaments
(extra reading)
Name 3 important signalling genes?
FGF8
BMP4
Shh
(extra reading)
What is the role of FGF8 in tooth development?
(K/O studies)
(author?)
K/O resulting in large defects in proximal structures derived from 1st pharyngeal arch = teeth, jaws, lateral skull wall, middle ear, part of tongue.
(Trumpp et al., 1999)
(extra reading)
What is the role of BMP4 in tooth development?
(Author?)
BMP4 antagonises FGFs - where it is expressed, it inhibits FGFs and thus determines tooth location.
(Neubeuser, 1997)
(extra reading)
What are the 2 roles of Shh in tooth development?
What has been shown in tooth development from K/O studies?
(author?)
Important in crown formation + bud stage of tooth development.
K/O shows deficits in tooth size, morphology and organisation of matrix cells.
(Cho et al., 2011)
