Chapter 8 B: Teeth Embryological Development Flashcards
Pathologies in the dental organ are caused by?
Disorders in the odontogenesis
What are the characteristics of odontogenesis that differeinate it from other organs?
- its a very long and dynamic process
Very long process:
Because it ranges from earlier development embryonic stadiums to practically adolescence
Dynamic process:
It requires complex interactions between structures in development, constant interaction with the environment, the process is then very sensitive to embryological aggressions, manifesting itself in different pathologies
The stomodeum is
- the development of the primitive cranium and the oronasal cavity
- the primitive oral pit or stomodeum is the invagination of the surface epithelium positioned anteriorly between the forebrain and the adjacent centrally developing heart
During the 3rd prenatal week, the deep end of the oral pit is lined with ____, which is in close contact with the ____ of the foregut
Ectoderm, endoderm
The area of contact between the two epithelia (ecto and endoderm) is called
Oropharyngeal membrane
The Oropharyngeal membrane then disintegrates to create an?
Anterior external opening of the gastrointestinal tract in the 4th week of life
The ectoderm is?
The outermost layer of the embryo
Mesoderm is?
Intermediate, is one of the three cell layers constituting the embryo
The endoderm is?
The inner tissue layer of the three layers in which divides the tissues of the embryo
When does the face develop? and from what?
During the fifth to seventh week of uterine life , from four primordia that surround a central depression (the primitive oral pit) and develop different parts of our face
The facial primordia are?
- frontal process
- maxillary process
- mandibular arch or prominence
The frontal process is ?
A single process located above the oral pit
The maxillary processes are?
2, located lateral to the oral pit
The mandibular arch or prominence is?
Located below the oral pit
Where do the two maxillary processes arise from?
The first pharyngeal arch
The mandibular process gives rise to?
The mandible, the lower part of the face, and the body of the tongue
The upper face arises from the ?
Frontal process
The two maxillary processes will form the ?
Cheeks and most of the upper lip
The 20 primary and 32 permanent teeth develop from the interaction of?
The oral epithelial cells and the mesenchyme
What are the 3 stages of tooth development ?
Bud, cap, bell
The oral epithelial cells come from?
Enamel organ
EPC EO
The mesenchyme cells come from?
Dental papilla
MC DP
Enamel develops from the ?
Enamel organ
OPC E EO
Dentin develops from the?
Dental papilla
MC D DP
What other cells other than the oral epithelial cells and the mesenchymal cells contribute to the tooth development?
Neural crest cells
What is the first sign of tooth formation ?
The development of dental lamina rising from the oral epithelium
After primary teeth develop from the buds, the leading edge of the lamina continues to grow to develo the permanent teeth, this part of the lamina is called?
Successional lamina
How many of the permanent teeth replaces the 20 primary teeth ? and how many molars develop behind the primary dentition ?
20
12
What are the last teeth to develop and when do they develop?
Third molars, 15 years after birth
Which teeth do not succeed primary teeth?
Molars
What do the molars form from (the general/successional lamina)?
The general lamina
What forms the general and the successional lamina?
The initiating dental lamina, and it begins to function in the 6th prenatal week and continues to function until the fifteenth year, producing all 52 teeth
The bud stage?
- rounded, localised growth of epithelial cells surrounded by proliferating mesenchymal cells
The cap stage ?
As the rounded epithelial bud enlarges, it gains a concave surface, 11th week
The epithelial cells become the enamel organ
The mesenchyme cells the dental papilla which becomes the dental pulp
The tissue sounding these 2 structures is the dental follicle
The bell stage?
The tooth reaches morphodifferentiation and histodifferentiation , 14th week
The inner enamel epithelial cells are characterised by the shape of the tooth they form
The cells of the enamel organ have differentiated into the outer enamel epithelial cells (which cover the enamel organ) and the inner enamel epithelial cells (which becomes the ameloblasts that form the enamel of the tooth
And there’s the Stellate reticulum and stratum intermedium cells
Cells in the periphery of the dental papilla become odontoblasts (they differeinate from mesenchymal cell), the odontoblasts form predentin then after 24 hours dentin
After enamel organ is differentiated the dental lamina begins to degenerate by lysis
Where do the stratum intermedium cells lie and what is their function?
Adjacent to the IEE
Assist the ameloblasts in the formation of enamel
What is the function of the OEE?
To organise a network of capillaries that will provide the ameloblasts with nutrition
Which process happens first, amelogenesis or dentinogenesis?
Dentinogenesis
The dental papilla then forms into the ?
Dental pulp
As the odontoblasts move pulpward, the cell process known as? Elongates
Odontoblast process
The dentinal matrix is first a mesh work of collagen fibers then within 24 hours it?
Calcifies
Before calcification: pre dentin
After: dentin
Where do the odontoblasts maintain their elongating processes?
In the dentinal tubules
Where is the site of initial formation?
Cusp tips
What are the 2 phases of dentinogenesis?
Predentin and dentin
Dentinogenesis steps?
Collagen matrix formation then the deposition of calcium phosphate crystals in the matrix
The initial calcification appears as ___ then they coalesce until the matrix is?
Crystals, calcified
What is the only part that is uncalcified?
The newly formed band of dentinal matrix along the pulpal border
When do ameloblasts begin enamel deposition?
After a few micrometers of dentin have been deposited at the DEJ
When do the cells of the IEE differntiate ?
Bell stage , they elongate and are ready to be active secretory ameloblasts
The 5 functional stages are?
- Morphogenesis
- Organisation and differentiation
- Secretion
- Maturation
- Protection
What are the short conical processes that develop at the apical end of the ameloblasts during the secretory stage?
Tome’s processes
What are the junctional complexes that appear at the junction of the cell bodies and tome’s processes and maintain contact between adjacent cells?
Terminal bar apparatus
What establishes the DEJ?
The fist enamel deposited on the surface of dentin
Does the center of the rod form at the same time as the rod walls?
No, causes an indent
What happens when ameloblasts begin secretion?
The overlying cells of the stratum intermedium change in shape from spindle to pyramidal
What holds the ameloblasts and the stratum intermedium together?
Desmosomes
What do the substance needed for enamel production that arrive via blood vessels pass through ?
Stellate reticulum, to the stratum intermedium and ameloblasts
Which produces the protein Amelogenin
The initial deposition of mineral amounts to ___% of the total enamel
25
The other 70% is due to a growth of the crystal
5% of enamel is water
Which is the first enamel mineralised?
The first matrix deposited
Matrix formation and mineralisation continue
Peripherally to the tips of the cusps
Laterally to the side of the crowns
What is the last region of the crown to mineralise?
The cervical region , during this process, protein of the enamel changes or matures and is termed enamel
The mineral content of enamel is?
Dentin?
95
69
What is the most highly calcified tissue in the human body?
Enamel
Because of the high mineral content of enamel?
Almost all water and organic materials are lost during maturation
Does mineralisation of the enamel continue after teeth eruption?
Yes
What happens after the ameloblasts have completed their contributions to the mineralisation phase?
They secrete an organic cuticle on the surface of the enamel (developmental or primary cuticle)
How do the ameloblasts attach themselves to the primary cuticle?
Hemidesmosomes
Difference between desmosomes and hemidesmosomes ?
Desmosomes: attaching a cell to an adjacent cell
Hemidesmosomes: attaching a cell to a surface membrane
The hemidesmosomes attachment plaque is developed by the ameloblast and this stage of plaque formation and attachment is known as?
Protective stage of ameloblast function
The reduced enamel epithelium is formed by?
The ameloblasts shorten and contact the stratum intermedium and other enamel epithelium
Where do the IEE and OEE join to form the root sheath?
Cervical region or base of enamel organ
When the crown is completed, cells in this region of the enamel organ continue to grow, forming a double layer of cells called?
Epithelial root sheath or Hertwig’s root sheath
The inner layer of the root sheath forms from?
The IEE or ameloblasts
In the root, these cells induce odontoblasts of the dental papilla to differntiate and form?
Dentin
Where does the root sheath originate?
At the point that enamel deposits end
The length , curvature, thickness, and the number of roots depend on?
The inner root sheath cells
As the formation of root dentin takes place, cells of the outer root sheath function in?
Deposition of intermediate cementum
Intermediate cementum?
A thin layer of acellular cementum that covers the end of dentinal tubules and seals the root surface
Then the outer root sheath cells disperse into small clusters and move away from the root surface and are called?
Epithelial rests
At the proliferating end, the root sheath bends at a 45 degree angle , this area is called?
Epithelial diaphragm
What does the epithelial diaphragm encircle?
The apical opening of the dental pulp during root development
Pulp proliferation zone is ?
In pulp adjacent to the epithelial diaphragm , cellular proliferation occurs
The root thickness until the apical opening is restricted to?
1-3mm which is enough to allow neural and vascular communication between the pulp and the periodontium
Cementoid is?
Non calcified cementum that soon calcifies into mature cementum
Which set of teeth require less time to develop?
Primary
When do permanent teeth begin formation ?
At or after birth
Primary teeth function in the mouth for ?
8.5 years
These 8.5 years can be divided into 3 periods:
- Crown development and root development: 1 year
- Root maturation and root resorption: 3.75 years
- Shedding of teeth: 3.5 years
The movements related to coach eruption begin during crown formation and require adjustments relative to the forming of bony crypt, this is what phase?
Preeruptive phase
Tooth eruption is also involved in the initiation of root development and continues until the tooth’s emergence into the oral cavity, and the teeth continue to erupt until they reach incisal or occlusal contact, this is which phase?
Pre functional eruptive phase
Then they develop functional eruptive movements, which include compensation for jaw growth and occlusal wear of the enamel, this is which phase?
Functional eruptive phase
So the 3 phases of teeth eruption are?
- pre eruptive phase
- pre funcional eruptive phase
- functional eruptive phase
Pre eruptive phase:
- includes all the movements of the primary and permanent tooth crowns
- phase is finished with early initiation of root formation
- the developing crowns move constantly
- the permanent anterior teeth begin developing lingual to the insical level of the primary teeth
- then as the primary teeth erupt, the permanent successors are positioned lingual to the apical third of their roots
- except molars that have no primary predecessors
Pre functional eruptive phase:
- starts with initiation of root formation and ends when the teeth reach occlusal contact
4 major events occur in this phase: root formation, movement, penetration, intraoral occlusal or incisal movement
Root formation:
- first step is proliferation of the epithelial root sheath
Inc in fibrous tissue
Movement:
Inicisally or occlusally through bony crypt of the jaws to reach oral mucosa
REE fuses with oral epithelium
Penetration :
Only the organic developmental cubical covers the enamel
Intraoral occlusal or incisal movement
Erupting tooth continues until clinical contact
Increasing apical shift of the gingival attachment
Possible cause of tooth eruption?
-most frequent? Root growth, and pulpal pressure
- other causes: cell proliferation, increased vascularity, increased bone formation around teeth
- endocrine influence, vascular changes,enzymatic degradation
- most important ones: elongation of the root, modification of the alveolar bone and periodontal ligament
6/4 rule?
For every 6 months of age, 4 teeth erupt
6,4
12,8
18, 12
24, 16
30,20
Appearance in the oral cavity of primary teeth?
MONTHS
LCI 6-8
UCI 7-10
ULI 8-11
LLI 8-13
UFM 12-15
LFM 12-16
UC 16-19
LC 17-20
LSM 20-26
USM 25-28
Appearance in oral cavity of permanent teeth?
YEARS
LFM 6-7
UFM 6-7
LCI 6-7
UCI 7-8
LLI 7-8
ULI 8-9
LC 9-10
UFPM 10-11
LFPM 10-11
USPM 10-12
LSPM 11-12
UC 11-12
LSM 11-12
USM 12-13
LTM 17-20
UTM 18-20
