Histological Development of Teeth Flashcards
Define odontogenesis
Tooth development
When does odontogenesis of primary dentition form?
Embryonic and fetal period
When does odontogenesis of permanent teeth form?
During the fetal period
What does the inner enamel epithelium (IEE) eventually differentiate into?
Ameloblasts
What makes enamel?
Ameloblasts
What makes dentin?
Odontoblasts
Where do odontoblasts differentiate from?
Outer cells of the dental papilla
When do odontoblasts begin dentinogenesis?
When repolarization occurs away from the basement membrane
Outer cells of the dental papilla are induced by __________ to differentiate into _____________
pre-ameloblasts / odontoblasts
What is dentinogenesis?
Apposition of predentin
Why is dentin thicker than enamel?
Because odontoblasts begin production awhile before amelogenesis occurs
During which stage of tooth development do the odontoblasts begin laying down dentin matrix?
Apposition
What are the 6 stages of odontogenesis and when do they occur?
- Initiation/dental lamina stage (6-7 weeks)
- Bud stage (8th week)
- Cap stage (9th-10th week)
- Bell stage (11-12 week)
- Apposition stage (varies)
- Maturation stage (varies)
What tissue arises from the ectoderm?
Enamel (and epithelial tissue)
Dental sac cells eventually become what?
Cementoblasts
When does cementogenesis occur and what is the first thing that happens?
When HERS disintegrates and the cementoblasts move to cover root dentin they lay down cementum matrix
What is the cementum matrix called?
Cementoid
What happens to cementoblasts that become trapped in the cementoid?
They become cementocytes
What happens when cementoid becomes calcified?
Differentiates into cementum which differentiates into the DCJ
What does the dental sac eventually produce?
The peridontium: PDL (fibroblasts), Cementum (cementoblasts), and alveolar bone or lamina dura (osteoblasts)
What does REE stand for and how does it form?
Reduced Enamel Epithelium. It forms when the layers of the enamel organ are compressed
What does the REE first fuse to?
The oral epithelium
When can the tooth begin to erupt?
As the formation of REE occurs
Explain the process of teething eruption?
The enzymes from the REE disintegrate the fused tissue, forming an epithelial tunnel which gives a path of eruption
Why might newly erupted teeth have extrinsic stain?
The presence of Nasmyth’s Membrane, which is the residue of fused REE and oral epithelium
What does HERS stand for?
Hertwig’s Epithelial Root Sheath
What is the function of HERS?
Shape the root/s and induce dentin formation (odontogenesis) in the root area
True or False: HERS contains stellate reticulum and stratum intermedium
False; HERS lacks these, which is why it induces odontogenesis
What happens when dentin formation is completed?
The basement membrane and HERS disintegrates; these cells may become epithelial rests of malassez
What can epithelial rests of malassez form?
Cysts
Simply explain what happens during the apposition stage
Enamel, dentin, and cementum are secreted in successive layers.
How are the tissues originally secreted in the apposition stage?
Secreted as gel-like matrix that is later calcified with calcium hydroxyapatite to harden
Where do all teeth develop from?
THE ECTODERM AND MESENCHYME***
The tooth germ is comprised of what?
The enamel organ, the dental papilla, and the dental sac
The dental papilla will produce the future _______ and _______ tissue
dentin and pulp
What gives rise to the oral epithelium? (OE)
The ectoderm
What is the site of origin of initiation of permanent teeth?
Successional dental lamina
In the dental lamina/initiation stage, what is formed when the oral epithelium grows deeper into the ectomesenchyme?
The dental lamina
Which dentition corresponds with the dental lamina?
Primary dentition
What is the stellate reticulum?
Star-shaped cells in many layers providing nutrition and help support the production of enamel
What happens to stellate reticulum and stratum intermedium after enamel is formed?
They are lost
What is stratum intermedium?
Compressed layer of flat to cuboidal cells providing nutrition and help support the production of enamel
In the bell stage, what are the 4 cells within the enamel organ?
Inner enamel epithelium (IEE)
Outer enamel epithelium (OEE)
Stellate reticulum
Stratum intermedium
In the apposition stage, what happens to the IEE as they differentiate into ______________?
They elongate and become columnar / pre-ameloblasts
What is the cervical loop, what does it consist of, and where is it?
The most cervical portion of the enamel organ that consists of IEE and OEE only. In the CEJ area (root development)
What is responsible for root development?
Cervical loop which also forms HERS
What is the function of the OEE?
A protective barrier for the rest of the enamel organ during enamel production
What is the Tomes’ process?
The tip of the ameloblast where enamel matrix squirts out
Where does amelogenesis start?
At cusp tips and moves cervically
___________ always forms AFTER ________ starts
Amelogenesis / dentin
What does the mesoderm form?
Mesenchyme, which becomes CT for all tooth components except enamel, skeletal, and muscular)
What does the mesenchyme form?
Cementum, dentin, pulp***
Where do neural crest cells originate from?
Neuroectoderm, then migrate into mesenchyme (mesenchyme is in the mesoderm) –> gives rise to dental tissues
In the dental lamina/initiation stage, what influences the ectomesenchyme?
Neural crest cells that have migrated to the area
Explain the bud stage
Large amounts of growth of the dental lamina into buds that will form each tooth germ.
The BM remains between bud and estomesenchyme
Explain the cap stage (simply)
Unequal growth in different parts of the tooth bud.
In the cap stage, what depression develops in the dental lamina of each tooth bud?
The enamel organ
In the cap stage, what is the area of ectomesenchyme in the concavity of the enamel organ?
The dental papilla
In the cap stage, the remaining ectomesenchyme around the outside of the enamel organ is what?
The dental sac/follicle
Mesenchyme = _________
Mesoderm
What are the two cell types in the dental papilla?
Outer cells and central/inner cells
What do the inner/central cells of the dental papilla become?
The pulp
What do the outer cells of the dental papilla become?
Odontoblasts (Dentin)
What is repolarization and when does it happen?
The nucleus moving away from the basement membrane / apposition (preameloblasts)
What happens when preameloblasts come into contact with predentin?
This induces them to change into ameloblasts
In the apposition stage, what does the disintegrating BM mineralize into?
The DEJ
What happens in the maturation stage?
The matrix layers becomes calcified. This process takes years (into the teens)
When does root formation begin?
After the crown is completely shaped and beginning to erupt
How is HERS formed?
The cervical loop grows deep into the ectomesenchyme of the dental sac, moving away from the newly completed crown area to enclose more of the dental papilla which becomes HERS
What is anadontia and when is the stage of misfire?
Single or multiple teeth missing.
Initiation/dental lamina stage
What are supernumerary teeth and when is the stage of misfire?
Extra teeth.
Initiation/dental lamina stage
What is micro/macrodontia and when is the stage of misfire?
Abnormally small/large teeth.
Bud stage
What are dens in dente and when is the stage of misfire?
Enamel organ invaginates into dental papilla.
Cap stage.
What is gemination and when is the stage of misfire?
Tooth germ tries to divide.
Cap stage.
What is fusion and when is the stage of misfire?
Union of two adjacent tooth buds.
Cap stage
What is a tubercle and when is the stage of misfire?
Extra cusp due to effects on enamel organ.
Cap stage
What is an enamel pearl and when is the stage of misfire?
Extra enamel on root.
Apposition and maturation
What is enamel dysplasia and when is the stage of misfire?
Faulty development of enamel from interference involving ameloblasts.
Apposition and maturation
What is concrescence and when is the stage of misfire?
Union of root structure of 2 or more teeth by cementum.
Apposition and maturation
What is amelogenesis imperfecta?
type of enamel dysplasia; hereditary etiology; very thin enamel that chips easily or no enamel at all
What is dentin dysplasia?
faulty development of dentin (less common than enamel dysplasia)
What is dentinogenesis imperfecta?
hereditary basis; results in blue-gray or brown teeth with an opalescent sheen; enamel is normal, but chips due to lack of support from dentin
What do the central cells do while cementoid becomes calcified?
They form the pulp
