Odontogenesis Flashcards
At what week does the stomodeum form? What is it derived from?
Begins at week six. Derived from ectoderm, lined with epithelium
What do dental placodes give rise to?
Tooth buds/enamel organs
What does the basement membrane separate? What does it give rise to?
Separates dental lamina and ectomesenchyme
Gives rise to the future Dentinoenamel Junction
What is embryonic connective tissue? What does it surround and give rise to?
Ectomesenchymal tissue
Surrounds the dental lamina in each arch and gives rise to Dental papilla (dentin/pulp) and the dental follicle (cementum/PDL/alveolar bone)
Where does the dental Papilla form?
Inside the enamel organ concavity
Where does the dental follicle form?
Around the enamel organ
When does tooth formation occur?
Weeks 6/7
What two types of tissue interact during the initiation stage of tooth formation?
Epithelial tissues and ectomesenchyme tissues
When does the bud stage take place? What is it surrounded by?
Week eight
Buds are surrounded by ectomesenchyme
When is the cap Stage? And what is formed during the cap stage?
Occurs weeks 9 to 10
Proliferation of epithelial cells form the tooth germ
What is the enamel organ? What are the two types of epithelium?
Ectodermal tissue that gives rise to tooth enamel
Outer enamel epithelium (OEE, convex) and inner enamel epithelium (IEE, concave)
What is the enamel knot? What is it composed of?
Mass of stellate reticulum cells
Signal center for cusp formation during the bell stage
Composed of an enamel cord and an enamel navel
What is the enamel cord?
String of cells running from enamel knot to the outer enamel epithelium at the enamel navel
What is the enamel navel?
Surface depression in outer enamel epithelium where the cord attaches
What is the cervical loop?
Inferior circumference of the junction of OEE and IEE and gives rise to the cervix of the tooth: future CEJ
What do the dental Papilla give rise to?
Dentin and Pulp
What does the dental follicle give rise to? What does it surround?
Gives rise to cementum, PDL and alveolar bone.
Membranous sac that forms around the enamel organ and dental Papilla
What does vestibular lamina form?
Forms the oral vestibule
When does the bell stage occur? What happens here?
Occurs during weeks 11 and 12
Morphodifferentiation and Histodifferentiation occur
The dental Papilla/Ectomesenchyme instructs the enamel Organ in how to change
What is morphodifferentiation?
Tooth shape change from cap to bell to tooth
Enamel knot signals cusp formation- cells atrophy in incisors
What is Histodifferentiation? Where does it primarily occur?
Cellular changes that occur primarily in the enamel organ
OEE changes from squamous to low cuboidal
What is stellate reticulum?
Core cells
Push apart OEE and IEE and helps form cap shape
What is stratum intermedium (SI)?
New flat layer of cells appear/form between the SR and IEE
What happens to IEE during histodifferentiation?
Cells change from squamous to tall columnar
IEE cells form pre-Ameloblasts that will give rise to enamel
What happens to the dental papilla during the bell stage?
 outer cells form preodontoblasts that will give rise to Dentin
Central cells will form the pulp
What happens to the dental follicle during the bell stage?
Forms a membrane around the entire tooth germ
Follicle will become encapsulated by bone and become either the maxilla or mandible
What happens to Dental lamina during the bell stage?
Starts to disintegrate and forms epithelial cell rests called cell rests of Serres
These proliferate posteriorly and give rise to the lamina of the permanent nonsuccedaneous molars
What happens to the stellate reticulum during the apposition stage?
It collapses
Which dental tissue forms first?
Dentin. Once Dentin forms then enamel can form
How are odontoblasts formed?
Pre-odontoblast attach to the basement membrane
What do the odontoblast do during the apposition stage?
Lay down the first layer of Dentin matrix (formed by collagen) and begin dentinogenesis
What is the first layer of formed Dentin called
Mantle Dentin
When do Ameloblasts form? What do they compose And what is it called?
After the mantle Dentin forms
Forms the first layer of enamel matrix and begins Amelogenesis
This first layer is called aprismatic enamel
What is aprismatic enamel?
First layer of formed enamel
Forms in response to dentin formation
What does the basement membrane get renamed as during the apposition stage?
Membrane performative
Disintegrates after attachment of odontoblasts and Ameloblasts
What forms the dentinoenamel junction?
Mantle Dentin and aprismatic enamel
What happens to the dental papilla during the apposition stage?
Form the dental pulp and become innervated with sensory nerves
What happens to ameloblasts after enamel is formed?
The Ameloblasts die. This is why teeth cannot repair themselves
What is dentinogenesis?
Dentin formation
During what stage does dentinogenesis occur?
Apposition stage
Where is mantle Dentin found? What is it formed by?
Found in Coronal and radicular Dentin
Formed by odontoblast and is the layer closest to the DEJ & DCJ
What are Korff’s fibers? What type of Dentin are they found in?
Bushy collagen fibers, only found at the DEJ. Perpendicular to DEJ and Crown and parallel when in the root 
Only in mantle Dentin between the odontoblast
What is the Dentin matrix formed by?
Odontoblasts
Collagen fibers formed around (peritubular dentin) and between (intertubular) the odontoblastic processes
Where is Circumpulpal Dentin found?
In Coronal and ridicular Dentin
 no Korff’s fibers, forms all remaining Dentin and the bulk of the tooth
What is housed in Dentin tubules?
Odontoblast and processes in formed Dentin. Peritubular dentin forms the tubul. and intertubular Dentin forms between the Dentin tubules
How is calcium hydroxyapatite formed?
When calcium salts crystallize during the mineralization process
Where does calcium hydroxyapatite crystallization occur?
At matrix vessels when they rupture and release the calcium hydroxyapatite in the Dentin matrix
What aids in mineralization?
Odontoblast producing mineralizing proteins like phospholipids and Phosphophoryn
What percentage is Dentin mineralized?
65 to 70%
What is mantle Dentin?
First Dentin formed
Closest to the DEJ & DCJ
Mantle Dentin always next to Junction with Enamel
What is Circumpulpal Dentin?
All remaining Dentin right up to the pulp
What is peritubular Dentin?
Forms Dentin tubules, highly calcified
What causes Dentin sensitivity?
Dentin is perforated and has channels. When recession occurs this portion is exposed and sensitivity can occur
What is inter-tubular Dentin?
Forms between the tubules, a little less calcified
What is pre-Dentin?
Newest formed, non-mineralized Dentin matrix. Closest to the pulp
Made from collagen
What is coronal Dentin?
Dentin of the crown, forms before ridicular Dentin and contains the DEJ
What is radicular Dentin?
Dentin of the root, last to form after coronal and contains the DCJ
What is amelogenesis?
Enamel formation
What is Tome’s process?
Very end of the ameloblast, creates a rod space
What is the enamel matrix?
Formed by ameloblasts
Step 1: ameloblasts retreat, Tome’s process creates rod space/substance
Step 2: rod space back-filled with more matrix forming rod segment
What are rod segments? What are they created by?
Increments of formed enamel matrix
Created by 4 separate ameloblasts
What are enamel rods/enamel prism?
Formed by rod segments
Stacked on one another, very specific keyhole shape
What is inter-rod substance?
Secreted by ameloblasts and found between enamel rods
What is the rod sheath?
Organic material between rods and rod substance
What percentage is enamel mineralized after the 2nd stage?
96% mineralized. Only 4% matrix left
What is the source of calcium hydroxyapatite?
Mantle dentin and stratum intermedium
When does termination of amelogenesis occur?
When reduced enamel epithelium forms
What is reduced enamel epithelium?
Cellular sheath that forms on formed enamel
Consists of 4 layers
What are the 4 layers of reduced enamel epithelium?
Post ameloblasts
Stratum intermedium
Remnants of stellate reticulum
Outer enamel epithelium
How are post ameloblasts formed?
Ameloblasts change from tall columnar to low cuboidal
No longer produce enamel matrix
What happens to stratum intermedium, remnants of stellate reticulum and outer enamel epithelium During termination of amelogenesis?
None histodifferentiate
Some remnants of stellate reticulum may be left over
Stratum intermedium and outer enamel epithelium remain in the same sheath
What is another word for the primary enamel cuticle?
Nasmyth’s Membrane
What is the primary enamel cuticle?
Protective covering located between reduced enamel epithelium and formed enamel
Wears away after the tooth erupts
What forms after the primary enamel cuticle wears away?
Secondary enamel cuticle/pellicle
What is the function of reduced enamel epithelium?
Protects the underlying enamel
Participates in the early formation of the dentogingival junction
What happens to the reduced enamel epithelium once the teeth erupt?
Remnants may form epithelial cell rests
Some cells are resorbed, others stay and have potential to give rise to cysts later on
During which stage does organization occur?
Bell stage
IEE elongate, organelles become polarized forming preameloblasts
When does the formative process occur?
During apposition & amelogenesis
Ameloblasts form in response to mantle dentin formation and then forms aprismatic enamel
When does maturation occur?
During amelogenesis and after termination
Completion of selective resorption & calcification processes
When does the protective stage occur?
During termination
Formation of REE and primary enamel
When does induction occur?
When dentinogenesis & amelogenesis reaches the cervical loop
How does root formation begin?
With the formation of Hertwigs Epithelial Root Sheath (HERS)
What is Hertwigs Epithelial Root Sheath?
Forms from cervical loop
Grows inferiorly and encompasses the dental papilla
Formation of coronal and radicular mantle dentin is the same except for what?
In radicular dentin formation Korff’s fibers will be arranged parallel to the DCJ instead of the DEJ
Forms AFTER coronal dentin
When does the apical foramen form? What is it?
When root formation is complete
Opening in root apex for nerves, blood vessels and lymphatic vessels
In what direction does dentin form? What does the PDL allow for?
Forms in a coronal direction
PDL allows for tooth movement occlusally
When is root formation complete for single root teeth?
2 to 3 years after eruption
When does cementum formation occur?
When HERS breaks down
What is the hyaline layer of hopewell-smith?
Covers mantle dentin
Produced by IEE
facilitates adhesion of cementum
What happens when HERS breaks down?
After partial breakdown, cell rests of Malassez form
Potential to form cysts when trapped
What do cementoblasts form?
Cementum matrix
Describe the formation of cementum
First the matrix forms
Then the matrix calcifies with calcium hydroxyapatite derived from mantle dentin
