L2 Flashcards
Odontogenesis:
The formation of tooth tissues from
stem cells originating in the
ectoderm primary germ layer
3Odontogenesis begins in the
sixth embryonic week
Two basic tissues that arise from the ectoderm primary germ layer are involved in tooth development
:epithelium and mesenchyme
These odontogenic tissues contain stem cells that become the
specialized cells that form tooth tissues
Dentinogenesis:
formation of dentin tissue
Amelogenesis:
formation of enamel tissue
Cementogenesis:
formation of cementum tissue
Pulp: This was what part of the tooth germ and
what 2 formative (blast) cell types arose
from its stem cells?
Dental papilla: Odontoblast: Fibroblast
Periodontal Lig. This was what part of the tooth germ and
what 3 formative (blast) cell types arose
from its stem cells?
Dental follicle: Fibroblast: Cementoblast: Osteoblast
Fate of cervical loop part of enamel organ:
Outer and inner layers come together, at the cervical loop, forming a double epithelial layer called
Hertwig’s epithelial root sheath
Hertwig’s epithelial root sheath
main functions
The sheath serves 2 main functions:
1. Determines root dentin outline
2. Determines number of root canals of tooth
Cervical Loop
rim of the epithelial bell (enamel organ)
- site where inner and outer cell layers merge (meet)
Fate of enamel organ cell layers after completion over enamel:
The 4 cell layers of enamel organ come together to form a stratified epithelial layer over the enamel surface called ‘reduced enamel epithelium’ that protects the enamel from surrounding connective tissue until the tooth enters the oral cavity
3 parts of Tooth Germ:
Enamel organ, Dental Papilla, dental follicle
Enamel organ:
(avascular)
* Inner epithelial cells differentiate into ameloblasts – specialized epithelial cells
* After the formation of enamel is complete, the ameloblasts, along with the other
layers of the enamel organ come together over the surface of the enamel
as a protective structure called: ‘reduced enamel epithelium’
Dental papilla: (vascular)
Its undifferentiated cells (stem cells) become odontoblast, fibroblast, reserve cells
* Ultimately becomes pulp tissue of tooth
Dental follicle:
(vascular)
- Its stem cells become cementoblast, fibroblast, osteoblast, and reserve cells
- Ultimately becomes periodontal ligament of the periodontium
the enamel organ is attached to both mesenchymal parts of the tooth germ by
a
basal lamina
Tooth Germ:
The epithelial enamel organ and a closely associated ectomesenchymal tissue that is continuous from around the epithelium to within the epithelium:
Combined, these tissues are called a Tooth Germ
Secondary Dental Lamina
Secondary dental lamina (arrow) is lingual to primary tooth germ:
Ten secondary lamina arise in each arch; one for each secondary tooth
Secondary dental lamina
arises from the
primary dental lamina
NOT the oral epithelium
Bell Stage (enamel organ) At this stage
4 distinct epithelial cell layers of the enamel organ are recognized,
as marked in the image
Four distinct epithelial cell layers of the enamel organ
1= Inner epithelial layer;
2= Stratum intermedium epithelial layer
3= Stellate reticulum epithelial layer
4= Outer epithelial layer
Cap stage:
Note site of enamel knot (encircled) concentration of epithelial cells of cap that is a signaling center: determines if tooth will develop to become an anterior or posterior tooth:
Note: a total of 16 epithelial buds arise from the
primary dental lamina
of each arch: 10 primary teeth and 6 permanent molars
*
Also note: each succedaneous tooth has its own
secondary dental lamina that
arises from the lingual side of the primary dental lamina:
(Total of 10 secondary dental laminae in each arch)
Primary buds: (Timeline: 6 to 8 weeks in utero)
Central incisors:.. 6 weeks in utero
Second molars:… 8 weeks in utero
Permanent buds: (Timeline 4 months in utero to 5 years postnatal)
First molar: ….. 4 months in utero
Central incisor: …5 months in utero
Second molar: … 10 months postnatally
Third molar: ….. 5 years postnatally
Note epithelial bud cells
are continuous with cells of
primary dental lamina
Vestibular lamina:
band of epithelial cells: lies
facial to developing tooth site
Epithelial Bud Stage- primary dental lamina
Cells at the deep end of the dental lamina, where a tooth is destined to
form, will develop into epithelial knobs, each know as an ‘epithelial bud’
Each epithelial bud is surrounded by mesenchymal tissue
PDL = primary dental lamina; VL = vestibular lamina
Fate of the 2 invaginated bands of epithelium:
The facial most epithelial band is the:
- vestibular lamina:
Cell death will occur in the center of the vestibular lamina,
leaving a space known as the ‘vestibule’
* The lingual most epithelial band is the
- primary dental lamina (odontogenic epithelium):
Cells arising from the dental laminae
become the odontogenic epithelial part of a Tooth Germ
1 Primary Dental Lamina Stage:
During the 6th embryonic week, two epithelial invaginations appear in the lower anterior region of the lower jaw and later in the same week in the upper jaw.
These invaginations descend into the underlying mesenchymal tissue (ectomesenchyme) and continue posteriorly within the mesenchyme as continuous epithelial bands
* facial band is called: vestibular lamina
* lingual band is called: primary dental lamina
Epithelial Stages: based on histologic shapes of the epithelial tissue
within a mesenchymal tissue environment
1 = epithelial dental lamina stage
2 = epithelial bud stage
3 = epithelial cap stage
4 = epithelial bell stage (enamel organ):
(at the bell stage the epithelium is arranged
in 4 distinct layers:
Tooth Germ Stage:
Odontogenic epithelial and mesenchymal tissues combined:
Cells of each tissue induced specifically to become
formative cells of dentin, enamel, cementum and pulp tissues
Three parts of Tooth Germ:
1 Enamel Organ (Bell): epithelium
2 Dental Papilla: mesenchyme
3 Dental Follicle: mesenchyme
Cells from these 3 parts give rise
to the specialized cells that
form tooth tissues
Dentin forms
first, then enamel, then cementum, then pulp
Salivary glands form from
ectoderm
Meckel’s cartilage
becomes jaw.
Vestibular lamina
becomes vestibule
Primary dental lamina connected to
basal lamina always
Trigeminal ganglion
V3
Bottom of epithelial bud
from neural crest (condensed cells)
