ADULT TOOTH STRUCTURE
Teeth
1.
In adult humans there are 32
permanent teeth.
2.
These are preceded during childhood
by 20 deciduous teeth.
3.
The tooth lies in a bony socket, the
alveolus, that is covered my an oral
mucosa called the gingiva (gums) that
consist of,
a. keratinized stratified squamous
epithelium
b. lamina propria of loose connective
tissue that lies directly adjacent to the
bone of the alveolus.
The tooth consists of two major parts,
a. the crown - the portion that
protrudes above the gum line
and is covered by enamel.
and
b. the root - the portion that
extends into the alveolus.
Internally, the tooth consists of a
layer of dentin that surrounds a
pulp consisting of loose
connective tissue, nerves and
blood vessels.
In the dentin, directly adjacent to
the pulp is a layer of specialized
cells called odontoblasts secrete organic matrix that
mineralizes and forms the
dentin.
Crown region
Dentin is covered by a layer of calcified organic
matrix - the enamel
a. Hardest substance in body
b. Formed by cells called ameloblasts before
tooth “erupts” from socket
Root region
Dentin is covered by calcified organic matrix - the
cementum - similar to bone, but no haversian
system
Between the cementum and the bone of the
socket lies the periodontal ligament - consists of
fibroblasts and collagen fibers with
glycosaminoglycans in between.
a.
forms cushion between tooth and bone
b.
Attaches tooth to bone - Sharpey’s fibers
http://www.odont.uio.no/studier/ressurser/histologi/snitt/snitt.php?size=2&katalog=043&info=&large=
http://www.odont.uio.no/studier/ressurser/histologi/snitt/snitt.php?katalog=043&size=2&quiz=true
http://www.odont.uio.no/studier/ressurser/histologi/snitt/snitt.php?katalog=043&info=&large=
TOOTH DEVELOPMENT
http://en.wikipedia.org/wiki/Image:Molarsindevelopment11-24-05.jpg
There are a number of terminologies that are used to describe the
early development of teeth prior to the cap stage.
In some cases, there is disagreement about what a given term
represents (e.g. dental lamina, tooth bud).
The following description of tooth development tries to make
sense out of the available reference material I’ve been able to
find; however, be aware that you may see other terminologies
used in dental school.
7
1. Prior to the 5th - 6th week of gestation in human embryos, the
developing jaws are solid masses of tissue with little differentiation.
2. Tooth development begins during the 5th - 6th week of gestation.
8
3. The first indication is the appearance of a thickened plate of
epithelium (vestibular lamina = labialgingival lamina) between the
tongue and the jaw. This, and the following events occur in both the
upper and lower jaw.
4. This thickened epithelium spreads over the jaw surface.
5. An invagination (labial groove = labiogingival groove) forms in
this thickened epithelium. This becomes the vestibule that separates
the lip or cheek from the gum.
http://dentaldominion.blogspot.com/2
011/09/dental-lamina.html
9
6. The vestibular lamina overlying the forming gums grows into the underlying
gum tissue and forms the dental lamina. Neural crest cells in the underlying
mesenchyme of the gums induce the formation of the dental lamina. The dental
lamina forms a C-shaped band of tissue in the gums of the upper and lower jaw
that is also called the dental ledge.
This ingrowth of the dental lamina is sometimes called the tooth bud.
A - dental lamina = dental ledge; B - Mesenchymal containing neural crest cells
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
6. The vestibular lamina overlying the forming gums grows into the underlying
gum tissue and forms the dental lamina. Neural crest cells in the underlying
mesenchyme of the gums induce the formation of the dental lamina. The dental
lamina forms a C-shaped band of tissue in the gums of the upper and lower jaw
that is also called the dental ledge.
http://dentaldominion.blogspot.com/2011/09/dental-lamina.html
Carlson, P. 530
P. 530, Fig. 16-14, Carlson
7. In 10 distinct regions of each jaw (maxilla and mandible), the cells of
the dental ledge proliferate rapidly by mitosis forming a cup-shaped
structure called the enamel organ (A) that is surrounded by jaw
mesenchyme. The enamel organ remains connected to the labialgingival
or vestibular lamina by the cord-like remains of the dental ledge (B).
8. Five enamel organs will develop on both the right and left sides of both
the upper and lower jaw. These will form the child’s “milk” (primary)teeth.
Enamel
organ
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
http://32teethonline.com/pedopage2.htm
9. The mesenchyme that fills the enamel organ cup will become the
dental papilla (D) that eventually forms the dentin and the pulp of
the tooth.
10. The enamel organ and dental papilla are surrounded by a sheath
of connective tissue called the dental sac (E).
11. The entire structure is called the cap stage of tooth development.
A, Enamel organ; B, Dental lamina; C, Vestibular lamina; D, Dental Papilla; E, Dental sac
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
Carlson, P. 530
12. The cap stage of tooth development continues to differentiate, forming the
bell stage. Concurrent with this, the successional lamina (D), that will form
the secondary (adult) tooth later in life, forms as a outgrowth of the original
dental lamina (E).
13. This differentiation includes the enamel organ. As is the case for the optic cup, the
cup of the enamel organ consists of two opposing layers of cells that result from the
formation of the cup. These are an inner layer of cells (adjacent to the dental papilla F) that is called the inner enamel organ epithelium (A) and an outer layer of cells
(adjacent to the dental sac - G) called the outer enamel organ epithelium (B).
A - Inner enamel epithelium; B - Outer enamel epithelium; C - Stellate reticulum; D - Successional
lamina; E - Dental lamina; F - Dental papilla; G - Dental sac.
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
14. The ectodermally derived tissue between these two layers forms a matrix of cells
called the stellate reticulum (C). This matrix is essentially a loose connective tissue with
lots of extracellular material (mainly mucopolysaccharides) between the cells.
15. The inner enamel organ epithelium (A) will eventually differentiate into cells called
ameloblasts that will be responsible for forming the enamel of the teeth. - Crown
region
16. Neural crest cells in the dental papilla (F) will form an epithelial layer directly
adjacent to the inner enamel organ epithelium that will differentiate into cells called
odontoblasts which will be responsible for forming the tooth dentin.
17. The remainder of the dental papilla (F) will form the dental pulp of the tooth.
A - Inner enamel organ epithelium; B - Outer enamel organ epithelium; C - Stellate reticulum; D Successional lamina; E - Dental lamina; F - Dental papilla; G - Dental sac.
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
P. 531, Fig. 16-15, Carlson
Outer
enamel
organ
epithelium
Inner
enamel
organ
epithelium
Dental papilla
Dental sac
See Pp. 532 - 533, Figs. 16-16 and 16-17, in Carlson - similar figures
Dental lamina
Outer enamel
organ epithelium
(Inner enamel
organ epithelium)
Successional
lamina
Dental sac
Dental papilla
18. The lips of the cup that forms the enamel organ are called the cervical loop. This
structure consists of a portion of the inner and outer enamel epithelium at the region
where they join.
19. Research indicates that the inner enamel epithelium portion of the loop is a source
of stem cells for the developing ameloblasts (the cells that produce the tooth
enamel). The cervical loop will partially degenerate as the root of the tooth develops
and will become Hertwig's Epithelial Root Sheath. In species with continuously
growing teeth (e.g. rodents), the cervical loop is retained through adulthood, thus
emphasizing its importance in providing stem cells to produce ameloblasts for enamel
formation.
A - Inner enamel epithelium; B - Outer enamel epithelium; C
- Stellate reticulum; D - Successional lamina; E - Dental
lamina; F - Dental papilla; G - Dental sac.
A, Cervical loop; B, Inner enamel
epithelium; C, Outer enamel
epithelium; D, Stratum intermedium;
E, Stellate reticulum
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
20. As differentiation of the inner enamel epithelium proceeds, cells called
preameloblasts form from the inner enamel organ epithelium, adjacent to the dental
papilla. These cells induce neural crest cells in the dental papilla to differentiate into
preodontoblasts.
C
D
A - Inner enamel epithelium; B - Outer enamel epithelium; C
- Stellate reticulum; D - Successional lamina; E - Dental
lamina; F - Dental papilla; G - Dental sac.
B
A - Preameloblasts; B - Preodontoblasts;
C - Stellate reticullum; D - Dental papilla
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
21. The preodontoblasts become odontoblasts as they begin to secrete predentin
(which will become dentin). The predentin blocks nutrients from moving from the pulp to
the preameloblasts. This causes the preameloblasts to become ameloblasts and begin
their secretion of enamel. The odontoblasts and ameloblasts move away from each other as
the dentin and enamel layers increase in thickness.
22. As this begins to occur, the developing tooth enters the crown stage.
E
D
C
B
A
1 - Ameloblasts; 2 - Enamel; 3 - Dentin; 4 - Odontoblasts; 5 - Pulp
A - Odontoblasts; B - Predentin; C - Ameloblasts;
D - Dentin; E - Enamel
http://www.histol.chuvashia.com/atlas-en/digestive-05-en.htm
http://www.slideshare.net/MPDODZ/odontogenesis-10680431
Dental papilla
Outer
enamel
organ
epithelium
Enamel
organ
(Inner enamel
organ epithelium)
P. 533, Fig. 16-17, Carlson
23. Once enamel depostion is completed and the crown is fully formed, the enamel
organ collapses and the cells form a sheath called the reduced enamel epithelium
that covers the crown of the tooth until eruption.
Enamel space
A - Reduced enamel epithelium; B - Maturative/protective ameloblasts; C - Capillary
http://www.cram.com/flashcards/oucod-oral-histology-practical-chapter-1-odontogenesis-1727662
Pictures start on slide 56
24. Following the formation of the crown, the root forms. The inner and outer enamel
epithelial layers of the cervical loop region continue to grow toward the future base of
the tooth. (Hertwig’s epithelial root sheath).
25. The root sheath induces neural crest cells in the pulp mesenchyme to differentiate
into additional odontoblasts that form the dentin of the root.
26. The central region of the root is called the radicular pulp cavity.
D
C
B
F
E
A
A - Epithelial diaphragm; B - Radicular pulp cavity; C - Dentin;
D - Enamel space; E - Alveolar Bone; F, Root
http://www.cram.com/flashcards/oucod-oral-histology-practical-chapter-1-odontogenesis-1727662
Pictures start on slide 56
27. The leading edge of Hertwig’s epithelial root sheath turns inward toward the
root of the tooth and forms the epithelial diaphram.
D
C
B
F
E
A
A - Radicular pulp cavity; B - Dentin; C Dental sac; D - Point at which epithelial root
sheath begins to disintegrate; E - Epithelial
diaphram; F - Epithelial rests
A - Epithelial diaphragm; B - Radicular pulp cavity; C - Dentin;
D - Enamel space; E - Alveolar Bone; F, Root
http://www.cram.com/flashcards/oucod-oral-histology-practical-chapter-1-odontogenesis-1727662
Pictures start on slide 56
28. In regions where the root odontoblasts have formed and are secreting dentin, the
epithelial root sheath begins to break down. At this time, cells from the dental sac
that surrounds the developing tooth migrate to the surface of the newly formed dentin
and become cementoblasts. These cells secrete the cementum layer that acts as an
attachment region for the peridontal ligaments that bind the root of the tooth to the
bone.
A - Radicular pulp cavity; B - Dentin; C Dental sac; D - Point at which epithelial root
sheath begins to disintegrate; F cementoblasts move toward dentin; E Epithelial diaphram
A - Cementoblasts; B - Odontoblasts; C - Predentin
http://www.cram.com/flashcards/oucod-oral-histology-practical-chapter-1-odontogenesis-1727662
Pictures start on slide 56
29. As the epithelial root sheath degenerates it leaves small groups of cells around the root
that are called epithelial rests.
A - Epithelial rests; B - Mantle dentin; C - Globular dentin; D - Circumpulpal dentin
http://www.cram.com/flashcards/oucod-oral-histology-practical-chapter-1-odontogenesis-1727662
Pictures start on slide 56
30. Once the tooth is fully formed it is ready to undergo eruption. This process involves
active movement of the tooth such that it penetrates the gum tissues and extends above
them.
31. In humans, eruption of the milk (primary) teeth generally begins in the second month
after birth and continues until the end of the second year.
32. It is likely that there are a number of factors involved in eruption. While there is no
consensus on the cause of tooth eruption, there seems to be agreement that root growth,
alveolar bone remodeling, and possibly the peridontal ligaments are involved in this process.
33. Permanent (secondary) teeth develop in the same manner as primary teeth. The primary
teeth will be replaced and 12 additional teeth (32 total) will be added to the dentition.
34. 28 of the secondary teeth erupt
between the ages of 6 and 13
years.
The four wisdom teeth may erupt
between 17 and 21 years; however,
they often remain impacted.
http://www.uic.edu/classes/orla/orla312/Teeth%20in%20Function%3B%20Life%20History%20of%20Teeth.htm
HYPERDONTIA
THE END