Tooth Development Txt

8/8/2019 Tooth Development Txt

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ADULT TOOTH STRUCTURE


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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

epitheliumb. lamina propria of loose connective

tissue that lies directly adjacent to the

bone of the alveolus.

Teeth


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a. the crown - the portion that

protrudes above the gum line.

and

b. the root - the portion that extendsinto the alveolus.

Internally, the tooth consists of a

layer of dentin that surrounds a

pulp consisting of loose

connective tissue, nerves andblood vessels.

In the dentin, directly adjacent to the

pulp is a layer ofspecialized

cells called odontoblasts -

secrete organic matrix that

calcifies and forms the dentin.

The tooth consists of two major parts,


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Dentin is covered by a layer of calcified organic

matrix - the enamel

a. Hardest substance in body

b. Formed by 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 peridontal ligament - consists of

fibroblasts and collagen fibers with

glycosaminoglycans in between.

a.

forms cushion between tooth and boneb. Attaches tooth to bone - Sharpeys fibers

Crown region


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http://www.iob.uio.no/studier/undervisning/histologi/section/043/index.php

Figure at web link below.


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TOOTH DEVELOPMENT

http://en.wikipedia.org/wiki/Image:Molarsindevelopment11-24-05.jpg


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There are a number of terminologies that are used to describe theearly development of teeth prior to the cap stage.

In some cases, there is disagreement about what a given termrepresents (e.g. dental lamina, tooth bud).

The following description of tooth development tries to make senseout of the available reference material Ive been able to find;however, be aware that you may see other terminologies used indental school.


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1. Prior to the 6th week of gestation in human embryos, thedeveloping jaws are solid masses of tissue with little differentiation.

2. Tooth development begins during the 5th - 6th week of gestation.


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3. The first indication is the appearance of a thickened plate ofepithelium (vestibular lamina = labialgingival lamina) between thetongue and the jaw. This, and the following events occur in both theupper and lower jaw.

4. This thickened epithelium spreads over the jaw surface.

5. An invagination (labial groove) forms in this thickened epithelium.This becomes the vestibule that separates the lip or cheek from thegum.


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6. The vestibular lamina overlying the forming gums grows into the underlyinggum tissue and forms the dental lamina. Neural crest cells in the underlyingmesenchyme of the gums induce the formation of the dental lamina. The dentallamina forms a C-shaped band of tissue in the gums of the upper and lower jawthat is also called the dental ledge.

This ingrowth of the dental lamina is sometimes called the tooth bud.

http://dentistry.ouhsc.edu/oral-histology/Chapter 1/Chap1.html

A - dental lamina; B - Mesenchymal containing neural crest cells


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6. The vestibular lamina overlying the forming gums grows into the underlyinggum tissue and forms the dental lamina. Neural crest cells in the underlyingmesenchyme of the gums induce the formation of the dental lamina. The dentallamina forms a C-shaped band of tissue in the gums of the upper and lower jaw

that is also called the dental ledge.


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P. 530, Fig. 16-14, Carlson


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http://32teethonline.com/pedopage2.htm

7. In 10 distinct regions of each jaw, the cells of the dental ledgeproliferate rapidly by mitosis forming a cup-shaped structure calledthe enamel organ (A) that is surrounded by jaw mesenchyme. Theenamel organ remains connected to the labialgingival or vestibular

lamina by the cord-like remains of the dental ledge (B).

Enamelorgan


8. Five enamel organs will develop on the right and left sides of both theupper and lower jaw. These will form the childs milk (primary)teeth.


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9. The mesenchyme that fills the enamel organ cup will become thedental papilla (D) that eventually forms the dentine and the pulp ofthe tooth.

A, Enamel organ; B, Dental lamina; C, Vestibular lamina; D, Dental Papilla; E, Dental sac


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.


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Fig. 16-14, p. 530, Carlson


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12. The cap stage of tooth development continues to differentiate, forming thebell stage. Concurrent with this, the successional lamina (D), that will formthe secondary tooth later in life, forms as a outgrowth of the dental lamina (E).

A - Inner enamel epithelium; B - Outer enamel epithelium; C - Stellate reticulum; D - Successional

lamina; E - Dental lamina; F - Dental papilla; G - Dental sac.http://dentistry.ouhsc.edu/oral-histology/Chapter 1/Chap1.html

13. This differentiation includes the enamel organ. As is the case for the optic cup, thecup of the enamel organ consists of two adjacent 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).


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Outer enamel

organ

epithelium

Inner enamel

organ

epithelium

Dental papilla

Dental sac

Fig. 16-15, p. 531, Carlson


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14. The ectodermally derived tissue between these two layers forms a matrix of cells calledthe stellate reticulum. This matrix is essentially a connective tissue with lots ofextracellular material (mainly mucopolysaccharides) between the cells.

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.


15. The inner enamel organ epithelium will differentiate into cells called ameloblaststhat will be responsible for forming the enamel of the teeth. - Crown region

16. Neural crest cells in the dental papilla will form an epithelial layer directly adjacentto the inner enamel organ epithelium that will differentiate into cells calledodontoblasts which will be responsible for forming the tooth dentine.

17. The remainder of the dental papilla will form the dental pulp of the tooth.


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See Pp. 532 - 533, Figs. 16-16 and 16-17, in Carlson- similar figures

Dental papilla

(Inner enamel organ

epithelium)

Dental sac

Outer enamel

organ epithelium


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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 enamelepithelium; C, Outer enamel

epithelium; D, Stratum intermedium;E, Stellate reticulum

18. The lips of the cup that forms the enamel organ are called the cervical loop. Thisstructure consists of a portion of the inner and outer enamel epithelium at the regionwhere they join.

19. Research indicates that the inner enamel epithelium portion of the loop is a source ofstem 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 willbecome Hertwig's Epithelial Root Sheath. In species with continuously growing teeth(e.g. rodents), the cervical loop is retained through adulthood, thus emphasizing itsimportance in providing stem cells to produce ameloblasts for enamel formation.


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A - Inner enamel epithelium; B - Outer enamel epithelium; C -Stellate reticulum; D - Successional lamina; E - Dental lamina;

F - Dental papilla; G - Dental sac.


A - Preameloblasts; B - Preodontoblasts; C- Stellate reticullum; D - Dental papilla

DB

A

C

20. As differentiation of the inner enamel epithelium proceeds, cells calledpreameloblasts form from the inner enamel organ epithelium, adjacent to the dentalpapilla. These cells induce neural crest cells in the dental papilla to differentiate intopreodontoblasts.


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http://www.histol.chuvashia.com/atlas-en/digestive- 05-en.htm


A - Odontoblasts; B - Predentin; C - Ameloblasts;D - Dentin; E - Enamel

A

CD

B

E

1 - Ameloblasts; 2 - Enamel; 3 - Dentin; 4 - Odontoblasts; 5 - Pulp

21. The preodontoblasts become odontoblasts as they begin to secrete predentin(which will become dentin). The predentin blocks nutrients from moving from the pulp tothe preameloblasts. This causes the preameloblasts to become ameloblasts and begintheir secretion of enamel. The odontoblasts and ameloblasts move away from each other asthe dentin and enamel layers increase in thickness.

22. As this begins to occur, the developing tooth enters the crown stage.


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Dental sac


(Inner enamel organ

epithelium)

Dental papilla

Outer enamel

organ

epithelium

Enamel

organ


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A - Reduced enamel epithelium; B - Maturative/protective ameloblasts; C - Capillary

23. Once enamel depostion is completed and the crown is fully formed, the enamelorgan collapses and the cells form a sheath called the reduced enamel epitheliumthat covers the tooth until eruption.



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24. Folloowing the formation of the crown, the root forms. The inner and outer enamelepithelial layers of the cervical loop region continue to grow toward the future base ofthe tooth. (Hertwigs epithelial root sheath).

25. The root sheath induces neural crest cells in the pulp mesenchyme to differentiate intoadditional odontoblasts that form the dentin of the root.

26. The central region of the root is called the radicular pulp cavity.

A - Epithelial diaphragm; B - Radicular pulp cavity; C - Dentin; D- Enamel space; E - Alveolar Bone; F, Root

A

B

C

E

D

F


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A - Epithelial diaphragm; B - Radicular pulp cavity; C - Dentin; D- Enamel space; E - Alveolar Bone; F, Root

A

B

C

E

D

F

A - Radicular pulp cavity; B - Dentin; C -Dental sac; D - Point at which epithelial rootsheath begins to disintegrate; E - Epithelial

diaphram; F - Epithelial rests

26. The leading edge ofHertwigs epithelial root sheath turns inward toward theroot of the tooth and forms the epithelial diaphram.


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28. In regions where the root odontoblasts have formed and are secreting dentin, theepithelial root sheath begins to break down. At this time, cells from the dental sac thatsurrounds the developing tooth migrate to the surface of the newly formed dentin andbecome cementoblasts. These cells secrete the cementum layer that acts as anattachment region for the peridontal ligaments that bind the root of the tooth to thebone.

A - Cementoblasts; B - Odontoblasts; C - Predentin

A - Radicular pulp cavity; B - Dentin; C -Dental sac; D - Point at which epithelial rootsheath begins to disintegrate; E - Epithelial

diaphram


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29. As the epithelial root sheath degenerates it leaves small groups of cells around the rootthat are called epithelial rests.

A - Epithelial rests; B - Mantle dentin; C - Globular dentin; D - Circumpulpal dentin


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30. Once the tooth is fully formed it is ready to undergo eruption. This process involves activemovement 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 monthafter birth and continues until the end of the second year.

http://www.uic.edu/classes/orla/orla312/Teeth%20in%20Function%3B%20Life%20History%20of%20Teeth.htm

32. It is likely that there are a number of factors involved in eruption. While there is noconsensus 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 primaryteeth will be replaced and 12 additional teeth 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 eruptbetween 17 and 21 years; however,they often remain impacted.


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