Hist 3

Early tooth development

BY:dr.Nafha Shihab.(Periodontist)

2015May 3, 2023 1oral histology lab. by:dr.Nafha Shihab

. Morphological stages of tooth development

May 3, 2023 2oral histology lab. by:dr.Nafha Shihab

MORPHOLOGICAL1. Dental lamina2. Bud stage3. Cap stage4. Early bell stage5. Advanced bell stage6. Formation of enamel and dentin matrix

PHYSIOLOGICALInitiation

ProliferationHistodifferentiationMorphodifferentiationApposition


Tooth development can be divided into 3 stages:1. Bud Stage2. Cap Stage3. Bell Stage


1.Bud Stage


BUD STAGE PROLIFERATION• This is the initial stage of

tooth formation where enamel organ resembles a tooth bud

• The enamel organ consists of peripherally located low columnar cells & centrally located polygonal cells

• The surrounding mesenchymal cells proliferate, which results in their condensation in two areas

• The area of condensation immediately below the enamel organ is the dental papilla

• The ectomesenchymal condensation that surrounds the tooth bud & the dental papilla is the tooth sac


• The dental papilla as well as the dental sac are not well defined during the bud stage, they become more defined during the cap & bell stages

• The cells of the dental papilla form the dentin and pulp while the dental sac forms cementum & periodontal ligament


• Epithelial outgrowth called Enamel Organ because it will form the enamel

• Dental Papilla:Ball of condensed ectomesenchymal cells (it will form dentin and pulp).

• • Epi.condensation is

poor morphodifferentiated & histodifferentiated.

• The cells of tooth bud have high RNA +enzymatic activity with low glycogen content

Enamel Organ

Dental Papilla


2. Cap Stage


: as the epithelial bud continues to proliferate into the ectomesenchyme, morphogenesis has progressed, the deeper surface of the enamel organ invaginate to form a cap-shaped structure. A greater distinction develops between the more rounded cells in the central portion of the enamel organ and the peripheral cells which are becoming arranged to form the outer and inner dental epithelia. oral histology lab. by:dr.Nafha

ShihabMay 3, 2023 10

In the late cap stage of tooth development, the central cells of the enlarging enamel organ have become separated. The resulting tissue is termed the stellate reticulum- is a group of cells located in the center of the enamel organ of a developing tooth.

oral histology lab. by:dr.Nafha ShihabMay 3, 2023 11

http://en.wikipedia.org/wiki/Cell_(biology)

http://en.wikipedia.org/wiki/Enamel_organ

http://en.wikipedia.org/wiki/Tooth_development

http://en.wikipedia.org/wiki/Tooth

These cells are star-shaped and synthesize glycosaminoglycans. As glycosamingoglycans are produced, water is drawn in between the cells and stretch them apart. The cells of the outer enamel epithelia remain cuboidal, where as those of inner enamel epithelia become more columnar.


http://en.wikipedia.org/wiki/Glycosaminoglycan

http://en.wikipedia.org/wiki/Water

The adjacent ectomesenchymal cells are continue to prolipherat and surround the enamel organ. The part of the ectomesenchyme lying beneath the inner enamel epithelia is called dental papilla. The ectomesenchymal tissue surrounding both enamel organ and dental papilla is called dental sac or dental follicle.oral histology lab. by:dr.Nafha


Dental follicle or dental sac is the condensed ectomesenchymal tissue surrounding the enamel organ and dental papilla. This gives rise to cementum and the periodontal ligament

Dental follicle or sac

Enamel organ

Enamel knot

Dental papilla


OUTER & INNER ENAMEL EPITHELIUM

• The peripheral cells of the cap stage are cuboidal , cover the convexity of the cap & are called the outer enamel epithelium

• The cells in the concavity of the cap become tall columnar cells & represent the inner enamel epithelium


Transitory structures:During the early stages of tooth

development, three transitory structures may he seen, which are

enamel knot, enamel cord enamel niche.


1-Enamel knot: it is a localized mass of cells in the center of

the inner enamel epithelia. The enamel knot is a signaling center of the tooth that provides positional information for tooth morphogenesis and regulates the growth of tooth cusps. The enamel knot produces a range of molecular signals from all the major signaling families, such as Fibroblast Growth Factors (FGF), Bone morphogenetic proteins (BMP) and other signals. oral histology lab. by:dr.Nafha


http://en.wikipedia.org/wiki/Cusp_(dentistry)

2-Enamel cord: it’s a strand arises in the

enamel organ as a vertical extension of the enamel knot at the early bell stage of development. Its termed enamel septum when enamel cord extend from enamel knot to the outer enamel epithelia.oral histology lab. by:dr.Nafha


3-Enamel niche: it is created because the dental

lamina is a sheet rather than a single strand and often contains a concavity filled with connective tissue. A section through this arrangement creates the impression that the tooth germ has a double attachment to the oral epithelium by two separate strands.oral histology lab. by:dr.Nafha


• The cells in the center of the enamel organ are densely packed and form the enamel knot(EK)

•

enamel knot



• At the same time a vertical extension of the enamel knot, called the enamel cord occurs

enamel cord


Enamel niche


Bell stageContinued growth of teeth germs leads to the next stage of tooth development- the bell stage, so called because the enamel organ comes to resemble a bell which is in its final shape (Morphodifferentiation). During this stage, the cells that will be making the hard tissues of crown (Ameloblasts and odontoblasts) acquire their distinctive phenotype (Histodifferentiation).

•


Early bell stage: the enamel organ shows four distinct layers:

The outer enamel epithelium: is a layer of cuboidal cells located on the periphery of the enamel organ in a developing tooth and is separated from the surrounding ectomesenchymal tissue by a basement membrane of l-2µm thickness. The outer enamel epithelial cells contain large, centrally placed nuclei and relatively small amounts of the intracellular organelles associated with protein synthesis (e.g. endoplasmic reticulum, Golgi complex & mitochondria) and they contact each other via desmosomes and gap junctions.oral histology lab. by:dr.Nafha






Involved in the maintenance of the shape of the enamel organ and in the exchange of substances between the enamel organ and the environment in order to provide nutritional supply for the metabolic activity of the avascular (without blood supply) enamel organ.



The stellate reticulum: is a group of star shaped cells located in the center of the enamel organ of a developing tooth. These cells synthesize glycosaminoglycans, causing water to be drawn in between the cells and stretch them apart generating hydrostatic pressure within the stellate reticulum which is in equilibrium with that of the dental papilla, allowing the maintenance of tooth shape. Stellate reticulum is lost after the first layer of enamel is laid down. This brings cells in inner enamel epithelium closer to blood vessels at the periphery.






http://en.wikipedia.org/wiki/Glycosaminoglycan

http://en.wikipedia.org/wiki/Water

Stratum intermedium: several layers of squamous cells closely attached by desmosomes and gab junction, lying between the inner enamel epithelium and stellate reticulum. The cells of stratum intermedium characterized by high degree of alkaline phosphatase enzyme which is important in the mineralization of the enamel. This layer, along with the inner enamel epithelium, is responsible for the tooth enamel formation.


Inner enamel epithelium: is a layer of columnar cells that differentiate prior to amelogenesis into the ameloblasts; located on the rim nearest the dental papilla of the enamel organ in a developing tooth and are separated from the peripheral cells of dental papilla by a basement membrane and cell free zone about 1-2 µm wide. The inner enamel epithelial cells rich in RNA but unlike the stratum intermedium do not contain alkaline phosphatase. The cells of this layer exert an organizing influence on the underlying ectomesenchymal cells, which differentiate into odontoblasts.



http://en.wikipedia.org/wiki/Dental_papilla




Dental papilla (d.p.): before the inner enamel epithelia differentiate into ameloblast to produce the enamel, the peripheral cells of d.p. differentiate into odontoblasts (dentin forming cells) under the organizing influence of inner enamel epithelium.

Dental sac (d.s.): Before formation of dental hard tissue begins, the d.S. shows a circular arrangement of its fibers and it resemble a capsular structure. With the development of the root, the fibers of d.S. differentiate into periodontal fibers that become embedded in the cementum and alveolar bone.



•Advance (late) bell stage or appositional stage: this stage of tooth development is associated with the formation of the dental hard tissues. Dentine formation always precedes enamel formation. During this stage the boundary between inner enamel epithelia and odontoblasts outlines the future dentino enamel junction (D.E.J.). In addition, the basal margin of the enamel organ (cervical loop) gives rise to the epithelial root sheath.The rim of the enamel organ where the outer and inner enamel epithelium join is called the cervical loop, at which there is considerable mitotic activity.


http://en.wikipedia.org/wiki/Inner_enamel_epithelium

http://en.wikipedia.org/wiki/Cervical_loop

Function of dental lamina:

•The first phase is concerned with the initiation of the entire deciduous dentition that begins at the 6 weeks of intra-uterin life of embryo.

•The second phase deals with the initiation of the successors of the deciduous teeth. It is preceded by the growth of the free end of the dental lamina (successional lamina), lingual to the enamel organ of each deciduous tooth, and occurs from about the fifth month in embryo for the permanent central incisors to 10 months of age for the second premolar

•The third phase is preceded by the extension of the dental lamina distal to the enamel organ of the second deciduous molar and the formation of permanent molar tooth germs.


Fate of dental lamina

•Dental lamina is functional in developing 52 teeth from 6 prenatal weeks until 4 years after birth (development of third permanent tooth).

•The dental lamina degenerates by mesenchymal invasions in late bell stage.

•Developing tooth lose its connection with dental lamina.

•Sometimes remnants of dental lamina remains in the jaws as epithelial rests of Serres ( Serres’ pearls) .


Disturbance of epithelial-mesenchymal interactions:

Malformation of teeth related to variation in size, shape, number or in structure:•macrodontia (enlarge tooth).•microdontia ( small size tooth).•gemination( partial cleavage of tooth germ).•fusion (union of 2 adjacent teeth).•hypodontia (reduction in No. of teeth).•anndontia ( complete absence of teeth).•dens in dente( tooth within tooth).


Malformation of teeth related to the development of specific dental tissue:•Amelogenesis imperfecta.•Dentinogenesis imperfecta.•Truma and infection of deciduous teeth may cause malformation in permanent teeth.


QUIZoral histology lab. by:dr.Nafha


M C Q 1. Inner enamel epithelium Consists of epithelial cells rich in RNA and contain alkaline

phosphatase. The cells of this layer exert an organizing influence on the underlying

ectomesenchymal cells, which differentiate into odontoblasts.

located on the rim nearest the dental folicle of the enamel organ in a developing tooth.

is a layer of tall cuboidal cells that differentiate prior to amelogenesis into the ameloblasts.








M C Q2. Malformation of teeth related to

variation in size:macrodontia.Germination.fusion.hyperdontia



Date post:	12-Apr-2017
Category:	Health & Medicine
Upload:	ahmed-sibrahim
View:	349 times
Download:	0 times

Hist 3

Health & Medicine