Upload By : Ahmed Ali Abbas

Babylon University College of Dentistry

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Structure of the Oral

Tissues

& Tooth Development I

By :Ahmed Ali Abbas

Tooth function:

Mastication.

Speech.

Esthetic.

Tooth consists of:

Enamel.

Dentin.

Pulp.

Cementum.

Tooth Attachments:

Cementum.

PDL.

Alveolar bone.

Gingiva.

The entire primary dentition is initiated between 6 and 8 weeks of

embryonic development.

The successional permanent teeth between week 20 in utero and 10

months after birth; and the permanent molars between week 20 in

utero (first molar) and 5 years of age (third molar).

Primary Epithelial Band a continuous band of thickened

epithelium forms around the

mouth in the presumptive upper

and lower jaws. These bands are

roughly horseshoe-shaped and

correspond in position to the

future dental arches

Each band of epithelium will

give rise to 2 sub divisions:

1. Dental lamina

2. Vestibular lamina

DENTAL LAMINA

continued and localized proliferative activity leads to the formation of

a series of epithelial outgrowths into the mesenchyme at sites

corresponding to the positions of the future deciduous teeth

A. Bud Stage

B. Cap Stage

C. Bell Stage

D and E. Dentinogenesis and

amelogenesis

F. Crown formation

G. Root Formation and eruption

H. Function

Characterized by:

First incursion into the ecto-mesenchyme of the jaw.

Little change of the shape and function of epithelial cells

Condensation of ecto-mesenchyme.

Bud stage is characterized by rounded, localized growth of

epithelium surrounded by proliferating mesenchymal cells,

which are packed closely beneath and around the epithelial

buds

In the bud stage, the enamel organ consists of

peripherally located low columnar cells and centrally

located polygonal cells

Characterized by:

1. Tooth bud is separated from the dental lamina by lateral lamina.

2. Tooth germ will be called enamel organ.

3. Enamel niche, enamel knot, enamel cord, and stellate reticulum.

4. Dental papilla pulp and dentin.

5. Dental follicle or sac PDL and cementum.

6. Dental organ consists of (enamel organ, dental papilla, and dental

follicle).

7. Histodifferentiation.

V.L.

Condensation of the ectomesenchyme immediately subjacent to

the tooth bud caused by lack of extracellular matrix secretion by

the cells thus preventing separation. Histodifferentiation begins

at the end of cap stage.

Epithelial outgrowth called Enamel Organ because it will eventually

form the enamel

Dental Papilla: Ball of condensed ectomesenchymal cells (it will form

dentin and pulp). The peripheral cells adjacent to the inner dental

epithelium will enlarge and later differentiate into odontoblasts

Dental follicle or dental sac is the condensedectomesenchymal tissue surrounding theenamel organ and dental papilla. This givesrise to cementum and the periodontal ligament(support structures for tooth)

Enamel Organ

Enamel Knot

Dental Papilla

Enamel niche: It is an artifact produced during

sectioning of the tissue. It occurs because the

enamel organ is a sheet of proliferating cells

rather than a single strand and contains a

concavity filled with ectomesenchyme

dental lamina

vestibular lamina

lip furrow

enamel niche

Enamel Knot: Densely packed accumulation of cellsprojecting from the inner enamel epithelium intodental papilla. Exact role not known, but currentlybelieved to be the organizational center for cuspdevelopment.

Continued growth leads to bell stage,where the enamel organ resembles abell with deepening of the epitheliumover the dental papilla

Continuation of histodifferentiation(ameloblasts and odontoblasts aredefined) and beginning ofmorphodifferentiation (tooth crownassumes its final shape)

It can be divided into:

1. Early bell stage.

2. Late or advance bell stage.

Stellate reticulum: Star-shaped cells with processes, present between the

outer and the inner dental epithelium. They have a cushion-like consistency

that may support and protect the delicate enamel organ.

Outer Enamel Epithelium

Stellate reticulum

Stratum intermedium

Inner Enamel epithelium

Dental papilla

Stratum intermedium: Cell layer between

the inner dental epithelium and stellate

reticulum which have high alkaline

phosphatase activity. They assist inner

enamel epithelium (ameloblasts) to form

enamel.

A - dental papilla

B - inner enamel epithelial cells

C - outer enamel epithelium

D - stellate reticulum

E - stratum intermedium

F - odontoblasts

Cervical loop: Area where the inner

and the outer dental epithelium

meet at the rim of the enamel organ.

This point is where the cells will

continue to divide until the tooth

crown attains its full size and

which after crown formation will

give rise to the epithelium for root

formation.

You must remember the following:

Hard tissue formation starts at the late stages of the bell stage

Differentiation of cells into odontoblasts and ameloblasts

Dentin is formed before enamel

Dentin initiates the

formation of enamel