Structure of the Oral Tissues

& Tooth Development I

بسم الله الرحمن الرحيم

Tooth function: Mastication. Speech. Esthetic.

Tooth consists of:Enamel. Dentin. Pulp. Cementum.

Tooth

Tooth Attachments:

Cementum. PDL.Alveolar bone. Gingiva.

Tooth

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).

Time line of tooth development

Development of the ToothPrimary 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

Development of the ToothDENTAL 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

Tooth DevelopmentA. Bud StageB. Cap StageC. Bell StageD and E. Dentinogenesis andamelogenesisF. Crown formationG. Root Formation and eruptionH. Function

Bud stage

Bud stageCharacterized by: First incursion into the ecto-mesenchyme of

the jaw. Little change of the shape and function of

epithelial cellsCondensation of ecto-mesenchyme.

Bud stage

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

Bud StageIn the bud stage, the enamel organ consists of peripherally located low columnar cells and centrally located polygonal cells

Cap stage

Cap stage 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.

Cap Stage

V.L.

Cap Stage 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.

Cap Stage Epithelial outgrowth called Enamel Organ because it will eventually form the enamelDental 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

Cap Stage 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 (support structures for tooth)

Enamel Organ

Enamel Knot

Dental Papilla

Cap Stage

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 ectomesenchymedental lamina

vestibular lamina

 lip furrow

enamel niche

Cap Stage

Enamel Knot: Densely packed accumulation of cells projecting from the inner enamel epithelium into dental papilla. Exact role not known, but currently believed to be the organizational center for cusp development.

Bell Stage

Bell Stage

Continued growth leads to bell stage, where the enamel organ resembles a bell with deepening of the epithelium over the dental papillaContinuation of histodifferentiation (ameloblasts and odontoblasts are defined) and beginning of morphodifferentiation (tooth crown assumes its final shape)It can be divided into:1. Early bell stage. 2. Late or advance bell stage.

Early 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

Early Bell Stage 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 papillaB - inner enamel epithelial cellsC - outer enamel epitheliumD - stellate reticulumE - stratum intermediumF - odontoblasts

Bell Stage 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.

Late

Bel

l Sta

ge

You must remember the following:Hard tissue formation starts at the late stages of

the bell stageDifferentiation of cells into odontoblasts and

ameloblastsDentin is formed before enamelDentin initiates the formation of enamel

Late Bell Stage

Deposition of dental hard tissues is

called “apposition”

After the crown attains its final shape

during cap to early bell stage, the

inner dental epithelial cells stop to

proliferate, except the cells at the

cervical loop

First layer of dentin appears at the

cusp tips and progresses cervically,

and the columnar cells of the inner

enamel epithelium become elongated

and show reverse polarization, with

the nuclei adjacent to stratum

intermediate (ameloblasts)

The boundary between the

odontoblasts and inner dental

epithelium defines the future dentino-

enamel junction

Late Bell

Stage

For dentinogenesis and amelogenesis to take place normally, the differentiating odontoblasts and ameloblasts will receive signals form each other – “reciprocal induction”