Dental Embryology - Basic Science Core

Embryology Exam 1

ODONTOGENESIS

• Development results in a complex and intricate cascade of gene expression that takes place to self- organize,

• Expand in number, and differentiate along the proper developmental trajectory (teeth).

Odontogenesis Genes (5)

1) Bone morphogenetic protein BMP

2) Sonic Hedgehog (shh)

3) Ectodysplasin A (Eda)

4) Wingless-related integration site(wnt)

5) Fibroblast growth factor(FGF)

DIFFERENTIATION (MOLECULAR SIGNALING IN TOOTH)

The epithelium derived from the first pharyngeal arch is essential for tooth development, and over 90 genes, including Sonic Hedghog (Shh) are expressed in cells of the developing oral epithelium and mesenchyme

STAGES OF TOOTH BUD DEVELOPMENT (5)

1) Initiation

• Phase of deciduous tooth 5th month in utero

• Phase of permanent tooth – 6 th month

• Phase of accessional tooth 4th month in utero until 4 to 5 years

2) Proliferation

3) Histodifferentiation

4) Morpho differentiation

5) Apposition

Primary epithelial band.

• The maxillary and mandibular processes have a thickened epithelium called the primary epithelial band.

• The epithelium rests on a basal lamina.

• The underlying embryonic connective tissue is called ectomesenchyme because neural crest cells from the ectoderm migrate into the mesenchyme.

Dental Lamina

• Parts of the dental lamina will develop into teeth.

• The dental lamina is surrounded by a condensation of ectomesenchymal cells (MC) that will become the dental papilla and dental follicle

At about 6-7 weeks of development, the primary epithelial band grows into … (2)

1) vestibular lamina

2) dental lamina

The Vestibular Lamina

• The vestibular lamina will become the space between the cheek and gingiva.

PLACODE

• Dental placodes are believe to initiate the various tooth families

• Placode is a determinant in tooth formation. Smaller-than the normal

  placodes lead to missing and smaller teeth , whereas larger placodes

  induce supernumerary and larger teeth

dental papilla (DP)

The dental papilla (DP) is a crescent-shaped Condensation of ectomesenchymal cells that will develop into cells that will produce the dentin, cementum and pulp of a tooth.

A Bud in tooth development

• At about 8 weeks of development, along the dental lamina (DL) at

  each site where a tooth will develop, the epithelium thickens to form a

  bud (B).

• Some cells in each bud will develop into ameloblasts that will

  produce the enamel crown for one tooth.

8 Weeks in development is also known as the ______ Stage

• The Bud Stage

• In this stage bud stage of tooth development as the dental laminae fold inward over the developing maxilla and mandible.

10 Weeks in development is also known as the ______ Stage

• Cap Stage

CAP STAGE AND THE ENAMEL ORGAN

• At about 10 weeks, the bud develops into the cap

  shaped enamel organ

• Since the cells are interconnected with desmosomes, they become star-shaped (i.e. stellate) as they are forced apart by the increasing intercellular fluid volume.

The enamel organ layers of cells (3)

• 1) the outer enamel epithelium

  (OEE),

• 2) the inner enamel epithelium (IEE)

• 3) the stellate reticulum (SR).

Inner enamel epithelium Cells

• Cells of the inner enamel epithelium will differentiate into enamel-producing Ameloblasts

• The IEE begins to enclose the ectomesenchymal cells that form the

  dental papilla (DP).

The stellate reticulum (SR)

• The SR cells secrete glycosaminoglycans that

  draw water into the enamel organ and cause it

  to swell.

I am on Slide 15, I need to go back, I will start agian on slide 28

The Formation of the Permanent Dentition

• The successional permanent teeth develop between week 20 of fetal development and 10 months after birth.

• The permanent molars start to develop between week 20 of fetal development (first permanent molar) and age 5 years (third molar). The permanent molars have no deciduous precursors. Once the body of the mandible grows long enough, the dental lamina grows posteriorly into the ectomesenchyme and forms tooth buds for the first, second and third molars. This is why 3rd molars are located far back in the mandibular ramus.

DENTAL HARD TISSUE FORMATION

Dental Hard Tissues result from the

histodifferentiation of

• Enamel from Ameloblasts

• Dentin from Odontoblasts

• Cementum from Cementoblasts

Ameloblasts →

• Become Enamel

Odontoblasts →

• Become Dentin

Cementoblasts →

• Become Cementum

Amelogenesis

• At the junction between the enamel organ and the dental papilla, the Ameloblasts differentiate first, and then odontoblasts.

• Odontoblasts secrete pre-dentin first which then stimulates Ameloblasts to produce enamel facing the pre-dentin.

• Ameloblasts mature through several morphologically distinct functional stages during enamel production.

• The enamel matrix is deposited by ameloblasts directly on the surface of the previously formed pre-dentin

Ameloblasts and Enamel Formation

• Ameloblasts continue to produce enamel matrix until the full

  thickness of the enamel is achieved

Maturation of the enamel matrix

• Maturation of the enamel matrix involves removal of organic material (proteins) and water and continued mineralization from influx of calcium and phosphate into the maturing enamel.

• Active ameloblasts have many mitochondria to fuel the transport of organic material out and mineral into the enamel.

AMELOBLAST FUNCTIONAL STAGES (3) (Do not need to know)

1) Presecretory Stage

2) Secretory Stage

3) Post- secretory or Maturation Stage

Presecretory Stage

Golgi and rough

endoplasmic reticulum of ameloblasts produce

vesicles of proteins:

1. Morphogenic Stage

2.Histodifferentiation Stage

Secretory Stage

ameloblasts deposit the proteins

and minerals of the enamel onto predentin:

1. Initial Secretory Stage (no

Tome’s Process)

4. Secretory Stage (with Tome’s Process)

• Secretory Stage ameloblasts release

  secretory granules of enamel matrix

  proteins and hydroxyapatite from Tome’s

  process

Post- secretory or Maturation Stage

ameloblasts alternate between two morphologies

that remove protein and transport mineral ions that

harden the enamel:

5. Ruffle-ended Ameloblast

6. Smooth-ended Ameloblast

7. Protective Stage

8. Desmolytic stage

• Secretory Stage ameloblasts release

  secretory granules of enamel matrix

  proteins and hydroxyapatite from Tome’s

  process

Enamel cannot exist without

• Dentin, as dentin is a cushion for the enamel

• REMOVE unsupported enamel in dentistry

Ruffle-ended maturation stage

Ruffle-ended maturation stage ameloblasts secrete enzymes to

remove proteins and additional mineral ions to harden the enamel.

Smooth-ended maturation stage

Smooth-ended maturation stage ameloblasts absorb water and

degraded proteins from the enamel matrix.

DEVELOPMENT OF DENTIN

As dentin is produced, it creates a pattern of incremental lines. In a

tooth section of a person who received tetracycline intermittently, the

drug has been incorporated at successive dentin-forming fronts,

highlighting the incremental line patterns.

Hertwig's Epithelial Root Sheath (HERS)

of the dental follicle.

cementoblasts