Odontogenesis

Question 1

Define Odontogenesis

Answer 1

The formation of tooth tissues from stem cells originating in the ectoderm primary germ layer

Question 2

What week does odontogenesis begin in?

Answer 2

the 6th

Question 3

What are 2 basic tissues that arise from the ectoderm primary germ layer and are involved in tooth development?

Answer 3

Epithelium
Mesenchyme

*They contain stem cells that become specialized cell that form tooth tissues

Question 4

What are the histologic stage of tooth development?

Answer 4

Epithelial Stages

Tooth germ stage

Question 5

What are epithelial stages based on?

Answer 5

histological shapes of the epithelial tissue within a mesenchymal tissue environment

Question 6

What are the epithelial stages?

Answer 6

1 - epithelial dental lamina stage
2- epithelial bud stage
3 - epithelial cap stage
4 - epithelial bell stage (enamel organ) - at this stage the epithelium is arranged in 4 distinct layers)

Question 7

What is the tooth germ stage?

Answer 7

Odontogentic epithelial and mesenchymal tissues are combined. Cells of each tissue are specifically induced to become the formative cells of the dentin, enamel, cementum and pulp tissues.

Question 8

What are the 3 parts of tooth germ?

Answer 8

1 - Enamel organ (bell) - epithelium
2 - Dental papilla - mesenchyme
3 - Dental follicle - mesenchyme

Question 9

What happens during the Primary Dental Lamina stage, and when does it happen?

Answer 9

It happens during the 6th week. Two epithelial invaginations appear in the lower anterior region of the lower jaw and in the upper jaw. These invaginations descend into the underlying mesenchymal tissue (ectomesenchyme) and continue posteriorly within the mesenchyme as continuous epithelial bands. The facial band is called vestibular lamina and the lingual band is called primary dental lamina.

Question 10

What is the fate of the 2 invaginated bands of epithelium?

Answer 10

The vestibular lamina will have cell death in the center, leaving a space called the vestibule.
The primary dental lamina is odontogenic. Cells arising from the primary and secondary dental laminae become the odontogenic epithelial part of a tooth germ.

Question 11

What happens in the epithelial bud stage?

Answer 11

Cells at the deep end of the dental lamina, where tooth is destined to form, will develop into epithelial knobs, each known as an ‘epithelial bud.’ Each knob is surrounded by mesenchymal tissue.

Question 12

What are the timelines for Primary epithelial buds?

Answer 12

Central incisors - 6 weeks in utero

Second molars - 8 weeks in utero

Question 13

What are the timelines for Permanent epithelial buds?

Answer 13

First molar - 4 months in utero
Central incisor - 5 months in utero
Second molar - 10 months postnatally
Third molar - 5 years postnatally

Question 14

How many epithelial buds arise from the primary dental lamina in each arch?

Answer 14

16, 10 primary teeth and 6 permanent molars

Question 15

Each succedaneous tooth has its own secondary dental lamina that arises from which side of the primary dental lamina?

Answer 15

Lingual

Question 16

What happens in the epithelial cap stage?

Answer 16

The epithelial bud becomes a cap. Mesenchyme is inside and surrounding the cap. A dense concentration of epithelial cells call an enamel knot forms in the cap. The knot is a signaling center that determines if the tooth will develop into an anterior or posterior tooth.

Question 17

What happens in the epithelial bell stage?

Answer 17

The epithelial cap becomes a bell shaped epithelial structure called an enamel organ.

Question 18

What are the 4 layers of the enamel organ?

Answer 18

1 - Inner epithelial layer
2 - stratum intermedium epithelial layer
3 - stellate reticulum epithelial layer
4 - outer epithelial layer

Question 19

How many secondary lamina arise in each arch?

Answer 19

10, one for each secondary tooth

Question 20

True or false: Secondary dental lamina arises from oral epithelium.

Answer 20

False! It arises from primary dental lamina.

Question 21

What is the combination of the epithelial enamel organ and the ectomesenchymal tissue that is continuous from around to within the epithelium called?

Answer 21

A Tooth Germ!!!!

Question 22

What are the 3 parts of a tooth germ?

Answer 22

1 - Enamel organ: epithelium
2 - Dental papilla: mesenchyme
3 - Dental follicle: mesenchyme

Question 23

What is the destiny of the enamel organ?

Answer 23

It is avascular. Inner epithelial cells differentiate into ameloblasts. After formation of enamel is complete, the ameloblasts, along with the other layers of the enamel organ come together over the surface of the enamel as a structure called reduced enamel epithelium. It protects the enamel from the surrounding connective tissue until the tooth enters the oral cavity.

Question 24

What is the destiny of the Dental papilla?

Answer 24

It is vascular. Its undifferentiated (stem) cells become odontoblast, fibroblast, and reserve cells. Ultimately it becomes the pulp tissue of the tooth.

Question 25

What is the destiny of the dental follicle?

Answer 25

It is vascular. Its stem cells become cementoblast, fibroblast, osteoblast, and reserve cells. Ultimately it becomes the periodontal ligament of the periodontium.

Question 26

What attaches the enamel organ to both mesenchymal parts of the tooth germ?

Answer 26

basal lamina

Question 27

Pretend you are looking at a light, acellular layer between odontoblasts and ameloblasts. This is the future site of what?

Answer 27

the DEJ

Question 28

What is the cervical loop of the enamel organ?

Answer 28

The rim of the enamel organ (bell). The site where inner and outer cell layers meet/merge. A double epithelial layer is formed there called Hertwig’s epithelial root sheath.

Question 29

What is the fate of Hertwig’s epithelial root sheath?

Answer 29

It serves 2 main functions.:
1 - Determines root dentine outline
2 - Determines number of root canals of tooth

Question 30

The pulp was what part of the tooth germ and what 2 formative (blast) cell types arose from its stem cells?

Answer 30

Dental papilla. Odontoblasts and Fibroblasts

Question 31

The periodontal ligament was what part of the tooth germ and what 3 formative (blast) cell types arose from its stem cells?

Answer 31

Dental follicle. Fibroblasts, Cementoblasts, Osteoblasts