Odontogenesis

Question 1

what is odontogenesis?

Answer 1

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

Question 2

when does odontogenesis begin?

Answer 2

6th embryonic week

Question 3

what two basic tissues that arise from the ectoderm primary germ layer are involved in tooth development?

Answer 3

epithelium and mesenchyme

they contain stem cells that become the cells that form tooth tissues

Question 4

what are the epithelial stages?

Answer 4

epithelial dental lamina stage
epithelial bud stage
epithelial cap stage
epithelial bell stage (enamel organ)

Question 5

what is the epithelial stages classified based on?

Answer 5

histologic shapes of the epithelial tissue within a mesenchymal tissue environment

Question 6

what are tooth germ stage based on?

Answer 6

odontogenic epithelial and mesenchymal tissue combines/ cells of each tissue induced specifically to become formative cells of dentin, enamel, cementum and pulp tissues

Question 7

what are the three parts of tooth germ?

Answer 7

enemel organ (bell): epithelium
dental papilla: mesenchyme
dental follicle: mesenchyme

Question 8

primary dental lamina stage

Answer 8

two epithelial invaginations appear in lower anterior region of the lower jaw and later in the same week in the upper jaw
invaginations descend into the underlying mesenchymal tissue (ectomesenchyme) and continue posteriorly within the mesenchyme as continuous epithelial bands

Question 9

what is the facial band called?

Answer 9

vestibular lamina

Question 10

what is the lingual band called?

Answer 10

primary dental lamina

Question 11

fate of vestibular lamina

Answer 11

cell death will occur in the center of the vestibular lamina leaving a space known as the “vestibule”

Question 12

fate of primary dental lamina

Answer 12

cells arising from the dental laminae (primary and secondary) become the odontogenic epithelial part of a tooth germ

Question 13

what is an epithelial bud?

epithelial bud stage

Answer 13

cells at the deep end of the dental lamina, where a tooth is destined to form, will develop into epithelial knobs- epithelial bud
surrounded by mesenchymal tissue

Question 14

timeline of primary buds

Answer 14

6 to 8 weeks in utero- upper arch a little behind

Question 15

timeline of permanent buds

Answer 15

4 months in utero to 5 years postnatal

Question 16

how many epithelial buds arise from the primary dental lamina of each arch?

Answer 16

16, 10 primary teeth and 6 permanent molars

each succedaneous tooth has its own secondary dental lamina that arises from lingual side of primary dental lamina

Question 17

cap stage

Answer 17

odontogenic epithelial in shape of a cap. site of enamel knot concentration of epithelial cells of cap is a signaling center- determines if tooth will develop to become anterior or posterior tooth

Question 18

epithelial bell stage

Answer 18

epithelial cap undergoes growth and develops into a bell shaped epithelial structure called enamel organ.
epithelium arranged into 4 distnct cell layers

Question 19

4 epithelial cell layers of enamel organ

Answer 19

1. inner epithelial layer
2. stratum intermedium epithelial layer
3. stellate reticulum epithelial layer
4. outer epithelial layer

Question 20

secondary dental lamina

Answer 20

lingual to primary tooth germ

arises from primary dental lamina not oral epithelium

Question 21

tooth germ

Answer 21

combined epithelial enamel organ and closely associated ectomesenchymal tissue that is continuous from around the epitheum to within the epithelium

Question 22

destiny of enamel organ

Answer 22

avascular
inner epithelial cells differentiate into ameloblasts- specialized epithelial cells
after formaton of enamel is complete, the ameloblasts and other layers of enamel organ come toether over the surface of the enamel as protecrive structure called reduced enamel epithelium

Question 23

destiny of dental papilla

Answer 23

vascular
undifferentiated cells (stem cells) become odontoblast, fibroblast, reserve cells
ultimately become the pulp tissue of tooth

Question 24

destiny of dental follicle

Answer 24

vascular
its stem cells become cementoblast, fibroblast, osteoblast and reserve cells
ultimately becomes periodontal ligament of periodontium

Question 25

cervical loop

Answer 25

rim of the epithelial bell (enamel organ)

site where inner and outer cell layers merge

Question 26

what forms at the cervical loop?

Answer 26

double epithelial layer called hertwig’s epithelial root sheath

Question 27

what are the functions of root sheath?

Answer 27

determines root dentin outline

determines number of root canals of tooth

Question 28

when does central incisors primary buds occur

Answer 28

6 weeks in utero

Question 29

when does second molars primary buds occur

Answer 29

8 weeks in utero

Question 30

when does first molar permanent buds occur

Answer 30

4 months in utero

Question 31

when does central incisor permanent buds occur

Answer 31

5 months in utero

Question 32

when does second molar permanent buds occur

Answer 32

10 months postnatally

Question 33

when does third molar permanent buds occur

Answer 33

5 years postnatally