Tooth development

Question 1

what is the stomodeum

Answer 1

• lined ectodermal layer

- underlying layer of mesenchyme

Question 2

what embryonic layer do teeth develop from

Answer 2

• the ectoderm

Question 3

what is the dental lamina

Answer 3

• a band of thickened oral epithelium extending along the occlusal borders of the embryonic jaws within the stomodeum

Question 4

what is mesenchyme

Answer 4

• non-specialized connective tissue

Question 5

what are the 3 parts in tooth development

Answer 5

1. enamel organ
2. dental papilla
3. dental sac

Question 6

what is the enamel organ

Answer 6

• knob to cap like growth
• comes from dental lamina - which came from epithelium
• will become enamel
• from ectoderm

Question 7

what is the dental papilla

Answer 7

• beneath the enamel organ
• comes from mesenchyme
• will become dentin and pulp

Question 8

what is the dental sac

Answer 8

• each tooth has its own
• comes from mesenchyme
• will become the periodontal ligament
• periodontal ligament will form cementum and lamina dura

Question 9

what are the 3 life cycles of the tooth

Answer 9

1. bud
2. cap
3. bell

Question 10

what is the bud stage

Answer 10

• where the primary dental lamina exists
• begins with thickening of oral epithelium to form the dental lamina
• dental lamina invaginates
• extends through underlying mesenchyme
• cells grow and form a bud
• 20 buds are forms -> 10 in each arch, where the primary teeth will later form

Question 11

what is the cap stage

Answer 11

• 6-9 weeks
• proliferation of cells -> forms depression deepest part of tooth bud
• form cap structure -> enamel organ (first part of the tooth germ)
• enamel organ begins to surround mesenchyme
• cells not only grow in this stage but also begin to differentiate (mesenchyme becomes connective tissue which becomes dental papillae beneath the enamel organ, like pulp and dentin), forms dental sac surrounding the lower border of dental papillae and part of enamel organ
• end cap stage, these 3 structures form tooth germ -> will develop in the primary dentition

Question 12

what are the 4 components of the enamel organ in the cap stage

Answer 12

1. outer enamel epithelium
2. inner enamel epithelium
3. stellate reticulum
4. stratum intermedium

Question 13

what is the outer enamel epithelium

Answer 13

• outside layer on surface of enamel organ
• cuboidal cells
• protective layer for entire EO

Question 14

what is the inner enamel epithelium

Answer 14

• lines inside of enamel organ - the concave part
• cuboidal elongate to columnar as they differentiate
• become ameloblasts - enamel formation
• IEE separate from dental papilla by basement membrane - future DEJ

Question 15

what is the stellate reticulum

Answer 15

• cells between the OEE and IEE
• loose network of epithelial cells - star shaped
• provide protection/cushion
• part in the nourishment for IEE - transport to stratum intermedium

Question 16

what is the stratum intermedium

Answer 16

• layer of flat epithelial cells inside the stellate reticulum
• between SR and IEE
• nourishes IEE by changing vascular fluids from stellate reticulum to usable form for IEE

Question 17

what is the basement membrane

Answer 17

• future DEJ
• future outline, shape and form of the crown
• cells on either side of the basement membrane differentiate: change shape and function
• above the basement membrane: inner enamel epithelial cells -> ameloblasts
• below basement membrane: peripheral cells of the dental papilla -> odontoblasts
• once ameloblast and odontoblast are formed -> formation of dentin and enamel starts

Question 18

what is the secondary dental lamina

Answer 18

• 2nd dental lamina appears before dentin and enamel formation begins
• forms from primary dental lamina, secondary dental lamina will develop in permanent tooth germ and will develop slowly as the primary tooth develops and erupts
• will develop in succedaneous teeth
• primary dental lamina disintegrates

Question 19

what are succedaneous teeth

Answer 19

• replace the primary teeth
• formed by secondary dental lamina
• incisors, canines and premolars
• permanent molars are non succedaneous (will get their own buds at 20 weeks)

Question 20

what is dentinogenesis and when does it occur

Answer 20

• dentin formation
• occurs 5th week in utero
• dentin is the 1st mineralized layer to appear

Question 21

what are the cells inside the basement membrane

Answer 21

• odontoblasts columnar shape, move inwards, signals the ameloblasts to move outwards
• attached to the basement membrane
• move downwards toward pulp area
  as dentin migrates down:
• form extension -> odontoblastic process
• deposit dentin matrix (fibers and ground substance)
• matrix mineralized progressively as it is produced
• forms dentin tubules containing odontoblastic process

Question 22

what is predentin

Answer 22

• most recently formed layer, hasn’t been mineralized, layer closest to the pulp
• dentin layer adjacent to pulp

Question 23

what forms the dentin

Answer 23

• the dental papilla

Question 24

what happens once a bit of dentin has been produced

Answer 24

• dental papilla will start producing pulp

Question 25

what is the primary enamel cuticle

Answer 25

• also called Nasmyth’s membrane
• when ameloblasts are done forming enamel matrix, they hit the primary enamel cuticle
• these ameloblasts produce primary enamel cuticle - secretion of an organic cuticle (squished cells between the enamel and OEE)
• this is mineralized creating a smooth coating over enamel