Tooth Development

Question 1

The 3 primary embryonic layers

Answer 1

1. ectoderm
2. mesoderm
3. endoderm

Question 2

what embryonic tissues are the teeth developed from

Answer 2

• ectoderm = enamel

- ectomesenchyme (neural crest) [4th cell line] = all other tooth and supporting tissues

Question 3

what cells are in the neural tube and what do they form

Answer 3

neural crest (ectomesenchyme) cell line and form brachial arches (forming facial structures)

Question 4

what are the 5 stages of tooth development

Answer 4

1. initiation
2. morphogenesis
3. cytodifferentiation
4. matrix secretion
5. root formation

Question 5

what occurs in tooth initiation (stage 1) of tooth development

Answer 5

• primary epithelium band forms
• after formed (7 weeks) called dental lamina
• grows into jaw creating two parts
  i. vestibular lamina (makes buccal sulcus)
  ii. dental lamina (forms enamel organ)
  - horse shoe shaped at 8 weeks

Question 6

what occurs in tooth morphogenesis (stage 2) of tooth development (3 phases)

Answer 6

1. bud stage
   
   • dental lamina thickens forming enamel organ bud
   • dental papilla forms (from ectomesenchymal condensation around bud)
2. bud to cap stage
3. cap stage
   
   • enamel organ forms cap over dental papilla
   • enamel organ now has external and internal enamel epitheliums that meet at the cervical loop

Question 7

what occurs in tooth cytodifferentiation (stage 3) of tooth development

Answer 7

• at 14 weeks
• tooth shape being defined
• 4 layers
  i. internal enamel epithelium
  ii. external enamel epithelium
  iii. stratum intermedium
  iv. stellate reticulum (holds sugars for other layers as Blood vessels so far away)

Question 8

what occurs in tooth matrix secretion (stage 4) of tooth development

Answer 8

• 18 weeks
• apposition of enamel and dentine begin
• dental papilla cells next to internal enamel epithelium differentiate into odontoblasts (once this started, IEE cells differentiate into ameloblasts

Question 9

describe enamel formation (with reference to its two stages)

Answer 9

1. protein matrix deposition
2. organic content removed
   - all by action of ameloblasts

Question 10

describe the ameliogenesis process (7 stages)

Answer 10

• earlier stage at cervix and latest at cusp
  1. morphogenic
  2. histodifferentiation
  
  • • IEE cells become columnar and nucleus moves basally
      3. secretory (initial)
      4. secretory (tomes process)
  • • secrete partially mineralised enamel matrix (amelogenins)
      5. maturative (ruffle ended)
      6. maturative (smooth)
  • • ameloblasts secrete enzymes to breakdown protein in matrix thus mineralising enamel
      7. protective
  • ameloblasts regress forming cube like cells forming the protective reduced enamel epithelium (plays roll in eruption and tooth attachment)

Question 11

what occurs in the root formation secretion (stage 5) of tooth development

Answer 11

• migration of cervical loop after crown fully formed (root shape defined by this = called hertwig’s epithelial root sheath (HERS which also induces formation of root dentine)
• HERS persists as debris of malassez
• mesenchymal cells contact dentine and differentiate into cementoblasts
• sharpeys fibres embedded int cementum at this time

Question 12

name of entire dental papilla and enamel organ together

Answer 12

dental follicle

Question 13

defects that can occur in teeth in tooth development stages

Answer 13

• infection causing enamel pausing of deposition
• gemination (tooth germ breaks into two teeth)
• fusion (two germs fuse in development)
• concrescence (teeth joined - can be of cementum under bone)