Tooth development

Question 1

Describe cell types in tooth development

Answer 1

All cells from ectoderm

• Dermal ectoderm - epithelial cells
• Neural crest cells - mesenchymal cells
• Neural ectoderm

Question 2

List the stages of tooth development

Answer 2

1) Initiation stage
2) Bud stage
3) Cap stage
4) Bell stage
5) Root formation

Question 3

Describe initiation stage

Answer 3

• Oral cavity found between maxillary process + frontonasal prominence, and mandibular process
• Primary epithelial band = U-shaped band formed from oral epithelial cells
• Band differentiates into:
  1) vestibular lamina -> Forms cheeks and lips
  2) Dental lamina -> Forms tooth buds

Question 4

Describe bud stage

Answer 4

• epithelial swells bud out of dental lamina
• Neural crest mesenchyme surrounds buds
• Anomalies in initiation stage and bud stage -> defines NUMBER of teeth
  1) Hypodontia (<6 teeth missing) or oligodontia (>6 teeth missing)
  2) Supernumerary teeth

Question 5

Describe cap stage

Answer 5

• Concave surface forms on end of tooth bud
• Structures of cap:
  1) Outer enamel epithelium
  2) Inner enamel epithelium
  3) Cervical loop
  4) Stellate reticulum
  5) Enamel knot (transient structure)
  6) Dental follicle
  7) Dental papilla

Question 6

Describe early bell stage

Answer 6

Early bell stage = stratum intermedium forms; no hard tissue

• Enamel cord = cell strand between OEE to IEE (nutrient highway)
• Successional lamina = elongation of primary tooth germ on lingual side that form permanent tooth
• Anomalies in cap and early bell -> Defines SHAPE of crown and DEJ
  1) Dens invaginatus/evaginatus (invaginated/evaginated odontoma)
  2) Macrodontia (large tooth size)
  3) Microdontia (small tooth size)

Question 7

Describe late bell stage’s reciprocal induction

Answer 7

Hard tissue formation.
Reciprocal induction:
- IEE produces pre-ameloblasts
- Pre-ameloblasts induce dental papilla to produce odontoblasts
- Pre-dentine secreted by odontoblasts
- Pre-dentine induces pre-ameloblasts to form ameloblasts
- Ameloblasts secrete enamel

Question 8

Describe late bell stage’s enamel formation

Answer 8

• Each ameloblast forms one Tomes process: each ameloblast forms 1 rod and contributes to 3 adjacent interrods (tails)
• Enamel components: 96% hydroxyapatite, 4% proteins (90% amelogenins)
• Histological features: Striae of Retzius (incremental lines), perikymata, Hunter-Schreger Bands
• Anomalies in ENAMEL formation in Late Bell stage: amelogenesis imperfecta -> poor matrix deposition, fluorosis -> tooth discolouration

Question 9

Describe late bell stage’s dentine:

Answer 9

• Odontoblasts form from dental papilla cells
• Dentine produces form DEJ to pulp core
• Dentin Components: 70% hydroxyapatite, Type 1 collagen (Mantle dentine has Type 3 vollagen (von Korff’s fibre) - near DEJ
• Histological features: DEJ (Scalloped, rod-less enamel, enamel spindles/tufts)
• Anomalies in DENTINE formation in Late Bell Stage: dentinogenesis imperfecta (Yellow/brown or blue/grey teeth, weak teeth, type 1: associated with osteogenesis imperfecta, type 2: mustation of DSPP gene)