Tooth formation

Question 1

Describe the initiation stage of tooth development

Answer 1

· In this stage, embryonic oral epithelium, derived from the ectoderm of the first pharyngeal arch, begins thickening

• As the epithelium begins thickening, it grows downward into the underlying connective tissue, bifurcating into dental lamina and vestibular lamina
• Certain points in the dental lamina will develop an additional growth of cells called’placodes’ which will become the dental lamina

Question 2

Describe the bud stage of tooth development

Answer 2

· The placode proliferates into a bud
· At this stage, there is a dense condensation of ectomysenchymal cells surrounding the tooth bud
· The tooth bud is referred to as the enamel organ
· The enamel organ consists of low columnar cells peripherally and and central polygonal cells

Question 3

Describe the cap stage of tooth development

Answer 3

· The cells do not divide uniformly in the bud. Rather, there is differential proliferation
· This leads to a concavity in the enamel organ, resulting in a cap shape
· In this stage, the enamel organ consists of inner and outer enamel epitheliumand stellate reticulum
· Externally in the concavity of the cap there is a dense amount of ectomysenchymal cells
* The dense accumulation is known as “dental papilla”. It will give rise to dentine and pulp
· Around the periphery of the cap are the mysenchymal cells are known as the dental follicle. It will give rise to PDL and cementum

Question 4

Describe the early bell stage of tooth development

Answer 4

• Marked by morphodifferentiation: the shape of the crown of the tooth is formed within the enamel organ
• Marked by histodifferentiation: IEE and dental papilla give rise to ameloblasts and odontoblasts respectively
• Dental lamina disintegrates, separating the tooth germ from the oral epithelium
  · In this stage, the inner oral epithelium secretes growth factors andsignalling molecules which stimulates dental papilla to form odontoblasts
  · The stratum intermedium has a role in helping form enamel
  · The cervical loop, where inner and outer oral epithelium meet, is where the root sheath will form

Question 5

Describe the late bell stage of tooth development

Answer 5

· Characterised by the mineralisation of enamel and dentine
· Stellate reticulum collapses
*The ameloblasts and outer enamel epithelium fuse to form reduced enamel epithelium

Question 6

Describe the root formation stage of tooth development

Answer 6

· The cervical loop proliferates and forms the “Hertwigs epithelial root sheath”
· It is bent at a 45D angle
· It grows coronally, not fromits free end
· The inner layer of the root sheath initiates the formation of odontoblasts = dentine
· As dentine forms and mineralises, the adjacent root cells will disintegrate
* Dental follicle cells will take the place of the disintegrated root cells.
* This will differentiate to form cementoblasts = cementum