1. Tooth Development Odontogenesis

2. Stages of tooth development
initiation stage – 6th to 7th week
bud stage – 8th week
cap stage – 9th to 10th weeks
bell stage – 11th to 12th weeks
apposition stage – vaires per tooth
maturation stage – varies per tooth

3. Tooth formation First signs of formation – day 11
Thickening of the epithelium where tooth formation will occur on the 1st branchial arch
Earlier signals – earliest mesenchymal markers for tooth formation are the Lim-homeobox genes (Lhx-6 and Lhx-7) – expressed as early as day 9 in the neural crest cells of the tooth region

4. Tooth formation
more than 90 genes have been identified in the oral epithelium, dental epithelium and dental mesenchyme!! so exact signaling mechanisms remain unclear

5. Tooth formation -initial stage-
involves the physiologic process of induction
induction of ectodermal tissues by the developing mesenchyme
mechanisms remain unknown
at the 6th week the stomatodeum is lined with ectoderm – outer portion is the oral epithelium
this gives rise to the primary epithelial bands

6. Tooth formation -initial stage-
also is a developing mesenchyme which contains neural crest cells that have migrated to the area
a basement membrane separates the developing oral epithelium and mesenchyme

7. Cross section (A)
Neural crest cells

8. Basement membrane
ECTODERM
MESODERM
ectomesenchymal cells

9. Primary epithelial Band

10. Tooth formation -initial stage-
Primary epithelial bands: Horseshoe-shaped bands that appear approximately around the 37th day of development, one for each jaw.
There are two subdivisions: vestibular lamina and dental lamina

11. Tooth formation -initial stage-
The dental lamina develops a series of epithelial outgrowths - grow deep into the mesenchyme
develops in the future spot for the dental arches
will form the midline for these arches
arches then form posteriorly from this point
the ingrowths represent the future sites for each deciduous tooth

12. Tooth formation -initial stage-
the vestibular lamina cells rapidly enlarge and then degenerate – forms a cleft that becomes the vestibule of the oral cavity
The initiation of tooth formation starts around the 37th day of gestation.

13. Early Dental Lamina Tongue Dental lamina Vestibular lamina
©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

14. Late Dental Lamina

15. Tooth type determination
Patterning means the determination of specific tooth type at the correct position.
Homodont are animals with same shaped teeth
Heterodont are the most mammals with different tooth types
Two theories for the determination of tooth type

16. Tooth type determination
The field model theory proposes that factors responsible for the determination reside within the ectomesenchyme, but graded fields for each tooth
The clone model theory proposes that each tooth is derived from a clone of ectomesenchymal cells programmed by the epithelium to produce a given pattern.

17. Bud stage marked by the incursion of epithelium into the mesenchyme
period of extensive proliferation and growth of the dental lamina
forms into buds or oral masses that penetrate into the mesenchyme
each tooth bud is surrounded by the mesenchyme

18. Bud stage
buds + mesenchyme develop into the tooth germ and the associated tissues of the tooth
this developing tooth forms from both the ectoderm and mesenchyme and from neural crest cells that have migrated into the mesenchyme

20. Tongue
Bud stage
Future dental papilla

21. Cap stage
characterized by continuation of the ingrowth of the oral epithelium into the mesenchyme.
tooth bud of the dental lamina proliferates unequally in different parts of the bud
forms a cap shaped tissue attached to the remaining dental lamina
looks like a cap sitting on a ball of condensing mesenchyme

22. Cap stage occurs for the primary dentition (during the fetal period)
this stage marks the beginning of histodifferentiation (differentiation of similar epithelial cells into functionally and morphogically distinct components)
the tooth germ also begins to take on form – start of morphodifferentiation

23. Cap stage
a depression forms in the deepest part of each tooth bud and forms the cap or enamel organ (or dental organ) – produces the future enamel (ectodermal origin)

24. Cap stage
below this cap is a condensing mass of mesenchyme – dental papilla – produces the future dentin and pulp tissue (mesenchymal origin)

25. Cap stage
the basement membrane separating the dental organ and the dental papilla becomes the future site for the dentinoenamel junction (DEJ)

26. Cap stage
remaining mesenchyme surrounds the dental/enamel organ and condenses to form the dental sac or the dental follicle

27. Cap Stage of Tooth Development
Dental (enamel) organ
Dental papilla
dental follicle
©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl
Oral Histology, 5th edition, A R Ten Cate

28. Cap Stage
©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

29. Cap stage
together the enamel organ + dental papilla + dental follicle is considered the developing tooth germ or tooth primordium
these primordium will be housed in the developing dental arches and will develop into the primary dentition

30. Cap stage
Enamel knots are clusters of nondividing epithelial cells visible in sections of molar cap stage tooth germs.
They play an important role by the cuspal morphogenesis.

31. Bell stage
Continuation of histodifferentiation and morphodifferentiation
cap shape then assumes a more bell-like shape
differentiation produces four types of cells within the enamel/dental organ
1. inner enamel epithelium
2. outer enamel epithelium
3. stellate reticulum
4. stratum intermedium

32. Bell stage
the dental papilla undergoes differentiation and produces two types of cells
outer cells of the DP – forms the dentin-secreting cells (odontoblasts)
central cells of the DP – forms the primordium of the pulp

33. Differentiation of the Enamel organ
outer enamel (dental) epithelium (OEE):
cuboidal shape
protective barrier during enamel production
very little cytoplasm
cells are separated from the dental follicle by a basement membrane

34. Differentiation of the Enamel organ
inner enamel (dental) epithelium (IEE)
short, columnar cells
differentiates into the enamel secreting cells = ameloblasts
separated from the dental papilla below it by a basement membrane also
cells accumulate large amounts of glycogen

35. Differentiation of the Enamel organ
cervical loop:
the IEE and OEE are continuous
region where they connect – curved rim of the EO = cervical loop

36. Differentiation of the Enamel organ
stellate reticulum
star-shaped cells in many layers
center of the enamel organ
forms a network = reticulum
supports production of enamel

37. Differentiation of the Enamel organ
stratum intermedium
inner layer of compressed flat to cuboidal cells
very high levels of the enzyme alkaline phosphatase
supports production of enamel

38. Bell stage – other events
Two important events occur at the bell stage:
the dental lamina begins to break up into discrete islands of epithelial cells (epithelial pearls) – separates the oral epithelium from the developing tooth
these pearls may form cysts and delay eruption or they may develop into supernumerary teeth

39. Bell stage – other events
the IEE completes its folding and you can begin to identify the shape of the future crown pattern.

40. Bell stage – crown formation
the dental papilla is separated from the enamel organ by a basement membrane
immediately below this BM is a region called the acellular zone
this is where the first enamel proteins will be laid down

41. Tooth Development Odontogenesis