1. ORAL HISTOLOGY
LECTURE - 4

2. HARD TISSUE GENESIS
Tooth
Enamel
Dentine
Cementum
Bone

3. Derivatives Oral Ectoderm Head ectomesenchyme (from neural crest)
Enamel
Head ectomesenchyme (from neural crest)
Dental Papilla
Dentin
Pulp
Dental Follicle (sac)
Cementum
Periodontal ligament
Portion of alveolar bone (part of cribriform plate)

4. Hard tissue genesis cont.
The principal formation of both tooth hard tissues are the same as they require cells to produce matrix
Dentine, cementum and bone require collagen while enamel doesn’t
In addition enamel is secreted by ectodermal cells whereas dentine, cementum and bone are secreted by mesodermal cells

5. Development of the tooth bud (tooth germ)

6. Dentition Primary dentition – develops during prenatal period
20 teeth
Permanent dentition – develops as the jaw grows and matures
32 teeth
period in between – during the preteen years
mixed dentition period

7. Tooth development
Tooth development is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth.
Although many diverse species have teeth, non-human tooth development is largely the same as in humans.

8. Tooth development cont.
For human teeth to have a healthy oral environment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development.
Primary teeth start to form between the sixth and eighth weeks in utero, and permanent teeth begin to form in the twentieth week in utero.
If teeth do not start to develop at or near these times, they will not develop at all.

10. Tooth bud/germ
The tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth.
These cells are derived from the
ectoderm
ectomesenchyme

11. The initiation of tooth formation starts around the 37th day of gestation.
At this time there is a formation of primary epithelial band on each jaw

12. Primary epithelial bands is a Horseshoe-shaped bands that appear approximately around the 37th day of development, one for each jaw.
There are two subdivisions of this band:
vestibular lamina
dental lamina

13. Primary epithelial bands

14. The tooth bud/germ is organized into three parts:
1. Enamel organ
2. Dental papilla
3. Dental follicle.

15. Histologic slide showing a tooth bud.
A: enamel organ B: dental papilla C: dental follicle

16. The enamel organ The enamel organ is composed of
outer enamel epithelium
inner enamel epithelium
stellate reticulum
Stratum intermedium.
These cells give rise to ameloblasts, which produce enamel and the reduced enamel epithelium.

17. Enamel organ cont.
The location where the outer enamel epithelium and inner enamel epithelium join is called the cervical loop
The growth of cervical loop cells into the deeper tissues forms Hertwig's Epithelial Root Sheath, which determines the root shape of the tooth.

18. Diagram (enamel organ)

19. The dental papilla
The dental papilla contains cells that develop into odontoblasts, which are dentin-forming cells.
Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth.
Mesenchymal cells within the dental papilla are responsible for formation of tooth pulp.

20. The dental follicle
The dental follicle gives rise to three important entities:
Cementoblasts
osteoblasts
fibroblasts.
Cementoblasts → cementum
Osteoblasts → alveolar bone
Fibroblasts → periodontal ligaments

21. Tooth development stages

22. Tooth development is commonly divided into the following stages:
The bud stage
The cap stage
The bell stage
The Crown stage.

23. The staging of tooth development is an attempt to categorize changes occuring histologically.
Frequently it is difficult to decide what stage should be assigned to a particular developing tooth

24. The bud stage
The bud stage is characterized by the appearance of a tooth bud without a clear arrangement of cells.
Stage technically begins once epithelial cells proliferate into the ectomesenchyme of the jaw
The tooth bud itself is the group of cells at the end of the dental lamina.

26. 1.Tooth bud
2.Oral epithelium
3.Ectomesenchyme
A: enamel organ
B: dental papilla
C: dental follicle

27. The cap stage
It is characterized by continuation of the epithelial proliferation (ingrowth) into the ectomesenchyme to forms a cap like structure aggregation of cells
This stage marks the beginning of histodifferentiation

29. The bell stage
It is the histodifferentiation and morphodifferentiation stage
The dental organ is bell-shaped
majority of its cells are called stellate reticulum because of their star-shaped appearance.
Cells on the periphery of the enamel organ separate into three important layers.
Outer enamel epithelium (Cuboidal cells)
Inner enamel epithelium (The columnar cells adjacent to the dental papilla)
Stratum intermedium (The cells between the inner enamel epithelium and the stellate reticulum)
The rim of the dental organ where the outer and inner enamel epithelium join is called the cervical loop.

30. Histologic slide of tooth in early bell stage
Histologic slide of tooth in late bell stage.

31. In summary, the layers in order of innermost to outermost consist of
Dentine
Enamel (formed by inner enamel epithelium, or 'ameloblasts', as they move outwards/upwards)
Inner enamel epithelium and stratum intermedium (specialised stratified cells that support the synthetic activity of the Inner Enamel Epithelium)
Stellate reticulum cells.
The outer enamel epithelium layer.

32. Other events occur during the bell stage.
The dental lamina disintegrates, leaving the developing teeth completely separated from the epithelium of the oral cavity
The two (tooth and oral epithelium) will not join again until the final eruption of the tooth into the mouth.

33. The Crown stage
Hard tissues including enamel and dentin, develop during the next stage of tooth development.
This stage is called the crown or maturation stage leading to completion of crown formation

35. Formation of the periodontium
The periodontium, which is the supporting structure of a tooth, consists of the cementum, periodontal ligaments, gingiva, and alveolar bone.
Cementum is the only one of these that is a part of a tooth.
Alveolar bone surrounds the roots of teeth to provide support and creates what is commonly called a "socket".
Periodontal ligaments connect the alveolar bone to the cementum, and the gingiva is the surrounding tissue visible in the mouth.

36. ROOT FORMATION
The root of the tooth is composed by dentin and cementum.
Dentinogenesis is initiated by the odontoblasts.
Odontoblasts are formed as epithelial cells continue to proliferate from the cervical loop as a double layer of cells known as Hertwig's root sheath.
Cementum is then deposited on the surface

37. The fate of the dental lamina
Rests of Serres
The rest of Serres are rests of the dental lamina identified in the gingival soft tissues.
They are round to ovoid aggregates of epithelial cells that have clear cytoplasm (glucogen rich).
They result from early breakup of the dental lamina during bell stage.
Rests of Malassez
The rests of Malassez result from breakup of the Hertwig's root sheath during root formation.
They can be identified in the periodontal ligament and are responsible for the development of radicular cysts.

38. Murakoze cyane!!!

39. ORAL HISTOLOGY lecture -5

40. TOOTH ERUPTION
Tooth eruption is a continuous process from the beginning of the formation of tooth bud /germ until the tooth is extracted or lost.
We tends to think of eruption only when the tooth in the oral cavity but tooth eruption is a CONTINUOUS process.

41. Reduced enamel epithelium (REE)
Represent the fusion of the 4 cell layers of the enamel organ (OEE, SR, SI and IEE)
It covers the area of the crown to the cervical line
REE remains with the tooth indefinitely until the tooth erupt in the oral cavity
It will play a role in the eruption process

42. Direction of tooth movement
There are 4 movement that occurs during the process of tooth eruption
AXIAL- movement along the long axis of the tooth
DRIFTING/BODILY – whole tooth movement (mesial, distal buccal, lingual)
TILTING – movement along the transverse axis of the tooth
ROTATION – Movement along the longitudinal axis of the toot

43. Phases of eruption The eruption process is divide into three phases
Pre- eruptive
Eruptive
Post - eruptive

44. Phase I (Pre- eruptive phase)
From the initial formation of tooth germ to beginning of root formation
Events
Multiple tooth bud formation
Growth in height of the maxilla and the mandible
tooth germ keeps pace with the growth of mandible and maxilla by positioning itself for eruption

45. Phase II ( eruptive phase)
This phase is from the start of root formation till the tooth reaches its contact with opposing tooth (occlusal plane)
Events
Formation of epithelial root sheath of Hertwing
Formation of root dentine
Organization of PDLs
Formation of alveolar bone and cementum

46. Phase III ( post-eruptive phase)
This is from the time the tooth reaches the occlusal plane till it is lost.
Events
Continuous attrition/grinding of molars and central incisors
Axial eruption to compensate for the attrition (occlusal enamel loss)
Continuous deposition of bone and cemenum
Physiological mesial drift

47. Theories of tooth eruption
These are
PUSH THEORIES
PULL THEORIES

48. PUSH THEORIES
Postulate that there is a pushing forces that allow the tooth to erupt in the oral cavity.
These theories are
Root growth theory
Pulp proliferation theory
Tissue fluid or blood pressure theory
Bone growth theory

49. PULL THEORY
Also known as PERIODONTAL FIBER THEORY.
It is considered that traction on the oblique principle fibers of the PDLs pull the tooth towards the oral cavity
Interferance of these fibers delay/stop eruption
RECENTLY – The dental follicle is important in tooth eruption and removal of the follicle causes stoppage of eruption.

50. Clinical consideration
Eruption of teeth in the oral cavity is termed as “teething”
It has been shown that teething is not painful however, once it is infected teething became painful.

51. The End