Development of tooth power point presentation

2. Presented by
K Sushmitha
I MDS

3. Contents
• Introduction
• Initiation of tooth development
• Primary epithelial band
• Dental lamina
• Vestibular lamina
• Tooth developmental stages
-Bud
-Cap
-Bell (Early & Advanced)
• Root formation
• Histophysiology
• Molecular insights
• Amelogenesis
• Dentinogenesis
• Clinical considerations
• Conclusion
• References

4. Introduction

5. Initiation of tooth development
The primitive oral cavity is called stomodeum – lined by
stratified squamous epithelium - oral ectoderm.
The oral ectoderm contact the endoderm of the
foregut to form the bucco-pharyngeal membrane.
At about 27th day of gestation buccopharyngeal
membrane ruptures and the primitive oral cavity
establishes a connection with the foregut

6. Primary epithelial band

7. • Thickening of epithelial band occurs due to
change in orientation of mitotic spindle &
cleavage plane of dividing cells.
• Quickly give rise to 2
subdivisions
ˉ vestibular lamina
ˉ dental lamina

8. Dental Lamina
• 6 weeks old embryo -basal cells of oral ectoderm proliferates – GERMINAL
BAND OF EPITHELIUM.
• Represents the first sign of tooth development.
• Primordium for the ectodermal portion of deciduous teeth

9. • Permanent molars arise from distal
extension of dental lamina.
• First permanent molar - initiated - 4th month
in-utero.
• 2nd molar - first year after birth
• 3rd molar - 4th or 5th years

10. • Develops - 5th
month IUL (permanent central
incisor)
• 10th
month of age after birth(second
premolar)

11. Initiation
• Primary dentition 6-7 weeks of IU
• Successional permanent teeth 5th
month IU to 10 months after
birth

12. Fate of dental lamina

13. Cell rests of Serres

14. Vestibular Lamina
• Lip furrow band
• V shaped – forms vestibular grove.

15. Tooth Development

16. Formation of Enamel Organ
 At certain points on DL representing -10 mandibular & 10 maxillary deciduous
teeth - cells multiply still more rapidly.
 Forming little knobs - grow into underlying mesenchyme

17.  Each of these little outgrowths represents – beginning of enamel organ of tooth
bud of deciduous teeth
 Not all develop at same time
 First- mandibular anterior region
 Differential growth - Change in shape

18. Dental Papilla
• On the inside of the cap - ectomesenchymal cells increases.
• Tissue appears - more dense than the surrounding mesenchyme
• Represents the beginning of the dental papilla

19. Dental sac/ Dental follicle
• Surrounding - combined enamel organ & dental papilla
• 3rd
part of the tooth bud forms - dental sac/follicle
• Consists - ectomesenchymal cells and fibres that surrounds the dental papilla and
the enamel organ.
Dental follicle

20. Tooth germ
 Includes all the formative tissues for the entire tooth and its supporting
structures
Ectodermal component - Enamel organ -- enamel.
Ectomesenchymal component
• Dental papilla - dentin and pulp.
• Dental follicle or dental sac - cementum, periodontal ligament,
and part of alveolar socket

21. • Development of tooth – interaction of cells.
• Upto 12 days- first arch epithelium - retains ability.
• When combined with neural crest cells in other regions.
• But transferred to neural crest cells as revealed in various recombinant
experiments.

22. • Like any other organ development –numerous & complex gene expressions
– occurs to control – development process- through molecular signals.
• Experimental studies to understand the genetic control and molecular
signalling have been done on mice as it is amenable for genetic
manipulations to produce “ knock-out mice” or “null mice”

23. Stages of tooth development

24. Bud stage

26. Cap stage/ Proliferation
• During ninth week - as tooth bud continues to proliferate laterally.
• Does not expand uniformly into a large sphere
• Rather show differential growth leading to cap shape.

27. • Characterized by a shallow invagination on the deep surface of the bud

28.  3 layers of cap stage
• Outer dental epithelium
• Inner dental epithelium
• Stellate reticulum

30. Stellate reticulum
 Polygonal cells – b/w OEE & IEE - begin to separate due to water being drawn
into the enamel organ from the surrounding dental papilla.
 polygonal cells  star shaped
 Maintain contact with each other by their cytoplasmic process
 star shaped cells – forms cellular network- hence the name SR.
 Shock absorber

31. Transient structures
• Enamel Knot:
• Densely packed cells in the center of enamel organ.
• Center of epithelial invagination will shows a knob like enlargement.
• Function of enamel knot - reservoir of dividing cells for the growing EO.

32. • Enamel cord : Vertical enamel knot
• Enamel septum : when EC meets OEE
• Enamel navel : small depression - attachment of enamel cord to outer
dental epithelium (resembles umbilicus)

33. Bell stage
•As the invagination of epithelium deepens - margins continue to grow
•Enamel organ assumes a bell shape
•In this stage - crown shape is determined.
•Four different types of epithelial cells-
1. Inner enamel epithelium
2. Stratum intermedium
3. Stellate reticulum
4. Outer enamel epithelium

34. Consists of a single layer of cells
Differentiate prior to amelogenesis into tall columnar cells-
Ameloblasts(4-5 in diameter; 40 high)
The cells of the inner enamel epithelium exert an organizing influence on
mesenchymal cells in the dental papilla
later differentiate into odontoblasts.
Inner enamel epithelium

35. Stratum intermedium
• Few layers of squamous cells forms stratum intermedium - between IEE and SR
• These cells are closely attached by desmosomes & gap junctions
• Cytoplasmic granules, glycogen deposits- high degree of metabolic activity.
• This layer seems to be essential to enamel formation.

36. Stellate reticulum
• SR expands further due to continued accumulation of inter-cellular fluid
• star shaped cells,- having a large processes that anastomose with those of
adjacent cells
• enamel formation starts – SR collapses to a narrow zone
• Thereby reducing distance b/w the OEE & IEE

37. Outer enamel epithelium
• Cells - flatten to form low cuboidal cells
• OEE is thrown into folds which are rich in capillary network – source of nutrition
for EO

38. Dental papilla
• Enclosed in the invaginated portion of EO.
• Before IEE begins to produce enamel, peripheral cells of DP-
odontoblasts.
• First they assume cuboidal form, then columnar.
• Acquires a specific potential for dentin production.
• BM-separating EO& DP- ‘membrana preformativa’

39. Cervical Loop
• Region where IEE & OEE meet at the rim of the enamel organ
• This is the point where cells continue to divide until tooth attains its full size &
which after crown formation gives rise to epithelial component of root
formation.

40. Advanced bell stage
• Characterized by commencement of mineralization & root formation.
• Boundary b/w IEE & odontoblasts –
outlines future DEJ.
• Formation of dentin occurs first as a
layer along future DEJ
• Begins at cusp tips, proceeds cervically
and apically.

41. • After 1st layer of dentin- ameloblasts-
enamel- cusp area.
• Proceeds coronally & cervically from DEJ
towards surface.
• Cervical portion of enamel organ will gives
rise to “HERS“
• Outlines future root; responsible for shape,
length, size& no. of roots.

42. Root formation
• Begins after enamel & dentin formation has reached future CEJ.
• Enamel organ - imp role – HERS - molds shape of root
and initiates radicular dentin formation.
• Cells of IEE & OEE - proliferate as double
layered sheath from cervical loop.
• Devoid of SI& SR.

44. HISTOPHYSIOLOGY
 Initiation :- ectomesenchyme will instructs the epithelial cells to form the enamel.
 Proliferation:- Proliferative growth causes regular changes in size and proportions of tooth germ.
 Histodifferentiation:- Ectodermal and mesenchymal cells differentiated into specialized cells
 Morphodifferentiation :- Shape of the tooth is decided
 Apposition :- Formation of mineralized hard tissues. It is characterized by regular and
rhythmic deposition of extracellular matrix.

45. Molecular insights in tooth morphogenesis
• Role of epithelial mesenchymail interactions: Interactions between epithelium and mesenchymal
tissues components have particularly important function in developing teeth, as well as all other
organs forming as ectodermal appendages.
• It takes place by the expression of the various genes.
 BMP- 2, 4 & 7
Msx 1, Msx 2
Shh
Wnt 7
Lef-1
Pax-9
Activin-A
Msx1 BMP-4
Fgf-8 + BMP-4 Pax-9

46. Patterning of dentition: The determination of specific tooth type at their correct
positions in the jaw. It is remarkably a consistent process.
• Field theory (Butler, 1939): All tooth primordia are initially equivalent.
• Controlled by varying concentrations of morphogens in local environment.
• A number of diffusible signalling molecules may be involved which would
produce periodicity along the developing dental axis.
• Clonal model (Osborn, 1978): Tooth primordial cells being equipped with
necessary positional information.
• Westgaard and Ferguson: Proposed hybrid progress zone model.

47. Homeobox code model
• It is based on the observations of the spatially restricted expression of several
homeobox genes.
• Msx-1 &Msx-2 restricted to distal midline mesenchymal regions of incisors &
canines.
• Dlx-1 &Dlx-2 restricted to mesenchymal cells of multicuspid teeth.
• Expression of Barx-1 overlaps with Dlx-1& Dlx-2.
• This model proposes that the overlapping domain of these genes will provide the
positional information for tooth type determination.

48. Molecular insights in bud stage:
• Msx-1 &Msx-2 and Dlx-1& Dlx-2 might act parallelly at lamina stage.
• These genes will express at different levels in bud stage due to transitions.

49. Molecular insights in cap stage:
• Recent studies - enamel knot- acts as signaling center
• E. knot-organization centre - orchestrates cuspal morphogenesis.
• Fgf-4 & Slit-1: best markers; both primary& sec. knots.

50. Amelogenesis
• Process of formation of enamel.
• It takes place under 3 stages.
• Presecretory stage
-Morphogenic phase
-Differentiation phase
• Secretory stage
• Maturation stage
-Transition phase
-Maturation proper

51. Proteins in enamel matrix:
Amelogenins: Predominant and comprises about 80% of the young enamel
matrix and contains high levels of amino acids proline, glutamine, histidine and
leucine.
Non-amelogenins: Tuftelin, sheathlin, enamelin, sulphated enamel proteins
and amelotin.

52. Dentinogenesis
• The process of formation of dentin.
• Stages of dentin development:
-Differentiation of odontoblasts
-Deposition of organic matrix
-Mineralization

53. Clinical considerations

54. Enamel pearls
Cause:
• If the cells of the epithelial root sheath of
Hertwig remain adherent to the dentin
surface,
• they may differentiate into ameloblasts
and produce enamel, called enamel
pearls.
• They appear as small, spherical enamel
projections especially at the cemento-enamel
junction (CEJ) or in the furcation area in
molars.

55. Bare dentine
• If the epithelium root sheath of Hertwig is delayed
in its separation from the dentin, a zone of the root is
devoid of cementum.

56. Accessory root canals
Causes :-
• If the continuity of the epithelial root sheath of
Hertwig is broken prior to odontoblastic
differentiation and dentin formation
• As a result of disturbance in the fusion of the
tongue like extension of the diaphragm.
• Large blood vessel may disturb the course of the
root sheath lead to accessory root canal.

57. Cell rests of Serres when proliferates will lead
to:
• Odontogenic keratocyst
• Lateral periodontal Cyst
• Gingival Cyst
• Glandular odontogenic Cyst

58. Conclusion

59. References
 Orban Oral Histology And Embryology 12th Edition
 Tencate’s Oral Histology Antonio Nanci 8th Edition
 Oral Development And Histology James Avery Third Edition.
 Inderbeer Singh: Human Embryology

60. Thank you