Diese Präsentation wurde erfolgreich gemeldet.
Wir verwenden Ihre LinkedIn Profilangaben und Informationen zu Ihren Aktivitäten, um Anzeigen zu personalisieren und Ihnen relevantere Inhalte anzuzeigen. Sie können Ihre Anzeigeneinstellungen jederzeit ändern.
MOLECULAR BIOLOGY OF
ODONTOGENESIS
SUKESH KUMAR.V
PG 1ST YEAR
DEPT. OF ORAL PATHOLOGY
CONTENTS
Introduction
-Dental Lamina
-Tooth development
-Developmental stages
-Bud stage
-Cap stage
-Bell stage
-Hard tiss...
Tooth formation occurs in the 6th week of intrauterine
life with the formation of primary epithelial band. At
about 7th we...
Tooth Development
A. Bud Stage
B. Cap Stage
C. Bell Stage
D and E. Dentinogenesis and
amelogenesis
F. Crown formation
G. R...
• The primitive oral cavity, or stomodeum, is lined by stratified squamous
epithelium called the oral ectoderm
• The oral ...
• Membrane ruptures at about 27th day of gestation and the primitive oral
cavity establishes a connection with the foregut...
Initiation of Tooth Development
Each band of epithelium will give
rise to 2 sub divisions:
1. Dental lamina and
2. Vestibu...
The vestibular lamina cells rapidly enlarge and then degenerate – forms a cleft
that becomes the vestibule of the oral cav...
Stomodeum
Developing Tongue
Dental lamina
Maxillary Process
Mandibular process
Dental Lamina
• Dental lamina appears as a thickening
of the oral epithelium adjacent to
condensation of ectomesenchyme
• ...
Tooth development is a continuous process, however can be
divided into 3 stages:
1. Bud Stage
2. Cap Stage
3. Bell Stage
M...
1. Bud Stage
• Bud stage is characterized by rounded, localized growth of
epithelium surrounded by proliferating mesenchym...
• The dental papilla as well as the dental sac are not well defined
during the bud stage, they become more defined during ...
CAP STAGE
• As the tooth bud continues to proliferate, it does not expand
uniformly into a large sphere
• Instead unequal ...
2. Cap Stage
Condensation of the ectomesenchyme immediately subjacent to the tooth bud
caused by lack of extracellular mat...
2. Cap Stage
Enamel organ
Dental papilla
Dental follicle or sac
Dental follicle or dental sac is the condensed ectomesench...
2. Cap Stage
Lateral Lamina: extension from the dental lamina that is connected
to the enamel organ
Enamel niche: It is an...
Dental organ or tooth germ is a term used to constitute the structure that has
enamel organ, dental papilla and dental fol...
Enamel knots are clusters of nondividing epithelial cells visible
in sections of molar cap stage
Enamel knot precursor cel...
3. Bell Stage
• Continued growth leads to bell stage, where the enamel organ resembles a
bell with deepening of the epithe...
3. Bell Stage (Early)
Inner dental epithelium: Short columnar cells bordering the dental papilla.
These will eventually be...
3. Bell Stage (Early)
Stellate reticulum
Inner dental epithelium
Stratum intermedium
Dental papilla
Stellate reticulum: St...
Stellate reticulum
Inner dental epithelium
Stratum intermedium
Membrana preformativa
Outer dental epithelium
Dental Papill...
Inner dental epithelium
Outer dental epithelium
Cervical loop
Cervical loop: Area where the inner and the outer dental epi...
Enamel cord
 Enamel cord: Pattern of enamel knot that extends between the inner and
outer dental epithelium
Enamel knot
3...
Advanced Bell Stage
Essentials of Oral Histology and Embryology,
Ed: James Avery, 2nd edition. 2000.
Future crown patterning also occurs in the bell stage, by folding of the
inner dental epithelium. Cessation of mitotic act...
Hard Tissue Formation
Deposition of dental hard tissues is
called “apposition”
After the crown attains its final
shape dur...
For dentinogenesis and amelogenesis to take place normally,
the differentiating odontoblasts and ameloblasts will receive
...
At the same time or soon after the first layer of dentin (mantle dentin) is formed,
the inner dental epithelial cells diff...
Root Formation
Development of root begins after the enamel and dentin formation has
reached the future cementoenamel junct...
Hertwig’s epithelial
root sheath
Inner dental epithelium
Outer dental epithelium
Stratum intermedium
Eventually the root s...
The epithelial rests appear as small clusters of epithelial cells which are located in
the periodontal ligament adjacent t...
Primary apical formen
Epithelial diaphragm: the proliferating
end of the root sheath bends at a near
45-degree angle. The ...
Secondary apical foramen form as a result of two or three tongues of
epithelium growing inward toward each other resulting...
Soon after root formation begins, tooth begins to erupt until it reaches
its final position
While roots are forming, the s...
MOLECULAR EVENTS
• Odontogenesis is a complex & also co-ordinated process
involving ectomesenchymal (EMI) interactions.
• ...
• More than 300 genes are involved in this intricate process.{2}.
• Major molecular signals during tooth formation include...
Growth factors / Homeobox genes Abbrevation Factor/
Protein
Growth
factors
Fibroblast growth factor Fgf
Secreted
protein
B...
ROLE OF EMI IN TOOTH DEV.
• Before an insight into role of EMI in tooth dev, it is important
to know about 2 terms viz;
• ...
ROLE OF EMI IN TOOTH DEV.
• Removal of epithelium from mandibular arches at E10 or
before, results in a total & rapid loss...
ROLE OF EMI IN TOOTH DEV
• Therefore, at the pre-bud stages of tooth development by
E11.5, both epithelial and mesenchymal...
Jaw
mesenchyme
Oral ectoderm
Nonoral ectoderm
Nondental
mesechyme
Nondental
mesechyme
Oral ectoderm
Jaw
mesenchyme
Nonoral...
ROLE OF EMI IN TOOTH DEV
• In contrast, at Early bud stage (E12.5), the odontogenic
potential has switched to the mesenchy...
Signal are transferred from cell to cell through signaling molecules.
Transmit information to adjacent cells
Molecules get...
ROLE OF GROWTH FACTORS
• Classic studies demonstrated the importance of Cross talk
between dental epithelium and mesenchym...
Fgf- Fibroblast growth factor
• Several members of FGF family are expressed in early
developing tooth germs
• They functio...
• Fgf-4,8,9: have been implicated as epithelial signals regulating
mesenchymal gene expression & cell proliferation during...
Growth factors
Bmp- Bone morphogenetic protein :
• Bmps have been shown to participate in epithelial
mesenchymal siganalin...
• Bmp 4 – associated with shift of odontogenic potential from
epithelium to mesenchyme.
• Bmp 2, 4, 7 – are restricted to ...
Growth factors
Hedgehog superfamily
• Discovered in Drosophila – as a signal regulating
segmental & imaginal disc patterni...
Growth factors
Wnt- wingless homolouge in vertebrates
• contains 20 secreted glycoproteins.
• involve in cell proliferatio...
ROLE OF TRANSCRIPTION FACTORS
• Experiments have revealed the expression of numerous
transcription factors in the developi...
HOMEOBOX GENES
• 180 base pair sequence code for homeodomain of a 60
amino acid DNA binding motif.
• Originally discovered...
HOMEOBOX GENES
Msx homeobox gene family
• Msx 1, Msx 2 - related to Drosophil gene muscle segment
homeobox.
• Msx 1 – on c...
HOMEOBOX GENES
Dlx family
• dista less family of homeobox gene, contains 6 members.
• Dlx 1, 2 – Ch 2q32 expressed in epit...
HOMEOBOX GENES
Barx homeobox genes
• Bar class genes expressed in craniofacial structures.
• Brax 1 – maxillary and mandib...
HOMEOBOX GENES
Pax homeobox genes
• loacted on Ch 14, play a role in early development.
• Pax 9 proteins possess 128 AA DN...
HOMEOBOX GENES
Lim homeobox genes:
Lhx is member of the LIM homeobox gene family expressed in
mesenchyme of palate
• Lhx 1...
LIM homeobox genes (Lhx 6 and 7) constitue to that
group of gene clusters which are dispersed outside the
homeobox gene cl...
TOOTH TYPE DETERMINATION
The determination of specific tooth types at their correct positions in
the jaws is referred to a...
TOOTH TYPE DETERMINATION
2.Clone model
Proposes that, A clone of ectomesenchymal cells which are
programmed by epithelium ...
TOOTH TYPE DETERMINATION
BARX-1,DLX-1
MOLARIFORM
TEETH
MSX-1,DLX-1
CANINIFORM
TEETH
MSX-1,MSX-2,ALX-3
INSISIFORM TEETH
TOOTH INITIATION AND POSITION
• It appear to originate from oral epithelium
• The Pax-9(paired box homeotic gene) is the e...
• The expression of several genes in ectomesenchyme
(Pax-9 and Activin-A) marks the site for tooth germ
initiation.
• The ...
TOOTH INITIATION AND POSITION
oral epithelium
Nondental
epithelium
Jaw mesenchyme
Pax-9
Msx-1
Pax-9
Msx-1
-FGF8 is an epit...
Positioning the sites of tooth formation :
Antagonistic signaling by BMP4
Dental epithelium
Nondental
epithelium
FGF8 Pax9...
• Other genes being involved are
-Otlx-2(Otx related homeobox genes)
-Dlx-2(distaless homologue in vertebrates)
-Msx-1 & M...
BUD STAGE
• It is the first epithelial incursion into the ectomesenchyme of
the jaw.
• Epithelium is separated from the un...
• Lef-1(Lymphoid enhancing factor) is seen in the epithelium of
tooth bud and it later shifts to the ectomesenchyme. Any
m...
• The ectomesenchyme surrounding the tooth bud and
dental papilla is the dental sac.
• Both become more well-defined in th...
BUD TO CAP TRANSITION
• Marks the onset of morphologic difference between tooth
germs that give rise to different types of...
• Blocking shh signaling shows that at E11-E12 , shh is required
for dental epithelium proliferation to form tooth buds, w...
CAP STAGE
• This stage appear like the enamel organ is present over the
dental papilla like a cap.
• As the tooth bud cont...
ENAMEL KNOT
• Cluster of non dividing epithelial cells visible in sections of
molar cap stage tooth germs.
• Enamel knot p...
ENAMEL KNOT
• Controls growth & patterning of tooth cusps.
• Each tooth germ has single enamel knot at cap stage & as
thes...
BELLSTAGE
• Bell stage so called because the continuous growth of tooth
germ leads to deepening of the undersurface of the...
ROOT INITIATION AND MORPHOGENESIS
• Root formation is initiated by enamel organ epithelial
invagination between the dental...
ROOT INITIATION AND MORPHOGENESIS
• Bmps have been found to get expressed sequentially at various
stages of root odontobla...
GENE MUTATIONS- TOOTH ABNORMALITIES
Msx, Dlx Tooth agenesis, Craniosynostosis,
Tricho- dento-osseous syndrome
Msx Autosoma...
GENE MUTATIONS- TOOTH ABNORMALITIES
Barx-1 Axenfeld Reiger syndrome
Iridogoniodysgenesis syndrome
Pitx-2 -Maxillary teeth ...
CONCLUSION
• The considerable understanding profile of gene expression ,
unveiling the molecular basis involved in tooth m...
REFERENCES
• Antonio Nanci. Ten Cate`s. Oral histology development, structure, and
fuction
• Essentials of Oral Histology ...
Molecular Basis of Tooth Development
Molecular Basis of Tooth Development
Molecular Basis of Tooth Development
Molecular Basis of Tooth Development
Nächste SlideShare
Wird geladen in …5
×

Molecular Basis of Tooth Development

1.088 Aufrufe

Veröffentlicht am

BE UPDATE TO IT,, AS IT IS 3 years back from 2017
Kindly mail me if you feel, needy of this presentation
you can find my mail id @ slide share,,, if not mail me @
sukesh3567@gmail.com.
Good luck

Veröffentlicht in: Bildung
  • Als Erste(r) kommentieren

Molecular Basis of Tooth Development

  1. 1. MOLECULAR BIOLOGY OF ODONTOGENESIS SUKESH KUMAR.V PG 1ST YEAR DEPT. OF ORAL PATHOLOGY
  2. 2. CONTENTS Introduction -Dental Lamina -Tooth development -Developmental stages -Bud stage -Cap stage -Bell stage -Hard tissue formation -Root formation MOLECULAR EVENTS -Ectomesenchymal interactions (EMI) -Growth Factors -Transcription Factors & Homeobox Genes. -Tooth Initiation, Position & Gene interactions in various steps of development -Gene Mutations & Tooth abnormailities -Conclusion.
  3. 3. Tooth formation occurs in the 6th week of intrauterine life with the formation of primary epithelial band. At about 7th week the primary epithelial band divides into a lingual process called dental lamina & a buccal process called vestibular lamina. All deciduous teeth arises from dental lamina, later the permanent successors arise from its lingual extension & permanent molars from its distal extension INTRODUCTION
  4. 4. Tooth Development A. Bud Stage B. Cap Stage C. Bell Stage D and E. Dentinogenesis and amelogenesis F. Crown formation G. Root Formation and eruption H. Function
  5. 5. • The primitive oral cavity, or stomodeum, is lined by stratified squamous epithelium called the oral ectoderm • The oral ectoderm contacts the endoderm of the foregut to form the buccopharyngeal membrane
  6. 6. • Membrane ruptures at about 27th day of gestation and the primitive oral cavity establishes a connection with the foregut • Most of the connective tissue cells underlying the oral ectoderm are of neural crest or ectomesenchyme in origin • These cells instruct the overlying ectoderm to start the tooth development, which begins in the anterior portion of the future maxilla & mandible and proceeds posteriorly 3= Connective tissue cells
  7. 7. Initiation of Tooth Development Each band of epithelium will give rise to 2 sub divisions: 1. Dental lamina and 2. Vestibular lamina • 2- 3 weeks after the rupture of buccopharyngeal membrane, certain areas of basal cells of oral ectoderm proliferate rapidly, leading to the formation of primary epithelial band • The band invades the underlying ectomesenchyme along each of the horse-shoe shaped future dental arches.
  8. 8. 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.
  9. 9. Stomodeum Developing Tongue Dental lamina Maxillary Process Mandibular process
  10. 10. Dental Lamina • Dental lamina appears as a thickening of the oral epithelium adjacent to condensation of ectomesenchyme • 20 areas of enlargement or knobs appear, which will form tooth buds for the 20 primary teeth • Not all will appear at the same time. The first to develop are those of the anterior mandible region • At this early stage the tooth buds have already determined their crown morphology Successional lamina: •Lingual extension of Dental lamina •lamina from which permanent teeth develop • The dental lamina begins to function at 6th prenatal week and continues to 15th year of birth (3rd molar) Primary epithelial band Ectomesenchyme
  11. 11. Tooth development is a continuous process, however can be divided into 3 stages: 1. Bud Stage 2. Cap Stage 3. Bell Stage MORPHOLOGICAL 1. Dental lamina 2. Bud stage 3. Cap stage 4. Early bell stage 5. Advanced bell stage 6. Formation of enamel and dentin matrix PHYSIOLOGICAL Initiation Proliferation Histodifferentiation Morphodifferentiation Apposition
  12. 12. 1. Bud Stage • Bud stage is characterized by rounded, localized growth of epithelium surrounded by proliferating mesenchymal cells, which are packed closely beneath and around the epithelial buds  In the bud stage, the enamel organ consists of peripherally located low columnar cells and centrally located polygonal cells •The area of condensation immediately below the enamel organ is the dental papilla • The ectomesenchymal condensation that surrounds the tooth bud & the dental papilla is the tooth sac
  13. 13. • The dental papilla as well as the dental sac are not well defined during the bud stage, they become more defined during the subsequent cap & bell stages • The cells of the dental papilla form the dentin and pulp while the dental sac forms cementum & periodontal ligament
  14. 14. CAP STAGE • As the tooth bud continues to proliferate, it does not expand uniformly into a large sphere • Instead unequal growth in different parts of the tooth bud leads to the cap stage which is characterized by a shallow invagination on the deep surface of the bud
  15. 15. 2. Cap Stage Condensation of the ectomesenchyme immediately subjacent to the tooth bud caused by lack of extracellular matrix secretion by the cells thus preventing separation. Histodifferentiation begins at the end of cap stage. Epithelial outgrowth is called Enamel Organ because it will eventually form the enamel Dental Papilla: Ball of condensed ectomesenchymal cells (it will form dentin and pulp). The peripheral cells adjacent to the inner dental epithelium will enlarge and later differentiate into odontoblasts Enamel Organ Dental Papilla
  16. 16. 2. Cap Stage Enamel organ Dental papilla Dental follicle or sac Dental follicle or dental sac is the condensed ectomesenchymal tissue surrounding the enamel organ and dental papilla. This gives rise to cementum and the periodontal ligament (support structures for tooth) Enamel knot
  17. 17. 2. Cap Stage Lateral Lamina: extension from the dental lamina that is connected to the enamel organ Enamel niche: It is an artifact produced during sectioning of the tissue. It occurs because the enamel organ is a sheet of proliferating cells rather than a single strand and contains a concavity filled with ectomesenchyme. Because enamel organ sits over dental papilla like a cap, this stage is known as the CAP STAGE. We can also see that the inner and the outer dental epithelium are being organized Lateral lamina
  18. 18. Dental organ or tooth germ is a term used to constitute the structure that has enamel organ, dental papilla and dental follicle Enamel Knot: Densely packed accumulation of cells projecting from the inner enamel epithelium into enamel organ. Exact role not known, but currently believed to be the organizational center for cusp development.
  19. 19. Enamel knots are clusters of nondividing epithelial cells visible in sections of molar cap stage Enamel knot precursor cells are first noted by expression of p21 gene expression Enamel knot and enamel cord are temporary structures that disappear before enamel formation begins. It has been speculated that the function of the enamel knot and cord may be to act as a reservoir of dividing cells for the growing enamel organ
  20. 20. 3. Bell Stage • Continued growth leads to bell stage, where the enamel organ resembles a bell with deepening of the epithelium over the dental papilla • Continuation of histodifferentiation (ameloblasts and odontoblasts are defined) and beginning of morphodifferentiation (tooth crown assumes its final shape) Dental lamina Outer dental epithelium Inner dental epithelium Dental papilla Dental follicle Cervical loop
  21. 21. 3. Bell Stage (Early) Inner dental epithelium: Short columnar cells bordering the dental papilla. These will eventually become ameloblasts that will form the enamel of the tooth crown by differentiating into tall columnar cells. The cells of inner dental epithelium exert an organizing influence on the underlying mesenchymal cells in the dental papilla, which later differentiate into odontoblasts. Outer dental epithelium: Cuboidal cells that cover the enamel organ. Their function is to organize a network of capillaries that will bring nutrition to the ameloblasts. In preparation to formation of enamel, at the end of bell stage, the formerly smooth surface of the outer dental epithelium is laid in folds. Between the folds, adjacent mesenchyme of the dental sac forms papillae that contain capillary loops and thus provide nutritional supply for the intense metabolic activity of the avascular enamel organ Stellate reticulum Inner dental epithelium Stratum intermedium Dental papilla Outer dental epithelium
  22. 22. 3. Bell Stage (Early) Stellate reticulum Inner dental epithelium Stratum intermedium Dental papilla Stellate reticulum: Star-shaped cells with processes, present between the outer and the inner dental epithelium. These cells secrete glycosaminoglycans, which attract water, thereby swelling the cells and pushing them apart. However, they still maintain contact with each other, thus becoming star-shaped. They have a cushion-like consistency that may support and protect the delicate enamel organ. It is absent in the portion that outlines the root portions. Stratum intermedium: Cell layer between the inner dental epithelium and stellate reticulum which have high alkaline phosphatase activity( basal medium). They assist inner dental epithelium (ameloblasts) to form enamel. Outer dental epithelium
  23. 23. Stellate reticulum Inner dental epithelium Stratum intermedium Membrana preformativa Outer dental epithelium Dental Papilla: Before the inner dental epithelium begins to produce enamel, the peripheral cells of the mesenchymal dental papilla differentiate into odontoblasts under the organizing influence of the epithelium. First, they assume a cuboidal shape and then a columnar form and acquire the specific potential to produce dentin. The basement membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called the “membrana preformativa” Dental papilla
  24. 24. Inner dental epithelium Outer dental epithelium Cervical loop Cervical loop: Area where the inner and the outer dental epithelium meet at the rim of the enamel organ. This point is where the cells will continue to divide until the tooth crown attains its full size and which after crown formation will give rise to the epithelium for root formation. Is also called “Zone of Reflexion”. 3. Bell Stage
  25. 25. Enamel cord  Enamel cord: Pattern of enamel knot that extends between the inner and outer dental epithelium Enamel knot 3. Bell Stage •Dental lamina (and the lateral lamina) will disintegrate and loose contact with oral epithelium. Sometimes, these epithelial cells will persist when they are called “epithelial pearls” or “cell rests of Serre” •Clinical significance of epithelial pearls : Cysts will develop in these (eruption cysts) and prevent eruption, or they may form odontomas (tumors) or may form supernumery teeth
  26. 26. Advanced Bell Stage Essentials of Oral Histology and Embryology, Ed: James Avery, 2nd edition. 2000.
  27. 27. Future crown patterning also occurs in the bell stage, by folding of the inner dental epithelium. Cessation of mitotic activity within the inner dental epithelium determines the shape of a tooth. Crown Pattern Determination
  28. 28. Hard Tissue Formation Deposition of dental hard tissues is called “apposition” After the crown attains its final shape during cap to advanced bell stage, the inner dental epithelial cells stop to proliferate, except the cells at the cervical loop First layer of dentin appears at the cusp tips and progresses cervically, and the columnar cells of the inner dental epithelium become elongated and show reverse polarization, with the nuclei adjacent to stratum intermediate (ameloblasts) The boundary between the odontoblasts and inner dental epithelium defines the future dentino-enamel junction
  29. 29. For dentinogenesis and amelogenesis to take place normally, the differentiating odontoblasts and ameloblasts will receive signals form each other – “reciprocal induction” Stages of Apposition 1. Elongation of inner dental epithelium 2. Differentiation of odontoblasts 3. Formation of dentin 4. Formation of enamel
  30. 30. At the same time or soon after the first layer of dentin (mantle dentin) is formed, the inner dental epithelial cells differentiate into ameloblasts and secrete enamel proteins. These proteins further will help in the terminal differentiation of odontoblasts. The ameloblasts will then start laying down organic matrix of enamel against the newly formed dentinal surface. The enamel matrix will mineralize immediately and form the first layer of enamel. The formation of enamel is called amelogenesis. Ameloblasts First layer of enamel Dentin Odontoblasts
  31. 31. Root Formation Development of root begins after the enamel and dentin formation has reached the future cementoenamel junction Epithelial cells of the inner and outer dental epithelium proliferate from the cervical loop of the enamel organ to form the Hertwig’s epithelial root sheath. The root sheath determines if a tooth has single or multiple roots, is short or long, or is curved ir straight Hertwig’s epithelial root sheath
  32. 32. Hertwig’s epithelial root sheath Inner dental epithelium Outer dental epithelium Stratum intermedium Eventually the root sheath will fragment to form several discrete clusters of epithelial cells known as epithelial cell rests of malassez. These will persist in adults within the periodontal ligament
  33. 33. The epithelial rests appear as small clusters of epithelial cells which are located in the periodontal ligament adjacent to the surface of cementum. They are cellular residues of the embryonic structure known as Hertwig's epithelial root sheath. Epithelial Cell Rests of Malassez
  34. 34. Primary apical formen Epithelial diaphragm: the proliferating end of the root sheath bends at a near 45-degree angle. The epithelial diaphragm will encircle the apical opening of the dental pulp during root development
  35. 35. Secondary apical foramen form as a result of two or three tongues of epithelium growing inward toward each other resulting in multirooted teeth
  36. 36. Soon after root formation begins, tooth begins to erupt until it reaches its final position While roots are forming, the supporting structures of tooth also develop – periodontal ligament and cementum As the root sheath fragments, the dental follicle cells will penetrate between the epithelial cells and lie close to the newly formed root dentin These cells will differentiate into cementoblasts, which will make cementum Fibers of the periodontal ligament, which will also form from the cells of the dental follicle will get anchored in the organic matrix of the cementum which will later get mineralized TOOTH ERUPTION AND DEVELOPMENT OF SUPPORTING STRUCTURES
  37. 37. MOLECULAR EVENTS • Odontogenesis is a complex & also co-ordinated process involving ectomesenchymal (EMI) interactions. • Molecular interactions between epithelium & mesenchyme leads to generation of tooth components viz; Enamel Dentine & Cementum. • Signalling between epithelium & mesenchymal components is regulated by a set of genes termed as “Homeobox” genes.{1}
  38. 38. • More than 300 genes are involved in this intricate process.{2}. • Major molecular signals during tooth formation include, several multifactorial growth factors such as -Transforming Growth factor(TGF) -Fibroblast growth factor (FGF) -Epidermal Growth factor (EGF) -Hedgehog (HH) -Wnt Families.{2} -Several Transcription factors of Homeobox, paired box, & high mobility group(HMG) box gene families are expressed at sites of tooth formation & have been implicated in the determination of tooth shape and identity.{2}
  39. 39. Growth factors / Homeobox genes Abbrevation Factor/ Protein Growth factors Fibroblast growth factor Fgf Secreted protein Bone morphogenetic protein Bmp Sonic hedgehog Shh Wingless homologue in vertebrates Wnt Homologous to drosophila slit proetin Slit Homeobox Genes BarH1 homologue in vertebrates Barx Transcription Factor Receptor Distaless homologue in vertebrates Dlx Muscle segment homeobox like gene Msx Glioma associated oncogene homolouge Gli Lymphoid enhancer binding factor 1 Lef Lim homeobox domain gene Lhx Paired box homeotic gene Pax TF expression in the pituitary gland Pitx Otx related homeobox gene Otlx Veretbrate homologue of the Drosophila runt gene Runx Patched cell surface receptor for hh Ptc Smoothed Ptc coreceptor for Shh Smo
  40. 40. ROLE OF EMI IN TOOTH DEV. • Before an insight into role of EMI in tooth dev, it is important to know about 2 terms viz; • ODONTOGENIC POTENTIAL: represents an instructive induction capability of a tissue to induce gene expression in an adjacent tissue & to intiate tooth development. • ODONTOGENIC COMPETENCE: represents the capability of a tissue to respond to odontogenic signals & to support tooth formation. • Tissue recombination experiments between dental epithelial & mesenchymal tissue have demonstrated that odontogenic potential resides in dental epithelium and then shifts to mesenchyme.{3}
  41. 41. ROLE OF EMI IN TOOTH DEV. • Removal of epithelium from mandibular arches at E10 or before, results in a total & rapid loss of almost all ectomesenchymal homeobox gene expression, indicating that ectomesenchymal gene expression is dependent on epithelial signaling. • Removal of epithelium at E11,doesnot affect EM gene expression indicating that gene expressions are established & maintained at this stage. • These results indicate that the inducing signals arise from the epithelium, however, the EM dependency over the epithelium ceases with in 24 hours, i.e, from E10 to E11.{1}
  42. 42. ROLE OF EMI IN TOOTH DEV • Therefore, at the pre-bud stages of tooth development by E11.5, both epithelial and mesenchymal gene expression domains are independently fixed & interact with eachother controlling the morphogenic pathways, which is termed as “epithelial-mesenchymal interactions”{1}. • Tissue recombinant experiments have shown that, the presumptive dental epithelium posses the odontogenic potential, capable of inducing tooth formation when confronted with non-dental mesenchyme; however only cranial neural crest cell (NCC) derived mesenchyme is Odontogenic competent.{3}. • Teeth failed to form when dental epithelium was recombined non neural crest derived mesenchyme such as skin or limb mesenchyme.{3}
  43. 43. Jaw mesenchyme Oral ectoderm Nonoral ectoderm Nondental mesechyme Nondental mesechyme Oral ectoderm Jaw mesenchyme Nonoral ectoderm Tissue recombination experiments reveal sources of secreted factors that control tooth development at early stages Ectodermal signals are required for the initiation of tooth development
  44. 44. ROLE OF EMI IN TOOTH DEV • In contrast, at Early bud stage (E12.5), the odontogenic potential has switched to the mesenchyme ,which becomes able to instruct non-dental epithelium to form tooth specific structures. (Reciprocal signaling){3} Tissue recombination experiments have shown that at induction of tooth primordia at a later stages is by Mesenchyme
  45. 45. Signal are transferred from cell to cell through signaling molecules. Transmit information to adjacent cells Molecules get attached to receptors of target cells. Cell molecular cascade is activated in the cytoplasm. Activation of transcription factors. Enter the nucleus and regulate gene expression. New proteins are produced. Change in behavior of target cell. Continues signaling process.
  46. 46. ROLE OF GROWTH FACTORS • Classic studies demonstrated the importance of Cross talk between dental epithelium and mesenchyme during tooth development. • These cross talk between two layers are mediated by diffusible signaling molecules. • These diffusible molecules are GROWTH FACTORS.{3} • Growth factors mediate inductive interactions during odontogenesis
  47. 47. Fgf- Fibroblast growth factor • Several members of FGF family are expressed in early developing tooth germs • They function at distinct steps of development from intiation to the formation of the last tooth cusp. • binds to cell surface receptors which are single transmembrane proteins with intercellular tyrosine kinase domains. • expression of different patterns of Fgf in epithelium and mesenchyme as regulatory signaling cascade during tooth development, such as Growth factors
  48. 48. • Fgf-4,8,9: have been implicated as epithelial signals regulating mesenchymal gene expression & cell proliferation during tooth inititation & later during epithelial folding morphogenesis & the establishment of tooth shape. • Fgf-10:expression observed in presumptive dental epithelium & mesenchyme during tooth inititation, & also in dental papilla mesenchymal cells of cap & bell stages, both in incisors and molars. • Fgf-3: expression observed in dental mesenchyme at later bud stage, also in dental papilla mesenchymal cells of cap & bell stages,both in incisors and molars • Also participates in signaling functions of primary enamel knot. • The dynamic expression patterns of different FGFs in epithelium(E)and mesenchyme(M) & their interaction suggest existence of regulatory siganling cascades b/w E&M.{2}
  49. 49. Growth factors Bmp- Bone morphogenetic protein : • Bmps have been shown to participate in epithelial mesenchymal siganaling regulating tooth morphogenesis. • The expression of several Bmps has been localized to the developing tooth at several stages such as,
  50. 50. • Bmp 4 – associated with shift of odontogenic potential from epithelium to mesenchyme. • Bmp 2, 4, 7 – are restricted to epithelial cell population, Enamel knot together with other signaling molecules suggesting functions such as signals regulating the shape of teeth. • Bmp 5 – expressed in epithelial ameloblasts, may be involved in the induction & formation of Dentine & Enamel. • Bmp 3 – expression is confined mesenchymal cells, in particular Dental Follicle cells that give rise to cementoblasts {2}.
  51. 51. Growth factors Hedgehog superfamily • Discovered in Drosophila – as a signal regulating segmental & imaginal disc patterning • In Mammals – Sonic hh, Indian hh, Desert hh. • Encode secreted proteins involved in signaling between cells.{2}
  52. 52. Growth factors Wnt- wingless homolouge in vertebrates • contains 20 secreted glycoproteins. • involve in cell proliferation, migration, differentiation, and ectomesencymal interaction. • Also involved in skeletal development and bone remodelling{2}
  53. 53. ROLE OF TRANSCRIPTION FACTORS • Experiments have revealed the expression of numerous transcription factors in the developing tooth where the expression patterns of these factors often overlap with those of growth factors suggesting a potential relationship between the two class of gene products.{3} • Homeobox genes(HOX) are group that encodes for transcription factors.{2}. • HOX gene network appears to be active in human tooth germs between 18-24 weeks of development, which explains pivotal importance of these genes in development{2}.
  54. 54. HOMEOBOX GENES • 180 base pair sequence code for homeodomain of a 60 amino acid DNA binding motif. • Originally discovered in fruit fly “Drosophila melanogaster”- responsible for specifying segment identity. • Colinearity property(spatial arrangement of genes along chromosome is in the same order of expression along antero-posterior axis) Genes located 3` end- expressed anteriorly 5` end- expressed posteriorly
  55. 55. HOMEOBOX GENES Msx homeobox gene family • Msx 1, Msx 2 - related to Drosophil gene muscle segment homeobox. • Msx 1 – on chromosome • Msx 2 protein , a transcriptional repressor play a role in craniofacial development. • Msx 1, 2 – expressed in several embryonic structures including premigratory & migratory neural crest, neural crest derived mesenchyme of pharyngeal arches and median nasal process. {2}
  56. 56. HOMEOBOX GENES Dlx family • dista less family of homeobox gene, contains 6 members. • Dlx 1, 2 – Ch 2q32 expressed in epithelium- mesenchyme of maxillary and mandibular divisions of 1st brachial arch. • Dlx 5, 6 – Ch 7q22. • Dlx 7 – Ch 7 • Dlx 3 – Ch 3 • These are involved in the patterning of ectomesenchyme of the first brachial arch with respect to tooth development. • Loss of function mutation of these genes-failure of dev. Of upper molars{2}
  57. 57. HOMEOBOX GENES Barx homeobox genes • Bar class genes expressed in craniofacial structures. • Brax 1 – maxillary and mandibular processes and in tooth primordia. • Barx 2 – located on human Ch 11q25 - oral epithelium prior to tooth development.{2}.
  58. 58. HOMEOBOX GENES Pax homeobox genes • loacted on Ch 14, play a role in early development. • Pax 9 proteins possess 128 AA DNA-binding domain, a paired- domain , which make sequence specific contact with DNA. • Expressed in Pharyngeal pouches, developing vertebral column, neural crest derived mesenchyme of maxillary and mandibular arches, contributing to palate and tooth formation.{2}. • Activates transcription of Msx1 at bud stage.{1}
  59. 59. HOMEOBOX GENES Lim homeobox genes: Lhx is member of the LIM homeobox gene family expressed in mesenchyme of palate • Lhx 1, 2 – differential regulation during orofacial ontogenesis.{2} Runx 2 • key regulator of osteoblast differentiation and bone formation. • Dental epithelium regulates mesenchymal Runx2 Expression during bud & cap stage.{2}
  60. 60. LIM homeobox genes (Lhx 6 and 7) constitue to that group of gene clusters which are dispersed outside the homeobox gene clusters and they are transcriptional regulators controlling pattern formation. Lhx 6/7 expressed (oral portion of mesenchyme). Marks the region where tooth buds form Goosecoid (Gsc) expression. Marks the aboral portion of the mesenchyme •FGF8 activates LIM homeobox genes (Lhx 6 and 7), which is unaffected by BMP4 . •Therefore the jaw is divided into a tooth-forming LHX-positive domain and non-tooth-forming GSC-positive domain. {1} Overall called Odontogenic Homeobox Code ESTABLISHMENT OF ORO-ABORAL AXIS
  61. 61. TOOTH TYPE DETERMINATION The determination of specific tooth types at their correct positions in the jaws is referred to as patterning of the dentition. -Incisiform, caniniform, molariform Are Three Families Of Teeth Determination of teeth shape of different families: 2 Hypothetical models: 1. Field model 2. Clone model 1.Field model Proposes that, Factors responsible for tooth shape reside within the ectomesenchyme in distinct but graded fields for each tooth family. Support: Each fields express differing combination of Homeobox genes.
  62. 62. TOOTH TYPE DETERMINATION 2.Clone model Proposes that, A clone of ectomesenchymal cells which are programmed by epithelium to produce teeth of a given pattern. Support: Isolated presumptive first molar tissues continue to develop 3 molar teeth in their positional sequence. Both models can be combined
  63. 63. TOOTH TYPE DETERMINATION BARX-1,DLX-1 MOLARIFORM TEETH MSX-1,DLX-1 CANINIFORM TEETH MSX-1,MSX-2,ALX-3 INSISIFORM TEETH
  64. 64. TOOTH INITIATION AND POSITION • It appear to originate from oral epithelium • The Pax-9(paired box homeotic gene) is the earliest mesenchymal gene that define localization of the tooth germ • Inducing factor: Fgf-8(secreted fibroblast growth factor) • Repressing factor: BMP-2 and BMP-4 (bone morphogenetic protein)
  65. 65. • The expression of several genes in ectomesenchyme (Pax-9 and Activin-A) marks the site for tooth germ initiation. • The antagonistic interaction between Fgf 8 and Bmp4 regulates the expression of Pax 9 but not of Activin-A this proves that they do not have a direct role in tooth in initiation
  66. 66. TOOTH INITIATION AND POSITION oral epithelium Nondental epithelium Jaw mesenchyme Pax-9 Msx-1 Pax-9 Msx-1 -FGF8 is an epithelial signal required for initiation of tooth development -FGF8 is expressed throughout entire dental epithelium FGF 8 FGF 8
  67. 67. Positioning the sites of tooth formation : Antagonistic signaling by BMP4 Dental epithelium Nondental epithelium FGF8 Pax9 BMP4 Jaw mesenchyme (neural crest) Pax-9 Msx-1 Pax-9 Msx-1 Sites of co- expression of FGF8 and BMP4 Pax9 induces expression of BMP4 in the condensing mesenchyme BMP4 produced in the dental mesenchyme induces LEF1 expression in the epithelium
  68. 68. • Other genes being involved are -Otlx-2(Otx related homeobox genes) -Dlx-2(distaless homologue in vertebrates) -Msx-1 & Msx-2(Msh-like genes in vertebrates). -Hox-7, Hox-8 play an important role in tooth initiation & later in morphogenesis.{1} -Hox-8-uniform expression in cuspless incisors , which lack an enamel knot, navel and septum.
  69. 69. BUD STAGE • It is the first epithelial incursion into the ectomesenchyme of the jaw. • Epithelium is separated from the underlying ectomesenchyme by a basement membrane. • Round ovoid swellings rise from the basement membrane at 10 different points corresponding to the future deciduous teeth positions
  70. 70. • Lef-1(Lymphoid enhancing factor) is seen in the epithelium of tooth bud and it later shifts to the ectomesenchyme. Any mutation in this gene will result in arrest at bud stage.{1} • Dlx-2 expression at the bud stage resides downstream of Msx- 1 • Bmp-4 and Fgf-3 are required for maintaining Dlx-2 expression
  71. 71. • The ectomesenchyme surrounding the tooth bud and dental papilla is the dental sac. • Both become more well-defined in the cap and bell stage. • Cells of the dental papilla will form the tooth pulp and dentin • cells in the dental sac/ dental follicle will form cementum, alveolar bone and pdl
  72. 72. BUD TO CAP TRANSITION • Marks the onset of morphologic difference between tooth germs that give rise to different types of teeth. • Msx-1 is expressed with Bmp-4 in the mesenchymal cells that condense around tooth buds. • Absence of Msx-1 embryos, tooth development is arrested at bud stage indicating that Msx-1 is required for expression of Bmp-4 • Bmp-4 maintains Msx-1 expression in tooth bud mesenchyme indicating that bmp-4 induces its own expression via msx-1. • BMP-4 in bud mesenchyme maintains – BMP-2 & SHH expression in epithelium, which are in same pathway.
  73. 73. • Blocking shh signaling shows that at E11-E12 , shh is required for dental epithelium proliferation to form tooth buds, where as blocking E13 affects tooth bud morphology but still can form teeth. • Another Homeobox gene with a role in bud to cap transition is Pax-9. • Pax-9 is expressed in bud stage mesenchyme & also in domains similar to activin-betaA & Msx-1 in patches of mesenchyme that masks the sites of tooth formation.
  74. 74. CAP STAGE • This stage appear like the enamel organ is present over the dental papilla like a cap. • As the tooth bud continues to proliferate from the bud stage it does not expand uniformly.
  75. 75. ENAMEL KNOT • Cluster of non dividing epithelial cells visible in sections of molar cap stage tooth germs. • Enamel knot precursor cells first detected at the tip of tooth bud by expression gene p21 followed by shh. • Histologically it is detected in cap stage by the expression of gene Bmp-2, Bmp-4, Bmp-7, Fgf-4, Fgf-9, Wnt-10 , Slit-1 & shh. • Receptors for enamel knot signals are localised in the epithelial cells surrounding enamel knot.
  76. 76. ENAMEL KNOT • Controls growth & patterning of tooth cusps. • Each tooth germ has single enamel knot at cap stage & as these disappear secondary enamel knots appear at the tips of future cusps of molars. • Fgf-4 & slit1 are best molecular markers for enamel knot because these are only two genes expressed in primary and secondary enamel knots.
  77. 77. BELLSTAGE • Bell stage so called because the continuous growth of tooth germ leads to deepening of the undersurface of the epithelial cap that resembles the shape of a bell • Tooth assumes it’s morphodifferentiation and histodifferentiation at this stage
  78. 78. ROOT INITIATION AND MORPHOGENESIS • Root formation is initiated by enamel organ epithelial invagination between the dental papilla. • Following fenestration of HERS, the epithelial cells persist as epithelial cell rests of malassez & probably are involved in cementum maintainence. • HERS cells undergo E-M transition under influence of TGFβ1. • Dlx-2 in present in odontogenic cells from tooth initiation and morphogenesis to root formation. • Dlx-2 with Msx-2, Dlx-5 : role in HERS cell differentiation and osteocalcin gene expression.{1}
  79. 79. ROOT INITIATION AND MORPHOGENESIS • Bmps have been found to get expressed sequentially at various stages of root odontoblastic differentiation. • Bmp-4 is expressed in mesenchyme lining the root sheath epithelium, which inturn expresses Msx-2. • Bmp-4 : early pre-odontoblasts lining HERS epithelium. • Bmp-2, Bmp-7 : pre-odontoblst and odontoblast , absent from mature odontoblasts. • Bmp-3 : expressed intensly in dental follicle cells, particularly in cementoblasts.{1}
  80. 80. GENE MUTATIONS- TOOTH ABNORMALITIES Msx, Dlx Tooth agenesis, Craniosynostosis, Tricho- dento-osseous syndrome Msx Autosomal dominant oligodontia Pax-9 mutations cause selective tooth agenesis predominantly molars and premolars. Runx-2 Cleidocranial dysplasia. Supernumarary teeth (arrested at bud stage) Lhx-8 Cleft palate Alx-4 Foramina parietalia permagna – c/f: mild dysmorphism , dental abnormalities, &thumb broadening{2}
  81. 81. GENE MUTATIONS- TOOTH ABNORMALITIES Barx-1 Axenfeld Reiger syndrome Iridogoniodysgenesis syndrome Pitx-2 -Maxillary teeth development arrested at placodal stage -Mandibular teeth development arrested at budstage -Rieger syndrome(characterized by oligodontia) Pitx-2 + Lef-1 abnormalities in late stages of tooth development Pitx-2+ a-catenin mutations in early stages of tooth development.
  82. 82. CONCLUSION • The considerable understanding profile of gene expression , unveiling the molecular basis involved in tooth morphogenesis will provide important insight for studying genetically related dental abnormalities & tooth regeneration in humans. • The knowledge of developmental & molecular biology along with experimental embryology, stem cell biology makes tooth regenration a realistic possibility in the near future, which would greatly improve the quality of human life.
  83. 83. REFERENCES • Antonio Nanci. Ten Cate`s. Oral histology development, structure, and fuction • Essentials of Oral Histology and Embryology,Ed: James Avery, 3rd edition. • orban`s oral histology and embryology 13th edition. • {1} Chatterjee S, Boaz K. Molecular biology of odontogenesis,jofs • {2} Sivakumar G, vijayashree priyadharsini, Saraswathi TR. Gene network in odontogenesis and associated disorders. Jofs. • {3}Making a tooth : Growth factors , transcription factors , & stem cells. • Epithelial-mesenchymal signalling regulating tooth morphogenesis.

×