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Tooth development
Tooth development
Tooth development
 Introduction
 Initiation of Tooth Development
 Tooth development
 Developmental Stages
 Root development
 Histophysiology
 Crown Pattern Determination
 Nerve & Vascular supply during early development
 Formation of Permanent Dentition
 Hard Tissue Formation
 Formation of Supporting Tissues
 Tooth Eruption
 References
 Tooth development (ODONTOGENESIS) is the
complex process by which teeth form from the
embryonic cells, grow, and erupt into the oral cavity.
 For human teeth to have healthy oral environment,
enamel, dentin, cementum & the periodontium all
must develop during appropriate stages of fetal
development.
 Entire primary dentition is initiated between 6th and
7th weeks of embryonic development.
 Successional permanent teeth initiated between 20th
week in utero and 10th month after birth.
 Permanent molars between 20th week in utero (first
molar) and 5th year of life (third molar).
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 buccopharyngeal membrane.
At about 27th day of gestation buccopharyngeal
membrane ruptures and the primitive oral cavity
establishes a connection with the foregut.
Most of connective tissue cells
underlying the oral ectoderm are of
neural crest.
These cells induce the overlying
ectoderm to start tooth
development.
Which begins in anterior portion of
what will be the future maxilla and
mandible and prooced posteriorly
 About 37 days of
development –
continuous band of
thickened epithelium
forms around the mouth
presumptive upper and
lower jaws.
 Bands are roughly horse
shoe shaped and
correspond in position
of the future dental
arches.
 Thickening of epithelial band occurs due to change
in orientation of mitotic spindle & cleavage plane of
dividing cells.
 Each band of epithelium is called PRIMARY
EPITHELIAL BAND.
 Quickly give rise to 2 subdivisions
- vestibular lamina
- dental lamina
Tooth development
 Lingual (inner) process of primary epithelial band.
 Primordium for the ectodermal portion of deciduous
teeth.
 Permanent molars arise from distal extension.
 Successional lamina: lamina from which permanent
teeth develop.
 Fate: Remnants of dental lamina persists as epithelial
pearls or islands within the jaw as well as gingiva--
Cell Rest of Serres.
Maxillary Process
Dental Lamina
Mandibular Process
 Buccal (outer) process of primary epithelial band.
 Lip Furrow Band
 Cells rapidly enlarge.
 Becomes the vestibule between the lips and cheek &
the tooth-bearing area.
Primary epithelial
band
Vestibular lamina (labially)
Dental lamina (lingually)
Milk teeth
Its Lingual extension
(successional)
All permanents except
molars
Distal extensiongives rise to
permanent molars
 10 small swellings
develop in the region of
future primary teeth.
 They form enamel organ
and give rise to the
enamel of the teeth.
TOOTH DEVELOPMENT
 Peripheral condensation
of ectomesenchymal
cells around enamel
organ forms dental
papilla
 Surrounding dental
papilla and enamel organ
is dental follicle or sac
Tooth development
 Tooth germ is formed by
Enamel organ enamel
+
Dental papilla pulp and dentin
+
Dental sac cementum and PDL
MORPHOLOGIC PHYSIOLOGIC
STAGES PROCESS
1.Initiation
2.Proliferation
3.Histodifferentiation
4.morphodifferentiation.
5.apposition
1.Bud Stage
2.Cap Stage
3.Bell Stage
*Early Bell Stage
*Advanced Bell Stage
 The epithelium of the dental lamina is
separated from the underlying
ectomesnchyme by a basement membrane.
 The cells of the epithelium proliferate faster
than the adjacent cells.
 The enamel organ consist in this stage
peripherally located low columnar cells &
centrally located polygonal cells
Tooth development
 The next step is mitosis of cells of tooth bud and
surrounding mesenchyme.
 As a result of increased mitotic activity and
migration of neural crest cells in to the area of the
ectomesenchymal cells surrounding the tooth bud
condense.
 The area of ectomesanchymal condensation
immediately adjacent to enamel organ is called dental
papilla.
 The condensed ectomesenchyme that surround the
tooth bud and dental papilla is the dental sac.
 Both dental papilla and dental sac become more well
defined as enamel organ grows into the cap and bell
shapes.
Tooth development
 Shallow invagination on
the deep surface of the
bud.
 Peripheral cells are
cuboidal, cover the
convexity of the cap–
Outer Enamel
Epithelium.
 Cells in the concavity of
the cap become tall,
columnar– Inner Enamel
Epithelium
Tooth development
 Polygonal cells located between the outer and inner
enamel epithelia. They begin to separate as more
intercellular fluid is produced and form a cellular
network called the stellate reticulum.
 The cells assume a branched reticular form.
 The spaces in this reticular network are filled with a
mucoid fluid that is rich in albumin, which gives the
stellate reticulum a cushionlike consisstency that may
support and protect the dellicate enamel-forming
cells.
 Organizing influence of proliferative epithelium of
enamel organ
 Papillary cells proliferate
 Budding of capillaries and mitotic figures
 Later differentiate – odontoblasts – dentin

marginal condensation in the ectomesenchyme
surrounding the enamel organ and dental papilla.
in this zone a denser and more fibrous layer
Develops
primitive dental sac
formation of cementum and the periodontal ligament
 Temporary structures, disappear before enamel
formation begins.
1. Enamel Niche: Enamel organ has double attachment
of dental lamina to the overlying oral epithelium
enclosing ectomesenchyme.
 The center of
enamel organ
contains densely
packed cells & are
called enamel knot.
 They extend slightly
into the dental
papilla & form knob
like projection
 A vertical projection
is seen from this
knot known as
enamel cord.
 Both knot & cord are
temporary
structures.
 Function : both acts
as a reservoir of
dividing cells.
 Enamel Septum: Enamel cord extends to meet outer
enamel epithelium.
 Enamel Navel: (resembles umbilicus) Outer enamel
epithelium at a point of meeting shows small
depression
 Enamel organ
resembles a bell.
 Undersurface of the
epithelial cap deepens.
 Continuation of
histodifferentiation
(ameloblasts and
odontoblasts are
defined) & beginning
of
morphodifferentiation
(tooth crown assumes
its final shape).
 Consists of four distinct
layer:
a. Inner Enamel Epithelium
b. Stratum Intermedium
c. Stellate Reticulum
d. Outer Enamel
Epithelium
Tooth development
Consists of a single layer of cells
differentiate prior to amelogenesis into
tall columnar cells
Ameloblasts
The cells of the inner enamel epithelium
exert an organizing influence on
mesenchymal cells in the dental papilla
later differentiate into odontoblasts.
 Formed by a few layers of squamous cells between
the inner enamel epithelium and the stellate
reticulum.
 The well-developed cytoplasmic organelles acid
mucopolysaccharides, and glycogen deposits indicate
a high degree of metabolic activity.
 This layer seems to be essential to enamel formation.
 It is absent in the part of the tooth germ that
outlines the root portions of the tooth that does not
form enamel.
 The stellate reticulum expands further mainly by an
increase in the amount of intercellular fluid.
 The cells are star shaped, with long processes that
anastomose with those of adjacent cells.
 Before enamel formation begins, the stellate
reticulum collapses, reducing the distance between
the centrally situated ameloblasts and the nutrient
capillaries near the outer enamel epithelium.
 This change begins at the height of the cusp or the
incisal edge and progresses cervically.
 These cell flatten to a low cuboidal form.
 At the end of the bell stage, the formerly
smooth surface of the outer enamel
epithelium is laid in folds. Between the folds
the adjacent mesenchyme of the dental sac
forms papillae that contain capillary loops and
thus provide a rich nutritional supply for the
intense metabolic activity of the avascular
enamel organ.
 Extends lingually.
 Successional Dental
Lamina as gives rise to
enamel organs of
permanent successors
of deciduous teeth
(permanent incisor,
canines & premolars).
 The dental papilla is enclosed in the
invaginated portion of the enamel organ.
 Before the inner enamel 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 form; later they assume a columnar
form and acquire the specific potential to
produce dentin
The basement membrane
separates the
enamel organ and the dental papilla
just prior to dentin formation
membrana preformativa
 Before formation of dental tissues begins the
dental sac shows a circular arrangement of its
fibers and resembles a capsular structure.
 With the development of the root, the fibers
of the dental sac differentiate into the
periodontal fibers that become embedded in
the developing cementum and alveolar bone.
 This point is where the cells
continue to divide until the tooth
crown attains its full size.
 The inner epithelium begins at the
point where the outer epithelium
bends to form the concavity into
which the cells of the dental
papilla accumulate. The region
where the internal and external
dental epithelia meet at the rim of
the enamel organ is known as the
zone of reflexion or cervical loop.
Cervical loop
 Commencement of mineralization & root formation.
 Boundary between inner enamel epithelium & odontoblasts–-
outlines future DEJ.
 1st formation of dentin.
 Proceeds pulpally & apically.
 After first layer of dentin is formed, ameloblast which has
already differentiated from IEE cells lay down enamel over
dentin in future incisal & cuspal areas.
 Proceeds coronally & cervically.
 Cervical portion of the enamel organ gives rise to Hertwig’s
epithelial root sheath.
 Outlines the future root.
 Responsible for the shape, length, size & number of roots.
 After odontoblasts
form due to
organizing influence
of epithelial cells,
they instruct
ameloblasts in turn
to secrete enamel
matrix
(reciprocal
induction)
Tooth development
 Root formation commences once the enamel and
dentin formation have reached the future
cementoenamel junction(CEJ).
 Cervical loop from the enamel organ forms the
Hertwigs epithelial root sheath (HERS).
 HERS determines shape of the roots and inititates
radicular dentin formation.
 HERS consists of the outer and inner enamel
epithelium only.
• At the future CEJ, HERS turn inwardly to a
horizontal plane forming the epithelial diaphragm.
• Plane of diaphragm remains relatively fixed during
development and growth of the root.
• Proliferating cells of epithelial diaphragm induce
proliferation and differentiation of cells of dental
papilla to odontoblasts and form root dentin.
• The cells of dental follicle proliferate and invade the
root sheath dividing it in to network of strands.
• Degradation of the HERS allows contact of the
dental follicle cells with the dentin surface and they
differentiate into cementoblasts.
• The cementoblasts cover the root dentin and undergo
cementogenesis – laying down cementoid
Tooth development
Tooth development
The first layer of dentin has been laid down
the epithelial root sheath loses its structural
continuity & its close relation to the surface of the
root.
Its remnants persists as an epithelial network of
strands or tubules near the external surface of the
root.
These epithelial remnants are found in the periodontal
ligament of erupted teeth
called rests of malassez.
Root sheath forms epithelial diaphragm
Outer and inner epithelia bend at future
CEJ into a horizontal plane
Narrowing of wide cervical opening of
tooth germ
Cells of epithelial diaphragm and
connective tissue of pulp proliferate
adjacent to diaphragm
Free end of epithelium proliferates coronal
to diaphragm
Differentiation of odontoblasts and formation
of dentin after root lengthening
Connective tissue of dental sac proliferates and
invades continuous double epithelial layer
forming epithelial strands
Connective tissue cells come in contact with
outer surface of dentin causing differentiation
of cementoblasts and deposition of cementum
Proliferation of epithelium in diaphragm lags
behind connective tissue
Width of apical foramen is reduced by further
apposition of dentin and cementum to apex of
root
 Division of root trunk in 2/3 roots is due to
differential growth of epithelial diaphragm
Expansion of cervical opening occurs in long
tongue like extensions of horizontal
diaphragm
Before division of root trunk, free ends of
these epithelial flaps grow towards each
other and fuse
Single cervical opening of coronal enamel is
divided into 2-3 openings
On pulpal aspect – dentin formation starts
and on periphery – root development starts
• Anterior teeth, premolars and molars all begin as a
single root – root trunk.
• Root of the posterior teeth divides from the trunk
into the correct number of root branches.
• Differential growth of the Hertwig’s epithelial root
sheath results in the division of the root trunk into
two or three roots.
Tooth development
Tooth development
Tooth development
 INITIATION
• The dental lamina and associated tooth buds represent
those parts of the oral epithelium that have potential for
tooth formation.
• Initiation induction requires ectomesenchymal-epithelial
interaction.
• Lack of initiation results in absence of either a single
tooth or multiple teeth, or there may be a complete lack
of teeth.
• Abnormal initiation may result in the devalopment of
single or multiple supernumerary teeth.
• Enhanced proliferative activity ensues at the points
of initiation and results successively in the bud, cap
and bell stages of the odontogenic organ.
• Causes regular changes in the size and proportions of
the growing tooth germ.
• Histodifferentiation is the process in which a mass of similar
epithelial cells transforms itself into morphologically and
functionally distinct components.
• Histodifferentiation begins in the late cap stage and reaches
its highest development in the early bell stage.
• The organizing influence of the inner enamel epithelium on the
mesenchyme is evident in the bell stage and causes the
differentiation of the adjacent cells of the dental papilla into
odontoblasts.
• With the formation of dentin, the cells of inner enamel
epithelium differentiate into ameloblasts and enamel matrix is
formed.
• The morphologic pattern is established by
differential growth.
• The cells arrange themselves along the site which
out lines the basic form and relative size of the
future tooth.
• The advance bell stage is the important stage for it
outlining the future dentinoenamel junction
• The dentinoenamel and dentinocemental junctions
which are different and characteristic for each
tooth, acts as blue print pattern.
• Inconformity with this pattern, ameloblasts,
odontoblasts and cementoblasts deposit the enamel,
dentin and cementum, giving the completed tooth its
characteristic form and size.
• Disturbances may cause supernumerary cusps or
roots, loss of cusps or roots, peg tooth.
• Apposition is the deposition of the matrix for the
hard dental structures.
• There is regular and rhythmic layer like deposition
of the extracellular matrix resulting in additive
growth.
• This matrix is partially calcified- serves as a frame
work for later calcification proper.
• Disturbances can cause hypocalcified or
hypomineralized enamel or dentin.
Tooth development
 Future crown patterning -- bell stage, by folding of
the inner enamel epithelium.
 Cessation of mitotic activity within the inner enamel
epithelium determines the shape of a tooth.
 The point at which inner enamel epithelium cell
differentiation first occurs represent the site of
future cusp development.
Tooth development
 Vascular supply:
 Cap stage.
 Blood vessels grow in the dental follicle and enter
the dental papilla.
 The number of blood vessels reaches a maximum at
the beginning of the crown stage, and the dental
papilla eventually forms in the pulp of a tooth.
 Pioneer nerve fibres approach developing
tooth during bud to cap stage development.
 Nerve fibre ramify and form a rich plexus
around the tooth germ in that structure.
 Nerve fibres penetrate dental papilla when
dentinogenesis begins.
 Initial innervation – sensory for future p.d.l &
pulp.
 Arises from dental lamina.
 Form in essentially the same manner, though at
different times.
 The tooth germs that give rise to permanent incisors,
canines and premolars form as a result of further
proliferative activity within the dental lamina, lingual
to the deciduous tooth germ.
 The developing permanent molars have no deciduous
predecessor and their tooth germs originate from
the dental lamina that extends posteriorly beneath
the oral epithelium after the jaws have grown.
Tooth development
 The next step in development of tooth is terminal
differentiation of ameloblast and odontoblast and
formation of enamel and dentin.
 Until crown assumes the final shape durind cap to
early bell stage,all cells of inner enamel epithelium
continually divide.
 First layer of dentin appears at the cusp tips and
progresses cervically, & the columnar cells of the
inner enamel epithelium becomes elongated & show
reverse polarization, with the nuclei adjacent to
stratum intermediate (ameloblasts).
 Undifferentiated ectomesenchymal cells increase
rapidly in size and ultimetly differentiated into
odontoblast .
 In the absence of epithelial cells no dentin develops.
 As devlpoment continues ,progressive dfferentiation
of cells of IEE down cusp slopes,
 odontoblast are differentiate begin to elaborate the
organic matrix of dentin,which ultimately mineralize.
 As the organic martrix deposited,odontoblast move
towards center of dental papilla,leaving behind the
cytoplasmic extension around which dentin is formed
 Inner enamel epithelial cells continue their
differentiation into ameloblast that produce organic
matrix against the newly formed dentinal surface.
 Organic matrix is mineralize and becomes initial
enamel layer of crown.
 Ameloblast moving away from the dentin , leaving
behind an ever increasing thickness of enamel.
 the differentiating odontoblasts and ameloblasts
receive signals from each other n viceversa –-
Reciprocal Induction.
 cells of enamel organ receives its nourishment from
two sources-blood vessels of dental papilla.
-vessels situated at periphery of OEE.
Tooth development
 While roots are forming, the supporting tissues of
the tooth also develop.
 The supporting tissues(cementum, PDL, bone) of the
tooth are formed from the dental follicle.
 As the root sheath fragments, ectomesenchymal cells
of dental follicle penetrates between the epithelial
cells & lie close to the newly formed root dentin.
 These cells differentiate into cementum-forming
cells- Cementoblasts.
 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 later gets mineralized.
 Bone in which ligament fiber bundles are embedded is
also formed by cells that differentiate from dental
follicle.
 After formation of root is initiated, the tooth begins
to erupt.
 Axial movement-- from its developmental position
within the jaw to its final functional position in the
occlusal plane.
 Formation of reduced enamel epithelium.
 REE + oral epithelium = solid mass of epithelial cells
over crown of the tooth.
 Central cells in this mass disintegrate–- epithelial
canal–- crown of the tooth erupts
Tooth development
Tooth development
Tooth development
 TYPES OF OPEN
APICES
These can be of two
configurations.
 NON BLUNDERBUSS
Broadly opened apex
(Cylinder – shaped root
canals).
 BLUNDERBUSS
Funnel shaped apex
(Apical opening can be
wider than the coronal
root canal orifice
(inverted root canal
conicity)
Acc to BEENA PHILIP MATHEW *
MITHRA N. HEGDE **,Endodontology.
 Diagnosis:
-visual examination
-clinical examination
-radiographic examination
-laser doppler flowmetry-potential aid to vitality
testing and pulp
revascularization.
 Management:
-apexification
-apexogenesis
 Ten Cate’s Oral Histology Development, Structure,
and Function Antonio Nanci : 7th edition.
 Orban’s Oral Histology and Embryology : 12th edition.
 Inderbeer Singh: Human Embryology
 James k avery-oral development and histology,3rd
edition
Tooth development

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Tooth development

  • 4.  Introduction  Initiation of Tooth Development  Tooth development  Developmental Stages  Root development  Histophysiology  Crown Pattern Determination  Nerve & Vascular supply during early development
  • 5.  Formation of Permanent Dentition  Hard Tissue Formation  Formation of Supporting Tissues  Tooth Eruption  References
  • 6.  Tooth development (ODONTOGENESIS) is the complex process by which teeth form from the embryonic cells, grow, and erupt into the oral cavity.  For human teeth to have healthy oral environment, enamel, dentin, cementum & the periodontium all must develop during appropriate stages of fetal development.
  • 7.  Entire primary dentition is initiated between 6th and 7th weeks of embryonic development.  Successional permanent teeth initiated between 20th week in utero and 10th month after birth.  Permanent molars between 20th week in utero (first molar) and 5th year of life (third molar).
  • 8. 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 buccopharyngeal membrane. At about 27th day of gestation buccopharyngeal membrane ruptures and the primitive oral cavity establishes a connection with the foregut.
  • 9. Most of connective tissue cells underlying the oral ectoderm are of neural crest. These cells induce the overlying ectoderm to start tooth development. Which begins in anterior portion of what will be the future maxilla and mandible and prooced posteriorly
  • 10.  About 37 days of development – continuous band of thickened epithelium forms around the mouth presumptive upper and lower jaws.  Bands are roughly horse shoe shaped and correspond in position of the future dental arches.
  • 11.  Thickening of epithelial band occurs due to change in orientation of mitotic spindle & cleavage plane of dividing cells.  Each band of epithelium is called PRIMARY EPITHELIAL BAND.  Quickly give rise to 2 subdivisions - vestibular lamina - dental lamina
  • 13.  Lingual (inner) process of primary epithelial band.  Primordium for the ectodermal portion of deciduous teeth.  Permanent molars arise from distal extension.  Successional lamina: lamina from which permanent teeth develop.  Fate: Remnants of dental lamina persists as epithelial pearls or islands within the jaw as well as gingiva-- Cell Rest of Serres.
  • 15.  Buccal (outer) process of primary epithelial band.  Lip Furrow Band  Cells rapidly enlarge.  Becomes the vestibule between the lips and cheek & the tooth-bearing area.
  • 16. Primary epithelial band Vestibular lamina (labially) Dental lamina (lingually) Milk teeth Its Lingual extension (successional) All permanents except molars Distal extensiongives rise to permanent molars
  • 17.  10 small swellings develop in the region of future primary teeth.  They form enamel organ and give rise to the enamel of the teeth. TOOTH DEVELOPMENT
  • 18.  Peripheral condensation of ectomesenchymal cells around enamel organ forms dental papilla  Surrounding dental papilla and enamel organ is dental follicle or sac
  • 20.  Tooth germ is formed by Enamel organ enamel + Dental papilla pulp and dentin + Dental sac cementum and PDL
  • 22.  The epithelium of the dental lamina is separated from the underlying ectomesnchyme by a basement membrane.  The cells of the epithelium proliferate faster than the adjacent cells.  The enamel organ consist in this stage peripherally located low columnar cells & centrally located polygonal cells
  • 24.  The next step is mitosis of cells of tooth bud and surrounding mesenchyme.  As a result of increased mitotic activity and migration of neural crest cells in to the area of the ectomesenchymal cells surrounding the tooth bud condense.  The area of ectomesanchymal condensation immediately adjacent to enamel organ is called dental papilla.  The condensed ectomesenchyme that surround the tooth bud and dental papilla is the dental sac.  Both dental papilla and dental sac become more well defined as enamel organ grows into the cap and bell shapes.
  • 26.  Shallow invagination on the deep surface of the bud.  Peripheral cells are cuboidal, cover the convexity of the cap– Outer Enamel Epithelium.  Cells in the concavity of the cap become tall, columnar– Inner Enamel Epithelium
  • 28.  Polygonal cells located between the outer and inner enamel epithelia. They begin to separate as more intercellular fluid is produced and form a cellular network called the stellate reticulum.  The cells assume a branched reticular form.  The spaces in this reticular network are filled with a mucoid fluid that is rich in albumin, which gives the stellate reticulum a cushionlike consisstency that may support and protect the dellicate enamel-forming cells.
  • 29.  Organizing influence of proliferative epithelium of enamel organ  Papillary cells proliferate  Budding of capillaries and mitotic figures  Later differentiate – odontoblasts – dentin 
  • 30. marginal condensation in the ectomesenchyme surrounding the enamel organ and dental papilla. in this zone a denser and more fibrous layer Develops primitive dental sac formation of cementum and the periodontal ligament
  • 31.  Temporary structures, disappear before enamel formation begins. 1. Enamel Niche: Enamel organ has double attachment of dental lamina to the overlying oral epithelium enclosing ectomesenchyme.
  • 32.  The center of enamel organ contains densely packed cells & are called enamel knot.  They extend slightly into the dental papilla & form knob like projection
  • 33.  A vertical projection is seen from this knot known as enamel cord.  Both knot & cord are temporary structures.  Function : both acts as a reservoir of dividing cells.
  • 34.  Enamel Septum: Enamel cord extends to meet outer enamel epithelium.  Enamel Navel: (resembles umbilicus) Outer enamel epithelium at a point of meeting shows small depression
  • 35.  Enamel organ resembles a bell.  Undersurface of the epithelial cap deepens.  Continuation of histodifferentiation (ameloblasts and odontoblasts are defined) & beginning of morphodifferentiation (tooth crown assumes its final shape).
  • 36.  Consists of four distinct layer: a. Inner Enamel Epithelium b. Stratum Intermedium c. Stellate Reticulum d. Outer Enamel Epithelium
  • 38. Consists of a single layer of cells differentiate prior to amelogenesis into tall columnar cells Ameloblasts
  • 39. The cells of the inner enamel epithelium exert an organizing influence on mesenchymal cells in the dental papilla later differentiate into odontoblasts.
  • 40.  Formed by a few layers of squamous cells between the inner enamel epithelium and the stellate reticulum.  The well-developed cytoplasmic organelles acid mucopolysaccharides, and glycogen deposits indicate a high degree of metabolic activity.  This layer seems to be essential to enamel formation.  It is absent in the part of the tooth germ that outlines the root portions of the tooth that does not form enamel.
  • 41.  The stellate reticulum expands further mainly by an increase in the amount of intercellular fluid.  The cells are star shaped, with long processes that anastomose with those of adjacent cells.  Before enamel formation begins, the stellate reticulum collapses, reducing the distance between the centrally situated ameloblasts and the nutrient capillaries near the outer enamel epithelium.  This change begins at the height of the cusp or the incisal edge and progresses cervically.
  • 42.  These cell flatten to a low cuboidal form.  At the end of the bell stage, the formerly smooth surface of the outer enamel epithelium is laid in folds. Between the folds the adjacent mesenchyme of the dental sac forms papillae that contain capillary loops and thus provide a rich nutritional supply for the intense metabolic activity of the avascular enamel organ.
  • 43.  Extends lingually.  Successional Dental Lamina as gives rise to enamel organs of permanent successors of deciduous teeth (permanent incisor, canines & premolars).
  • 44.  The dental papilla is enclosed in the invaginated portion of the enamel organ.  Before the inner enamel 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 form; later they assume a columnar form and acquire the specific potential to produce dentin
  • 45. The basement membrane separates the enamel organ and the dental papilla just prior to dentin formation membrana preformativa
  • 46.  Before formation of dental tissues begins the dental sac shows a circular arrangement of its fibers and resembles a capsular structure.  With the development of the root, the fibers of the dental sac differentiate into the periodontal fibers that become embedded in the developing cementum and alveolar bone.
  • 47.  This point is where the cells continue to divide until the tooth crown attains its full size.  The inner epithelium begins at the point where the outer epithelium bends to form the concavity into which the cells of the dental papilla accumulate. The region where the internal and external dental epithelia meet at the rim of the enamel organ is known as the zone of reflexion or cervical loop. Cervical loop
  • 48.  Commencement of mineralization & root formation.  Boundary between inner enamel epithelium & odontoblasts–- outlines future DEJ.  1st formation of dentin.  Proceeds pulpally & apically.  After first layer of dentin is formed, ameloblast which has already differentiated from IEE cells lay down enamel over dentin in future incisal & cuspal areas.  Proceeds coronally & cervically.  Cervical portion of the enamel organ gives rise to Hertwig’s epithelial root sheath.  Outlines the future root.  Responsible for the shape, length, size & number of roots.
  • 49.  After odontoblasts form due to organizing influence of epithelial cells, they instruct ameloblasts in turn to secrete enamel matrix (reciprocal induction)
  • 51.  Root formation commences once the enamel and dentin formation have reached the future cementoenamel junction(CEJ).  Cervical loop from the enamel organ forms the Hertwigs epithelial root sheath (HERS).  HERS determines shape of the roots and inititates radicular dentin formation.  HERS consists of the outer and inner enamel epithelium only.
  • 52. • At the future CEJ, HERS turn inwardly to a horizontal plane forming the epithelial diaphragm. • Plane of diaphragm remains relatively fixed during development and growth of the root. • Proliferating cells of epithelial diaphragm induce proliferation and differentiation of cells of dental papilla to odontoblasts and form root dentin.
  • 53. • The cells of dental follicle proliferate and invade the root sheath dividing it in to network of strands. • Degradation of the HERS allows contact of the dental follicle cells with the dentin surface and they differentiate into cementoblasts. • The cementoblasts cover the root dentin and undergo cementogenesis – laying down cementoid
  • 56. The first layer of dentin has been laid down the epithelial root sheath loses its structural continuity & its close relation to the surface of the root. Its remnants persists as an epithelial network of strands or tubules near the external surface of the root. These epithelial remnants are found in the periodontal ligament of erupted teeth called rests of malassez.
  • 57. Root sheath forms epithelial diaphragm Outer and inner epithelia bend at future CEJ into a horizontal plane Narrowing of wide cervical opening of tooth germ Cells of epithelial diaphragm and connective tissue of pulp proliferate adjacent to diaphragm Free end of epithelium proliferates coronal to diaphragm
  • 58. Differentiation of odontoblasts and formation of dentin after root lengthening Connective tissue of dental sac proliferates and invades continuous double epithelial layer forming epithelial strands Connective tissue cells come in contact with outer surface of dentin causing differentiation of cementoblasts and deposition of cementum Proliferation of epithelium in diaphragm lags behind connective tissue Width of apical foramen is reduced by further apposition of dentin and cementum to apex of root
  • 59.  Division of root trunk in 2/3 roots is due to differential growth of epithelial diaphragm Expansion of cervical opening occurs in long tongue like extensions of horizontal diaphragm Before division of root trunk, free ends of these epithelial flaps grow towards each other and fuse Single cervical opening of coronal enamel is divided into 2-3 openings On pulpal aspect – dentin formation starts and on periphery – root development starts
  • 60. • Anterior teeth, premolars and molars all begin as a single root – root trunk. • Root of the posterior teeth divides from the trunk into the correct number of root branches. • Differential growth of the Hertwig’s epithelial root sheath results in the division of the root trunk into two or three roots.
  • 64.  INITIATION • The dental lamina and associated tooth buds represent those parts of the oral epithelium that have potential for tooth formation. • Initiation induction requires ectomesenchymal-epithelial interaction. • Lack of initiation results in absence of either a single tooth or multiple teeth, or there may be a complete lack of teeth. • Abnormal initiation may result in the devalopment of single or multiple supernumerary teeth.
  • 65. • Enhanced proliferative activity ensues at the points of initiation and results successively in the bud, cap and bell stages of the odontogenic organ. • Causes regular changes in the size and proportions of the growing tooth germ.
  • 66. • Histodifferentiation is the process in which a mass of similar epithelial cells transforms itself into morphologically and functionally distinct components. • Histodifferentiation begins in the late cap stage and reaches its highest development in the early bell stage. • The organizing influence of the inner enamel epithelium on the mesenchyme is evident in the bell stage and causes the differentiation of the adjacent cells of the dental papilla into odontoblasts. • With the formation of dentin, the cells of inner enamel epithelium differentiate into ameloblasts and enamel matrix is formed.
  • 67. • The morphologic pattern is established by differential growth. • The cells arrange themselves along the site which out lines the basic form and relative size of the future tooth. • The advance bell stage is the important stage for it outlining the future dentinoenamel junction
  • 68. • The dentinoenamel and dentinocemental junctions which are different and characteristic for each tooth, acts as blue print pattern. • Inconformity with this pattern, ameloblasts, odontoblasts and cementoblasts deposit the enamel, dentin and cementum, giving the completed tooth its characteristic form and size. • Disturbances may cause supernumerary cusps or roots, loss of cusps or roots, peg tooth.
  • 69. • Apposition is the deposition of the matrix for the hard dental structures. • There is regular and rhythmic layer like deposition of the extracellular matrix resulting in additive growth. • This matrix is partially calcified- serves as a frame work for later calcification proper. • Disturbances can cause hypocalcified or hypomineralized enamel or dentin.
  • 71.  Future crown patterning -- bell stage, by folding of the inner enamel epithelium.  Cessation of mitotic activity within the inner enamel epithelium determines the shape of a tooth.  The point at which inner enamel epithelium cell differentiation first occurs represent the site of future cusp development.
  • 73.  Vascular supply:  Cap stage.  Blood vessels grow in the dental follicle and enter the dental papilla.  The number of blood vessels reaches a maximum at the beginning of the crown stage, and the dental papilla eventually forms in the pulp of a tooth.
  • 74.  Pioneer nerve fibres approach developing tooth during bud to cap stage development.  Nerve fibre ramify and form a rich plexus around the tooth germ in that structure.  Nerve fibres penetrate dental papilla when dentinogenesis begins.  Initial innervation – sensory for future p.d.l & pulp.
  • 75.  Arises from dental lamina.  Form in essentially the same manner, though at different times.  The tooth germs that give rise to permanent incisors, canines and premolars form as a result of further proliferative activity within the dental lamina, lingual to the deciduous tooth germ.  The developing permanent molars have no deciduous predecessor and their tooth germs originate from the dental lamina that extends posteriorly beneath the oral epithelium after the jaws have grown.
  • 77.  The next step in development of tooth is terminal differentiation of ameloblast and odontoblast and formation of enamel and dentin.  Until crown assumes the final shape durind cap to early bell stage,all cells of inner enamel epithelium continually divide.  First layer of dentin appears at the cusp tips and progresses cervically, & the columnar cells of the inner enamel epithelium becomes elongated & show reverse polarization, with the nuclei adjacent to stratum intermediate (ameloblasts).
  • 78.  Undifferentiated ectomesenchymal cells increase rapidly in size and ultimetly differentiated into odontoblast .  In the absence of epithelial cells no dentin develops.  As devlpoment continues ,progressive dfferentiation of cells of IEE down cusp slopes,  odontoblast are differentiate begin to elaborate the organic matrix of dentin,which ultimately mineralize.  As the organic martrix deposited,odontoblast move towards center of dental papilla,leaving behind the cytoplasmic extension around which dentin is formed
  • 79.  Inner enamel epithelial cells continue their differentiation into ameloblast that produce organic matrix against the newly formed dentinal surface.  Organic matrix is mineralize and becomes initial enamel layer of crown.  Ameloblast moving away from the dentin , leaving behind an ever increasing thickness of enamel.  the differentiating odontoblasts and ameloblasts receive signals from each other n viceversa –- Reciprocal Induction.  cells of enamel organ receives its nourishment from two sources-blood vessels of dental papilla. -vessels situated at periphery of OEE.
  • 81.  While roots are forming, the supporting tissues of the tooth also develop.  The supporting tissues(cementum, PDL, bone) of the tooth are formed from the dental follicle.  As the root sheath fragments, ectomesenchymal cells of dental follicle penetrates between the epithelial cells & lie close to the newly formed root dentin.
  • 82.  These cells differentiate into cementum-forming cells- Cementoblasts.  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 later gets mineralized.  Bone in which ligament fiber bundles are embedded is also formed by cells that differentiate from dental follicle.
  • 83.  After formation of root is initiated, the tooth begins to erupt.  Axial movement-- from its developmental position within the jaw to its final functional position in the occlusal plane.  Formation of reduced enamel epithelium.  REE + oral epithelium = solid mass of epithelial cells over crown of the tooth.  Central cells in this mass disintegrate–- epithelial canal–- crown of the tooth erupts
  • 87.  TYPES OF OPEN APICES These can be of two configurations.  NON BLUNDERBUSS Broadly opened apex (Cylinder – shaped root canals).  BLUNDERBUSS Funnel shaped apex (Apical opening can be wider than the coronal root canal orifice (inverted root canal conicity) Acc to BEENA PHILIP MATHEW * MITHRA N. HEGDE **,Endodontology.
  • 88.  Diagnosis: -visual examination -clinical examination -radiographic examination -laser doppler flowmetry-potential aid to vitality testing and pulp revascularization.  Management: -apexification -apexogenesis
  • 89.  Ten Cate’s Oral Histology Development, Structure, and Function Antonio Nanci : 7th edition.  Orban’s Oral Histology and Embryology : 12th edition.  Inderbeer Singh: Human Embryology  James k avery-oral development and histology,3rd edition