(dental basic seminar)development of tooth with basic embryology (public health dentistry)
DESCRIPTION
i tied to explain with the germ layersTRANSCRIPT
GOOD MORNING GOOD MORNING
Dr.Sharanprakash R Shetgar
1st yr MDS public health dentistry
Narsinhbhai Patel Dental college and Hospital Visnagar
THE DEVELOPMENT OF THE DEVELOPMENT OF TOOTH & IT’S INNERVATION TOOTH & IT’S INNERVATION
Content
Introduction Embryological basis of dental tissue genesis Stages in tooth development Histophysiology Transitory structures Genes signaling Development of Root Conclusion References References
Introduction
Development of tooth is a complex process, in which reciprocal and sequential interaction between the oral epithelium and mesenchymal cells, regulate cell activities like proliferation, condensation, adhesion, migration, differentiation and secretion, which leads to the formation of a functional tooth organ
How tooth development initiates
During the embryo ,there is formation of 3 layers
1)Ectoderm 2)Endoderm 3)Mesoderm
The primitive oral cavity or stomodaeum is lined by stratified squamous epithelium called ORAL ECTODERM
ECTODERM contacts with ENDODERM of foregut to form the buccopharyngeal membrane
27th day of gestation this membrane rapture and primitive oral cavity established
Connective tissue cells of underlying the ORAL ECTODERM are of neural crest or ectomesenchyme in origin, which induces the overlying ectoderm to start of tooth development.
Embryological basis of dental tissue genesis
4th week of intra uterine life
Lined by str. squ epi i.e oral ectoderm
CT cells overlying ectoderm
are
ectomesenchyme in origin,
induce tooth devp Ruptures at 27th day of gestation
Primary Epithelial band/ 6th week
Continuous band of thickened epithelium
Roughly horse shoe shaped
Thickening first seen in ant
midline
Oral ectoderm proliferates more rapidly then adjacent
cell.This leads to formation of the
Primary epithelial band
Formation of vestibule of oral cavity
Cells of vestibular lamina proliferate
Degeneration of central epi cells
Sulcus of the vestibule
7th week
Buccally locatedVestibular lamina
Lingually dental lamina
Dental lamina Cont. proliferative activity leads to
the forming of a series of epi
ingrowths into the ectomesenchyme
Dental laminae serves as ectodermal
portion of Deciduous teeth
Later, during the devpt of jaw, the
permanent molars arises from distal
extension of dental lamina
1st molar > 4th mt in utero 2nd molar > 1st yr 3rd molar >4th/5th year
8th week
Contd thickening of DL in 10 areas of upper/ lower arch
Thickenings correspond to position of future primary dentn
Function of dental lamina Phase 1: Initiation of entire deciduous
dentition (8th wk).
Phase 2:Initiation successors of deciduous dentition. (5thmt to 10th mt)
Phase 3:Initiation of permanent molars
Phase 4 :Disintegrations (up to 5 yrs ), Remnants of dental lamina epithelial pearls in jaw/ gingiva refers to Cell rest of Serres
Stages In Tooth Development Histophysiology
PHYSIOLOGICAL STAGES
Initiation. Proliferation. Histodifferentiation. Morphodifferentiation
. Apposition
MORPHOLOGICAL STAGES
•Dental lamina.•Bud stage.•Cap stage:•Bell Stage:
early. advanced.
A) Bud stage B )Bell stage C )Bell stage D )Dentinogenises E )Amelogenises F )Apposition of dentin and enamel G )Eruption H )Functional
Bud stage (8th week)
Basement membrane
Tooth bud
Enamel organ
spherical to ovoid epi
condensation
Cells undergo mitosis
& condense
Dental papilla > cell
subjacent to enamel
organ
Dental sac
>surrounds tooth bud
and dental papilla
BUD STAGE
Enamel organ ,surrounded by mesenchyme
EARLY CAP STAGE:
11th week
Peripheral cuboidal
cells--- OEE
Tall columnar cells in the
concavity--- IEE
Polygonal cells b/w outer
& IEE form a cellular
network--- SR
(12th week)
Cap Stage
Dental papilla dentin & pulpDental sac cementum & PL
13 th week
Early bell stage (14th week)
Dental lamina breaks down & degenerates Shows 4 distinct layers: OEE Stellate reticulum (SR) Stratum intermedium (SI) IEE
OEE
IEE
Outer enamel epithelium
Role of OEE:
OEE folds and forms the shape the enamel organ. B/w folds the adjacent mesenchyme of dental sac forms papillae that contains the blood capillary loops which provides the nutritional supply to avascular enamel organ
Early bell stage
Stellate reticulum
mechanical
Role of stellate reticulum
nutritive
Protects tissue Maintains toothshape
Early bell stage
Stratum intermedium Early bell stage
Desmosomal attachment
Gap junction
Possess attachmentsAbsents on root portion
B/w Stellate reticulam
& Staturm intermedium
B/w Staturam
intermedium & IEE
Nutritional supply for IEE Which is essential for Enamel formation
Inner enamel epithelium
FUNCTION:
Cells exert an
organizing influence
on the underlying
mesenchymal cells
in the DP that later
diff into odontoblasts
Early bell stage
17th week
DL begin
to degenerate
17 Week
Degeneration of dental lamina
Late bell stage (18th week)
Commencment of mineralization & root formation starts
Peripheral cells of dental papilla--- odontoblasts >DENTIN Ameloblast differentiated by IEE > ENAMEL over dentinEstablishment of Dentinoenamel junction (reciprocal induction )
Late bell stage
Enamel oragan
IEE
Ameloblast
Enamel
Dental papilla
Odontoblast
Dentin
Dental sac
Cementum,PDL &Aleveror Bone
TRANSITORY STRUCTURES Enamel knot
Enamel cord
Enamel niche
The Enamel knot
Localized mass of cells in IEE
Signaling centre during tooth development.
Produce molecules associated with signaling
BMP-2 & 7, FGF, P21, SHH & MSX-1
The Enamel cord
Strand of cells seen at bell stage extending from SI into SR.
ROLE:
Involved in the process by which cap stage is transformed into bell stage
Enamel niche
Seen where tooth germ appear to have a double attachment to dental lamina
Functional significance: unknown
Successional dental lamina
In dvpng primary tooth,
DL devps an extn to
lingual side
Successional lamina
Forms the perm incisors,
canines & premolars
Epithelial-mesenchymal interactions during tooth developmentCells signal to each other 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.
Questions to be answered
1. Which of the two components is
more important for inducing
morphogenesis and
histogenesis?
Enamel organ & dental papila
2. What determines the shape of
the tooth?
GENE SIGNALING
Genes expressed during tooth development
Lef – lymphoid enhancer- binding factor (TF)
Pax – paired box homeotic gene( TF)
Fgf – fibroblast growth factor (SP)
Msx – msh like genes in vertebates( TF)
Dlx-- distalless homologue
Wnt –wingless homologue
Lhx -- lim homeobox domain gene
Bmp – bone morphogenetic proteins
Shh -- sonic hedge hog
Hgf- hepatic growth factor
Barx – BarH1 homologue
Lim homeobox domain genes
Lhx-6 & 7–earliest mesenchymal markers for
tooth formn
exp in nueral crest ectomesenchyme
of first branchial arch at day 9
Fgf 8 & pax 9– earliest mesenchymal genes that
det positions of tooth germs
Shh – implicates tooth initiation
Role in determining tooth shape and position ( homeobox code model)
Primary epithelial band
ectomesenchyme
IncisorsMsx 1 & 2
CanineMsx 1 & 2, Dlx2
MolarsBarx1, Dlx2
BMPs & FGFRole of Bone morphogenetic protein 4 is activating Msx gene expression and cascade of differentiation with underlying ectomesncyne
On activation it inductive potential transfer to dental ectomesenchyme This reciprocal interaction involves genetic signaling
Signaling centers are present in Enamel knot prior cusp formation
Enamel knot a signaling center
Expresses locally•BMP-2,-4,-7•FGF-4•Shh•p21
Represents a
organizational center
which governs cuspal
morphogenesis
Development of Root
Enamel organ
Initiated through the contributions of the cells:
Dental papilla
Root pulp
Dental sac
CementumPDL
Root sheath development
Proliferating zone cervical loop
hertwig’s root sheath
Root sheath--- the architect
of root
Bent portion of root sheath --- epi diaphragm apical foramen
SINGLE ROOT FORMATION
Occurs by growth of root sheath, like
a cuff around the cells of pulp
Followed by devp of root dentin
As dentin matrix mineralizes, sheath
cells form a thin deposit of cementum
on root surface
Development of root
Formation of multirooted teeth
In devp of tooth with two / three roots
Horizontal epithelial flap sheath expands
eccentrically
Later flap proliferates and unites each other
Rests of Malassez >
HERES, remnants in peridonta ligaments
Enamel pearls >
Epithilial root sheath differentiate to enamel
Applied aspect
Will be continued later …
Conclusion ……………….
Being a public health dentist it’s our duty, not only to understand accurately
the mechanism of tooth development but also to understand the developmental defects for correct diagnosis and to
develop certain curative and preventive measures to diminish the disease burden
on the community
REFERENCESREFERENCES
ORAL CELLS AND TISSUES P.R. P.R.
GARANTGARANT. ORAL ANATOMY, HISTOLOGY AND EMBRYOLOGY 3RD ed BERKOVITZBERKOVITZ ORAL HISTOLOGY, DEVELOPMENT, STRUCTURE AND FUNCTION 6TH
ed . TENKATE. A. R.TENKATE. A. R. ORBAN’S ORAL HISTOLOGY AND EMBROLOGY 11TH ed.
BHASKAR.S.N.BHASKAR.S.N. ESSENTIALS OF ORAL HISTOLOGY AND EMBRYOLOGY 2ND ed
JAMES.K.AVERY.JAMES.K.AVERY. DENTISTRY FOR CHILD AND ADOLOSCENTS 8TH ed Mc DONALD.Mc DONALD. COLOUR ATLAS OF ORAL HISTOLOGY AND EMBRYOLOGY.
BERKOVITZ.BERKOVITZ.