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.