Development of tooth/endodontic courses

DEVELOPMENTDEVELOPMENT
OFOF
TOOTHTOOTH
www.indiandentalacademy.comwww.indiandentalacademy.com
INDIAN DENTAL ACADEMY
Leader in continuing Detal Education

CONTENTS
• Introduction
• Development of the oral cavity
• Formation of dental lamina
• Stages of tooth development
• Development of enamel,dentin,pulp,cementum and
periodontal ligament
• developmental anomalies & prosthodontic
considerations
• Recent research trends in tooth development
• Summary & conclusion
• References www.indiandentalacademy.com

INTRODUCTION
www.indiandentalacademy.com

GROWTH (Meridith)
Entire series of sequential anatomic and physiologic
changes taking place from beginning of prenatal
life to senility.
DEVELOPMENT (Moyers)
All the naturally occurring unidirectional changes in
the life of an individual ,from its existence as a
single cell to its elaboration as a multifunctional
unit, terminating in death.

Why study growth &development of teeth?
Diagnose developmental anomalies of teeth
treat them successfully
restore function,esthetics and comfort of the patient

• Hard, inert, acellular ENAMEL
• Less mineralized
More resilient, vital DENTIN
Hard
• Soft tissue PULP
• Tooth supporting
connective tissues CEMENTUM
PERIODONTAL LIGAMENT
ALVEOLAR BONE

DEVELOPMENT
OF THE
ORAL
CAVITY

Diploblastic
embryo
Triploblastic
head face teeth

Folding of the embryo
Rostrocaudal
axis
Lateral axis
2 planesin

Folding of the embryo

Consequences of folding of embryo
Frontal & pericardial bulges

Stomatodeum formation

Communication between
stomatodeum & foregut

Frontonasal process

Formation
of
dental lamina

oral cavity: ectoderm and underlying
connective tissue cells that
are neural crest
Anterior to posterior in future maxilla and
mandible
Development of dental lamina under 5 headings
Instructs overlying ectoderm to begin tooth
development

Condensation of ectomesenchymal cells
formation of primary epithelial band
formation of dental and vestibular lamina
enamel organ formation
formation of dental papilla & dental sac

Condensation of ectomesenchymal cells
Epithelium proliferates into connective tissue
Cells condense around epithelium
Occurs in the future dental arches
In mandible first and then maxilla
Begins anteriorly then proceeds posteriorly

Formation of the primary epithelial band
Thickening of ectodermal cells forms this band

Primary epithelial band

Not so much of proliferative activity at the
epithelium.....but change in orientation of mitotic
spindles at the region!*
*1970 Linde/Ruchwww.indiandentalacademy.com

formation of dental and vestibular lamina
Vestibular
lamina
(labially)
Dental lamina
(lingually)
Primary epithelial band
Distally gives
rise to
permanent
molars
Its Lingual extension
(successional)
All permanents except
molars
Milk
teeth

Formation of enamel organ
10 small swellings develop in the region
of future primary teeth
They form enamel organ and give rise to
the enamel of the teeth

Dental papilla and sac
Peripheral condensation
of ectomesenchymal
cells around enamel
organ forms dental
papilla
Surrounding dental
papilla and enamel
organ is dental follicle
or sac

Future…….!!!!
Tooth germ = enamel organ
+
dental papilla
+
dental sac/follicle
enamel
Pulp and
dentin
Cementum
Periodontal
ligament
bone

STAGES IN THE
DEVELOPMENT
OF TOOTH

• What initiates tooth development ?
• What determines tooth shape ?
• What determines tooth position ?

What initiates tooth development ?

Oral epithelium of first arch
Produces signalling molecules*
Expression of Lhx-6/7(lim-
homeobox) genes in the
mesenchyme
Initiation of tooth development
*Thesleff et al.1995www.indiandentalacademy.com

What determines tooth shape ?
Determination of specific tooth types at their
correct positions in jaws
Patterning of dentition
2 hypothetical models
field model clone theory

Field model* *(McCollum/Sharpe)2001
Factors responsible for tooth shape reside in the
ectomesenchyme in distinct but graded fields
for each tooth family
Premolar—Msx-1,Dlx-1,Dlx-2www.indiandentalacademy.com

Clone model* *(Osborne/Tencate)1983
Each tooth crown is derived from a clone of
ectomesenchymal cells programmed by the
epithelium to produce teeth of a given pattern

What determines tooth position ?
Pax-9 Gene *: Earliest mesenchymal gene
that defines location of tooth germ
Co-localizes with the exact sites where tooth
germs appear
*Tencate2000

3 morphological stages in tooth development are
seen------
BUD STAGE
CAP STAGE
BELL STAGE
early
advanced

BUD STAGE
• First morphological stage in tooth
development
• Derives its name from shape of developing
enemel organ
• Enamel organsmall ovoid epithelial mass
• Peripheral low columnar cells; centrally
polygonal cells
• Epithelial cells have RNA and enzymes
• Underlying ectomesenchymal cells closely
packed

Bud stage

Bud stage and its relation to adjacent structures

CAP STAGE
Bud stage 11th
week cap stage
Onset of morphological changes in tooth
different types of teeth
• Due to nonuniform expansion of enamel
organ
• Shallow invagination on deep surface of bud
• Dental papilla cells seem to be contained in
the invagination ; hence the name
• Distinct histologic structures seen nowwww.indiandentalacademy.com

Histology of cap stage
1) Inner and outer enamel epithelia:
Peripheral low cuboidal in shape
columnar cells------> (cap stage)
(bud stage) OUTER ENAMEL
EPITHELIUM
Cells in concavity of cap--->tall columnar
INNER ENAMEL
EPITHELIUM

Basal lamina separates
inner/outer epithelial
cells from dental
papilla and dental sac
respectively

2) Stellate reticulum:
polygonal central cells of bud stage
form /secrete glycosamino glycans
hydrophilic; turgor in enamel organ increases
central cells drawn apart
attached by desmosomes at corners
acquire star shape (stellate)

Stellate reticulum cells act as cushion for
the delicate cells of the enamel organ*
*Pannese E (1960)

Stellate reticulum

3) Dental papilla
Organizing influence of enamel epithelium
Papillary cells proliferate,mitotic activity
Later enlarge --->odontoblasts-->dentin
4)Dental sac
Further condensation occurs
Becomes denser---> forms cementum and
periodontal
ligament

5) Transient structures
Enamel knot
Clusters of non-dividing
epithelial cells
At deepest portion of
invagination of enamel
organ
Enamel cord
Linear condensation of
cells from inner to
outer enamel
epithelium

Functions of enamel knot & cord
2 schools of thought
Reservoir of cells tooth shape/form
• Represent an organizational centre that
orchestrates cuspal morphogenesis

BELL STAGE
Morpho and histodifferentiation occurs
2 stages
Early advanced

Histology of early bell stage
---> Outer enamel epithelium folds
Sac mesenchyme close to enamel organ
Rich nutrition supply
---> Inner epithelium form ameloblast
organizing influence on papillary cells
Form odontoblasts
Deposit dentin
Junction of inner/outer enamel epithelium
Cervical loop/zone of reflexion HERS
(Hertwig’s epithelial root sheath)www.indiandentalacademy.com

--->Stellate reticulum expands further
--->dental papilla cells under organizing
influence of inner enamel epithelium forms
odontoblasts.boundary between this
epithelium and papilla marks future DEJ
--->stratum intermedium
appears during this stage
2-3 layers of flattened squamous cells
high alkaline phosphate and glycogen
needed for enamel formation

Stratum intermedium

Advanced bell stage
Events occuring include--->
1) Crown pattern formation :
inner enamel epithelial cells stop dividing at
“growth center”where future cusp will
develop
Epithelial cells buckle inwards to form cusp
outline

Crown pattern formation

Primary tooth bud acquires its final shape

Tooth bud

2) Enamel & dentin
formation
After odontoblasts form
due to organizing
influence of epithelial
cells, they instruct
ameloblasts in turn to
secrete enamel matrix
(reciprocal induction)

3) Break up of dental lamina
breaks up into discrete islands of
epithelial cells
oral epithelium separated from tooth germ
these cells usually disintegrate but if persist
they are called epithelial pearls

Breakup of dental lamina

4) Root development
Occurs in later part of bell stage when
enamel and dentin formation reach future
CEJ
Hertwig’s epithelial root sheath(HERS)
formed from outer/inner enamel epithelia
Blue print of root development

HERS formed from inner/outer enamel epithelia

Development of root in multi-rooted teeth
Is different
Epithelial diaphragm expands eccentrically
Horizontal epithelial flaps formed
Unite and proliferate
Single apical opening is divided into 2-3
openings

Development of teeth with two
and three roots

DEVELOPMENT
OF
ENAMEL
(AMELOGENESIS)

Life cycle of ameloblasts has 6 stages---->
• Morphogenic
• Organizing
• Formative
• Maturative
• Protective
• Desmolytic

Morphogenic stage
• Cells short columnar
• Large oval nuclei
• Golgi apparatus and the
centrioles at proximal end
• Mitochondria scattered

Organizing stage
• Inner enamel
epithelium cells
become longer
• Golgi body/centrioles
migrate to distal end
(reversal of polarity)
• Mitochondria move
proximally
• Differentiation of
odontoblastsdentinwww.indiandentalacademy.com

Formative stage
• Begins after the first
dentin deposited
• Cell length increases
further
• Blunt processes
develop on ameloblast
surfaces facing
developing enamel
(TOME’S
PROCESSES)www.indiandentalacademy.com

Tome’s processes

Maturative stage
• Mineralization occurs
after matrix
deposition
• Ameloblasts display
microvilli at distal end
• Size of cells reduced
somewhat

Protective stage
• Ameloblasts cannot
be differentiated
from other enamel
organ cells
• All layers together
form reduced
enamel epithelium
• Protects mature
enamel
• Separates it from
connective tissuewww.indiandentalacademy.com

Desmolytic stage
• Reduced enamel epithelium causes atrophy
of connective tissue separating it from oral
epithelia
• Fusion of these epithelia occurs facilitating
eruption
• Epithelial cells secrete enzymes to destroy
connective tissues by desmolysis

Reduced enamel epithelium

Maturation of enamel
2 stages
Immediate partial maturation starting from
mineralization of crown tip cervically
matrix segments
• Organic matrix thinned down to accommodate
growing crystals

DEVELOPMENT
OF
DENTIN
DEVELOPMENT
OF
DENTIN
(DENTINOGENESIS)

• Before dentinogenesis,
inner enamel epithelial
cells short columnar
• Dental papillary cells
separated from them
by an acellular zone
• Papillary cells
small,undifferentiated

Epithelial cells become
taller,columnar with nuclei
migrated to opposite pole
papillary cells divide with
spindle 90° to basal lamina
acellular zone obliterated as
odontoblast differentiates

Daughter cell influenced by
epithelial cell differentiates
into pre-odontoblast
other cell not influenced by
this factor forms sub-
odontoblast
induction factor --->IGF and
others secreted by basal
lamina*
*Sasaki(1996) www.indiandentalacademy.com

Finally cells close to basement
membrane develop into
odontoblasts
later start depositing dentin
sub-odontoblast forms
reparative dentin later if at all
need arises

Mineralization of dentin
Odontoblasts differentiate
Deposit organic matrix(ground substance)
Type I collagen deposited
Matrix of mantle dentin formed
HAC deposited--->mantle dentin
Primary/circumpulpal dentin
Secondary dentinwww.indiandentalacademy.com

Deposition of minerals always lags behind the
formation of organic matrix
So there is always a layer of organic matrix
called ----->PRE-DENTIN between
odontoblasts and the mineralization front

predentin

DEVELOPMENT
OF
PULP

• Dental papilla forms pulp
• young papillary cells are highly vascularised
with undifferentiated cells
• Later form stellate shaped fibroblasts
• After ameloblasts/odontoblasts form and
dentin laid down--->pulp organ
• With maturation of dentin, pulp also forms
nerves and develops further

DEVELOPMENT
OF
CEMENTUM

Deposition of dentin along inner aspect of HERS
Breaks in HERS occur
New dentin comes in direct contact with sac
connective tissue
Collagen/cementoblasts form between epithelial
cells of root sheath
Cementoblasts lay down cementoid

Cementoid is lined by cementoblasts
Connective tissue fibres from periodontal
ligament pass between cementoblasts into
cementum
Attach tooth to surrounding bone
Sharpey’s Fibers
Later cementoid gets mineralized rhythmically
Incremental lines of Salterwww.indiandentalacademy.com

cementum lined by cementoblasts

Sharpey’s fibers

DEVELOPMENT
OF
PERIODONTAL
TISSUES

• After root
cementum is
deposited,some
cells of the dental
sac differentiate
into fibroblasts
• form ground
substance of
periodontal
ligament.
• Fibres embedded in
new cementum and
bone www.indiandentalacademy.com

development of periodontal fibers
The group of alveolar crest fibers (arrowheads),
first forming in A,
are initially oblique (B),
then horizontal (C),
and then oblique again (D).

DEVELOPMENTAL
ANOMALIES
AND
THEIR
PROSTHODONTIC
CONSIDERATIONS

HYPODONTIA
Therapeutic options include--->
• Traditional fixed prosthodontics
• Resin bonded bridges
• Osseo integrated implants with associated
prosthetic crowns

MICRODONTIA
• Most common
example is peg
shaped lateral
incisor
• Usually no
treatment is
necessary unless
desired for
aesthetic
restoration to full
size by porcelain
crowns

GEMINATION AND FUSION
• Usually requires
selected shaping of
teeth with or
without placement
of full crowns
• In severe cases,
teeth are surgically
removed and
prosthetic
replacement is
performed.

ANODONTIA
• Complete dentures for
both functional and
cosmetic purposes
• Dentures in relatively
young patients also but
must be reconstructed
periodically as the jaws
continue to grow

Amelogenesis imperfecta
Treatment depends on specific
type of defect
Hypo plastic type---
• Composite resins/porcelain
veneers bonded to anterior
teeth
• Often retain intracoronal
restorations (amalgam,
composite resins)
• If enamel too thin, full
coverage crowns neededwww.indiandentalacademy.com

Hypocalcified type
• Treatment begins early
• Primary teeth need
stainless steel crowns
• Early permanent
dentition open faced
stainless crowns with
composite inserts
needed
• In permanent dentition
PFM crowns for
anteriors; full coverage
for posteriors

Hypocalcified teeth
Composite crowns
PFM crowns

Dentinogenesis imperfecta
• ----->
Prevent attrition
Rehabilitate worn dentition
Restore aesthetics
Prevent caries
• Primary teeth-stainless
Steel crowns,open faced
anteriorly
• Permanent---PFM
bleaching
full crowns
Aim of treatment

after
before

RESEARCH TRENDS
IN
TOOTH
DEVELOPMENT

Current tooth replacement therapies
Artificial teeth implants
New trends
BIOLOGICAL TOOTH*
*Slavkin 1999

Made from individual’s own tissues,that could be
grown in the jaws and functionally and securely
integrated therein
Advantages---
• Functionally like natural tooth
• Maintains health and integrity of supporting
tissues
• Pulp supports it to maintain its integrity and
longevity
• Overall health of patient is well maintained
OUTLASTS ARTIFICIAL DENTAL PROSTHESIS*
*Fried et al 2000www.indiandentalacademy.com

Tooth stem cells----regeneration capacity
self renewal capacity
differentiate into multiple lineages
significant tools in tooth tissue
engineering
Cells useddental epithelial/mesenchymal
stem cells

Pamela/Robey(2005)
Constituent parts of tooth made
individually;process comparable to constructing
a building
Bone marrow stromal cells alveolar
Hydroxyapatite/tricalciumphosphate bone
Periodontal ligament stem cells-> periodontal lig.
Dental pulp cells+HA in enamel like matrix->
Enamel and pulp

BIOENGINEERING TEETH
DREAM?? REALITY??

SUMMARY

Stages in tooth growth
Morphologic changes physiologic processes
• Dental lamina initiation
• Bud stage proliferation
• Cap stage
• Early bell stage histodifferentiation
• Advanced bell
• Enamel/dentin morphodifferentiation
formation apposition

Disturbances in tooth development
• Initiation Absence of
single/multiple teeth
Anodontia
Supernumerary teeth
• Proliferation changes in size and
proportion of teeth
• Histodifferentiation
vit A deficiency in
ameloblasts--->atypical dentin (osteodentin)

• Morphodifferentiation
size and form of
teeth affected without impairing function of
ameloblasts/odontoblasts
e.g:twinning, Hutchinson’s incisors
• Apposition organic matrix
defect--->enamel hypoplasia
mineralization defect
hypocalcified enamel

CONCLUSION
The ultimate test of dental education is to
see how well it prepares the practitioner
to serve the patient.
Knowledge of development of teeth is
indispensable for a dentist,helping him not
only to diagnose a developmental disorder but
also to exactly pinpoint the event where
development was anomalous.
Bioengineering teeth seem to be a reality due
to the knowledge of teeth development.

“An understanding of basic sciences can be
the difference between an excellent
clinician and one who can treat his patients
only as a technician, between a leader and a
follower, between an innovator and one
whose clinical resources are limited and
dated!!”

REFERENCES
• Tencate’s Oral histology 6th
Edn Antonio Nanci
• Orban’s Oral histology and embryology 11th
Edn
Bhaskar S.N.
• Essentials of oral histology and embryology-A
Clinical approach 2nd
Edn James K Avery
• The developing Human Moore & Persaud
• Human Embryology 6th
Edn I.B.Singh
• Arch Oral Biology 1970:1315:15 Ruch/Lindewww.indiandentalacademy.com

•Colour atlas of oral pathology
4th Edn Hamiltan; Robbinson ; Miller
•Text book of oral pathology
4th Edn Shafer
•Various sites on the Internet

www.indiandentalacademy.comwww.indiandentalacademy.com

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