Tooth development and eruption /certified fixed orthodontic courses by Indian dental academy

GOOD MORNING
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Poet OGDEN NASH
must have known the
suffering
when he penned the
words ,
”..some tortures are
physical and some are
mental ,
But the one that is
both is DENTAL…!!! ”


EVOLUTION . . .

Evolutionary Concept
During evolution several significant changes
took place in the jaws and teeth. When the
reptilian evolve to mammalian , the dentition
went from “polyphydont ” (many set of teeth)
to “diphydont ” (only two sets of teeth) and
then to “homodent ” (all of same teeth) to
“heterodent”(different types of teeth like
incisors, canines , premolars and molars) .
There also arose the necessity for the teeth
and bones to develop somewhat
synchronously in order that the function of
occlusion could be facilitated.

Stages of tooth evolution
Graphically there are four stages of tooth
development:
 The reptilian stage (HAPLODONT)
 Early mammalian stage (TRICONODONT)
 Triangular stage (TRITUBERCULAR
MOLAR)
 QUADRITUBERCULAR MOLAR


…move towards future…the MAN.

The REPTILIAN stage

There is no occlusion. prehension both jaws single
Teeth mainly byconfined to simple or combat and
 Dentition includes for
Jaw movement simplest form of tooth , the that limits
Represented used many teeth in hinge movement.

procurement of
jaw movement. food.
cone.


Early mammalian (triconodont)
Not

seen now except a few breeds of dogs
and other carnivores.
Exhibits

three
cusps in line in
the posterior
teeth.


Largest
cusp is in
middle,with
smaller cusp
anteriorly
and
posteriorly.



Occlusion absent

tiger

Tritubercular (triangular)stage




According to some theories the triconodont
line of three changed to a three cornered
shape , with the teeth still bypassing each
other more or less when the jaw opened or
closed.
Usually seen in dogs and carnivores.

cheetah

HELLLO…..frens !!! meet other members of my FAMILY…..

Quadritubercular stage

During next stage of accommodation to the changes inon
It is thethe time as andevelopment created aof humans are the
The animals with dentition similar to that projection
triangularform and anatomy , the articulationantagonist of the
the tooth form that finally occluded with the of the jaws
anthropoid apes.
opposing accordingly.
changed jaw.


Hi..myself GIBBON


HA…HA…HAAA !!!

we are… GORILLAS’


HELLO….myself MONKEY


DON’T run..I am

ORANGUTAN


The shapes of individual teeth in these animals are
very close to their counterparts in HUMAN MOUTH.

NOTE the TEETH in OCCLUSION

SKULL of CHIMPANZEE

Characteristics of DENTITION
The teeth of the vertebrates are characterized
depending upon :
MODE

OF ATTACHMENT

ACRODONT

: teeth attached to the jaw by a
connective tissue.
PLEURODONT
THECODONT

socket.

: teeth are set inside the jaw.

: teeth are inserted in the bony


Depending on the NUMBER OF SUCCESSIVE
SET
POLYPHYODONT : teeth replaced throughout life .
ex:

SHARK TEETH

SHARK

…so better TAKE CARE

Depending on the NUMBER OF SUCCESSIVE SET
DIPHYODONT : two sets of teeth.
Ex:

HUMAN BEING
PRIMARY DENTITION

Step further towards CIVILIZATION…


so care for your TEETH…..
and SMILE

…..or BETTER choose yourself

PERMANENT DENTITION

Depending on the NUMBER OF SUCCESSIVE SET
MONOPHYODONT

: one set of teeth .

SHEEP and
GOAT
Ex.

GOAT

SHEEP

TYPE

or SHAPE OF TEETH

HOMODONT

: a single type of teeth

HETRODONT

: having various type of
teeth . Ex. Human being


ORIGIN OF TEETH


THEORY OF CONCRESCENCE




THEORY OF TRITUBERCULY






The mammalian dentition was produced by the
fusion of two or more primitive conical teeth and
each tubercle with its corresponding root originated
as a single tooth.

Each of the mammalian teeth was derived from a
single reptilian tooth by secondary differentiation of
tubercles and roots.
This theory is widely ACCEPTED.

THEORY OF MULTITUBERCULY


The mammalian dentition is a result of reduction
and condensation of primitive tuberculate teeth.

Development of TOOTH

Dr. Raj Kumar Jaiswal


CONTENTS














PRIMARY EPITHELIAL BAND
VESTIBULAR LAMINA
DENTAL LAMINA
BUD STAGE
CAP STAGE
Enamel Knot
Enamel Cord
Enamel Niche
BELL STAGE
Histodifferentiation and Morphodifferentiation
Structure of TOOTH GERM
DENTAL PAPILLA
BREAK UP of Dental Lamina
CROWN PATTERN Determination
Formation of PERMANENT DENTITION
Hard tissue formation / CROWN STAGE
ROOT FORMATION
FORMATION OF SUPPORTING TISSUE





Development of TOOTH involves many
BIOLOGICAL PROCESS including
EPITHELIAL MESENCHYMAL relationship
Morphogenesis
Fibrillogenesis
Mineralization


WHAT IS
ECTOMESENCHYME?


When the histology of primitive Oral cavity is
Examined ,it can be seen to be lined by
primitive 2-3 layered epithelium covering an
Embryonic Connective Tissue which
because of its origin from Neural Crest is
termed ECTOMESENCHYME.


Primary Epithelial Band





After 37th day of development, continuous
band of epithelium forms around the mouth
from the fusion of separate plates of
thickened epithelium.
Roughly ‘Horse Shoe’ shaped.
Gives rise to Vestibular lamina.
Dental lamina.


Primary Epithelial Band
Vestibular Lamina


Dental Lamina

Vestibular Lamina




Vestibule forms as a result of proliferation of
vestibular lamina into the ectomesenchyme.
Its cells rapidly enlarge and then degenerate
to form CLEFT which becomes the vestibule
between the cheek and tooth bearing area.


Dental Lamina


Within the Lamina itself continued and
localized proliferative activity leads to
formation of series of Epithelial Ingrowths
into the Ectomesenchyme at sites
corresponding to position of future
DECIDUOUS TEETH.
From THIS POINT development proceeds in
three stages :
 BUD stage
 CAP stage
 BELL stage

Bud Stage






First epithelial incursion into the
ectomesenchyme of jaw.
Simultaneous with the differentiation of each
dental lamina round and ovoid swelling arise
from basement membrane at ten different
point, corresponding to future deciduous
teeth.
These are primordia of enamel organ ‘the
tooth bud’ .

BUD STAGE

TOOTH BUD and
DENTAL LAMINA

EIGHT WEEK

CAP STAGE
ENAMEL
ORGAN

TENTH WEEK

BELL STAGE
ENAMEL ORGAN
of DECIDUOUS
TEETH
PRIMORDUM of
PERMANENT
TOOTH

About 4
MONTHS

PRIMORDIUM of
FIRST
PERMANENT
MOLAR










Enamel organ (dental organ)

Consists of:
 Peripherally located low columnar cells.
 Centrally located polygonal cells.
Functions of Dental organ
 Determining shape of crown
 Initiating dentin formation
 Establishing dentinogingival junction
 Forming enamel
As a result of increased mitotic activity (of cells of tooth
bud and surrounding mesenchyme)and migration of
neural crest cell into the area.
The ectomesenchymal cells surrounding tooth bud
condense.

Enamel Organ(dental organ)


Condensed Ectomesenchyme


Immediately subjacent to enamel organ
known as DENTAL PAPILLA





That surrounds tooth bud and dental papilla
known as DENTAL SAC





Tooth pulp
Dentin

Cementum
Periodontal ligament

Dental organ,Dental Papilla and Dental
follicle constitute TOOTH GERM

Tooth Germ


Cap stage(proliferation)




Tooth bud continues to proliferate BUT not
expand uniformly.
Unequal growth in different parts of tooth bud
lead to cap stage.
Outer enamel epithelium




Peripheral cells covering convexity are
CUBOIDAL

Inner enamel epithelium


Peripheral cells covering concavity are
COLUMNAR



Stellate reticulum (Enamel pulp)





Polygonal cells in center of epithelial
enamel organ between inner enamel
epithelium and outer enamel epithelium
separate as intercellular fluid accumulate.
Cells assume branched reticular network.
Mucoid fluid rich in albumin.


Gives cushion like consistency may
support and protect Enamel forming
cells

CAP STAGE
Oral Epithelium

Dental Lamina
Tongue
Tooth Germ
Meckel’s Cartilage
Lip

ENAMEL CORD

DENTAL LAMINA
PERMANENT TOOTH BUD
ENAMEL CORD or SEPTUM
DENTAL PAPILLA


ENAMEL NICHE


ENAMEL KNOT
The cells in the center of the ENAMEL ORGAN
are densely packed and form ENAMEL KNOT.

ENAMEL CORD

A vertical extension of ENAMEL KNOT that
arises in Increasing enamel organ.

The FUNCTION of both may be to act as a
reservoir of dividing cells for growing ENAMEL


Bell stage(Histodifferentiation
& Morphodifferentiation)


As the invagination of epithelium deepens & the
margin continues to grow the enamel organ
assumes a bell shape.
 Inner Enamel Epithelium


Consists of single layer of cell that differentiate
prior to Amelogenesis into tall columnar cells
called Ameloblasts.




AMELOBLASTS
 Attached to one another by JUNCTIONAL
COMPLEX.
 Attached to cells of stratum intermedium by
DESMOSOME.
 These exhert organizing influence on the
underlying mesenchymal cells in dental
papilla which later differentiate into
ODONTOBLASTS.
 High glycogen content.




Stratum intermedium







Between the Inner Enamel Epithelium & newly
differentiated stellete reticulum the epithelial
cells differentiate into a layer of
flattened(squamous) cells called stratum
intermedium.
High degree of metabolic activity.
Absent in part of tooth germ that outlines the
root portion of tooth but does not form enamel.
Along the inner enamel epithelium both layer
considered as single functional unit responsible
for formation of enamel.



Stellate reticulum






Expand further due to accumulation of
intercellular fluid.
Before enamel formation begins , stellate
reticulum collapses reducing the distance
between centrally located ameloblast and
nutrient capillaries near outer enamel
epithelium.
Change begins at the height of the cusp
or incisal edge and progress cervically.

Stellate Reticulum
Accumulation of intercellular fluid


Collapsed



Outer enamel epithelium





Cells flatten to low cuboidal form.
At the end of bell stage and preparatory
to formation of enamel the formerly
smooth surface is laid in folds.
Between these folds the mesenchyme of
dental sac forms papillae and thus
provide rich nutritional supply for the
intense metabolic activity of avascular
enamel organ.



Dental lamina


In all teeth except permanent molars the
dental lamina proliferates at its deep end
to give rise to enamel organ of
permanent teeth.
Distal extension




Dental papilla







Enclosed in invaginated portion of enamel
organ.
Before inner enamel epithelium produce
enamel the peripheral cells of mesenchymal
dental papilla differentiate into odontoblasts
under organizing influence of epithelium.
First assume cuboidal form and later
columnar and acquire specific potential to
produce dentin.
‘Membrana preformativa’ – basement
membrane that separates the enamel organ
and dental papilla just prior to dentin
formation.



Dental sac




Before formation of dental tissue begins,
dental sac shows circular arrangement of
its fibers and resembles capsular
structure.
With development of root, fibers of dental
sac differentiate into periodontal ligament
fibers that become embedded in
developing cementum and alveolar bone.


BELL STAGE
Gland of Serres
Oral Epithelium
Dental Lamina
Stellate Reticulum
Bud for Permanent Tooth
External Enamel Epithelium
Dental Papilla
Inner Enamel Epithelium


INITIAL

A B D DP
DF
E EO
O N HS

BELL
STAGES
STAGE

ADVANCE STAGES

AMELOBLAST
BONE
DENTINE
- DENTAL PAPILLA
- DENTAL FOLLICLE
ENAMEL
- ENAMEL ORGAN
ODONTOBLAST
NECK OF TOOTH
– HERTWIG ROOT SHEATH

Advanced Bell Stage


The boundary between the inner enamel
epithelium and odontoblasts outlines future
dentino-enamel junction and cervical portion
of enamel organ give rise to epithelial root
sheath of Hertwig.


ADVANCED BELL
STAGE
Oral Epithelium
Inner Enamel Epithelium
Enamel and Dentin
formation starting at
Cusp tip
Dental
Papilla
Cervical Loop
Alveolar Bone
Nerve Bundle

…magnified view showing HARD

TISSUE FORMATION

AMELOBLASTS

ENAMEL

STRATUM
INTERMEDIUM

STELLATE
RETICULUM
PRE DENTIN

DENTIN

ODONTOBLASTS

PULP


COLUMNAR AMELOBLASTS
ENAMEL MATRIX
MINERALIZING DENTINE
PREDENTINE
ODONTOBLASTS
FIBROBLASTS OF PULP
HERTWIG’s ROOT SHEATH

VERTICAL SECTION
through NECK of
TOOTH


Hertwig’s Epithelial Root Sheath
and Root Formation
Root development begins after enamel and
dentin formation has reached future cementoenamel junction.
HERS is formed from enamel organ.
 Molds the shape of root
 Initiates dentin formation.
 Consists of outer and inner enamel epithelium
only.

EPITHELIAL DIAPHRAGM AND PROLIFERATION ZONE OF PUL


ELONGATION
of HERS
CORONAL to
EPITHELIAL
DIAPHRAGM

ROOT
SHEATH
BROKEN




Prior to beginning of root formation , root
sheath forms EPITHELIAL DIAPHRAGM








The outer and inner enamel epithelium bend at
future CEJ into a horizontal plane narrowing the
wide cervical opening of the tooth germ.
The proliferation of cells of epithelial diaphragm
is accompanied by proliferation of cells of
connective tissue of pulp which occurs in area
adjacent to the diaphragm.
The free end of the diaphragm does not grow
into connective tissue but the epithelium
proliferates coronal to the epithelial diaphragm.
The differentiation of Odontoblast & formation of
Dentin follow the lengthening of root sheath.

ROOT FORMATION

INITIAL STAGES

CERVICAL LOOP

MIDWAY

FINAL STAGE

APICAL FORAMEN

At the same time the connective tissue of Dental sac
surrounding the root sheath proliferates and invades
continuous Double epithelial layer dividing it into network of
epithelial strands.
 Epithelium is moved away from the surface of dentin so that
the connective tissue cells come into contact with the outer
surface of the dentin and differentiate into cementoblast that
deposit a layer of cementum onto the surface of dentin.
 In last stages of root development the proliferation of the
epithelium in the diaphragm lags behind that of the pulpal
connective tissue.
Wide apical foramen is reduced first to width of
diaphragmatic opening itself and later is further narrowed by
apposition of dentin and cementum to the apex of the root.



In multi-rooted teeth:









Differential growth of epithelial diaphragm causes
division of the root trunk in 2/3 roots.
During the general growth of enamel organ the
expansion of its cervical opening occurs in such a
way that long tongue-like extension of horizontal
diaphragm develops.
Two extension in lower molars and three in upper.
Before division of the root trunk occurs the free end
of these horizontal epithelial flaps grow towards
each other and fuse.
The single coronal opening of the coronal enamel
organ is than divided into two-three openings.
On the pulpal surface of dividing epithelial bridges
dentin formation starts and on the periphery of
each opening root development follows in the same
way as for singlewww.indiandentalacademy.com
rooted teeth.

During of growth of TOOTH GERM…

EPITHELIAL
DIAPHRAGM HORIZONTAL EPITHELIAL FLAPS
PROLIFERAT and UNITE
EXPAND
ECCENTRICALLY E


FORMATION IN PROGRESS
as a result
BEGINNING OF
ROOT ELONGATION OCCURS
DENTIN
FORMATION AT
BIFURCATION

MESIAL

DISTAL

DEVELOPMENT OF TWO ROOTED TOOTH


Initiation
Specific cell of dental lamina have potential to
form enamel (dental) organ. Different teeth at
different time/definite time.
Initiation induction requires
ECTOMESENCHYMAL-EPITHELIAL
interaction.


LACK of INITIATION results in:

ABSENCE of either SINGLE TOOTH or MULTIPLE TEETH
LEADING TO CROSS BITE
DECIDUOUS DENTITION
PERMANENT DENTITION

FLATTENING of ARCH

MISSING LATERAL INCISORS

PARTIAL ANODONTIA

SUBMERGING LOWER 2 nd
MOLAR
Due to
CONGENITAL ABSENCE
PERMANENT 2 nd
PREMOLARS


OLIGODONTIA

IMPEDES THE
DEVELOPMENT
OF ARCH
Missing teeth


ABNORMAL INITIATION results in :
Development of
SINGLE or MULTIPLE SUPERNUMERARY teeth
CLIEDOCRANIAL DYSPLASIA
MESIODENS


Proliferation
Enhanced proliferative activity ensues at point
of initiation and results in the BUD,CAP, and
BELL stages of development.
Proliferative growth causes regular changes in
the size and proportions of the growing tooth
germ.


Histodifferentiation
The cells become restricted in their functions.
They differentiate and give up their capacity
to multiply as they assume their new function
; this law governs all differentiating cells.
This phase reaches its highest development in
the BELL stage , just preceding the
beginning of formation and apposition of
DENTIN and ENAMEL.


DISTURBANCES during this stage may lead to…
AMELOGENESIS IMPERFECTA : Hypoplastic type
AMELOGENESIS IMPERFECTA : Hypomineralized type
DENTOGENESIS IMPERFECTA
AMELOGENESIS IMPERFECTA :Hypomature type
SHORT Amber coloured tooth
MARKED Attrition


Morphodifferentiation

The morphologic pattern,or basic form and relative size
of the future tooth,is established by
morphodifferentiation,that is,by DIFFERENTIAL
GROWTH.
Morphodifferentiation therefore is IMPOSSIBLE without
proliferation.
The ADVANCED BELL stage marks not only active
histodiferentiation but also an important stage of
morphodifferentiation in the crown,outlining the future
DENTINOENAMEL JUNCTION.
The DENTINOENAMEL and CEMENTOENAMEL
junctions which are different and characteristic for
each type of tooth,act as BLUE-PRINT pattern.

Disturbances may effect the FORM and SIZE of the
tooth WITHOUT impairing the function of ameloblasts
and odontoblasts.
MICRODONTIA
MACRODONTIA of entire dentition in relation to basal bone
MICRODONTIA
Oversized LATERAL INCISORS
MACRODONTIA of UPPER teeth in relation to basal bone
PEG shaped LATERAL
CONCRESCENCE:
FUSION :union of the dentin
GEMINATION :incomplete
union of cellular
TWINNING:complete division
of two teeth,from two tooth
division of of twotooth bud
Cementum bud
of one toothsingleto teeth,from
buds.
create
two teeth
two buds.


Apposition
Apposition is the deposition of the MATRIX of
the hard dental structures.
Appositional growth of enamel and dentin is
characterized by regular and rhythmic
deposition of an extracellular matrix.
It is the fulfillment of the plans outlined at the
stages of Histodifferentiation and
Morphodifferentiation.
Both HYPOPLASIA and HYPOCALCIFICATION
can occur as a result of an insult to this
phase.

Factors affecting DEVELOPMENT


Systemic factors


ACCELERATING EFFECT :on the

whole very rare but reported to be due to
 Hyper thyroidism
 Hyper pitutarism
 Turner’s syndrome




RETARDING AFFECT : more common in
permanent dentition due to
 Hypo thyroidism
 Hypo pitutarism
 Cleidocranial dysostosis
 Down’s syndrome
 Achondroplasia
 Hypovitaminoses ( A and D)
 Osteopetrosis


Eruption of Tooth and
Theories of
eruption

Dr. Raj Kumar Jaiswal


Eruption



Latin – ‘erumpere’ – to break out.
Properly refers/understood to mean the
axial or occlusal movement of the tooth
from its developmental position within
the jaw to its functional position in the
occlusal position.


Theories of Eruption
Tooth eruption is an essential process for the
survival of many different species and although
the movement of teeth into function has been
the subject of extensive research there is no
consensus as to the mechanisms involved
Mechanism that brings about tooth movement is
still debatable and is likely to be a combination
of number of factors.


Most talked about theories are:
 Root formation(elongation)theory
 Bone remodeling theory
 Vascular pressure theory
 Periodontal ligament traction theory
 Pulp theory
 Genetic input theory


Root formation theory
In 1978 HUNTER attributed to mechanism of root
elongation
 Root

formation follows crown formation and involves
cellular proliferation of new tissue that must be
accommodated by either movement of the crown of
tooth or resorption of bone at the base of its socket.
It is the former that actually happens , but if occlusal
movement is prevented resorption of bone at the base
of socket occurs.
If root formation is to result in an eruptive force the
apical growth of root needs to be translated into
occlusal movement and requires the presence of a
fixed base.

BUT….


Bone

at the base of socket cannot act as a
fixed base because pressure on bone results
in its resorption.
Some teeth move a distance greater than the
length of their roots.
Eruption movement can occur after
completion of root formation.
Experimental resection preventing further
root formation does not stop eruptive tooth
movement.
All indicating root formation CANNOT be
responsible for eruptive tooth movement.

STOPPED

BONE
TOOTH GERM

BONE

OCCLUSAL MOVEMENT
OF CROWN


BONE RESORPTION

Advocates of root formation theory like a
postulated existence of “Cushion Hammock
Ligament”straddling the base of the socket from
one bony wall to the other sling.
Its function was to provide fixed base for
growing root to react against…

BUT

…the structure described as cushion hammock
ligament is Pulp delineating membrane that
runs across apex of the tooth and has no bony
insertion,it CANNOT act as FIXED BASE.

Bone remodeling theory
Is

important to permit tooth movement.
In animals that exhibit genetic deficiency of
OSTEOBLAST ,tooth eruption is prevented .
If tooth germ is removed experimentally and
dental follicle left intact an eruptive pathway is
forms in overlying bone.
Marks and Cahill have confirmed that tooth
has no active role in the process , since metal
or silicone replicas of calcified crowns ,
placed within follicle ,also erupts.

These experiment establish ABSOLUTE
requirement for DENTAL FOLLICLE to achieve:
Bony remodelling and tooth eruption.
Provides the source for new bone forming
cells and conduit for osteoclast derived from
Monocyte through its vascular supply.
RECENT STUDIES show that resorptive
process may be regulated by local growth
factors such as Transforming growth factor
Beta-1(TGF-ß1)and Epidermal growth factor
(EGF) produced within or around Dental follicle.

These growth factors seem to Chemoattaract
monocytes from the peripheral bood vessels
around the dental follicle.
Resorptive process begins with the formation of
osteoclasts from coalescence of the monocyte.


Factors influencing tooth to erupt Intraosseously:
 Density of bone.
 Rate of bone resorption.
 The overlying tissue
Bone
 Primary tooth root
 Gingiva
Must resorb to provide an eruptive path.


Force must be generated to move the tooth
vertically.
Resorption over tooth seems to be dependent only
on the presence of coronal portion of the dental
follicle .



Vascular pressure theory

CONSTANT suggested that blood pressure
provided the eruptive force but there has been
evidence for and against the theory.
FOR:
 Teeth develop in a vascular site and direct
relationship between conglomerates of beneath
the developing crown and number of cusps and
roots.
 Periodontal ligament has a rich vascular supply.
 Oscillatory movement of erupted teeth occurs in
synchrony with the pulse.
 Vasculature is under physiological control
throughout life.

Could the
VASCULATURE be
source of ERUPTIVE
FORCE…???


There is close relationship between Osmotic tissue
fluid pressure and Blood pressure.
 NESS and SMALE suggested that the pressures
derived from the vasculature would be exerted by
the tissue fluid.
 While tissue fluid osmolarity can reasonably be
anticipated to change Apical pressure…
Hypotensive rats show no changes in unimpeded
eruption rates.





The Pulsatile nature of blood flow within the
follicle and periodontal ligament and its
significance for tooth eruption has been noted.
Cyclic intermittent forces –impulses have been
shown to enhance cellular activity during bone
remodelling and gene expression within the
endothelium therefore their affects on bone
and the tooth.


Tooth develop,erupt and function in a vascular
site constantly exposed to PULSATIVE
forces arising from blood flow.
Repetative impulses acting on the calcified
crown similar to the action of a hammer on a
nail,are the likely the eruptive force.


BUT…..
Even the resection of root and thus the
vasculature CANNOT prevent the
eruption of tooth.


Periodontal ligament traction theory
The eruptive movement could be brought about a
combination of events envolving a force
initiated by the periodontal ligament fibroblasts.
This force is transmitted to the extracellular
compartment via FIBRONEXUS and to
collagen fibre bundle which align in an
appropiate inclination brought about by root
formation bring about tooth movement.
These fibre bundles have the ability to remodel for
eruption to continue and interferance with this
ability effects the process.

The removal of bone to create eruptive pathway is
also dictated by the tissues surrounding the
tooth.
Evidence to support this view:
 Experiments delineating the role of follicle (from
which periodontal ligament forms)
 Experiments on continuously erupting Rodent
incisor designed to eliminate the effects of root
growth and vascular supply show that as long
as periodontal ligament tissue is available
tooth movement occurs.





Drugs that interrupt proper collagen
formation in ligament also interfere with
eruption.
Tissue culture experiment have shown
that ligament fibroblast are able to
contract a collagen gel which in turn
brings about movement of disk of root
tissue attached to that gel.

PERIODONTAL LIGAMENT
Before CONTRACTION
ORAL MUCOSA

After CONTRACTION

BONE


Pulp theory
This theory suggests that a propulsive force is
generated by extrusion of pulp through
THREE mechanisms.




Growth of DENTINE
Interstitial PULP growth
Hydraulic effects within VASCULATURE


Here in first stage ,
There is growth of dentine.
This causes interstitial growth of the pulp tissue
VASCULAR SYSTEM DEVELOPS

Hydraulic effects within the vasculature
causes eruption of teeth


BUT……
HERZBERG and SCHOUR removed
the PULP of RODENTS incisors and found
that
its eruption rates were UNAFFECTED.


Genetic input theory
If tooth eruption is to be explained at the
cellular and molecular level ,a degree of
genetic control is highly likely. In normal
development of the occlusion,incisors
develop before premolars and this process of
eruption is disturbed in a number of Genetic
Disorders.


A classification of these relationships has been
represented by SANK.
 Inherited defects : amelogenesis imperfecta
 Disorders with supernumerary teeth or
crowding of teeth
 Growth retardation syndromes
 Miscellaneous disorders




Hypophostasia
Juvenile periodontitis
Papillion lefevre syndrome

Although variety of theories have attempted to
identify the eruptive force , none been fully
supported by experimental evidence.
Specific changes in the cellular activity of bone
surrounding the erupting tooth provide
indirect information about the mechanics of
the process that need to be accounted for in
ANY theory of eruption.


Mechanics of eruption
When a tooth starts to erupt there is change in
its momentum , therefore a force MUST be
present.
 The spherical bony crypt prior to calcification
of crown exists because forces are present
in the follicle that resists bone apposition.
Eventhough the magnitude and direction of the
individual forces cannot be determined,a
summation of their distribution can be
represented as series of RADIAL force
vector extending to the surface of a sphere.

Calcification the crown provides a new mass against
which the force within the follicle can act.
Although the action force is such that the tooth will
move occulusally , the bone resorption initially
occurs in the opposite direction along the axis of
force.
 Bone remodeling around the erupting tooth results
from the action of many forces within the follicle.In
order for a tooth to move the action of eruptive force
must be greater than the sum of forces resisting its
movement.
 As the tooth erupts the dynamic relationships
between the surrounding alveolar bone , the eruptive
force and the erupting tooth influence the rate of
eruption.



In order for a tooth to
the tooth erupts the
dynamic relationships between move the action of
the surrounding alveolar bone , eruptive force must be
greater than the sum of
the eruptive force and the
forces resisting its
erupting tooth influence the
Calcification of the
movement.
RATE OF ERUPTION.
crown provides a NEW
MASS against which the
force within the follicle can
SERIES OF RADIAL FORCE
act.
VECTOR EXTENDING TO THE
SURFACE OF A SPHERE.
As


On emergence the resistance is greatly reduced
resulting in accelerated rate of eruption until
a new equilibrium of forces is established.
However eruption is only part of total pattern of
physiologic tooth movement , because teeth
also undergoes complex movement related
to maintaining their position in the growing
jaws and compensating for masticatory wear.


Shedding of deciduous teeth
The physiologic process resulting in
elimination of the deciduous dentition is
called SHEDDING or EXFOLIATION.


Physiologic tooth movement
Is described as :
 Pre-eruptive tooth movement
 Eruptive tooth movement
 Post eruptive tooth movement


Pre-eruptive tooth movement
When deciduous tooth germ first differentiate
they are extremely small and there is a good
deal of space for them in the developing jaw.
Because the tooth germs grow rapidly, however
they become crowded together particularly in
the anterior of jaw.




This crowding is gradually alleviated by the
lengthening of the jaws , which permits the 2nd
deciduous molar tooth germ to move backwards
and anterior tooth germ move forward.



At the same time the tooth germs are also
moving bodily outward and upward , or
downward as the case may be , as the jaws
increases in length as well as in width and
height.



Successional tooth germs develop on the lingual
aspect of their deciduous predecessor in the
same bony crypt. From this position the tooth
germ shift considerably as the jaw develop.

INCISOR and CANINE
 Eventually come to occupy a position in their
own bony crypt on lingual surface of their
deciduous.
PREMOLARS
 Also in their own bony crypt finally position
between the divergent roots of the deciduous
molars.


ERUPTING INCISOR

DECIDUOUS INCISOR

BONE BETWEEN DECIDUOUS
TOOTH
AND SUCCESSOR
ENAMEL OF PERMANENT INCISOR
DENTIN


ERUPTING INCISOR
ENAMEL DISSOLVED AWAY

DENTIN

GINGIVA
PULP

FOLLICLE
ENAMEL SPACE
REDUCED ENAMEL
EPITHELIUM
ALVEOLAR BONE

ROOT OF DECIDUOUS TOOTH
AREA OF RESORPTION
PERMANENT TOOTH


ERUPTING CANINE

DECIDUOUS CANINE

RESORPTION

RESORPTION OF ROOT

RERSORPTION OF BONE

PERMANENT CANINE


ERUPTING PREMOLAR
DECIDUOUS FIRST MOLAR

ROOT RESORPTION
PERMANENT TOOTH GERM


PERMANENT MOLAR tooth germ


No predecessors , develop from backward
extension of the dental lamina as there is little
space to accommodate these tooth germ.


In MAXILLA : MOLAR tooth germ first
develop with their occlusal surface facing
DISTALLY,and can swing into position when
maxilla has grown sufficiently.



In MANDIBLE : permanent MOLAR develop
with their axis showing MESIAL inclination ,
vertical later.

OCCLUSAL surface facing DISTALLY,and can
swing into position

MAXILLA

PERMANENT MOLAR develop with
their axis showing MESIAL
inclination , VERTICAL later.

MANDIBLE

ERUPTION OF MOLAR
At 6 to 7 years
At 4 years 6 months

Perm.FIRST MOLAR at 3 years


EXFOLIATED

DECIDUOUS CANINE

DECIDUOUS MOLAR


Pre eruptive movements of both deciduous and
permanent tooth germs are best thought of as
the movement required to place the teeth within
the jaw in a position for eruptive tooth movement.
Pre eruptive tooth movements are combination of
two factors:
 Total bodily movement of the tooth germ
 Growth , in which one part of the tooth germ
remains fixed while rest continues to grow ,
leading to change in the center of tooth germ. Ex:
deciduous incisor maintain their position relative
to oral mucosa as jaw increase in height.

Histology
As pre eruptive tooth movements occurs in a
intraosseous location , such movement is
reflected in the patterns of bone remodeling
within the crypt wall.
Ex: bodily MESIAL movement –bone resorption
occurs on mesial surface of crypt
(OSTEOCLASTIC activity) and bone deposition
on distal surface / wall as a “Filling in process”
Whether bony remodeling to position bony crypt is
important as a mechanism or whether its merely
an adaptive e response is DEBATABLE.

Eruptive tooth movement
During this phase the tooth movement from
its position within the bone of the jaw to
the functional position in occlusion and
the principal direction of the movement is
occlusal or axial.


HISTOLOGY
Significant developmental event associated with the
eruptive tooth movement are:
 Formation of roots
 Periodontal ligament
 Dentogingival junction
The periodontal ligament develops only after root
formation has been initiated and once
established it must be remodeled to permit
continued tooth movement.


The architecture of tissue in advance of erupting
successional teeth from that found in advance of
deciduous teeth.
The fibrocellular follicle surrounding a successional
tooth retains its connection with the lamina
propria of oral mucous membrane by means of a
strand of fibrous tissue containing remnants of
the dental lamina known as GUBERNACULAR
CORD.


GUBERNACULAR CORD


“in dried skull holes can be identified in jaw on the
lingual surface of the deciduous teeth”
These holes which once contained the
gubernacular cord is known as
GUBERNACULAR CANAL.
As the successional tooth erupts its
gubernacular canal is rapidly widened by local
osteoclastic activity , delineating the eruptive
pathway for the tooth.


GUBERNACULAR CANALS




Once erupting tooth appears in the oral cavity its
subjected to environmental factor that help to
determine its position in dental arch.



Factors:Muscle forces -tongue
-cheek
-lips



Forces of contact of erupting teeth with other
erupting tooth or with other erupted tooth.



Once erupted it continues to erupt at the same
rate of 1mm every 3 month, only slowing as it
meets its antagonist in opposing arch.

Post eruptive tooth movement
These are those movements made by the tooth
after it has reached its functional position in the
occlusal plane.
Divided into 3 categories:
 Movements made to accommodate growing
jaws
 Compensation for occlusal wear
 Accommodation for interproximal wear


Movement made to accommodate the
Growing Jaws


These are completed toward the end of 2nd
decade when jaw growth ceases.



Recent studies have shown that
readjustment occurs between 14 and 18
years.








Seen histologically as readjustment of the
position of the tooth socket achieved by
formation of new bone at alveolar crest
and on the socket floor to keep pace with
height of jaws.
Apices of teeth move away 2-3mm away
from inferior dental canal (regarded as
fixed reference point)
Seen relatively earlier in girls than boys
and is related to burst of condylar growth
that separates jaws and teeth , permitting
further eruptive movement .

Compensation for OCCLUSAL
wear




Is often stated that it is achieved by continued
cementum deposition around apex of the tooth ,
but deposition of cementum occurs only after
tooth has moved .
No evidence as such is present that forces
causing tooth eruption are still available to bring
about sufficient axial movement to compensate
axial wear.


OCCLUSAL PLANE

DEPOSITION of CEMENTUM

ALVEOLAR BONE

ATTRITION

COMPENSATION OF OCCLUSAL
WEAR

Accommodation for INTERPROXIMAL wear
Wear also occurs at the contact points between
teeth and their proximal surfaces.
This interproximal wear is compensated by process
known as MESIAL or APPROXIMAL DRIFT.
Factors which bring about drift:
 Anterior component of occlusal force
 Contraction of transseptal ligament
 Soft tissue pressure

APPOSITION
RESORPTION

MESIAL DRIFT

Anterior component of force :

When teeth are brought in contact ,ex:when jaws
are clenched , a forwardly force is generated .
This force is a result of
 Mesial inclination of most teeth.
 Summation of intercuspal plane producing a
forwardly directed force.
In case of incisor which are inclined labially , it is
expected that they move in same direction BUT
infact they move MESIALLY explained by
“BILLIARD BALL ANALOGY”


Billiard ball analogy
“…if the two touching balls are in line with the
pocket , no matter how the first ball is struck
second enters the pocket as it travels at right
angle to the common tangent between the two
balls…”
Following this example the CANINES and
INCISORS move in direction at right angles to
the common tangent drawn through contact
points. This leads to IMBRICATION often found
in older dentition.

BILLIARD BALL ANALOGY


Cuspal inclination is a significant factor which
can be demonstrated by selectively grinding cusp
in such a way as to either enhance or even
reverse the direction of occlusal force.
 When opposing teeth are removed , thereby
eliminating the biting force the mesial migration
of teeth is slowed BUT not halted indicating the
presence of some other force.
Here the TRANSSEPTAL fibres of periodontal
ligament have been implicated.



Contraction of Transseptal
ligament
The periodontal ligament are important in maintaining
tooth position. It is suggested that transseptal fibre
running between adjacent teeth across the
alveolar process draw neighbouring teeth together
and maintain them in contact .
Evidence to support this:
 Relapse of orthodontically moved teeth is much
reduced if gingivectomy removing transseptal
ligament is performed.
 Demonstrated experimentally that in bisected tooth
the two halves separates from each other , if
however the transseptal ligament are previously
cut this separation does not occur.

OCCLUSAL PLANE
TRANSSEPTAL FIBRES

ACTION of

FIBRES

TRANSSEPTAL



The approximal contacts are disked , teeth
move to reestablish contact ,however if the
teeth is also ground out of occlusion and
approximate surfaces disked the rate of drift
is slowed.

So until the contrary is demonstrated it must be
assumed that the Mesial Drift is achieved by
contractile mechanism associated with
transseptal ligament fibres and enhanced by
occlusal forces.

Soft tissue pressure
The pressure generated by cheeks and tongue may
push teeth mesially. However if such pressure
from soft tissue is eliminated by constructing
acrylic dome over teeth mesial drift still occurs.
Suggesting soft tissue pressure does not have a
major role , however it does influence tooth
position even if it does NOT cause tooth
movement.


TYPES OF ERUPTION
Three distinct type of teeth are differentiated by their
eruption pattern :
 CONTINUOUSLY GROWING
 Tooth formation and eruption occurs throughout
the life.
RODENT
 Dental tissue are formed from a proliferative
base.
 Anatomic crown and root very similar
morphologically.
 Teeth have extensive wear.
 Eruption velocity relatively rapid , increases
whenever the velocity of wear increases or
antagonist tooth is removed.
 Ex. Incisor of rodents and lyomorphs.

CONTINUOUSLY EXTRUDING
Teeth stop forming once root formation is
SHEEP
CATTLE
complete.
 Well defined crown and root.
 Moderate occlusal wear.
 Height of clinical crown is maintained by
eruption and apical migration of epithelial
attachment without simultaneous deposition of
alveolar bone.
 As occlusal wear progress tooth eventually
loosens and exfoliates completely.
 Ex. Cheek teeth of cattle and sheep.



CONTINUOUSLY INVESTED TEETH
Human teeth belong to this type of eruption.
 Teeth stop forming after predictable amount of
root development has occurred.
 Distinct anatomic crown and root structure.
 Alveolar bone remodels in response to eruption.
 The clinical crown shortens(in absence of
periodontal disease) as the tooth erupts to
maintain vertical height and occlusal function and
brings about alveolar bone with it.



ERUPTION RHYTHM
The

circadian rhythm in eruption is potentially
significant in clinical practice.
 The teeth intrude transiently in conjunction with
masticatory activity and then erupts significantly
overnight.
The mean daily eruption velocity was seen to be
71um/day.


CLINICAL SIGNIFICANCE


Timing of eruption


Controlling intervention
 Excessive eruption of posterior teeth is a
major cause of the long face , and control of
eruption during growth seems to be key to
successful treatment.
 The amount of force , its direction and the
total hours of wear of appliance are often
considered the most important factor that
affect treatment outcome.




Teeth erupt primarily during night with
little or no net eruption during the day , it
is quite possible that wearing the
appliance is affective during the night and
early morning period when the eruption is
most active.




Daily rhythm in skeletal growth


Skeletal growth requires an adequate levels
of HGH which increases in the night.
 The rhythm in tooth eruption also reflects
this soon after the child goes to sleep.
 The clinician should be aware that there is
a rhythm in skeletal growth and
modification of treatment may be therefore
be more effective during night than during
the day.


TEETHING
Teething is a term limited by common usage to
eruption of primary dentition which ususally begins
in fifth or sixth month of a child’s life.
In most cases eruption of teeth causes no distress
to the child but sometimes causes local irritation ,
which is usually minor but may be fewer enough to
disturb child’s sleep.


Clinical features of TEETHING


LOCAL SIGNS
 Hypermia or swelling of the mucosa
overlying the erupting teeth.
 Patches of erythema on the cheeks.
 Flushing may also occur in the skin of
adjacent cheek.


TEETHING



SYSTEMIC SIGNS








General irritability and crying.
loss of appetite.
Sleeplessness , restlessness
Increased salivation and drooling
Increased thirst
Circumoral rash
Cough


Associated problems


SYSTEMIC




Fever
Diarrhea
Vomiting

LOCAL
Eruption

hematoma

Eruption

sequestrum

Ectopic

eruption

Transposition

REMNANTS OF ROOTS OF FIRST MOLAR


PERMANENT CANINE
Causing resorption of
DECIDUOUS LATERAL INCISO
and CANINE

MISSING PERMANENT
LATERL INCISOR

IMPACTED CANINE

Deciduous
INCISORS

Perm. CANINE

TRANSPOSITION

LOCAL FACTORS














Aberrant tooth position
Lack of space in arch
Very early loss of predecessor
Ectopic eruption
Congenital absence of teeth
Ankylosis of predecessor
Retained tooth or persisting deciduous root remnants
Arrested tooth formation (trauma)
Supernumerary tooth
Tumor
Cyst
Abnormal habit exerting muscular forces

…lastly the books


ORAL HISTOLOGY









Tencate
Orban

Dental Anatomy,Physiology and Occlusion
-Wheeler’s
Text book of PEDODONTICS
-Shoba Tandon
Kardos TB:The mechanics of tooth
eruption,Br Dent J 181:91,1996

THANK YOU…

Tooth development and eruption /certified fixed orthodontic courses by Indian dental academy

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