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Development of dentition

Intended Learning Outcomes
• Explain normal and abnormal dental
development
...
(C5)

Tooth development
• 28 to 30days – epithelium proliferates,
epithelial thickening on inferior border of
upper and superior border of lower arches
• 30 to 32 days – 3 to 4 cells thick epithelium,
cells being ovoid to cuboid with less
cytoplasm
• 32 to 34 days – mesenchyme immediately
below epithelium distinguishable
• 4th week – formation of dental lamina begins
and deciduous tooth buds begin to form
about two weeks later

Stages of tooth bud development
•
•
•
•
•

Initiation
Proliferation
Histo-differentiation
Morpho-differentiation
Apposition

Stages of tooth development

Chronology

Morphologic differences between primary and
permanent teeth special functional
• Resembles the corresponding permanent teeth except
adaptations
• Crown:

• Lighter in color, bluish white
• 6 months to 5 1/2 years
• 20 in number
• Smaller in all dimension
...
Cup shaped anterior
and squat shaped molars
...
Narrow occlusal
table
• Occlusal plane is flat
• Molars bulbous, constricted

• Darker in color, grayish or yellowish
white
• 6 years onwards
• 32 in number
• Larger
• Anterior – larger in cervico-occlusal
than M-D
• Cuspids less conical
• Cervical ridge is flatter
• Less converging buccal and lingual
surfaces
• Occlusal plane - more curved contour
• Less cervical constriction

• Enamel – thinner,
1mm
• Molar contact areas –
broader, flatter,
gingival
• Enamel rods at cervical
slopes occlusally from
DEJ
• More supplemental
grooves
• No mammelons
• First molar smaller
then second

• Enamel thicker 2 to 3
mm
• Contact point more
occlusal
• Enamel rods more
gingival
• Less supplemental
grooves
• Mammelons present
• First molar larger than
second

Root:
• Size – larger and
slender compared to
crown size
• Trunk – smaller and
closer to cervical
• Narrower
mesiodistaly
• Flare outwards
• Physiologic
resorption

• Shorter and bulbous
compared to crown
• Trunk – larger and
placed more apical
• Broader mesiodistaly
• Flare is minimal
• Physiologic
resorption not seen

Pulp:
• Large pulp chamber in
relation to crown size
• Outline follows DEJ more
closely
• Pulp horn closer to outer
surface
• High cellularity and
vascularity
• High potential for repair
• Root canals more ribbon
like and branching
• Floor of pulp chamber
porous
• Accessory canals

• Smaller in relation to
crown size
• Pulpal outline follows DEJ
less closely
• Pulp horns away from
outer surface
• Less degree of cellularity
and vascularity
• Less potential for repair
• Root canals well defined
and less branching
• No accessory canals

Histologic differences
• Large apical foramen
• More reparative
dentin – irregular
• Nerve fibres pass to
odontoblastic layer
• Density of
innervation is less
• Localization of
infection is poor

• Smaller foramen
• Less reparative dentin
formation
• Pulp nerve fibres stop
among odontoblasts
and even to
predentin
• Density of
innervation is more
• Infection in pulp is
localized

Mineral content:
• Enamel and dentin
less mineralized
• Neonatal lines
present
• Bands of retzius less
common
• Less regular dentinal
tubules
• Dentin is less dense
and cuts faster

• More mineralized

• Neonatal lines only in
permanent first molar
• More common

• Dentinal tubules more
regular
• Dentin more dense
and cuts slowly

Eruption
• Derived from Latin word “ERUMPERE” means
“TO BREAK THROUGH”
• Defined as process by which the forming tooth
migrates from its intraosseous location in the
jaw to its functional position within the oral
cavity (Massler and Schour)

•
-

Anatomic stages:
I – Preparatory stage
II – Migration of tooth towards oral epithelium
III – Emergence of crown tip into oral cavity
IV – First occlusal contact
V – Full occlusal contact
VI – Continuous eruption

TYPES

Passive

Active

Pre functional

Functional

ACTIVE ERUPTION
Pre-Functional
“Eruption from the developmental position inside
the jaw to the position of functional occlusion
inside the oral cavity relative to its
environment
...
”

ACTIVE ERUPTION
Pre-Functional

PASSIVE ERUPTION
• Age
• Gingival recession leads to exposure of more of tooth
structure

• Actual movement of gingiva
• Tooth remains in same position

Patterns of tooth movements
• Three phases:
- Phase I – Pre-eruptive phase
- Phase II – Pre-functional / eruptive phase
- Phase III – Functional / Post eruptive

Pre-eruptive phase
• Movement of the developing tooth germs
within the alveolar process prior to root
formation
• Growing tooth moves in two directions to
maintain its position in expanding jaws
• Bodily movement and eccentric movement

• Bodily movement – movement of entire tooth
germ, causes bone resorption in the direction
of movement and bone deposition behind it
• Eccentric growth – relative growth of one part
of the tooth while rest remains constant
• Root elongates but crown doesn’t increase in
size
...

• Four major events:
1) Root begin formation
2) Erupting tooth moves through bony crypt
and connective tissue of oral mucosa so that
reduced enamel epithelium (REE) contacts
oral epithelium
...
Lateral border of the oral
mucosa now becomes the dento-gingival junction
(DGJ)
...
Accomplished by proliferation of the
attachment epithelium apically and separation from
the crown in its coronal part

Changes in tissues overlying teeth
• Alteration of the connective tissue pathway
for the erupting tooth
• Degeneration of connective tissue fibres,
cells, blood vessels, terminal nerves due to
loss of blood supply as well as release of
enzymes
• Altered tissue space visible as inverted funnel
shaped area - Gubernacular cord – guides the
tooth
• Osteoclasts  Resorption of overlying bone

Changes in tissues around the teeth
• Delicate connective tissues  more
prominent, extending between the forming
root and the alveolar bone surface
• First PDL fiber bundles appear at the cervical
area of the root
• Crypt is remodeled and bone fills to conform
smaller root diameter

• As eruption proceeds, other collagen bundles
becomes visible
• Early in eruptive process, perforating fibers
attach on root surface and in alveolar process
...
The alveolar bone increases in
height and changes shape to accommodate
the crown

Changes in tissues underlying the
teeth
• Fine bony trabeculae appear
• Compensate for tooth eruption
• Become more dense as more connective
tissue and bone plates are laid down
• Once tooth comes into occlusion, bony ladder
is resorbed to make space for the developing
root tip

Post eruptive phase
• Begins when the tooth reaches the occlusion
and continues for long as tooth remains in oral
cavity
• Alveolar process increase in height and roots
continue to grow
• Alveolar bone density increases and principal
fibers of PDL orient themselves into different
groups
...
Teeth erupt slightly to compensate for
loss of tooth structure
• Mesial drift – due to resorption on mesial wall
and deposition on distal wall of socket
• Helps to accommodate the growing jaws,
compensate for occlusal and interproximal
wear

Shedding of deciduous teeth
• Two generations of teeth
• Needed because the infants jaws are small
and the size and number of teeth they can
support is limited and teeth once formed
cannot increase in size
• The physiologic process resulting in
elimination of deciduous dentition is called
shedding/exfoliation

Pattern of shedding
• Shedding is the result of progressive
resorption of roots of teeth and supporting
tissues
• Pressure generated by the growing and
erupting tooth dictates the pattern of
deciduous tooth resorption

Resorption of anterior teeth
• Permanent anterior tooth germ is lingual to
apical third of the roots of the primary tooth,
hence the resorption is in the occluso-labial
direction which corresponds to movement of
the permanent tooth germ
...


Resorption of posterior teeth
• Growing crowns of premolars are initially
between the roots of primary molars
• Resorption of inter-radicular bone followed by
adjacent surfaces of the root of the primary
tooth
• Alveolar process grows to compensate for
lengthening of the root, so primary molars move
occlusally which allows the premolar crown to be
more apical
• Premolars continue to erupt till primary molar
roots are completely resorbed and teeth exfoliate

Mechanism of resorption and shedding
• Exact mechanism of resorption and shedding
not known
...

• Initial removal of mineral followed by
extracellular dissolution of the organic matrix
• Growth and increased loading of jaws, these
forces far exceed the limit that the primary
tooth PDL can withstand  trauma to
ligament and initiation of resorption

Clinical implications
• Remnants of deciduous teeth – Parts of roots of
deciduous teeth that are not in path of eruption
remain embedded in jaw for considerable time
...
May be surrounded
by and ankylosed to bone, progressively resorbed
and replaced by bone OR if close to surface of jaw,
they may be exfoliated
• Retained deciduous teeth – no or impacted
permanent successor
...
Relief by pressure produced
by chewing
...
5%, 7
...
7%, 7
...
Develops few weeks before
eruption of primary or permanent tooth
...
Usually due to
trauma during function
...
Tooth usually breaks
through tissue and hematoma subsides

• Eruption sequestrum – usually seen with
eruption of permanent first molar
...
Spontaneous resolution
...


• Natal and Neonatal teeth
- Natal teeth / Congenital teeth / Fetal teeth /
Dentition Praecox – teeth present at birth
- Neonatal teeth – teeth that erupt within first one
month of life
- Usually have hypoplastic enamel and
underdeveloped roots with resultant mobility
- Good prognosis if normal development
- Prevalence – female to male – 3:1
- Teeth affected – Lower primary central incisor

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