SHEDDING
1. Describe the mechanism of exfoliation of
teeth. (C1)
2. Describe the morphology and function of
Odontoclasts (C1)
3. Relate the mechanism of exfoliation with
their clinical significance(C2)
TOOTH SHEDDING
Definition
The physiologic process resulting in the
elimination of the deciduous dentition allowing
the succeeding perm teeth to take their
functional position is called as shedding or
exfoliation.
PATTERN OF SHEDDING
Shedding of deciduous teeth is the result of
progressive resorption of roots of the teeth &
their supporting struct i..e the pdl
FORCES EXERTED BY ERUPTING PERMANENT
SUCCESSORS
Resorption of the roots of the deciduous
incisors & canines begin on their
lingual surface.
❖ Later these
developing tooth
germs occupy a
position directly
apical to the
deciduous tooth.
❖ In mandibular
incisors the apical
positioning of the
tooth germs does not
occur and permanent
tooth erupt lingually.
Resorption of the roots
of deciduous molars
often first begins on
their inner surface.
With continued
growth of the jaws
and occlusal
movement of the
deciduous molars, the
successional tooth
germs lie apical to the
deciduous molars.
When the bicuspids
begin to erupt,
resorption of the
deciduous molars is
again initiated and
continues until the
roots are completely
lost and the tooth is
shed.
HISTOLOGY OF SHEDDING
Broughtby resorption of dental hard tissues
& destruction of supporting pdl.
Cells
responsible for resorption of tooth --
ODONTOCLASTS
HISTOLOGY OF SHEDDING
Odontoclasts
Similar to osteoclasts but
involved in removal of dental
tissues, so they are called as
odontoclasts.
Derived
from the circulating
monocytes(TRAP positive).
Theyare identified on light
microscope as large
multinucleated cells occupying
resorption bays (Howship’s
lacunae) on the surface of
dental hard tissue.
Odontoclasts;
dissimilarities with Similarities
osteoclast
• Large multinucleated giant
cells
• Occupy resorption bays
Smaller and contain • Show ruffled border and
fewer nuclei clear zone.
Produce smaller • Cytoplasm – rich in
resorption lacunae. mitochondria & vacuoles.
• Acid phosphatase activity
Resorb dental hard seen within vacuoles.
tissues. • Process of resorption
Seen also in pulp similar
chamber and root • Similar origin; TRAP
canal of resorbing +monocytes
deciduous teeth • Odontoclast differentiation
promoted by RANKL &
inhibited by OPG
Vacuolated cytoplasm
Ruffled border--extensive folding of the cell
membrane
Peripheral to ruffled border – Clear zone
CZ– Devoid of organelles, rich in filaments--
- actin and myosin.
CZ – Represents attachment apparatus of
odontoclasts.
Cytoplasm– Rich
in mitochondria
Highly
vacuolated, close
to ruffled border.
Acid
phosphatase
activity occurs in
these vacuoles
Membrane specializations--Ruffled border &
clear zone appear after they contact resorbing
surface.
Can resorb all the dental hard tissues in the
same way as osteoclasts.
Dentinal tubules provide a pathway for easy
extension of odontoclast processes.
PDL
cells undergoing resorption express
RANKL & to a lesser extent OPG.
RANKL increases odontoclast formation
& initiates shedding.
The odontoclastic activity is promoted by
RANKL and inhibited by OPG as in case
of osteoclast differentiation in bone
resorption.
Pressure
Plays a role in shedding.
If a successional tooth is missing, shedding of the
deciduous tooth is delayed.
Increased force(erupting tooth,masticatory or
muscular) applied to a deciduous tooth can
initiate its resorption by damaging the
supporting apparatus.
It determines the pattern & rate of shedding of
deciduous teeth.
MECHANISM OF SHEDDING
Not yet fully understood.
Pressure from erupting teeth plays a key role;
odontoclasts appear at sites of pressure.
Cementoblasts are not responsive to hormones &
cytokines.
So cementoblastic layer has to be damaged by
inflammatory process prior to resorption.
Odontoclasts express ATPase, cathepsin K & MMP-9
similar to osteoclasts.
Odontoclasts attach to hard tissue surface creating a
sealed microenvironment.
Membrane of ruffled border acts as proton pump
Add H+ ions to extracellular environment- acidification
Odontoclasts phagocytose & dissolve them
intracellularly.
Organic matrix is degraded by enzymatic secretions
of primary lysosomes.
Resorption of dental soft tissues- pulp and pdl ---
apoptotic cell death.
CLINICAL CONSIDERATIONS
1. REMNANTS OF
DECIDUOUS
TEETH.
Sometimes parts of
the roots of deciduous
teeth are not in the
path of erupting
permanent teeth and
may escape
resorption.
2. RETAINED DECIDUOUS TEETH.
❖ Without permanent successors or successors are
impacted.
❖ Most common are upper lateral incisors.
CAUSES
Congenital absence of perm successor
Failure of eruption of perm successor
Eruption of perm tooth in lingual or labial
position so that dec tooth escape from pressure
exerted by them
Ankylosis of deciduous teeth or perm teeth.
SUBMERGED DECIDUOUS TEETH
Remains below the
level of normal
occlusal plane of other
teeth.
Most common cause:
Ankylosis due to
trauma.
3. SUBMERGED DECIDUOUS TEETH.
❖ Cause can be trauma to
either the dental follicle
or the developing pdl,
eruption of tooth ceases.
❖ Because of continued
eruption of adjacent
teeth and increased
height of alveolar bone,
they appear
“submerged”.
KEY POINTS
Physiologic process
Odontoclasts --- TRAP +ve Circulating monocytes.
Factors responsible for resorption:
a) Pressure exerted by the erupting perm successor
b) Increased masticatory force.
Patterns of shedding.
Mechanism of shedding.
The resorption of soft tissue such as pdl & pulp –
apoptotic cell death.
Clinical considerations
