المكان وشرف العلم شرف

• Definition of shedding:

Shedding is a physiologic process leads to elimination of deciduous teeth to allow for eruption of their permanent successors.

• Terminology:

1. Shedding. 2. Exfoliation.

• Significances of shedding:

1. Deciduous teeth can not withstand jaw growth from child to adult, so another set of larger teeth must be needed for larger jaw.

2. Growth of masticatory muscles leads to increase their force of mastication in which deciduous teeth can not withstand these forces leads to trauma to their periodontal ligament, so another set of larger teeth must be needed.

• Shedding of deciduous teeth result from progressive resorption

of their roots with degeneration of periodontal ligaments (PL).

• Resorption of root (cementum and dentin) was carried out by

multi-nucleated giant cells termed odontoclast cells.

• Odontoclast cells are similar histologically to osteoclast cells.

• Pattern of shedding depends on the pressure generated from the

growing permanent successor.

• Firstly,The permanent successor produce pressure on the bone

separating it from the deciduous roots leading to bone resorption.

• Then, the permanent successor become facing the deciduous

roots and act to resorb root directly with elimination of PL.

Permanent central incisor

Deciduous central incisor

• By eruption of deciduous molars, premolars become lied

apical to deciduous in their divergent roots.• Premolars produce pressure on the root of deciduous tooth

leading to root resorption.• Period of root resorption was alternated with a period of rest.• At period of rest, repair of deciduous root may done by

deposition of cementum like tissue.• So, the loosed deciduous molar become rigid again.• Root repair may leads into ankylosis of deciduous tooth.• Continuous resorption occurred until the roots become

completely lost and the deciduous molar shed.

Second premolar

Second deciduous molar

Shedding of deciduous teeth include:

1. Root resorption: Increased force of mastication leads

to trauma to the periodontal ligament which induce root

resorption by differentiation of a cells termed

odontoclast cells.

2. Degradation and degeneration of periodontal

ligaments.

ODONTOCLAST CELLSDefinition:Odontoclast is a multi-nucleated cells responsible for root resorption

Origin:1. Blood monocyte.

2. fUSION OF MANY UMC.Functions: 3. Root resorption during shedding.4. Resorption of remaining root.

Site:5.On the root resorption in a depression termed Hawships Lacuna.6.Within root canal and pulp chamber.

L M.:• Shape: Large MULTINUCLEATED Cells (8-20 nuclei).• Cytoplasm: Acidophilic Cytoplasm ( red). • Odontoclast cells contain:1. Acid Phosphtasee Enzyme.2. Collagenase Enzyme.3.Protease Enzyme.

E M.:1.Little RER and Golgi complex.2.Numerous mitochondria that produce citric acid.3.Lysosomes.4.Ruffled border: Border Of The Cell Facing The Resorbing

root Appeared Striated. Function of Ruffled border: Increase The Surface Area of the

working side.5.Clear zone: The region of cytoplasm adjacent to the ruffled

border are not contain cell organelles but contain actin and myosin for adhesion of the cell with Hawshyp’s lacuna.

Clear zone Ruffled border

A- Dental hard tissue decalcification:i.Removal of cementoid by the action of cementoblast

cells.ii.Removal Of Calcium By The Action Of Acid Phosphatase

Enzyme and citric acid secreted from odontoclast cells.B- Organic matrix degradation:iii.Collagen Breakdown Into Protein Occurred By The Action

Of Collagenase Enzyme secreted from odontoclast cells.iv.Protein Breakdown Into amino acids by the action of

Protease Enzyme secreted from odontoclast cells.C- Clearance:Clearance of the west products Into Blood Stream By The Action Of:

Blood Monocyte.

Dental hard tissue resorption

Dental soft tissues:

1. Periodontal ligaments.

2.Pulp.

process of degradation:

3.Dental soft tissue degradation occurred by the way of

apoptosis which means physiologic programmed cell

death.

4.the degraded part of the pulp is the only facing the

resorbed area.

5.the remaining of the pulp include pulp chamber is normal.

Dental soft tissue degradation

1. Retained deciduous teeth

2. Submerged teeth

3. Remaining roots

WITH MANY THANKSDr. Sherif Hassan