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*Root Formation

begins after the outline of the crown has been established but before the full crown is calcified.

During the bell stage

the OEE meets the IEE at the deepest part of the enamel organ and is known as the cervical loop.

Hertwig's epithelial root sheath

made up of layers from the OEE and the IEE at the deepest part of the enamel organ.

OEE and IEE undergo mitotic divisions to start the root formation in an

apical direction

*Dental papilla is on the

inside (where pulp comes from)

*Dental sac is on the


Tip of the root sheath turns horizontally and is now known as the

epithelial diaphragm of the root sheath.

The epithelial root sheath and diaphragm determine the

shape and number of roots.

As the root sheath grows, peripheral cells of the dental papilla alter into

odontoblasts which begin to secrete matrix and calcify.

As dentin forms

the root sheath begins to break down.

As the root sheath breaks down

this causes a direct contact between some of the odontoblasts and the dental sac cells.

Some dental sac cells change into

cementoblasts and start to lay down cementum to form the DCJ.

Sometimes a few epithelial root sheath cells stay in contact with the dentin and change into

ameloblasts and form small blobs of enamel on the surface of the dentin.

Small blobs of enamel on the surface of the dentin are called

enamel pearls. They're found in the bi/tri furcations of the roots.

Some remaining root sheath cells are found in the periodontal space next to the tooth and are called

epithelial rests of Malassez.

If remaining root sheath cells (aka epithelial rests of Malassez) begin to divide

they may lead to the formation of periodontal cysts (fluid filled sac).


Hard, yellowish covering of the root.
40-50% inorganic hydroxyapatite crystals.
50-55% organic compounds (collagen fibers and mucopolysaccharide ground substance) and water.

Cementum is also laid down in response to

trauma (as well as dentin).

Types of cementum:

1) cellular
2) acellular


first seen at the cervical line/CEJ. It may appear in 3 different arrangements with the enamel.

The three cementogenesis arrangements with enamel:

1) cementum overlaps the enamel: 60%
2) cementum meets the enamel: 30%
3) cementum and enamel do not meet: 10% (dentin is exposed)

Cementum overlaps the enamel:

60% of the time

Cementum meets the enamel:

30% of the time

Cementum and enamel do not meet:

10% of the time (dentin is exposed).

Acellular cementum

as cementum is laid down, cementblasts move away from the DCJ and secrete matrix.

*Acellular cementum is seen in

cervical 2/3rd of the root.

Cellular cementum

as cementum formation moves towards the apex, the cementoblasts get trapped in their own matrix and are referred to as cementocytes (no function).

Cementoblasts trapped in their own matrix are referred to as

cementocytes and they have no function.

Cellular cementum is seen in

middle and apical third of the root and overlaps the acellular cementum in the middle.
It is more vital than acellular cementum.

Cellular cementum is

more vital than acellular cementum.

Cellular cementum at the apex of the root can thicken leading to

hypercementosis which may cause a problem during tooth extraction (bulky roots).


thickened cellular cementum at the apex of the roots.

Sharpey's fibers

the parts of the pdl embedded in cementum.

Alveolar bone

the bone of the upper or lower jaw that holds the sockets of the teeth.

Adult bone:

65% inorganic crystal
35% organic: 89% collagen & 11% non collagenous material.

Adult bone has 3 layers

1) Cortical plate
2) Cribriform plate/alveolar bone proper
3) Spongy/cancellous bone

Cortical plate

layer of compact bone on the buccal or lingual surface.

Cribriform plate/alveolar bone proper

contains numerous holes for passage of blood vessels. Referred to as lamina dura in radiograph.

Spongy/cancellous bone

lies between the 2 layers and is the bone marrow.

What can we see on radiographs?

Cribriform plate, spongy bone, alveolar crest (tip of bone near CEJ between the teeth).

Periodontal Ligament (PDL)

mesodermal in origin. Develops after cementum has begun forming.

3 fiber groups of the PDL:

1) Gingival fibers
2) Transseptal fibers
3) Alveolodental fibers

1)Gingival fiber group includes

gingival fibers and circular gingival fibers

3)Alveolodental fiber group includes

alveolar crest group, horizontal group, oblique group, apical group, and interradicular group (not present in single rooted teeth).

Bone remodeling

increase the load on a bone and osteoclasts are created which break it down in response to the load. Remove the load and osteoblasts are created which create new bony cells. Repeat the process through repetitive motion and eventually the bone density increases.

The PDL acts as messenger between the

teeth and surrounding bony sockets.

Pressure between the PDL and bone causes the bone to create

osteoclasts and breakdown the bone to restore the normal spacing between the teeth and bone.

The corresponding tension on the PDL behind the movement causes the bone to create

osteoblasts, effectively building new bone to fill in the difference and restore the normal spacing between teeth and bone.

*The osteoclast (breakdown) process takes about

72 HOURS to get fully going.

*The osteoblast (rebuild) process takes about

90 DAYS.

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