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.
Tip of the root sheath turns horizontally and is now known as the
epithelial diaphragm of the root sheath.
As the root sheath grows, peripheral cells of the dental papilla alter into
odontoblasts which begin to secrete matrix and calcify.
As the root sheath breaks down
this causes a direct contact between some of the odontoblasts and the dental sac cells.
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.
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)
as cementum is laid down, cementblasts move away from the DCJ and secrete matrix.
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 at the apex of the root can thicken leading to
hypercementosis which may cause a problem during tooth extraction (bulky roots).
Adult bone has 3 layers
1) Cortical plate
2) Cribriform plate/alveolar bone proper
3) Spongy/cancellous bone
Cribriform plate/alveolar bone proper
contains numerous holes for passage of blood vessels. Referred to as lamina dura in radiograph.
What can we see on radiographs?
Cribriform plate, spongy bone, alveolar crest (tip of bone near CEJ between the teeth).
3)Alveolodental fiber group includes
alveolar crest group, horizontal group, oblique group, apical group, and interradicular group (not present in single rooted teeth).
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.
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.