Chapter 21 Flashcards
When does root formation begin?
Begins after the outline of the crown has been established but before the full crown is calcified
Layers of OEE and IEE make up what?
Epithelial root sheath (Hertwig’s epithelial root sheath)
Epithelial root sheath (Hertwig’s epithelial root sheath)
Begin to undergo rapid miotic division and grow deep into the underlying connectice tissues - The beginning of root formation
Dentinocemental junction
Some epithelial root sheath cells do not pull away and may become ameloblasts, forming small globes of enamel on the surface of the dentin
Enamel pearls
Found in bifurcations and trifurcations of roots
A hard, yellowish substance covering the root of the tooth
Cementum
% of inorganic hydroxypatite crystals in cementum
45% to 50%
% of organic components of water in cementum
50% to 55%
CEJ
First seen at the cervical line of the tooth, also called the cementoenamel
How many different relationships with the enamel of the crown
3
60% of the cases of cementum
overlaps the enamel
30% the cementum meets
the enamel at a sharp junctions
10% of the cases the cementum
and enamel do not meet, leaving dentin exposed at the cervical line
Acellular cementum
All of the cementoblasts remain on the surface rather than becoming trapped within the cementum
Where is acellular
In the cervical two thirds of the root
Cellular cementum
More vital than acellular cementum and therefore more responsive to remodeling itself
Where is cellular cementum
Apical 1/3 of the root
The cellular at the apex of the root tends to
inrease in thickness with the passage of time and as a result of stress causing thickening (hypercementosis)
Makes extraction a bit more difficult than usual
Hypercementosis
Periodontal membrane (ligament)
Forms the middle of the layer of cells in the old dental sac, the ends of the periodontal fibers become surrounded by cementoblasts, whose secretion hardens around the ends of the fibers, attaching them to the cementum
Parts of the periodontal ligament embedded in cementum are known as
Sharpey’s fibers
Sharpey’s fibers (SF)
Parts of the PDL surrounded by cementum on the tooth side and alveolar bone on the opposite side in the wall of the tooth socket
Alveolar bone
Is the bone of the upper or lower jaw that makes up the sockets for the teeth
3 layers of alveolar bone
Cortical plate
Cribiform plate or alveolar bone proper
Spongy or cancellous bone
First layer of alveolar bone
Layer of compact bone on the buccal or lingual surface is referred to as the cortical plate of bone.
Second layer of alveolar bone
Called the cribriform plate or alveolar bone proper. Radiographically it is referred to as the lamina dura
Bundle bone
The tooth socket is constantly being remodeled and additional bone laid down on the cribriform plate
A thickened lamina dura is caused by
bundle bone being laid down on the cribriform plate and is an indication of occlusal trauma to that tooth or teeth
Between the coritcal plate and cribriform plate
Layer of spongy or cancellous bone (3rd layer)
Spongy bone is a
bone marrow
Interproximal alveolar crest
The spongy bone and the crest of bone that joins two sockets
Three groups of the periodontal ligament
Gingival fibers, transseptal fibers, and alveolodental fibers
After a person has had a root canal on a tooth, it is still possible to feel pain at times from the
periodontal ligament
Gingival fibers
Run from the cementum into the free and attached gingival area; support the gingiva
Circular gingival fibers
run around the tooth in free gingiva and hold gingiva against the tooth
Transseptal fibers
Run from the cementum of the interproximal portion of one tooth, across the alveolar crest of bone, to the cementum of the interproximal portion of the adjacent tooth; hold the teeth in interproximal contact
Alveolodental fibers
Run from cementum to alveolar bone
what are the alveolodental fiber groups
Alveolar crest group Horizontal group Oblique group Apical group Interradicular group
Alveolar crest group
Runs from cementum, slightly apical to the alveolar crest of bone; helps resist horizontal movements of teeth
Horizontal group
Runs from cementum horizontally to the alveolar crest; helps resist horizontal movement
Oblique group
runs from cementum cornily into the alveolar bone; main fiber group for resisting occlusal stresses
Apical group
Runs from apex of the tooth into the adjacent alveolar bone; resists forces trying to pull the tooth from its socket
Interradicular group
Found only on multirooted teeth; runs from the alveolar crest of the bone between the roots of the tooth to adjacent cementum; resists the forces trying to remove the tooth
What happens when a tooth is lost
The posterior to the missing tooth will tilt forward into the unoccupied space (mesial drift)
If a tooth if moved too fast in orthodontic treatment
It is possible that the fibers attaching the tooth to bone will be torn out of their attachment; Before they can be re-embedded, the tooth could conceivably loosen and be lost or could cause external root resorption
