What is the composition of dentin?
70% mineralized inorganic material, 20% organic material, and 10% water
What is dentin mainly composed of?
How do the crystals of dentin compare to those of enamel?
they are platelike and smaller
What other minerals are present in dentin?
carbonate and fluoride
How does dentin appear on a radiograph compared to enamel?
it is more radiolucent
What is another name for the dentin matrix?
What is dentinogenesis?
the process of dentin matrix formation
During what stage does dentinogenesis begin?
the apposition stage
What is the initial material laid down by the odentoblasts?
pre-dentin or dentin matrix
What embryological structure do the odontoblasts originate from?
What does the pre-dentin initially consist of?
nonmineralized collagen fibers
What structure comes from the outer cells of the dental papilla?
What induces odontoblasts to produce pre-dentin in layers?
Which direction do the odontoblasts lay down pre-dentin?
moving away from the DEJ
About how much pre-dentin is laid down daily by the odontoblasts?
about 4 micrometers
Why is dentin continually produced throughout life?
because of the retention of the odontoblasts along the outer pulpal wall
How many steps or phases does it take for dentin to mature?
What do the calcium hydroxyapatite crystals form as during the primary mineralization?
globules or calcospherules, in the collagen fibers of the predentin, expanding and fusing together
What is globular dentin?
areas where primary and secondary mineralization have occured with complete crystalline fusion
How does globular dentin appear on dentin sections?
lighter rounded areas
How does interglobular dentin appear on dentin sections?
dark arclike areas
What is interglobular dentin?
areas where primary mineralization within the pre-dentin, and the globules of dentin did not fuse completely
Between globular dentin and interglobular dentin, which is more mineralized?
Where is interglobular dentin especially evident?
in coronal dentin and near the DEJ, and in certain dental anomalies
What are dentinal tubules?
long tubes in the dentin that extend from the DEJ in the crown area or the DCJ in the root area to the outer wall of the pulp
What can be contained inside the dentinal tubule?
hollow space, dentinal fluid, an odontoblastic process, and possibly an afferent axon
How do odontoblasts in the mature dentin attain nutrition?
by way of the dentinal tubule from tissue fluid originally from blood vessels located in the adjacent pulp tissue
What is dentinal fluid?
tissue fluid surrounding the cell membrane of the odontoblast, which is continuous to the cell body in the pulp
What is an odontoblastic process?
a long cellular extension located within the dentinal tubule and still attached to the cell body of the odontoblast within the pulp
Does the odontoblastic process run the entire length of the dentinal tubule?
it may or may not extend the full length to the DEJ or DCJ
What is another name for an afferent axon?
What sensation is involved with the myelinated afferent axon in the dentinal tubule?
Does the afferent axon extend to the DEJ or DCJ in the dentinal tubule?
How many types of curvatures are established by the dentinal tubules?
2, primary and secondary
What does the primary curvature resemble?
a large S shaped
What does the secondary curvature resemble?
small delicate curves noted in the primary curvature, noting smaller daily changes in odontoblast direction
Where are the dentinal tubules crowded?
near the pulp, because of the narrowing of this region
What is peritubular dentin?
dentin that creates the wall of the dentinal tubule
What is intertubular dentin?
dentin that is found between the tubules
Between peritubular and intertubular dentin, which is more mineralized than the other?
What is the description of peritubular and intertubular dentin?
What is the location of mantle dentin?
What is mantle dentin?
the first dentin formed
How are the collagen fibers arranged in the mantle dentin?
the fibers are perpendicular to the DEJ
Why is mantle dentin more mineralized than inner portions of dentin?
because it contains more peritubular dentin
What is circumpulpal dentin?
the layer dentin around the outer pulpal wall
Between mantle and circumpulpal dentin, which is formed and matured first?
How are collagen fibers arranged in circumpulpal dentin?
mainly parallel to the DEJ
What is the main type of dentin in a tooth ?
What is primary dentin?
dentin formed in a tooth before the completion of the apical foramen of the root, has a regular pattern of dentinal tubules
What is secondary dentin?
dentin that is formed after the completion of the apical foramen and continues to form throughout the life of the tooth, formed more slowly and is less mineralized
Where does secondary dentin lie?
fills in along the outer pulpal wall
What are 2 other names that tertiary dentin can be called?
reparative or reactive
What is tertiary dentin?
dentin that is formed quickly in localized regions in response to a localized injury to the exposed dentin
Where is tertiary dentin located?
forms underneath the exposed dentin's tubules along the out pulpal wall
What is sclerotic dentin?
type of tertiary dentin, associated with chronic injury of caries, and also in noted to increase with age
What type of dentin does the odontoblastic processes die and leave the dentinal tubule hollow, but then becomes retrofilled and occluded by a mineralized substance similar to peritubular dentin?
What is the odontoblastic layer?
this layer lines the outer pulpal wall and consists of the cell bodies of odontoblasts. secondary dentin may form in this area from the apposition of these odontoblasts, causing the cell bodies to realign themselves. cell bodies of the afferent axons from the dentinal tubules are located between cell bodies of the odontoblasts
What is the cell-free zone?
this zone contains fewer cells than the odontoblastic layer. the nerve and capillary plexus is located here
What is the cell-rich zone?
the zone contains an increased density of cells compared with the cell-free zone and also has a more extensive vascular system
What is the pulpal core?
this zone is located in the center of the pulp chamber, which, like the cell-rich zone, has many cells and an extensive vascular supply