Dentine histology Flashcards
Where does dentin originate from?
Ectomesenchyme. Dentin is the mineralised tissue that forms the bulk of the tooth.
What is dentin formed from?
Odontoblasts formed in the ectomesenchyme.
What other process uses the initiation of dentin formation for it to take place?
Enamel formation
Which part of the tooth is dentin covered by enamel and which part by cementum?
Root = cementum
Crown = enamel
What properties distinguish dentin from enamel?
Dentin is sensitive
Dentin is formed throughout life, increasing in thickness at the expense of the dental pulp.
What are the physical properties of dentin?
Dentin and enamel have complementary physical properties.
Fresh dentin is pale yellow in colour and contributes to the appearance of the tooth through the translucent enamel.
Dentin is harder than bone + cementum and softer than enamel.
Dentin can handle compressive forces well due to its organic matrix and tubular architecture.
Dentin is permeable, depending on the size and patency of the tubules which declines with age.
What is the chemical composition of dentin?
70% inorganic, 20% organic 10% water by MASS.
50% inorganic, 30% organic and 20% water by VOLUME
Inorganic part is calcium hydroxyappatite crystals. The crystallites are calcium poor and carbonate rich in comparison to pure hydroxyappatite.
Organic matrix is composed of collagen fibrils which are located around the crystallites as well as non-collagenous proteins.
What happens to the size of collagen fibrils in dentin when it is mineralised?
They became larger in diameter and are more closely packed than in predentin.
What are the non-collagenous proteins seen in dentin?
Dentine phosphoproteins, proteoglycans, Gla proteins, other acid proteins and growth factors
What are dentin phosphoproteins (PP-H)?
The term relates to the highly phosphorylated protein species which are important for binding calcium which is implicated in the process of mineralization
What do proteoglycans in dentin do?
Their major function is their role in collagen fibril assembly and their cell mediated effects such as cell adhesion, migration, proliferation and differentiation.
What do phospholipids do in denitn?
May be involved in the formation and growth of hydroxyapatite crystals
What direction do dentinal tubules move?
Dentin is permeated by tubules, the dentinal tubules, that run from the pulpal surface to the enamel-dentin and cementum-dentin junctions.
The dentin tubules follow a curved sigmoid course. They also taper from 2.5 to 1 µm or less peripherally
Dentinal tubules are approximately circular in transverse section although their appearance is obviously dependent on the plane in which the tissue is sections.
How dense are dentin tubules in different dentinal sections?
It ranges from 20000/mm2 in outer dentin to 50000/mm2 in inner dentin and 40000/mm2 in middle dentin
Where do dentinal tubules branch the most?
The most profuse branching is in the periphery near the enamel-dentin junction
How is predentin different to normal dentin?
The walls of the dentinal tubules in recently formed intertubular dentin at the pulp surface are comprised of mineralised type 1 collagen.
During maturation another type of dentin is deposited on the walls of the dentinal tubule narrowing the size of the lumen (peritubular dentin or intratubular dentin.
How is peritubular dentin different to intertubular dentin?
Peritubular dentin is about 15% more mineralised than intertubular dentin.
Peritubular dentin occupies 2/3rds of the CSA of the tissue; near predentin only 3%
What are the dentinal tubules composed of?
They contain the processes of the odontoblasts that are responsible for their formation.
In some parts of the tissue they also contain different nerve terminals.
It is also possible that processes from antigen presenting cells in the peripheral pulp may extend for a short distance into the tubules.
What happens in the dentinal tubules?
Initially the process of odontoblasts grows into the tubule and dentin is deposited while the peripheral termination remains at the outer end of the tubule.
The process reaches a predetermined length and moves pulpally as dentin is formed leaving behind an empty tubule in which peritubular dentin forms.
Th peripheral end of the process degrades sequentially and its remains form part of the matrix for the peritubular dentin.
What is predentin?
Predentin is the innermost unmineralised layer, where new dentin is being deposited throughout life.
What is the first dentin-formed layer in the crown?
The mantle dentin
What are the dentin zones in the root?
2 morphologically recognisable outer zones:
Hyaline layer
Granular layer (of Tomes)
What does predentin look like in demineralised sections?
The innermost layer of dentin, the predentin, has a distinct pale-staining appearance.
The predentin is the initially laid down dentin matrix before its mineralisation.
What do odontoblast processes do in predentin?
They secrete matrix components.
What type of dentin forms most of the tooth? and where is it located?
Primary dentin which outlines the pulp chamber and is referred to as circumpulpal dentin.
The outer layer is mantle dentin and it is mineralized differently
How does mantle dentin differ from the circumpulpal dentin?
It is slightly less mineralized (~5%)
Collagen fibers are largely oriented perpendicular to the enamel dentin junction.
The dentinal tubules branch profusely here
It undergoes mineralisation in the presence of matrix vesicles.
