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Interglobular dentin is a hypomineralized zone formed when calcospherites fail to fuse during globular mineralization. The organic matrix remains, so type I collagen is present, and dentinal tubules pass through uninterrupted. These areas are most common near the ADJ in circumpulpal dentin and are seen in vitamin D deficiency and rickets.
Interglobular spaces:
1). Do not contain dentinal tubules
2). Do not contain type I collagen
3). Are formed during the course of globular mineralization
4). Are seen only in secondary dentin
When an odontoblast dies (due to caries or attrition), its process degenerates, leaving an empty dead tract. These are overlaid by reparative dentin on the pulpal side. Dead tracts are more permeable to irritants unless sealed by sclerotic dentin.
Dead tracts are:
1). Tubules obliterated by minerals
2). Empty tubules after odontoblast death filled with air, appear black in ground section
3). Tubules filled with bacteria
4). Sclerotic dentin
Predentin is the unmineralized organic layer between odontoblasts and mineralized dentin. It stains pale and is about 10-30 microns thick. In vitamin D deficiency, its thickness increases.
Predentin thickness is:
1). 2-5 micron
2). 10-30 micron (average 10-12)
3). 100-150 micron
4). 0.5 mm
Peritubular dentin is hypermineralized (about 40% more than intertubular), lacks collagen, is rich in proteoglycans, and forms the wall of the tubule. It is also called intratubular dentin and is best seen in ground sections or SEM, as it dissolves in decalcified sections.
Which is true of peritubular dentin?
1). Is less mineralized than intertubular dentin
2). May be considered as intratubular dentin
3). Is best visualized in decalcified sections
4). Is found in interglobular dentin
Sclerotic dentin is the physiologic or reactive occlusion of tubules. Dead tracts are empty tubules after odontoblast death and appear black in ground sections. Transparent dentin is hypermineralized and translucent.
Obliteration of dentinal tubules by mineral deposits:
1). Occurs only when dentin exposed to oral fluids
2). Produces dead tracts
3). First occurs in predentin
4). Is seen in sclerotic and transparent dentine
Permeability is inversely proportional to the distance from the pulp. Near the pulp, there are more and wider tubules, making it more permeable. This is important for bonding, sensitivity, and bacterial ingress.
Which dentin is most permeable?
1). Sclerotic dentin
2). Primary dentin near pulp (more tubules, wider)
3). Transparent dentin
4). Reparative dentin
Odontoblast cell bodies remain in the pulp periphery; only their processes extend into dentin. Hydroxyapatite makes up about 70% by weight, and collagen type I makes up about 90% of the organic matrix. Incremental lines include lines of von Ebner (daily) and Owen's contour lines (accentuated).
Which is NOT present within dentin matrix proper?
1). Cell bodies
2). Hydroxyapatite
3). Collagen type I
4). Incremental lines
Intertubular dentin makes up the main body between tubules. It contains about 30% organic matrix (mostly collagen I) and apatite. It is less mineralized than peritubular dentin, which is hypermineralized and lacks collagen.
Which statement about intertubular dentin is true?
1). More mineralized than peritubular
2). Forms bulk between tubules, contains Type I collagen network, less mineralized than peritubular, contains proteoglycans
3). No collagen
4). Forms inside tubule
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