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Primary dentin is formed before root completion and has regular S-shaped tubules. Secondary dentin forms after root completion throughout life with slower deposition, more wavy and less regular tubules, and slightly less permeability. Both have predentin on the pulpal side, hydroxyapatite, and collagen.
Major difference between secondary and primary dentine is:
1). There is no predentine
2). There is no hydroxyapatite
3). There is no collagen fibers
4). Dentinal tubules pass in wavier course through secondary dentine
Odontoblasts are post-mitotic and long-lived. They cannot divide but remain functional throughout life as long as the tooth is vital.
Lifespan of odontoblast?
1). Dies after primary dentin formation
2). Lifelong as long as tooth vital - can form secondary and tertiary dentin
3). Replaced every month
4). Only till eruption
Enamel tufts are hypomineralized areas at the DEJ and contain enamel proteins. They are different from enamel spindles (odontoblast processes) and enamel lamellae (cracks).
Enamel tufts arise from:
1). DEJ due to hypocalcified prism boundaries
2). Dentin tubules
3). PDL
4). Cementum
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
Enamel is of epithelial origin and contains no collagen; its proteins are amelogenin, ameloblastin, and enamelin. Prismless enamel is the outer 30 microns with no prism pattern. Dentin, cementum, PDL, and dental sac all contain collagen types I and III.
Collagenous fibers are NOT found in:
1). Mantle dentin
2). Reparative dentin
3). Outer prismless enamel layer
4). Dental sac
Type I collagen makes up about 90% of the organic matrix of dentin. Small amounts of type III and V are also present. Type IV collagen is found in the basement membrane.
Type of collagen in dentin:
1). Type II
2). Type I (90%), Type III, V
3). Type IV
4). Type VII
Tertiary dentin is the least tubular and is sometimes atubular. It may contain cell inclusions.
Which dentin contains fewest tubules?
1). Primary
2). Secondary
3). Tertiary / reparative dentin (osteodentin)
4). Mantle dentin
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