86+ quick-fire dental facts • tap a card to flip
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
Tubule density and diameter decrease peripherally. Near the pulp, the diameter is 2.5-3 microns, and near the DEJ it is 0.8-1 micron. This explains greater sensitivity near the pulp and higher permeability, which is a basis for dentin bonding challenges.
Number of dentinal tubules per mm2 near pulp vs near DEJ:
1). Equal
2). More near pulp (45,000-65,000/mm2) vs near DEJ (15,000-20,000)
3). More near DEJ
4). No tubules near DEJ
Sclerotic dentin is a vital defense mechanism. Peritubular dentin thickens and occludes the tubule to reduce permeability and slow caries progression.
Sclerotic dentin is formed:
1). Before eruption
2). As defensive response to mild caries, attrition, age
3). Only after extraction
4). Only in enamel
Tomes' granular layer is a dark granular zone in root dentin just below cementum. It appears granular under light microscopy due to branching and looping of terminal dentinal tubules, which cause air entrapment. It is not present in the crown.
Tomes' granular layer is:
1). Extension of odontoblast process into enamel
2). Region lacking dentinal tubules / with looping terminal tubules in root
3). Following incremental lines
4). Derived from rests of Malassez
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
Classically, the process was thought to extend to the DEJ, but electron microscopy shows it extends only up to inner dentin in mature teeth. Tubules beyond contain fluid only. The exam answer often states up to the DEJ in coronal dentin and shorter in the root.
Odontoblastic process extends up to:
1). DEJ in crown (full thickness)
2). Only up to inner 1/3 dentin
3). Up to 1/2 in crown, less in root - but traditionally thought full length, recent evidence shows up to DEJ in some areas
4). Never beyond predentin
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
Odontoblasts are derived from neural crest ectomesenchyme of the dental papilla. They differentiate under the influence of the inner enamel epithelium via BMP and FGF signaling.
Odontoblasts are derived from:
1). Inner dental epithelium
2). Dental papilla ectomesenchyme (neural crest)
3). Dental sac
4). Oral epithelium
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