Oral Biology and Oral Histology
What this domain tests
This domain tests the structure, development, and function of dental and oral tissues: enamel, dentin, pulp, cementum, periodontal ligament, oral mucosa, salivary glands, and tooth eruption. Questions often link histology to clinical sensitivity, repair, and aging.
Core rules and concepts
- Enamel is about 96 percent mineral by weight, formed by ameloblasts, and cannot regenerate after eruption. Its rods and interrod enamel create optical bands and influence caries spread.
- Dentin is roughly 70 percent mineral, 20 percent organic matrix, and 10 percent water. Type I collagen dominates the organic matrix. Odontoblasts line the pulp and extend processes into dentinal tubules.
- Primary dentin forms before eruption, secondary dentin forms slowly afterward, and tertiary dentin forms in response to injury. Reactionary dentin is formed by surviving odontoblasts; reparative dentin follows new odontoblast-like cells.
- Cementum includes acellular extrinsic fiber cementum and cellular intrinsic fiber cementum. Sharpey fibers anchor the periodontal ligament.
- Principal periodontal ligament fibers include alveolar crest, horizontal, oblique, apical, and interradicular groups. The oblique group resists axial occlusal load.
- Masticatory mucosa is keratinized; lining mucosa is nonkeratinized. Junctional epithelium attaches to the tooth via hemidesmosomes and is permeable to bacterial products.
- Parotid saliva is serous, submandibular is mixed, and sublingual is predominantly mucous. Secretory IgA, amylase, and statherin are key salivary components.
Worked example
A patient has cervical dentin exposure and sharp sensitivity to cold. The reasoning is that lost enamel and cementum expose dentinal tubules, and fluid movement in tubules activates A-delta fibers. Management aims to occlude tubules or reduce nerve excitability, for example with fluoride varnish, bonding agents, or desensitizing toothpaste. Enamel cannot be regrown by cells, so the goal is surface protection and symptom control.
Traps that cost marks
Do not claim enamel regenerates. Not all cementum is acellular. Tertiary dentin is not the same as secondary dentin. Periodontal ligament fibers are not merely collagen; they are organized into functional groups. Also avoid treating junctional epithelium as a fully impermeable barrier.