BDS Oral Histology Syllabus

Distinguish peritubular from intertubular dentin.

Peritubular (intratubular) dentin is the highly mineralized dentin lining the wall of each tubule. Intertubular dentin is the less mineralized, collagen-rich dentin located between the tubules and forms the bulk of dentin.

Compare primary, secondary, and tertiary dentin.

Primary dentin forms before root completion (bulk of the tooth). Secondary dentin forms slowly after root completion throughout life, narrowing the pulp. Tertiary (reparative/reactionary) dentin forms locally in response to injury such as caries or attrition.

What are the incremental lines of von Ebner and the contour lines of Owen in dentin?

Lines of von Ebner are fine daily incremental lines reflecting rhythmic dentin apposition. Contour lines of Owen are accentuated incremental lines marking disturbances in mineralization.

What is interglobular dentin?

Areas of hypomineralized or unmineralized dentin found in the crown just below the mantle dentin, resulting from failure of calcospherites (globules) to fuse during mineralization.

What is the Tomes' granular layer?

A zone of granular-appearing dentin found in the root just beneath the cementum, thought to represent looping or terminal branching of dentinal tubules (interpreted as small hypomineralized areas).

Define sclerotic (transparent) dentin and dead tracts.

Sclerotic dentin is dentin in which tubules become occluded by mineral (often with age or in response to stimuli), appearing transparent. Dead tracts are groups of empty dentinal tubules (odontoblast processes have degenerated) appearing dark in transmitted light.

What is cementum and what is its approximate mineral content?

Cementum is the avascular, mineralized connective tissue covering the root dentin. It is about 45-50% inorganic mineral by weight, the remainder being collagen and water; it anchors periodontal ligament fibers to the tooth.

Compare acellular and cellular cementum.

Acellular (primary) cementum lacks cementocytes, covers the cervical/coronal two-thirds of the root, forms first and slowly, and anchors Sharpey's fibers. Cellular (secondary) cementum contains cementocytes in lacunae, is found mainly at the apical third and furcations, forms faster, and adapts to functional demands.

What are Sharpey's fibers in cementum?

The terminal portions of periodontal ligament collagen fiber bundles that are embedded and mineralized within the cementum (and alveolar bone), anchoring the tooth to its socket.

What cells form cementum, and what are cementocytes?

Cementoblasts form cementum by depositing cementoid, which then mineralizes. Cementocytes are cementoblasts that become entrapped within lacunae of cellular cementum; they maintain the matrix and communicate via canaliculi directed toward the periodontal ligament (nutrient source).

What is the dental pulp and what are its four histological zones from periphery to center?

The pulp is the loose connective tissue occupying the central pulp chamber and canals. Zones (outer to inner): odontoblastic layer, cell-free zone of Weil, cell-rich zone, and the pulp core (central zone).

Name the major cell types and functions found in the dental pulp.

Odontoblasts (form dentin), fibroblasts (produce/maintain matrix, most numerous), undifferentiated mesenchymal cells (repair), and defense cells (macrophages, dendritic cells, lymphocytes). The pulp also contains blood vessels and nerves.

What is the cell-free zone of Weil?

A relatively cell-poor layer just internal to the odontoblastic layer, containing the plexus of Raschkow (nerve plexus) and the capillary plexus; prominent in the coronal pulp.

What are pulp stones (denticles)?

Discrete calcified masses within the pulp. They may be true denticles (containing dentinal tubules, lined by odontoblasts) or false denticles (concentric layers of mineralized tissue without tubules), and are classified as free, attached, or embedded.

List the four principal tissues comprising the periodontium.

Gingiva, periodontal ligament (PDL), cementum, and alveolar bone.

Name the principal fiber groups of the periodontal ligament.

Alveolar crest, horizontal, oblique (most numerous, resist masticatory forces), apical, and interradicular fiber groups. Plus the gingival fiber groups above the crest.

What are the epithelial cell rests of Malassez?

Clusters of residual epithelial cells in the periodontal ligament derived from the fragmented Hertwig's epithelial root sheath. They can proliferate to form odontogenic (periapical) cysts.

What is the predominant fiber type of the PDL and its orientation function?

Type I collagen fibers (principal fibers). The oblique group runs from cementum (apically) to alveolar bone (coronally), suspending the tooth and converting occlusal (compressive) forces into tension on the bone.

Name the three major (paired) salivary glands.

Parotid, submandibular (submaxillary), and sublingual glands.

Classify the secretion type of each major salivary gland.

Parotid: purely serous. Submandibular: mixed, predominantly serous. Sublingual: mixed, predominantly mucous.

Describe the general histological organization of a salivary gland acinus and duct system.

Secretory acini (serous, mucous, or mixed with serous demilunes) drain into intercalated ducts, then striated ducts (intralobular), then interlobular excretory ducts. Myoepithelial cells surround acini and intercalated ducts to expel secretion.

What are serous demilunes?

Crescent (half-moon)-shaped caps of serous cells located at the periphery of mucous acini in mixed glands (e.g., submandibular); they secrete via intercellular canaliculi between the mucous cells.

What is the function of striated ducts in salivary glands?

Striated ducts modify saliva by reabsorbing sodium and chloride and secreting potassium and bicarbonate, making saliva hypotonic. Their basal striations are infoldings of the cell membrane packed with mitochondria (for active transport).

Name the minor salivary glands and their general secretory nature.

Labial, buccal, palatine, lingual (glands of von Ebner are serous; others such as Blandin-Nuhn are mixed), and glossopalatine glands. Most minor glands are mucous or mixed, except the serous glands of von Ebner associated with circumvallate papillae.

What is the approximate water content of saliva, and roughly how much is produced daily?

Saliva is about 99% water and 1% solids (electrolytes, proteins, enzymes). Daily production is approximately 0.5-1.5 liters.

Name key organic components of saliva and their functions.

Amylase (ptyalin) begins starch digestion; lysozyme, lactoferrin, and IgA provide antimicrobial defense; mucins lubricate; statherin and proline-rich proteins help maintain calcium/phosphate balance and enamel pellicle formation.

State two important functions of saliva.

Lubrication and moistening for speech, swallowing, and taste; protection and buffering (bicarbonate maintains pH, antimicrobial agents, and remineralization via calcium and phosphate). It also begins carbohydrate digestion via amylase.

Define xerostomia and name two salivary gland disorders.

Xerostomia is dry mouth from reduced salivary flow. Disorders include sialadenitis (gland inflammation, e.g., mumps affecting parotid), sialolithiasis (salivary stones, common in submandibular gland/Wharton's duct), Sjogren's syndrome, and pleomorphic adenoma (most common benign salivary tumor).

Classify the three functional types of oral mucosa.

Masticatory mucosa (gingiva and hard palate; keratinized, bound to bone), lining mucosa (cheek, lips, floor of mouth, soft palate, ventral tongue; non-keratinized, mobile), and specialized mucosa (dorsum of tongue, bearing taste buds and papillae).

Describe the two basic histological layers of oral mucosa.

The epithelium (stratified squamous, keratinized or non-keratinized) resting on a basement membrane, and the underlying lamina propria (connective tissue with papillary and reticular layers). A submucosa may lie beneath, depending on region.

Name the layers of keratinized oral epithelium from deep to superficial and state a key function of oral mucosa.

Stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Functions of oral mucosa include protection (barrier against mechanical, microbial, chemical insults), sensation (touch, pain, temperature, taste), secretion (minor glands), and thermal regulation.