Oral Histology quiz (ODS)

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Enamel

• Enamel is the hardest biological tissue in the body.
• It forms a protective covering over the crown of a tooth

Compostion

• Enamel is mineralized to 96%, with organic matter making up the remaining 4%
• The mineralized portion is formed of hydroxyapatite.
• Its crystals are cylindrical in shape with a hexagonal cross-section

Basic Structural Unit: Enamel Rod

• Enamel rods run from the dento-enamel junction to the enamel surface.
• The estimated number per tooth is 5 million to 12 million.
• The average diameter is 4 microns.
• Enamel rods are tapered at the end closer to the dento-enamel junction.
• Enamel rod diameter at DEJ = 1/2 Enamel rod diameter at Enamel Surface
• Enamel rods length is determined by how thick the enamel is. They’re thicker in cuspal/incisal areas and may reach up to 2.5 mm; shortest in the cervical.
• Enamel Rods do not run in perfect straight lines. They are wavy, producing Hunter-Shreger bands.
• The wavey pattern gets exaggerated in cuspal areas forming gnarly enamel.

Enamel Rod Direction

• In permanent teeth, the rods may be vertical, horizontal, or diagonal.
• In primary teeth, the rods may be vertical or horizontal.

Examination of rods

• Cross-striations are noticeable in cross sections of enamel rods
• In longitudinal sections, there are zones which alternate between light and dark lines because each enamel rod is separated from the others incrementally.
• In cross section, enamel rods have a keyhole shape, allowing for close stacking.

Rod and Interod Orentation

• Rod (head) crystals are parallel to the long axis of the enamel rods.
• Inter-rod crystals are at 65 degrees to the long axis of the enamel rods.
• The head of the enamel rod always points towards the cusps.
• The tail of the enamel rod always points towards the cervical line.
• Rod is made by the head; inter-rod is made by the tail

Formation

• The formation and angulation of the enamel crystals are influenced by ameloblasts.
• Enameloblasts have an extension called the Tomes process.
• The secretory side of the Tomes process secretes hydroxyapatite crystals at different angles.
• 1 enamel interrod formed by the contribution of 4 ameloblasts.

Aprismatic Enamel

• A layer of outer enamel (20-100 microns thick) where no enamel rods can be seen.
• More mineralized than the rest of the enamel.
• The last layer of enamel formed by ameloblasts. When this is formed, ameloblasts have lost their Tomes Process.
• All hydroxyapatite crystals are formed perpendicular to the surface and parallel to each other; there is no change in the angulation of crystals.

Gingiva

• Gingiva: The tissue within the oral cavity that overs the alveolar bone and roots of the teeth.
• The is borderd by the sulcular epithelium and the tooth

Junctional Epithelium

• Once the crown of tooth has developed and is ready for eruption is membrance of cuboidal
• The junction epithelium turnover is high and cells regenerated every 5-6 days.
• Composed of non-keratinized stratified epithelium made up of 3-24 layers.
• Possesses fewer desmosomes and tonofilaments than oral epithelium.
• Is attached to the tooth surface using hemidesmosomes and an internal basal lamina.

Gingival Categories

• Free/marginal/unattached: not directly attached to the tooth.
• Attached: tightly bound to the bone and underlying periosteum by epithelium and connective tissue.
• Interdental papilla: Fills the interproximal space between adjacent teeth.

Key gingival features:

• Gingival sulcus: V-shaped notch found between the tooth and the marginal gingiva.

Oral Epithelium

• Structure consists of mainly connective tissue and gingival epithelium.
• Gingival epithelium generally categorised into three different kinds depending on location/composition; sulcular epithelium,junctional epithelium
• Epithelial cells are mononuclear possessing intercellular bridges or desmosomes.
• Attached to basment membrane
• Cuboidal columnar shaped cells
• Hyperchromatic nucleus undergoing frequent mitotic division

Oral Epithelium Layers

• Basale (or the basal layer)
• Spinosum (or the prickle cell layer)
• Granulosum (granular layer)
• Corneum (corneal layer).

Stratum spinosum

• Larger polygon shape cells and is active in synthesis of protien and keratin.

Stratum granulosum

• Granular layered caused by keratonyaline granules.
• The granules are rich with filagrin protien provide steength to the epithilium.

Stratum corneum

• Made up larger flatter cells which are she through desquamanation
• natural shedding of skin.

Dentine

• Minute dentine tubules permeate the structure of the dentine.
• These extend from the DEJ to the pulp chamber
• These tubules traverse in S-shape, and are widely spread at the DE J compared to pulp.

Dental tubles

• The wall is called peritubular/intratubular dentine highly clacified.
• Dentine between called intertubular dentine less calcified and more collagen, making the bulk of dentine. This forms the odontoblasts process.
• Allows communication between pulp and dentine.

Pulp

• Pulpal anatomy is consistent with that of the tooth
• It's econsed in mineralised tissue and incased in the pool cavity
• Coronal pulp is located in the pulp chamber and root pulp located in the root canals
• Contains 75-80% water and 20-25% organic material
• Its organic material consists largely of cells & extracellular matrix

Pulp cells

• Odontoblasts
• Fibroblasts
• Undifferentiated cells
• Defense cells

Extracellular matric

• Fibres
• Ground Substance
• Blood Vessels
• Lymph Vessels
• Nerves

Structures

• Includes 4 zones
• The odontoblast zone lines the periphery
• The cell free zone: space between zones with few fibres
• The cell rich zone: contains all cells except odontoblasts
• The pulp core consists of blood vessels nerves and some cells.