Oral cavity

OVERVIEW OF THE DIGESTIVE SYSTEM — EXAM NOTES

1. Components of the Digestive System

• Digestive system =

  • Alimentary canal

  • Associated organs:

    • Tongue

    • Teeth

    • Salivary glands

    • Pancreas

    • Liver

    • Gallbladder

2. Major Functions

• Transport of ingested food & water

• Secretion of:

  • Fluids

  • Electrolytes

  • Digestive enzymes

• Digestion (mechanical + chemical)

• Absorption of digested products

• Excretion of indigestible remains

3. Key Concept (VERY IMPORTANT)

• Lumen of alimentary canal = physically & functionally external to the body

4. Digestion Process

• Food is:

  • Broken down physically + chemically

  • Converted into absorbable products

• Different segments of alimentary canal are:

  • Morphologically specialized for digestion & absorption

5. Daily Intake & Early Processing

• ~ 2 L/day of food and water ingested

• In oral cavity:

  • Food undergoes:

    • Maceration

    • Moistening

  • Forms bolus

  • Assisted by salivary gland secretion

6. Movement Through GI Tract

• Rapid passage through pharynx → keeps airway clear

• Slower passage through gastrointestinal tract

• Assisted by digestive juices (~7 L/day)

7. Digestion & Absorption Sites

• Major processes occur in:

  • Stomach

  • Small intestine

• Absorption:

  • Mainly in small intestine

  • Small portion in large intestine

8. Excretion

• Undigested food + other substances (mucus, bacteria, desquamated cells, bile pigments)

• Excreted as feces

HISTOLOGY-RELEVANT HIGH-YIELD SECTION

9. Alimentary Mucosa (VERY IMPORTANT)

Definition

• Surface across which most substances enter the body

Role

• Acts as an interface between body & environment

10. Functions of the Alimentary Mucosa

A. Secretion

• Produces:

  • Digestive enzymes

  • Hydrochloric acid

  • Mucin

  • Antibodies

B. Absorption

• Epithelium of mucosa absorbs:

  • Metabolic substrates (digestion products)

  • Vitamins

  • Water

  • Electrolytes

  • Recyclable materials:

    • Bile components

    • Cholesterol

  • Other essential substances

C. Barrier Function

• Prevents entry of:

  • Noxious substances

  • Antigens

  • Pathogenic organisms

D. Immunologic Protection

• Lymphatic tissue in mucosa:

  • First line of immune defense

ORAL CAVITY

1. Components

• Mouth and its structures:

  • Tongue

  • Teeth and supporting structures (periodontium)

  • Major salivary glands

  • Minor salivary glands

  • Tonsils

2. Divisions of Oral Cavity

• Vestibule:

  • Space between lips, cheeks, and teeth

• Oral cavity proper:

  • Lies behind teeth

  • Boundaries:

    • Superior → hard & soft palates

    • Inferior → tongue & floor of mouth

    • Posterior → entrance to oropharynx

3. Major Salivary Glands (Paired)

1. Parotid gland

• Largest gland

• Location → infratemporal region of head

• Duct → Parotid (Stensen’s) duct

• Opens at:

  • Parotid papilla

  • On cheek mucosa opposite upper second molar tooth

2. Submandibular gland

• Location → submandibular triangle of neck

• Duct → Submandibular (Wharton’s) duct

• Opens at:

  • Sublingual caruncle

  • On each side of lingual frenulum (floor of oral cavity)

3. Sublingual gland

• Location → inferior to tongue within sublingual folds (floor of oral cavity)

• Features:

  • Numerous small excretory ducts

  • Some ducts → enter submandibular duct

  • Others → open independently into oral cavity

4. Duct Length

• Parotid & submandibular glands → relatively long ducts

• Sublingual glands → relatively short ducts

5. Minor Salivary Glands

• Location → submucosa of oral cavity

• Drainage:

  • Empty directly into cavity via short ducts

• Named by location:

  • Buccal

  • Labial

  • Lingual

  • Palatine

6. Tonsils

• Aggregations of lymphatic nodules

• Located around posterior opening of oral and nasal cavities

7. Tonsillar (Waldeyer’s) Ring

• Lymphatic tissue forming immunologic protection

• Located at shared entrance to digestive & respiratory tracts

• Surrounds posterior orifice of oral & nasal cavities

8. Types of Tonsils

1. Palatine tonsils

• Located:

  • Either side of entrance to oropharynx

  • Between palatopharyngeal & palatoglossal arches

2. Tubal tonsils

• Located:

  • Lateral walls of nasopharynx

  • Posterior to opening of auditory tube

3. Pharyngeal tonsil (Adenoid)

• Located:

  • Roof of nasopharynx

4. Lingual tonsil

• Located:

  • Base of tongue (superior surface)

ORAL MUCOSA

1. Types of Oral Mucosa

• The oral cavity is lined by:

  • Masticatory mucosa

  • Lining mucosa

  • Specialized mucosa

2. Masticatory Mucosa

Location

• Gingiva (gums)

• Hard palate

Epithelium

• Keratinized stratified squamous epithelium

• In some areas → Parakeratinized stratified squamous epithelium

Parakeratinized Epithelium

• Similar to keratinized epithelium BUT:

  • Superficial cells retain nuclei

  • Cytoplasm does not stain intensely with eosin

• Nuclei:

  • Pyknotic (highly condensed)

  • Persist until cell exfoliation

Lamina Propria

• Thick papillary layer of loose connective tissue:

  • Contains blood vessels and nerves

  • Some nerves:

    • End as bare axon endings (sensory receptors)

    • Some end in Meissner’s corpuscles

• Deep to it:

  • Reticular layer (denser connective tissue)

Function/Structure

• Depth and number of connective tissue papillae:

  • Contribute to relative immobility

  • Protect from frictional and shearing stress

Special Attachment

• Palatine raphe (midline of hard palate):

  • Mucosa firmly adheres to bone

  • No submucosa

• Same applies to:

  • Gingiva

Submucosa (Hard Palate)

• When present:

  • Anterior → Fatty zone (adipose tissue)

  • Posterior → Glandular zone

• Continuous with soft palate submucosa

Collagen Bands

• In submucosal regions:

  • Thick collagenous bands extend from mucosa to bone

3. Lining Mucosa

Location

• Lips

• Cheeks

• Alveolar mucosal surface

• Floor of mouth

• Inferior surfaces of tongue

• Soft palate

Structures Covered

• Skeletal muscle:

  • Lips, cheeks, tongue

• Bone:

  • Alveolar mucosa

• Glands:

  • Soft palate, cheeks, inferior tongue

Features

• Fewer and shorter papillae

• Allows adjustment to movement of underlying muscles

Epithelium

• Generally Nonkeratinized stratified squamous epithelium

• In some places → Parakeratinized

Vermilion Border of Lip

• Epithelium is keratinized

Nonkeratinized Epithelium Layers

(ONLY 3 layers)

1. Stratum basale

   • Single layer on basal lamina

2. Stratum spinosum

   • Several cell layers

3. Stratum superficiale

   • Surface layer

Thickness

• Nonkeratinized lining epithelium:

  • Thicker than keratinized epithelium

Cells Present

• Keratinocytes

• Langerhans’ cells

• Melanocytes

• Merkel’s cells

Lamina Propria (Lining Mucosa)

• Contains:

  • Blood vessels

  • Nerves

  • Bare axon endings

  • Encapsulated sensory endings in some papillae

Histologic Identification

• Alveolar mucosa:

  • Numerous deep papillae

• Other lining mucosa:

  • Shallow papillae

4. Submucosa (Lining Mucosa)

General

• Present except:

  • Inferior surface of tongue

Contents

• Large blood vessels

• Nerves

• Lymphatic vessels

Special Features

• Contains:

  • Minor salivary glands (lips, tongue, cheeks)

Inferior Surface of Tongue

• Submucosa contains:

  • Collagen fibers

  • Elastic fibers

• Function:

  • Bind mucosa to underlying muscle

Sebaceous Glands

• Occasionally present (without hair follicle)

• Locations:

  • Lateral to corner of mouth

  • Cheeks opposite molar teeth

• Called:

  • Fordyce spots

• Visible to the eye

5. Submucosa – Vascular Supply

• Contains:

  • Larger blood vessels

  • Nerves

  • Lymphatic vessels

• Supplies:

  • Subepithelial neurovascular networks in lamina propria

6. Specialized Mucosa

• Function:

  • Taste sensation

• Location:

  • Dorsal surface of tongue

• Contains:

  • Papillae

  • Taste buds → responsible for taste generation

TONGUE –

1. General Structure

• Tongue = muscular organ projecting into oral cavity from inferior surface

2. Lingual Muscles

• Two types:

  • Extrinsic muscles

    • One attachment outside tongue

  • Intrinsic muscles

    • Confined entirely within tongue

Muscle Arrangement

• Striated muscle arranged in bundles:

  • Run in three planes

  • Each at right angles to others

Function

• Provides:

  • Flexibility

  • Precision of movement

• Essential for:

  • Speech

  • Digestion

  • Swallowing

Additional Feature

• Variable adipose tissue between muscle fibers

3. Dorsal Surface of Tongue

Division

• Divided into:

  • Anterior 2/3

  • Posterior 1/3

• Separated by:

  • Sulcus terminalis (V-shaped)

Foramen Cecum

• Located at apex of V

• Remnant of embryonic origin of thyroid gland

4. Lingual Papillae

• Cover dorsal surface anterior to sulcus terminalis

• With taste buds → form specialized mucosa

Types (4)

1. Filiform

2. Fungiform

3. Circumvallate

4. Foliate

5. Filiform Papillae

• Smallest & most numerous

• Shape:

  • Conical

  • Elongated

• Composition:

  • Connective tissue core

  • Covered by highly keratinized stratified squamous epithelium

• No taste buds

• Function:

  • Mechanical only

• Distribution:

  • Entire anterior dorsal surface

  • Tips point backward

  • Arranged in rows:

    • Diverge left & right from midline

    • Parallel to arms of sulcus terminalis

6. Fungiform Papillae

• Shape:

  • Mushroom-shaped projections

• Location:

  • Dorsal surface

  • Scattered among filiform papillae

• Visibility:

  • Seen as small spots

• More numerous:

  • Near tip of tongue

• Epithelium:

  • Stratified squamous

• rare Contain taste buds

7. Circumvallate Papillae

• Shape:

  • Large, dome-shaped

• Location:

  • Just anterior to sulcus terminalis

• Number:

  • 8–12 papillae

Structure

• Surrounded by:

  • Moat-like invagination

• Lined by:

  • Stratified squamous epithelium

• Contain:

  • Numerous taste buds

Associated Glands

• Lingual salivary (von Ebner’s) glands

  • Ducts open into base of moats

  • Secrete serous fluid

  • Function:

    • Flush material from moat

    • Allow rapid response of taste buds

8. Foliate Papillae

• Structure:

  • Parallel low ridges

  • Separated by deep mucosal clefts

• Orientation:

  • At right angles to long axis of tongue

• Location:

  • Lateral edge of tongue

9. Posterior Tongue (Base)

• Dorsal surface shows:

  • Smooth bulges

• Cause:

  • Presence of lingual tonsil in lamina propria

TASTE BUDS & TASTE –

1. Location of Taste Buds

• Present on:

  • Fungiform papillae

  • Foliate papillae

  • Circumvallate papillae

2. Structure of Taste Buds

• Appear as:

  • Oval, pale-staining bodies

• Extend through:

  • Full thickness of epithelium

Taste Pore

• Small opening at apex of taste bud

• Opens onto epithelial surface

3. Cell Types in Taste Buds (3)

1. Neuroepithelial (Sensory) Cells

• Most numerous

• Elongated cells:

  • Extend from basal lamina → taste pore

• Apical surface:

  • Contains microvilli

• Connections:

  • Tight junctions with neighboring cells

• Base:

  • Form synapse with afferent sensory neurons of:

    • Facial nerve (CN VII)

    • Glossopharyngeal nerve (CN IX)

    • Vagus nerve (CN X)

• Turnover time:

  • ~10 days

2. Supporting Cells

• Less numerous

• Elongated:

  • Extend from basal lamina → taste pore

• Features:

  • Microvilli on apical surface

  • Tight junctions present

• Do NOT synapse with nerve cells

• Turnover time:

  • ~10 days

3. Basal Cells

• Small cells

• Located:

  • Basal portion near basal lamina

• Function:

  • Stem cells for other two cell types

4. Additional Locations of Taste Buds

• Glossopalatine arch

• Soft palate

• Posterior surface of epiglottis

• Posterior wall of pharynx (down to level of cricoid cartilage)

5. Taste – Basic Concept

• Chemical sensation

• Caused by:

  • Interaction of tastants with receptors on:

    • Apical surface of neuroepithelial cells

6. Five Basic Taste Stimuli

• Sweet

• Salty

• Bitter

• Sour

• Umami

7. Mechanisms of Taste Transduction

General Mechanisms

• Tastants act by:

  • Opening ion channels → (salt, sour)

  • Closing ion channels → (sour)

  • Activating G protein–coupled receptors → (bitter, sweet, umami)

8. Taste Receptors

• Belong to:

  • T1R and T2R receptor families

• All are:

  • G protein–coupled receptors

9. Bitter Taste

• Detected by:

  • ~30 types of T2R receptors

• Each receptor:

  • Single transmembrane protein

  • Coupled to its own G protein

10. Signal Transduction Pathway

• Tastant → activates receptor → activates G protein

• G protein stimulates:

  • Phospholipase C

• Leads to:

  • ↑ Inositol 1,4,5-triphosphate (IP₃)

IP₃ Effects

• Activates:

  • Taste-specific Na⁺ channels

• Causes:

  • Na⁺ influx → depolarization

Depolarization

• Opens:

  • Voltage-gated Ca²⁺ channels

Result

• ↑ Intracellular Ca²⁺:

  • From extracellular influx

  • From intracellular stores (via IP₃)

• Leads to:

  • Neurotransmitter release

• Generates:

  • Nerve impulses in gustatory afferent fibers

11. Sweet Taste

• Receptors:

  • G protein–coupled

  • Two subunits:

    • T1R2

    • T1R3

• Mechanism:

  • Same second messenger cascade as bitter

12. Umami Taste

• Stimulated by:

  • Amino acids:

    • L-glutamate

    • Aspartate

    • Related compounds

• Common in:

  • Asparagus

  • Tomatoes

  • Cheese

  • Meat

Receptors

• Two subunits:

  • T1R3 (same as sweet)

  • T1R1 (unique)

Mechanism

• Same as bitter taste pathway

Special Note

• Monosodium glutamate (MSG):

  • Stimulates umami receptors

13. Important Functional Concept

• Neuroepithelial cells:

  • Express only one class of receptor proteins

• Therefore:

  • Different tastes (e.g., bitter vs sweet)

  • Are transmitted via different nerve fibers to CNS

SALTY & SOUR TASTE + TASTE DISTRIBUTION

1. General Concept

• Sodium ions (Na⁺) → responsible for salty taste

• Hydrogen ions (H⁺) → responsible for sour taste

• Both:

  • Act directly on ion channels

• Mechanisms:

  • Similar to signaling in synapses and neuromuscular junctions

2. Sour Taste

Cause

• Generated by:

  • H⁺ protons from hydrolysis of acidic compounds

Mechanism

• H⁺:

  • Blocks K⁺ channels

    • → alters membrane potential

    • → causes depolarization

• H⁺ also:

  • Enters cell via:

    • Amiloride-sensitive Na⁺ channels

    • Specific channels:

      • PKD1L3

      • PKD2L1

Further Steps

• Entry of H⁺:

  • Activates:

    • Voltage-sensitive Ca²⁺ channels

• Ca²⁺ influx:

  • Causes:

    • Migration of synaptic vesicles

    • Vesicle fusion

    • Neurotransmitter release

• Result:

  • Action potentials in sensory nerve fibers

3. Salty Taste

Cause

• Stimulated by:

  • Table salt (NaCl)

• Derived from:

  • Na⁺ ions

Mechanism

• Na⁺ enters neuroepithelial cells via:

  • Amiloride-sensitive Na⁺ channels

    • Same channels involved in sour taste

• These channels:

  • Different from voltage-sensitive Na⁺ channels (nerve/muscle)

Further Steps

• Na⁺ entry:

  • Causes:

    • Depolarization

• Leads to activation of:

  • Voltage-sensitive Na⁺ channels

  • Voltage-sensitive Ca²⁺ channels

Final Outcome

• Ca²⁺ influx:

  • Triggers:

    • Neurotransmitter release from synaptic vesicles

• Result:

  • Stimulation of gustatory nerve fibers

4. Regional Taste Sensitivity (Exam Point)

• Tip of tongue:

  • Detects → Sweet

• Immediately posterolateral to tip:

  • Detects → Salty

• More posterolateral regions:

  • Detect → Sour

• Circumvallate papillae:

  • Detect → Bitter and Umami

LINGUAL TONSIL + NERVE SUPPLY OF TONGUE

1. Lingual Tonsil

Definition

• Accumulations of lymphatic tissue at the base of the tongue

Location

• In lamina propria of root/base of tongue

• Located:

  • Posterior to sulcus terminalis

Structure

• Contains:

  • Diffuse lymphatic tissue

  • Lymphatic nodules with germinal centers

Epithelium

• Epithelial crypts:

  • Invaginate into lingual tonsil

• Epithelium may be:

  • Difficult to distinguish due to:

    • Large number of lymphocytes infiltrating it

• Between nodules:

  • Epithelium resembles lining epithelium

Associated Glands

• Mucous lingual salivary glands:

  • Present within lingual tonsil

  • May extend into muscle of base of tongue

2. Nerve Supply of Tongue

General Concept

• Complex nerve supply provided by:

  • Cranial nerves

  • Autonomic nervous system

3. General Sensation

Anterior 2/3 of tongue

• Carried by:

  • Mandibular division of trigeminal nerve (CN V)

Posterior 1/3 of tongue

• Carried by:

  • Glossopharyngeal nerve (CN IX)

  • Vagus nerve (CN X)

4. Taste Sensation

Anterior to sulcus terminalis

• Carried by:

  • Chorda tympani (branch of facial nerve, CN VII)

Posterior to sulcus

• Carried by:

  • Glossopharyngeal nerve (CN IX)

  • Vagus nerve (CN X)

5. Motor Innervation

• Musculature of tongue supplied by:

  • Hypoglossal nerve (CN XII)

6. Autonomic Innervation

Type

• Sympathetic and parasympathetic nerves

Function

• Supply:

  • Blood vessels

  • Small salivary glands of tongue

Ganglion Cells

• Present within tongue

• Belong to:

  • Postsynaptic parasympathetic neurons

• Function:

  • Supply minor salivary glands

Sympathetic Neurons

• Cell bodies located in:

  • Superior cervical ganglion

TEETH

1. General

• Teeth consist of:

  • Several layers of specialized tissues

2. Main Tissues of Teeth (3)

1. Enamel

• Characteristics:

  • Hard

  • Thin

  • Translucent

• Type:

  • Acellular mineralized tissue

• Location:

  • Covers crown of the tooth

2. Dentin

• Most abundant dental tissue

• Location:

  • Lies:

    • Deep to enamel (in crown)

    • Deep to cementum (in root)

Structure & Function

• Has:

  • Tubular structure

  • Specific biochemical composition

• Function:

  • Supports:

    • Enamel

    • Cementum

3. Cementum

• Characteristics:

  • Thin

  • Pale-yellowish

• Type:

  • Bone-like calcified tissue

Location

• Covers:

  • Dentin of the root

Properties

• Compared to dentin:

  • Softer

  • More permeable

Clinical Note

• Easily removed by:

  • Abrasion

• Especially when:

  • Root surface exposed to oral environment

ENAMEL –

1. General Features

• Hardest substance in the body

• Composition:

  • 96–98% calcium hydroxyapatite

2. Basic Characteristics

• Acellular mineralized tissue

• Covers:

  • Crown of the tooth

• Once formed:

  • Cannot be replaced

3. Origin & Nature

• Derived from:

  • Epithelium

• Unlike bone:

  • Not formed from connective tissue

• Properties:

  • More highly mineralized and harder than any other mineralized tissue

4. Crown Definitions

• Clinical crown:

  • Portion visible above gum line

• Anatomic crown:

  • Entire portion covered by enamel

  • Includes part below gum line

6. Boundaries

• Root:

  • Covered by cementum

7. Enamel Rods (Key Feature)

General

• Enamel composed of:

  • Enamel rods

• Rods:

  • Span entire thickness of enamel

Structure

• Made of:

  • Nonstoichiometric carbonated calcium hydroxyapatite crystals

Extent

• Each rod:

  • Extends from:

    • Dentinoenamel junction → enamel surface

Cross-section Appearance

• Keyhole shape:

  • Head:

    • Ballooned part

    • Oriented superiorly

  • Tail:

    • Directed inferiorly toward root

Crystal Orientation

• In head:

  • Crystals → parallel to long axis of rod

• In tail:

  • Crystals → more oblique

Interrod Region

• Spaces between rods:

  • Also filled with enamel crystals

8. Incremental Lines

• Striations (Contour lines of Retzius):

  • Represent:

    • Rhythmic growth of enamel

9. Neonatal Line

• Seen in:

  • Deciduous teeth

• Feature:

  • Wide hypomineralized line

• Significance:

  • Marks:

    • Nutritional changes between prenatal and postnatal life

10. Post-Eruptive Enamel

• Lacks:

  • Cells

  • Cell processes

• Not static:

  • Influenced by salivary gland secretions

11. Role of Saliva

• Essential for:

  • Maintenance of enamel

• Contains:

  • Digestive enzymes

  • Secreted antibodies

  • Inorganic (mineral) components

ENAMEL DEVELOPMENT (AMELOGENESIS) –

1. Cells Producing Tooth Tissues

• Enamel → produced by:

  • Ameloblasts (of enamel organ)

• Dentin → produced by:

  • Neural crest–derived odontoblasts

  • From adjacent mesenchyme

2. Enamel Organ

Origin

• Derived from:

  • Ectodermal epithelial cells of oral cavity

Tooth Development – Initial Stage

• Begins with:

  • Proliferation of oral epithelium

• Forms:

  • Dental lamina

  • Horseshoe-shaped band of tissue

Bud Stage

• Further proliferation from dental lamina:

  • Forms:

    • Rounded, bud-like outgrowth

• One for each tooth

• Projects into:

  • Underlying mesenchyme

• Represents:

  • Early enamel organ

Cap Stage

• Cell mass enlarges

• Develops:

  • Concavity opposite origin from dental lamina

Bell Stage

• Further growth leads to:

  • Bell stage

• Enamel organ now has 4 cellular components:

1. Outer enamel epithelium

• Single cell layer

• Forms:

  • Convex surface

2. Inner enamel epithelium

• Single cell layer

• Forms:

  • Concave surface

3. Stratum intermedium

• Cell layer:

  • Internal to inner enamel epithelium

4. Stellate reticulum

• Cells:

  • Stellate appearance

• Occupy:

  • Inner portion of enamel organ

3. Odontoblast & Ameloblast Formation

Odontoblasts

• Derived from:

  • Neural crest–derived preodontoblasts

• Location:

  • Adjacent to inner enamel epithelium in bell stage

• Features:

  • Become columnar

  • Epithelial-like appearance

• Function:

  • Form dentin

Ameloblasts

• Derived from:

  • Inner enamel epithelium cells

• Along with:

  • Stratum intermedium

• Function:

  • Enamel production

Dental Lamina

• Degenerates:

  • Early stage (before dentinogenesis & amelogenesis)

• Result:

  • Tooth primordium becomes:

    • Detached from origin

4. Amelogenesis (Enamel Formation)

• Defined as:

  • Matrix-mediated biomineralization process

5. Stages of Amelogenesis

1. Matrix Production (Secretory Stage)

• Also called:

  • Secretory stage

Sequence

• Dentin is produced first

• Then:

  • Partially mineralized enamel matrix

  • Deposited on:

    • Surface of previously formed dentin

Cells

• Secretory-stage ameloblasts

Function

• Produce:

  • Organic proteinaceous matrix

Cellular Machinery

• Activity of:

  • Rough endoplasmic reticulum (rER)

  • Golgi apparatus

  • Secretory granules

Outcome

• Enamel matrix production continues:

  • Until full thickness of enamel is achieved

2. Matrix Maturation Stage

Process

• Maturation of partially mineralized enamel involves:

  • Removal of organic material

  • Continued influx of:

    • Calcium

    • Phosphate

Cells

• Maturation-stage ameloblasts

Function

• Act as:

  • Transport epithelium

• Move substances:

  • Into and out of enamel

Cell Changes

• Undergo:

  • Cyclical morphological alterations

• Correspond to:

  • Cyclical calcium entry into enamel

AMELOBLASTS & ENAMEL MATRIX –

1. Secretory-Stage Ameloblasts

General

• Polarized columnar cells

• Function:

  • Produce enamel

Location

• Lie:

  • Directly adjacent to developing enamel

Tomes’ Process

• Present at:

  • Apical pole

• Surrounded by:

  • Developing enamel

Cytoplasmic Features

• Cluster of mitochondria

• Actin filaments:

  • In proximal terminal web (base of cell)

  • Responsible for:

    • Eosinophilic staining (H&E)

• Nucleus:

  • Located adjacent to mitochondria

• Main cytoplasm contains:

  • rER

  • Golgi apparatus

  • Secretory granules

  • Other cell elements

Junctional Complexes

• Present at:

  • Apical and basal parts

• Function:

  • Maintain:

    • Integrity

    • Orientation of ameloblasts

• Role:

  • Movement away from dentinoenamel junction

Actin Filaments

• Associated with junctional complexes

• Function:

  • Help movement of ameloblast over developing enamel

Enamel Rod Formation

• Rod follows:

  • Path of ameloblast

• Therefore:

  • Direction of enamel rod:

    • Reflects path of secretory-stage ameloblast

Basal Relation

• Adjacent to:

  • Stratum intermedium

Stratum Intermedium (Related Feature)

• Plasma membrane contains:

  • Alkaline phosphatase

• Function:

  • Enzyme active in calcification

Stellate Reticulum

• Located external to:

  • Stratum intermedium

• Separated from blood vessels by:

  • Basal lamina

2. Maturation-Stage Ameloblasts

Function

• Transport substances needed for enamel maturation

Histologic Feature

• Presence of:

  • Striated (ruffled) border

Cycle Types

• Ruffled border cells:

  • ~70% of cycle

• Smooth-ended cells:

  • ~30% of cycle

Structural Changes During Maturation

• No:

  • Stratum intermedium

• Cells from:

  • Stratum intermedium

  • Stellate reticulum

  • Outer dental epithelium

• Undergo:

  • Collapse

  • Reorganization

• Become:

  • Indistinguishable as separate layers

Papillary Layer

• Formed by:

  • Invagination of blood vessels

• Contains:

  • Stellate papillary cells

• Located adjacent to:

  • Maturation-stage ameloblasts

Cellular Features

• Maturation-stage ameloblasts & papillary cells:

  • Contain numerous mitochondria

• Indicates:

  • High energy requirement

  • Function as:

    • Transporting epithelium

3. Enamel Matrix Proteins

General

• Enamel matrix:

  • Highly heterogeneous

• Contains proteins:

  • Encoded by multiple genes

1. Amelogenins

• Function:

  • Establish & maintain:

    • Spacing between enamel rods

• Important in:

  • Early enamel development

2. Ameloblastins

• Produced by:

  • Ameloblasts (early secretory → late maturation stages)

• Function:

  • Not well understood

• Suggested roles:

  • Guide mineralization

  • Control:

    • Elongation of enamel crystals

  • Form:

    • Junctional complexes between enamel crystals

3. Enamelins

• Distributed:

  • Throughout enamel layer

• Undergo:

  • Proteolytic cleavage during maturation

• Low-molecular-weight products:

  • Retained in mature enamel

  • Often on surface of enamel crystals

4. Tuftelins

• Location:

  • Near dentinoenamel junction

• Properties:

  • Acidic and insoluble

• Function:

  • Aid in:

    • Nucleation of enamel crystals

Enamel Tufts

• Contain:

  • Tuftelins

• Feature:

  • Hypomineralization

• Have:

  • Higher organic content than rest of enamel

4. Final Maturation Changes

• Continued mineralization:

  • Leads to enamel becoming:

    • Hardest substance in body

Protein Removal

• During maturation:

  • Amelogenins and ameloblastins removed

Mature Enamel Contains

• Only:

  • Enamelins

  • Tuftelins

Fate of Ameloblasts

• Degenerate:

  • After enamel formation complete

• Timing:

  • Around tooth eruption through gum

DENTIN –

1. General

• Calcified material

• Forms:

  • Most of the tooth substance

2. Location & Composition

• Lies:

  • Deep to enamel (crown)

  • Deep to cementum (root)

• Hydroxyapatite content:

  • ~70%

  • Less than enamel

  • More than bone and cementum

3. Odontoblasts

Function

• Secrete:

  • Dentin

Location

• Form:

  • Epithelial-like layer

• Situated:

  • On inner surface of dentin

  • In contact with:

    • Pulp

Cell Features

• Columnar cells

• Contain:

  • Well-developed rER

  • Large Golgi apparatus

  • Other organelles for protein synthesis & secretion

Apical Surface

• In contact with:

  • Forming dentin

Junctional Complexes

• Present between odontoblasts

• Function:

  • Separate:

    • Dentin compartment

    • Pulp chamber

4. Dentin Formation & Tubules

Odontoblast Movement

• As dentin is deposited:

  • Odontoblasts:

    • Retreat inward

Dentin Tubules

• Odontoblast processes remain:

  • Embedded in dentin

• Located in:

  • Narrow channels → dentinal tubules

Growth

• Tubules & processes:

  • Continue to elongate

• Due to:

  • Rhythmic dentin deposition

5. Incremental (Growth) Lines

• Formed by:

  • Rhythmic growth of dentin

Types

• Incremental lines of von Ebner

• Lines of Owen (thicker)

Significance

• Mark:

  • Important developmental events:

    • Birth → neonatal line

    • Exposure to substances (e.g., lead)

6. Predentin

Definition

• Newly secreted organic matrix

• Location:

  • Closest to odontoblast cell body

• Status:

  • Not yet mineralized

Composition

• Proteins similar to bone

• Contains two unique proteins:

7. Predentin Proteins

1. Dentin Phosphoprotein (DPP)

• ~45 kDa

• Highly acidic phosphorylated protein

• Rich in:

  • Aspartic acid

  • Phosphoserine

• Function:

  • Binds large amounts of calcium

  • Involved in:

    • Initiation of mineralization

    • Control of:

      • Mineral size

      • Mineral shape

2. Dentin Sialoprotein (DSP)

• ~100 kDa

• Type:

  • Proteoglycan

• Rich in:

  • Aspartic acid

  • Glutamic acid

  • Serine

  • Glycine

  • Chondroitin 6-sulfate

• Function:

  • Involved in:

    • Mineralization process

8. Abacus Bodies

Formation

• Present in:

  • Golgi vesicles of odontoblasts

Structure

• Arrays of:

  • Filamentous collagen precursor

• Associated with:

  • Calcium-containing granules

Function

• Give rise to:

  • Abacus bodies

Maturation

• Become:

  • More condensed

• Develop into:

  • Secretory granules

1. General

• Calcified material

• Forms:

  • Most of the tooth substance2. Location & Composition

• Lies:

  • Deep to enamel (crown)

  • Deep to cementum (root)

• Hydroxyapatite content:

  • ~70%

  • Less than enamel

  • More than bone and cementum

3. Odontoblasts

Function

• Secrete:

  • Dentin

Location

• Form:

  • Epithelial-like layer

• Situated:

  • On inner surface of dentin

  • In contact with:

    • Pulp

Cell Features

• Columnar cells

• Contain:

  • Well-developed rER

  • Large Golgi apparatus

  • Other organelles for protein synthesis & secretion

Apical Surface

• In contact with:

  • Forming dentin

Junctional Complexes

• Present between odontoblasts

• Function:

  • Separate:

    • Dentin compartment

    • Pulp chamber

4. Dentin Formation & Tubules

Odontoblast Movement

• As dentin is deposited:

  • Odontoblasts:

    • Retreat inward

Dentin Tubules

• Odontoblast processes remain:

  • Embedded in dentin

• Located in:

  • Narrow channels → dentinal tubules

Growth

• Tubules & processes:

  • Continue to elongate

• Due to:

  • Rhythmic dentin deposition

5. Incremental (Growth) Lines

• Formed by:

  • Rhythmic growth of dentin

Types

• Incremental lines of von Ebner

• Lines of Owen (thicker)

Significance

• Mark:

  • Important developmental events:

    • Birth → neonatal line

    • Exposure to substances (e.g., lead)

Application

• Useful in:

  • Forensic medicine

6. Predentin

Definition

• Newly secreted organic matrix

• Location:

  • Closest to odontoblast cell body

• Status:

  • Not yet mineralized

Composition

• Proteins similar to bone

• Contains two unique proteins:

7. Predentin Proteins

1. Dentin Phosphoprotein (DPP)

• ~45 kDa

• Highly acidic phosphorylated protein

• Rich in:

  • Aspartic acid

  • Phosphoserine

• Function:

  • Binds large amounts of calcium

  • Involved in:

    • Initiation of mineralization

    • Control of:

      • Mineral size

      • Mineral shape

2. Dentin Sialoprotein (DSP)

• ~100 kDa

• Type:

  • Proteoglycan

• Rich in:

  • Aspartic acid

  • Glutamic acid

  • Serine

  • Glycine

  • Chondroitin 6-sulfate

• Function:

  • Involved in:

    • Mineralization process

8. Abacus Bodies

Formation

• Present in:

  • Golgi vesicles of odontoblasts

Structure

• Arrays of:

  • Filamentous collagen precursor

• Associated with:

  • Calcium-containing granules

Function

• Give rise to:

  • Abacus bodies

Maturation

• Become:

  • More condensed

• Develop into:

  • Secretory granules

SUPPORTING TISSUES OF TEETH (PERIODONTIUM) –

1. Components

Supporting tissues include:

• Alveolar bone (of maxilla & mandible)

• Periodontal ligament

• Gingiva

2. Alveolar Processes

• Contain:

  • Sockets (alveoli) for roots of teeth

3. Alveolar Bone Proper

• Thin layer of compact bone

• Forms:

  • Wall of alveolus

• Function:

  • Site of attachment for:

    • Periodontal ligament

• Remaining alveolar process:

  • Consists of:

    • Supporting bone

4. Periodontal Ligament (PDL)

Definition

• Fibrous connective tissue

• Joins:

  • Tooth to surrounding bone

Functions

• Bone remodeling (during tooth movement)

• Proprioception

• Tooth eruption

Histology

Tissue Types

• Contains:

  • Dense connective tissue

  • Loose connective tissue

Dense Connective Tissue

• Contains:

  • Collagen fibers

  • Fibroblasts

    • Elongated

    • Parallel to long axis of collagen fibers

Fibroblast Function

• Move back and forth:

  • Leave trail of collagen fibers

• Contain:

  • Internalized collagen fibrils

• These fibrils:

  • Digested by:

    • Lysosomal hydrolytic enzymes

• Function:

  • Produce collagen

  • Resorb collagen

  • Adjust continuously to:

    • Tooth stress and movement

Loose Connective Tissue

• Contains:

  • Blood vessels

  • Nerve endings

Additional Fibers

• Oxytalan fibers:

  • Thin

  • Longitudinally disposed

• Attach:

  • Bone ↔ cementum

• Some associated with:

  • Adventitia of blood vessels

5. Gingiva

Definition

• Part of mucous membrane:

  • Commonly called gums

Location

• Around:

  • Neck of tooth

Attachment

• Firmly attached to:

  • Tooth

  • Underlying alveolar bone

Parts of Gingiva

1. Gingival mucosa

• Same as:

  • Masticatory mucosa

2. Junctional Epithelium (Attachment Epithelium)

• Function:

  • Adheres firmly to tooth

Attachment Mechanism

• Secretes:

  • Basal lamina–like material

  • Adheres to tooth surface

• Cells attach via:

  • Hemidesmosomes

Epithelial Attachment

• Includes:

  • Basal lamina + hemidesmosomes

Age-related Change

• Young individuals:

  • Attachment to enamel

• Older individuals:

  • Attachment to cementum

  • Due to:

    • Passive tooth eruption

    • Gingival recession

6. Gingival Sulcus

• Located:

  • Above epithelial attachment

• Description:

  • Shallow crevice

• Lined by:

  • Crevicular epithelium

• Continuous with:

  • Junctional epithelium

7. Periodontium (Definition)

• All tissues involved in:

  • Attachment of tooth to maxilla & mandible

Includes

• Crevicular epithelium

• Junctional epithelium

• Cementum

• Periodontal ligament

• Alveolar bone