Week 1

Histology & Embryology: What are these subjects?

Histology- The study of the microscopic (cell level) structure of tissue

Embryology- The science that deals with the origin & development of an individual organism

Week 1

Cell Structure & Functions

What is the human body composed of?

-Cells

-Intercellular material (provides nutrition & take-up of waste products)

- Fluid (blood, lymph, and tissue fluid)

Cells are the smallest living units capable of independent existence.  

Week 1

What 8 vital functions do cells carry out?

-Absorption (taking up fluid)

-Assimilation (conversion of food into chemical substance of tissue)

-Respiration (Exchange of gasses)

-Irritability (Response to environmental changes)

-Conductivity (Electric conducting ability)

-Growth

-Reproduction

-Excretion (Ability to remove waste products)

Week 1

What components make a cell?

Cells vary in size, shape, structure & function, but share these characteristics:

- Cytosol

- Endoplasmic Reticulum (ER)

- Ribosomes

- Gogli Apparatus (complex)

-Lysosomes

- Mitochondria

- Microtubules

- Centrioles

- Plasma Membrane

- Genetic Mechanisms

Week 1

What is Cell Devision (Cell Cycle)?

•  Series of steps by which the cell divides

• Dependent on need for growth or replacement of tissues

-Some cells continually renew

- Others do not renew (adult neurons)

• Somatic cell division- mitosis

- 46 chromosomes (diploid number)

• Genetic cell division- meiosis, egg & sperm each having 23 chromosomes (haploid)

Week 1

Steps in Mitosis

• Interphase- resting stage

• Prophase- 

- Chromatin threads thicken into chromosomes

- Chromosomes split in half (chromatids)

- Chromatid pairs attach to centromeres

• Metaphase- 

- Centrioles migrate to opposite ends of cell

- Chromatids have lined up at equatoral line

- Chromatids split at the centromere into two sets of chromosomes

Week 1

Steps in Mitosis cont...

• Anaphase

- Daughter chromosomes move to cell poles, each with a diploid number

- Constriction appears in cell midbody

• Telophase

- Chromosomes elongate & disperse

- Regain chromatin thread appearance

- As nucleus appears & matures, the cleavage deepens and daughter cells separate

• Interphase

• Periods of Prenatal Development

- Proliferative, 0-2 weeks

• Fertilization

• Implantation

• Formation of embryonic disk

-Embryonic, 2-8 weeks

• Differentation occurs

• Various tissues develop & form organ systems

• Heart forms & starts beating by 4th week

• Face & Oral Structures develop 4th-7th week

- Fetal, 8 wks- 9 mos

• Tissues enlarge & become capable of function

What is Fertilization & Implantation?

• Fertilization- union of egg & sperm cells

- Zygote

- Morula- cells of zygote multiply

• migrates toward uterus, reaches by end of 1st week

• Endometrium has been thickening in preparation

• As morula increases, is termed...

- Blastocyst

• Becomes hollow & develops inner cell mass

• Implantation- blastocyst embeds in the uterine wall

• Enbryonic disk- inner cell mass of blastyocyst

• Embryonic disk becomes the embryo, composed of common walls of adjacent sacs (hollow spaces)

- Amnionic sac is lined with ectodermal cells

- Yolk sac is lined with endodermal cells

- A little later, mesodermal cells develop between the first two types

• These are the three germ layers from which all tissues and organs will develop!

• Ectoderm: 

- Nervous System

- Epithelium (covers body & lines some cavities)

- Tooth enamel

• Mesoderm

- Muscles

- Connective tissue: bone, cartilage, blood, dentin, pulp, cementum, periodontal ligament

• Endoderm

- GI tract epithelium & associated glands

Week 1

What do the ectoderm & endoderm contribute?

• On dorsal (back) surface of disk, ectodermal cells form the neural plate>neural tube> brain & spinal cord

• On ventral (belly) surface of disk, endodermal cells form an elongated tube that becomes the gastrointestinal tract

Week 1

Development of Human Tissues

• Epithelial Structures & Deriveratives Development

-Skin is a dual organ:

• Outer layer, epidermis, from ectoderm

• Inner layer, dermis, from mesoderm

• At first, only one layer of ectoderm cells cover 

embryo

• By 11-12 wks, ectoderm thickens to four layers

- Hair

- Teeth

- Nails

-Mammary Glands

- Sebaceous Glands

- Salivary Glands

Week 1

Nervous System Development

- Neural folds elevate in 3rd prenatal week

- 1st change in the shape of the flat sheet of cells

- Folds reach & close to form the neural tube

- Brain & spinal cord will form from this tube

- Cells lining the tube differentiate into neuroblasts> neurons

- Neurons will not divide further!

- 0n surface of developing brain & spinal cord are neural crest cells, they will also contribute to tissues of the face ( cartilage, teeth, muscles, ligaments)

Week 1

Connective Tissue Development

- Connective Tissue Proper

• Mesenchymal cells (important later in course!)

• Fibroblasts- Form many types of connective tissue structures

• Osteoblasts- Form bone

• Chondroblasts- Form cartilage

Week 1

Cartilage & Bone Formation

What  two types of growth can cartilage cells undergo?

- Early embryonic skeleton is cartilage

• Appositional (exogenous)- occurs on cartilage surface (like one layer of brick on another)

• Interstital (endogenous)- proliferation & expansion of cells from a matrix

- Later most of the cartilagenous skeleton is replaced by bone to provide rigidity & support

Week 1

Bone Formation

What 2 ways can bone development occur?

• Endochrondral Bone Development- When bone replaces cartilage

• Intramembranous Bone Formation- Direct transformation of connective tissue into bone

Week 1

Muscle Development

- By 10th week, muscle cells (myoblasts) have begun to migrate

- Myoblasts differentiate into muscle fibers that have the property of contractility

• Skeletal- conscious control of these muscles

• Smooth- involuntary muscles

•  Cardiac- heart muscle

Week 1

Cardiovascular System

• For the 1st few weeks, nutrition was derived from the yolk sac through the Vitelline Vascular System

• As the yolk sac is depleted, the Umbilical (vascular) System takes over.

• CVS originates from angioblasts of mesoderm during the 3rd week

• Outer cells organize into elongating tubes (blood vessels)

• Inner cells become blood cells

Week 1

What week does the heart begin to beat?

By the 4th week!

• Mesenchymal cells migrate into pericardial area to develop heart tubes

• Internal partitioning begins, & heart tubes enlarge and twist

• During the 4th week, when heart begins to beat, the umbilical circulation becomes active in transporting oxygen & nutrition

Week 2

Structure & Function of Cells, Tissues, & Organs

What are the body's primary tissues?

• Epithelial

• Neural

• Connective

• Muscle

Week 2

What is the origin of epithelial tissue?

• Most from ectoderm

• GI tract epithelium & associated organs- endoderm

• Abdominal cavity (perittoneum) & covering of viscera- mesoderm

Week 2

How is epithelial tissue classified?

By cell shape & arrangement

• Simple

• Stratified

Week 2

What are the different types of simple epithelium?

• Squamous

- Endothelial (spindle) lines ♥, blood & lymph vessels

- Mesothelial (oval-polygonal) lines pleural, pericardal, & peritoneal cavities

• Cuboidal (Cube)

- cilia may appear, found in kidneys, glands, respiratory passages

• Columnar (Rodlike)

- Cilia; most glands, small intestines, respiratory passages

• Pseudostratified (Rodlike with thin section)

- Cilia; respiratory passages, male reproductive organs

- All cells in contact with the basal lamina but not with the surface

Week 2

What are the different types of stratified epithelium?

• Squamus (Polyhedral)- Covering of the body, lining of mouth, pharnyx, vagina

Columnar (Columnar cells on cubiodal or columnar)- oropharnyx, larnyx

• Transitional (Cube to pear)- Distension causes cell flattening; urinary passages, bladder

Week 2

Neural Tissue

• Central Nervous System- CNS

• Brain- Made of neuroepithelial cells

• Spinal Cord

Week 2

Neural Tissue

• Peripheral Nervous System- PNS

• Afferent (sensory) System- info to CNS

• Efferent (motor) System- info away from CNS

• Somatic Nervous System (SOMA)- Carries info to voluntary muscles

• Autonomic Nervous System- Carries info to involuntary muscles (cardiac & smooth)

-Sympathetic Nervous System- 'fight or flight'

Parasympathetic Nervous System- modifies activity created by sympathetic nervous system

Week 2

Nervous System Cells

• Neuroglia Cells- Support nervous system

Neurons- Conduct & recieve impulses

• Dendrites- Recieve & conduct impulses to cell body

• Perikaryon (cell body)- Contains nucleus, cytoplasm, & rough ER

• Axon- Long, thin process can be few mm to several feet long, ends in axon terminals

Week 2

What are the two properties of neurons?

- Irritability

- Conductivity

Week 2

What does connective tissue do?

• Supports & connects other tissues

• Has the following properties:

-Relatively few cells (cell poor)

- Bulk made of intercellular ground substance

(matrix)

- Highly vascular (except cartilage)

Week 2

How can subtypes of connective tissue vary?

By:

-Proportion of cells

- Fiber

- Intercellular ground substance

- Location in body

Week 2

Muscle Tissue

What are the different muscle types?

• Skeletal- Voluntary, striated

• Smooth- Involuntary, found in viscera, blood vessels, and glands

• Cardiac- Involluntary, acts like a smooth muscle, looks like a striated

Week 2

What is perimysium, epimysium, and actin & myosin?

• Perimysium- sheath that covers each primary bundle of muscle fibers

• Epimysium- Outermost sheath covering each skeletal muscle

• Actin & Myosin- Proteins that allow muscles to contract

Week 3

What is the origin of epithelial tissue?

• Most from ectoderm

• GI tract epithelium & associated organs- endoderm

• Abdominal cavity (peritoneum) & covering of viscera-mesoderm

Week 3

How is Epithelial Tissue classified?

By Cell Shape & Arrangement

-Simple

- Stratifed

http://legacy.owensboro.kctcs.edu/gcaplan/anat/Histology/API%20histo%20epithelial.htm

• Embryo is a flat disk that bends down anteriorly as the brain expands

• Oral pit appears

• Cephalocaudal bend pushes ventrally

• Stomodeum appears between forebrain & heart

• Oropharyngeal membrane ruptures in the 5th week- opens oral cavity to the foregut

• Mandibular arch grows to form the maxillary processes (cheeks)

• Enlarging ♥ repositions in thorax, below mandibular arch

• Forming face grows away from midbrain, presses against chest & ♥

• During the 4th-7th weeks, pharyngeal arches I-V appear beneath the stomadeum

• Pharyngeal (branchial) Arch- bend around pharnyx as bars of tissue

• Pharyngeal arches are important in development of face & neck; each contain blood vessels, muscles, nerves & skeletal elements

• Separated by pharyngeal grooves

• On internal (pharnyx) surface are pharyngeal pouches

• Pharyngeal arches get progressively smaller

• The 3rd, 4th, & 5th arch are paired and divided by the ♥

• Ectoderm covers each arch, & inner lining of 1st & anterior of 2nd

• Remaining inner surface of arches is lined w/ endoderm (GI tract)

Defects could occur with exposure to:

• Irradiation

• Diatary deficiencies

• Drugs (illicit & certain legal)

• Chemicals

• Stress

• Aortic arch vessels course to brian & face

• Some are transient, others permanent

• Right & left aortic vessels in each arch ascend from ♥ to face, neck, brain, & posterior regions of body

• 1st & 2nd arch vessels present by 4th-5th week

• 3rd arch vessel prominent (common carotid arteries)

• 4th vessel- dorsal artery

• 5th vessel- transient

• 6th aortic arch vessel- pulmonary circulation

• Internal Carotid- first supplies neck & face, by 7th week is replaced by external carotid

• Internal carotid goes on to supply the brain

• 10th week- muscles of hyoid arch form thin sheet over face & posterior to ear- muscles of facial expression

 • Muscles attach to ossifying facial bones

• 4th branchial arch- site of forming pharyngeal constrictor muscles

• Nerves develop in conjunction with muscles

• By 7th week:

-Trigeminal nerve enters mandibular muscle mass (1st arch)

 -Facial nerves enter facial expression muscles (2nd arch)

- Glossopharyngeal nerve- supplies upper pharyngeal constrictor muscles (3rd arch)

- Vagus nerve- supplies inferior constrictor & laryngeal muscles (4th arch)

- Spinal Accessory nerve- supplies 5th arch

• Initial skeleton is cartilage

• Merckel's cartilage found in mandibular arch, develops into malleus & incus

• Reichert's cartilage found in hyoid arch.  This develops into:

-Stapes

- Styloid Process

- Upper body of hyoid

• Earliest elements are endochrondral

• Forms bases that underlies & supports brain

• Nasal ethmoid capsule- organ of smell

• Sphenoid- wings of bone, spread under brain

• Auditory capsules- organ of hearing

• Basioccipital cartilage- behind sphenoid

• Form protective covering of brain:

• Frontal

• Parietal

• Temporal- squamous portions

• Occipital

• Premaxillary

• Maxillary

• Zygomatic

• Temporal bone- petrous portion

• These spread upward around orbit

• Condylar Unit- Forms articulation

• Body- Center of mandibular growth

• Angular Unit- Forms in response to masticatory muscles

• Coronoid Unit- Responds to temporalis

• Alveolar Unit- Responds to developing & erupting teeth

• Articulations & growth sites between bones

• Examples:

- Zygomaticomaxillary

- Zygomaticotemporal

- Frontomaxillary

• Connective Tissue Type (syndesmosis)- Expand through growth of CT with osteogenic centers:

Simple- bones join evenly

Serrated- inderdigitating

Squamousal- overlapping or beveled

• Cartilage Type (synchondrosis)- Found in bones of midface- ethmoid, sphenoid; center of suture forms new cartilage, changes into bone at suture boundaries

Tissues around oral pit:

• Frontal processes- forehead

• Maxillary processes- cheeks

• Mandibular arch- lower jaw

• Tissues are as thin as a sheet of paper

• Embryo is only .25 in. long

• Oral pit w/ surrounding tissue masses evident

• Pharyngeal arches seen

• Arm buds evident

• Bulging ♥ in thorax has just begin to beat

• Frontal process dominates facial area, bulges forward & laterally

• Maxillary processes- small, wedge-shaped tissues lateral to pit

• Mandibular arch lies below pit, constricted in middle

• Embryo is .4 in. long

• As frontal prominences diminish, face broadens

• Eyes prominent & on side

• Thickened areas of epithelium border upper lip

• Nasal placodes develop into nostrils- still open into oral pit

• Frontal area now referred to as frontalnasal process

• Internasal area is as wide as the face

• Tissues adjacent to nostrils are:

- Lateral nasal processes

- Median nasal processes

What happens during the 6th week of facial development?

Card 1

• Embryo is .6 in. long

• Face is broader

• Eyes moving more to the front

• Oral pit widens into slit

• Maxillary processes & mandibular arch merge

• Upper lip composed of:

- Two lateral maxillary segments

- Median nasal part- philtrum

• Each nasal pit surrounded by:

-Lateral nasal processes

- Median nasal processes

What happens during the 6th week of facial development?

Card 2

• Lip is unified by medial nasal process fusing to each maxillary process

• If fusion fails= cleft lip

• Orbicularis oris forms to provide support around lip

• Nasolacrimal duct develops under an oblique groove from nostril to eye (related to tear production)

• Mandibular arch broadens, looses midline constriction

• First pharyngeal groove modifies into auditory groove

• Around external ear canal, six auricular hillocks form

- Three from mandibular arch

- Three from hyoid arch

What happens during the 7th week of facial development?

• Embryo is .8 in. long

• Eyes move toward the front

• Nose takes up less of face

• Eyes & nostrils on same horizontal plane

• Auricular hillocks fuse

• In just 3 weeks, separate tissue masses have:

-Enlarged

- Fused

- Merged into recognizable face

• Will seperate the oral & nasal cavities

• The thin palate will develop from 3 sections:

- Median palatine process (primary palate)- future premaxilla

- 2 lateral palantine processes

• The tongue seperates the palatine shelves

• In the posterior region, tongue is below the palate (attached to mouth floor)

• In anterior region, the tongue is even with the shelves

• Lateral palatine shelves push together

• Force the tongue down

• Thought to hapen rapidly (like an act of swallowing)

• Fusion will also occur w/ the nasal septum- separating the oral and nasal cavities

• If fusion fails, a cleft palate will occur

• The tongue develops from muscles of occipital somites

• The tongue has 2 parts

• Body is derived from mandibular arch

- two lateral lingual swellings

- Tuberculum impar

• Base of tonge is derived from the 2nd & 3rd pharyngeal arches

• Lateral lingual swellings enlarge, merge & overgrow the tuberculum impar

• Terminal sulcus (a V shaped groove) separates the tongue base & body

• In terminal sulcus, the foramen caecum gives rise to thyroid tissue

• The thyroid tissue descends to middle pharynx

• By 7th week, it migrates to front of trachea

• At this time, it is still attached to tongue by thyroglossal duct (eventually disappears)

• There are 2 possible malformations at this time:

-Thyroglossal cyst- blind pocket of thyroid epithelium

- Thyroglossal fistula- opening to neck

• Thyroid gland is functioning by the end of 3rd month

- Oral Epithelial Cells (from ectoderm)

- Mesenchymal cells (from mesoderm)

• Oral Epithelial Cells give rise to enamel organ (forms the enamel)

• Mesenchymal Cells give rise to the:

- Dental Papilla ( Dentin, Pulp)

- Dental Follicle/Dental Sac (Cementum, PDL, Alveolar Bone)

- The dental lamina is active from the 6th week in uetro until the persons 15th year- when the 3rd molar formation begins.

• Anterior teeth develop first

• As primary teeth erupt, the succedaneous permanent teeth development begins.

• During this time, the preborn child's tooth development could be interrupted by mom or child's exposure to: x-rays, drugs, nutritional deficiencies, or communicable disease.

- Bud

- Cap

-Bell

The Cap Stage

• This stage consists of the following:

- Enamel organ (originates from the lamina)

- Dental papilla (originates from mesenchyme to form dentin and pulp)

- Dental follicle (area surrounding the above structures, from mesenchyme, will form the cementum, PDL, and alveolar bone)

The Bell Stage

- The enamel organ and the dental papilla increase in size

• Outer enamel epithelium- Covering of outer convex surface, will bring nutrition to the ameloblasts and the other enamel organ cells.

• Stellate reticulum- Cells that fill the remainder of the enamel organ

• Stratum intermedium- Cells that lie adjacent to the inner enamel epithelium, function with ameloblasts to form enamel

• Inner enamel epithelium- Defines the shape of the future tooth, these cells elongate and differentiate into the ameloblasts (enamel producing cells)

- Also in the bell stage, the outer part of the dental papilla differentiate into odontoblasts (dentin producing cells)

- The general & lateral lamina begins to disintegrate through lysis ( with exception of the posterior portion that will later give rise to the permanent molars

- The young dental papilla is densely packed with cells

- It will keep pace with growth of the enamel organ

- The pulp cells are fibroblasts in a delicate reticulum

- There are a few large blood vessels in the central area, with smaller ones in the periphery

- The columnar shaped odontoblasts with cell processes that began forming during the bell stage are found on the periphery of the dental papilla

- Odontoblasts begin dentin formation

- Dental papilla is surrounded with dentin, central area is future pulp

- Odontoblasts reside in pulp for tooth's life

- Odontoblasts migrate pulpwardly, trailing their processes in the dentinal tubules

- The presence of many cell organelles indicate a high protein content

- Protein is secreted at the apical process portion

- Predentin is newly laid down dentin, not yet mineralized

Two phases:

- Formation of collagenous matrix

- Deposition of tricalcium phosphate crystals

• During crown development, 4 micrometers of dentin is laid down daily

• After the tooth reaches functional occlusion, 1 micrometer of dentin is laid down per day

There is a daily deposition of dentin= increment (visible lines)

- Dentin begins at DEJ, continues pulpwardly

- Root development continues even after eruption

Ameloblasts start depositing enamel after a few micrometers of dentin is deposited

- During the bell stage, the inner enamel epithelial cells elongate into secretory ameloblasts

• Morphogenesis

• Organization & differentation

• Secretation

• Maturation

• Protection

- The ameloblasts move peripherally from DEJ, depositing the enamel matrix (amelogenin)

- Enamel matrix forms in rods from DEJ to the surface

- Stratum intermedium cells change shape

- The stratum intermedium & ameloblasts work in tandem with each other

- Enamel matrix is layed down, followed by mineralization

- Amelogenin>Enamelin>Enamel

- Mineral crystals grow rapidly

• Matrix & mineralization occur:

- Peripherally to cusps

- Laterally to crowns

- Enamel is 96% mineral (inorganic)

- Dentin is 69% mineral (inorganic)

- When ameloblasts have completed their function, they change shape & function

- Their #'s of organelles & cell length decreases

- As each layer is layed down, ameloblasts absorb organic matrix & water

- Without this absorption, mineralization will not occur

- Occurs throughout enamel formation

- Ameloblasts secrete organic cuticle

- Desmosomes attach cell to cell

- Hemidesmosomes attach cell to membrane

- Tooth crown forms & mineralizes before the cervial area is formed

- Cervical area can be structurally deficient

- After mineralization is completed, the ameloblasts secrete the Primary (Developmental) Cuticle (Organic)

- Ameloblasts then contact the Stratum Intermedium, and lay down the reduced enamel epithelium

- This structure will later be important in the formation of the junctional epithelium

PDL forms attachment between bone & tooth; delicate fibers first appear inferior to cervical area (apical area)

- Fibroblasts form the PDL; these collagen fibers enbed in cementum & alveolar bone

- These fibers renew continually, especially in apical area

- PDL matures (more dense) when it reaches functional occlusion

Dental Follicle- Mesenchymal cells

- Form alveolar bone, PDL, and outer layer of cementum

- Alveolar process keeps pace with elongating roots

- Starts as bony trench, houses tooth germ

- Trench deepens> forms septa>tooth crypts

• Interdental Bone- Bone between adjacent teeth

• Interradicualar Bone- Bone between roots of multirooted teeth

• Alveolar Bone Proper- cribriform plate, lamina dura, lines tooth socket

• Supporting Bone

- Cancellous (spongy)

- Cortical (compact)

• Occurs from the time of tooth initation until crown completion

• Pattern is similar for primary & permanent teeth

• Developing crowns move constantly in jaws

• Tooth crown position responds to

-Adjacent crown position

- Growth of maxilla & mandible

• In early preeruptive phase, the anterior permanent teeth are lingual to and near the incisal of primary predecessor

- As primary tooth erupts, the permanent tooth is lingual & near apical of primary predecessor

• Developing premolars are enclosed in the roots of primary molars

• Maxillary molars develop in the tuberosity, occlusal surfaces pointed slightly distal

• Mandibular molars develop in the ramus, occlusal surfaces pointed slightly mesial

• Root formation

• Movement

• Penetration

• Intraoral or occlusal or incisal movement

During root formation:

• Space is required for elongating roots

• Epithelial root sheath proliferation causes:

- Initiation of radicular dentin & pulp

- Increase in fibrous tissue around dental follicle

• Mandible- Tooth eruption is superior

• Maxilla- Tooth eruption is inferior

• Teeth move through their bony crypts to reach the oral mucosa, allowing space for the elongating roots

• These cells intermingle and form a thin epithelium over the erupting crown:

- Reduced enamel epithelium

- Oral epithelium

• Eruption of teeth continues until contact with antagonists

• Clinical crown- That portion exposed in mouth to the gingival attachment

• Anatomic crown- That portion of tooth covered with enamel

• Occurs from the time that the tooth meets its antagonist (functional occlusion) and continues throughout the life of the tooth

• While root is completing, height of alveolar bone compensates

• Even after a tooth is functional, root completion takes:

- 1-5 years for deciduous teeth

- 2-3 years for permanend teeth

• The biggest changes occur when functional occlusion is reached:

- Alveolar bone mineral density increases

- PDL fibers increase and organize into groups

- Attrition

- Abrasion

• This change will result in new cementum being formed

• Diphydont- will have two dentitions

• Primary teeth are smaller and less numerous

• Primary dentition only functions from approx 2-8 years of age

• Then the individual enters the mixed dentition stage

• The hardest tissue of the body

• Resists mastication forces

• Covers the anatomic crown

• Consists of interlocking rods- like a jigsaw puzzle

• Ameloblasts deposit enamel in a keyhole shape

• As ameloblasts migrate peripherally,take variable paths- producing bending of rods

• Amounts & location of space between rods determines enamel's hardness & density (caries susceptibility)

• Hardness also makes enamel brittle

• Enamel composition:

-96% inorganic; hydroxyapatite (calcium phosphate crystals), also found in varying amounts in bone, dentin & cementum

- 4% organic; water & enamelin protein

• Enamelin is found between rods; makes enamel semipermeable

• By itself, enamel is a translucent white to grayish- white

• Dentin below provides the yellow color

• Enamel is thinnest at the cervical margin

• It is thickest at the occlusal or incisal  area

• It takes 4 ameloblasts to form each rod

• The rod looks like a key-hole or racquet, with head & tail

• Each rod is filled with crystals

• The rod forms perpendicular to the DEJ

• Rods interlock with each other

• Rods are intertwined at cusp tips= gnarled enamel

• Rod sheath is more organic than rod core

• Each rod group bends at a different angle than adjacent group-provides strength to the enamel

• Hunter-Schreger Bands- extend 1/2 way through enamel, show up as light & dark band unpon light transmission

• Incremental lines- rhythmic daily deposition of enamel (also called lines or striae of Retzius)

• Externally appear as perikymata

• Like growth rings of a tree

• Develop as enamel matrix mineralizes

• Ameloblasts deposit 4µ/day

• Neonatal lines- an exaggerated line that forms in those teeth that are laying down anamel at the time of birth

• Enamel that forms before birth is whiter & has fewer defects

• Visible cracks on enamel surface

• Leaf-like defects makes teeth more cares susceptible 

• Can extend for various depths

Develop in two ways:

- Enamel formation (enamelin in spaces)

- During functional occlusion & exposure to cold

• Defective hypocalcified zones from rod bending

• Related to organic enamelin between different oriented groups 

• Tufts extend from DEJ; 10-20% distance toward enamel surface

• If caries reach tufts, there will be lateral spread

• Termination of dentinal tubules in enamel

• May even contain odontoblastic processes

• Dentin forms first, enamel calcifies around it

•Shorter than tufts, found singly or in groups

• May be smooth or ridged (perikymata)

• If present, perikymata are prominent in cervical area, & on facial surface

• Prismless enamel- formed without a rod, can extend 20-40µ into enamel surface

• Mostly found in cervical area & in primary teeth

•Of great clinical importance!!

• Allows for passage of:

- Fluid

- Bacteria

- Bacterial products

• These defects lend to permeation of enamel:

- Lameliae

- Microlamellae- spaces within rods

- Tufts

-Spindles

• 70% inorganic (hydroxyapatite- calcium, phosphate)

• 20% organic

• 10% water

• Dentin runs the length of the tooth

- Coronal dentin

-Radicular dentin

• Dentin includes:

-Primary dentin

-Secondary dentin

- Tertiary dentin

 • Forms the body (bulk) of the tooth

• Mantle dentin

- 1st primary dentin formed

- nearly defect free

- found at the DEJ

• Circumpupal dentin

- Under mantle dentin

- makes up bulk of primary dentin

• (Inter)globular dentin

- areas of hypocalcification

Describe secondary dentin

• Begins forming after tooth reaches functional occlusion

• Develops at much slower rate- so as not to obliterate the pulp

• Also called reparative dentin

• Forms in response to injury or trauma

- Attrition, abrasion, caries, restorative procedures

• Found only under stimulated areas

• Can sometimes resemble bone- osteodentin

• Most newly formed dentin, found at DPJ

• Two stages:

- Organic matrix layed down

- Inorganic mineral added

• Found in the pulp, at the DPJ

• Trails its process in the dentinal tubule

• 30K-50K tubules/sq. mm

• Tubules may be connected by canaliculi

(may contain processes)

• Microtubules given off by canaliculi

• Intratubular (peritubular) dentin

- Immediately surrounds tubule

- More calcified

• Intertubular dentin

- Dentinal matrix

Empty tubules from loss of odontoblastic process

• Primary dentin is formed in increments

• These lines are called:

- Incremental lines

- Imbrication lines

- Linesof Von Ebner

- Neonatel line occurs at time of birth

- Scalloped

- Might give off spindles

- Tubules are tapered in this region

• Connective Tisssue

• Blood Vessels

• Nerves

Cells

- Radicular pulp (root portion)

- Coronal pulp ( crown portion)

• Apex- contains apical foramen & accessory canals

Pulp has 2 zones.

• Central Zone

- Nerve & blood supply

- Fibroblasts

• Peripheral Zone ( Odontogenic Zone)

- Odontoblasts

- Cell-free zone

- Cell- rich zone

• Initiative

• Formative

• Protective

• Nutritive

• Reparative

• Soft connective tissue

• Vacular tissue

• Lymphatic tissue

• Nervous tissue

• 20 primary

• 32 permanent 

• Pulp is soft & gelatinous

• Molar pulp is 4X larger than incisor pulp 

• In crown

• Pulp horns extend into cusps

• Coronal pulp decreases with age

• In root

• Anterior teeth: Single pulp root

• Posterior teeth: Maybe multiple pulp roots

• Decreases with dentinogenesis

• Apical area decreases with cementogenesis

• Apical foramen- opening to periodontium

• Foramen varies 0.3-0.6mm

• Could be several foramina per root:

- Largest in apical foramen

- Others are accessory canals

• 33% of teeth have accessory canals

• Central Zone

- Large Veins, arteries

- Nerve trunks

- Fibroblasts

- Collagen fibers

- Intracellular matrix

• Peripheral Zone

- Odontoblasts

- Cell free zones ( zone of Weill, Weill's basal layer)

- Cell rich zone

• Mature odontoblast is columnar in shape

• Those of crown are larger than root

• More cuboidal in shape than root

• Constricts at predentin border- process enters tubule 

Describe fibroblastic cells

• Most abundant cells of pulp

• Young pulp: produces collagen fibers & ground substance of pulp

• Larger in youth

• Aging: Smaller, spindle-shaped, few organelles

• Schwann Cells- myelin sheath

• Endothelial cells- Line blood vessels

• Pericytes- Contractive, around capillaries

• Undifferentiated cells- progenitor cells

•Macrophages

• Lymphocytes

• Other blood cells

• Pulpal cells surrounded by collagen fibers in extracellular matrix

• 2 types of collagen in pulp:

- Type I- Produced by odontoblasts

- Type II- Produced by fibroblasts

• Young pulp has fewer fibers than mature

• Matrix around fibers- promote cell life

• Pulp is very vascular!

• External carotids to:

- Superior (maxillary) artery

- Inferior (mandibular) artery

• Vessel walls thin in pulp due to dentin protection

• Vessels give off peripheral branches

• In pulp:

- Blood pressure is high

- Blood flow is rapid 

• Intima- Inner lining, endothelial cells

• Media- Middle layer, muscle cells

• Adventitia- Outer layer, collagen fiber

• Tooth is vital only while foramen is open

• Can be blocked due to formation of:

- Dentin

- Cementum

• Single nerves found in anterior teeth

• Multiple nerves found in posterior teeth

• Mature pulp organ- nerve plexus is found in roof & lateral walls of coronal pulp

• Parietal neural plexus passes into odontogenic zone

• Found in odontogenic zone

• Function: pain reception

• Few found in odontoblasts of root

• Also in blood vessels of pulp (constrict)

• Pulp sensitive to:

- Temperature changes

- Electrical & chemical stimuli

- Pressure

• The closeness between nerve plexus & odontoblasts is significant!

• Terminals are far from pain reception area

• Direct innervation theory

• Transduction theory

• Hydrodynamic theory