LISA MAYO, RDH, BSDHCONCORDE CAREER COLLEGE

DH227 Board ReviewOral Histology & Embryology

General Embryology

23 chromosomes in each germ cell (haploid)46 chromosomes after fertilization (diploid)Zygote: mitotic divisions

1. Morula2. Blastocele3. Blastocyst

3 periods of development1. Period of ovum (1st week)2. Embryonic Period (2-8 weeks): most congenital

malformations occur3. Fetal Period (3-9mo)

Gen Embryology

Facial & Oral structures dependent on grp of neural crest cells derived from ectoderm as neural tube develops Facial skeleton: Meckel’s cartilage Neck skeleton: hyoid bone Connective tissue components Tooth development

Gen Embryology

Neural crest cells migrate into each brachial arches and surrounds existing mesoderm1. Cartilage rod: 1st brachial arch2. Muscular component: 2nd, facial muscles3. Vasculature component4. Nerve component: 1st, trigeminal nerve

Internal brachial arches – corresponding pharyngeal pouches that give rise to1. External auditory meatus2. Pharyngotympanic tube3. Palatine tonsils4. Parathyroid glands

Five Pharyngeal (Branchial) arches develop below the oral pit

Each pharyngeal arch is associated with a specific Cranial Nerve 1st Pharyngeal Arch: Mandibular 2nd Pharyngeal Arch: Hyoid 3rd, 4th, and 5th Pharyngeal Arches are located

respectively below the other two arches and are separated down the middle by the pericardial cavity (heart).

5 Brachial Arches

Developing Pharyngeal Arches

3 ½ Weeks

Pharyngeal (Branchial) Arches

The cores of these arches will differentiate into the blood vessels, muscles, nerves, cartilages, and bones that will form the human face

Mandibular Arch: (1st Pharyngeal Arch)

Gives rise to the Maxillary Process which forms the cheeks

Eventually forms the: Mandible Muscles of Mastication

Innervated by V Cranial Nerve(Trigeminal Nerve)

Hyoid: 2nd Pharyngeal Arch)

Forms the: Facial muscles Vessels Hyoid bone

Innervated by the VII Cranial Nerve

(Facial Nerve)

3rd and 4th Pharyngeal Arches

Become the constrictor muscles of the throat

Innervated by other Cranial Nerves of the muscles of the neck

Question

Which of the following tissues derive from ectoderm?a. Boneb. Nervous tissuec. Dentin and pulpd. Chewing muscles

Answer

Which of the following tissues derive from ectoderm?a. Boneb. Nervous tissuec. Dentin and pulpd. Chewing muscles

NBQ

The first brachial arch gives rise to the mandible, and it innervated by the trigeminal nerve

a. Both statement are TRUEb. Both statements are FALSEc. The first statement is TRUE, the second

statement is FALSEd. The first statement is FALSE, the second

statement is TRUE

NBQ

The first brachial arch gives rise to the mandible, and it innervated by the trigeminal nerve

a. Both statement are TRUEb. Both statements are FALSEc. The first statement is TRUE, the second

statement is FALSEd. The first statement is FALSE, the second

statement is TRUE

NBQ

With the exception of the ____, the oral and nasal cavities develop from the first brachial arch and the frontal process

a. Lower lipb. Lower border of the cheeksc. Anterior portion of the hard palated. Base of tonguee. Base of the nasal septum

NBQ

With the exception of the ____, the oral and nasal cavities develop from the first brachial arch and the frontal process

a. Lower lipb. Lower border of the cheeksc. Anterior portion of the hard palated. Base of tonguee. Base of the nasal septum

Pharyngeal Grooves and

Pharyngeal Pouches

Development of Pharyngeal Arches

Each arch is separatedInternally by

Pharyngeal pouchesExternally by

Branchial clefts/grooves

Gill-like slits (pharyngeal arches) smooth to form Neck

Disappearing “Gills”

Tissues of the 2nd and 5th pharyngeal arches grow over the other arch grooves and make contact with each other

Pharyngeal Grooves & Pharyngeal Pouches

The 1st Pharyngeal Groove (covered by ectoderm) deepens to form the external auditory canal.

The 1st Pharyngeal pouch forms into the middle ear and Eustachian tube.

The membrane at the deepest part of this tube becomes the tympanic membrane.

2’nd Pharyngeal Pouch BecomesPalatine Tonsils

3’rd Pharyngeal Pouch BecomesParathyroid GlandsThymus

4’th Pharyngeal Pouch BecomesUltimobranchial Body

Pharyngeal Grooves & Pharyngeal Pouches

Prenatal Development

Pre-implantation: 1-7 days Embryonic: 2-8 weeksFetal: 9-38+ weeksMajor developmental malformation occur in

the embryonic period

NBQ

The olfactory (nasal) pits appear on the lateral sides of these

a. Maxillary processb. Olfactory processc. Mandibular processd. Frontal processe. Globular process

NBQ

The olfactory (nasal) pits appear on the lateral sides of these

a. Maxillary processb. Olfactory processc. Mandibular processd. Frontal processe. Globular process

Prenatal Development

3 primitive tissue precursors form1. Ectoderm: Form outer covering of body. Lining of

oral cavity. epithelium, salivary glands, nervous system, ameloblasts (enamel)

2. Endoderm: Epithelial linings of internal organs: GI tract, resp system, urinary tract

3. Mesoderm: connective tissues of skeletal, vascular, muscle, dermis, dental pulp, periodontal attachment, cementum, dentin

Derivatives of Ectoderm, Mesoderm, and Endoderm layers

The embryo is covered by a single layer of ectodermal cells which differentiate into multiple layers

Epidermal and dermal cells develop and differentiate into hair, teeth, nails and mammary, sebaceous, and salivary glands

Ectoderm

Medial somites in the mesoderm form the skeleton that will surround the neural tube.

Intermediate mesoderm forms the striated/voluntary muscle of the body.

Lateral mesoderm forms the dermis of the epithelium of the body and the GI tract. All peristaltic musculature is derived from mesoderm.

Mesoderm

The endoderm forms into the gastrointestinal tract, which elongates and develops “outpouchings” that form the pharyngeal pouches, lung buds, liver, gall bladder, pancreas, and urinary bladder.

Endoderm

Neural crest cells form the sensory system of the dorsal root ganglia of the cranial and spinal nerves

Ectoderm forms Neural Crest

Neural Tube Development: Week 3 - 9Neural Tube Development: Week 3 - 9

Closing of Neural Tube(3rd week of development)

Head and Neck Development

Folding of the embryo at 3-4 weeks forms a space (stomodeum) limited by a temporary barrier (oropharyngeal membrane). It will become the oral cavity

Pouches form called brachial arches FIRST MANDIBULAR ARCH: forms mandible, muscles

of mastication, nerve and blood supplies, Merkel’s cartilage which is the precursor of the mandible

SECOND ARCH (HYOID): forms facial muscles and vessels, hyoid bone

Head & Neck Development

Face forms week 4-7 w/ formation of stomodeum Tooth enamel forms from ectoderm lining the stomodeum

Upper Lip: complete within 6-8 weeks: Fusion of the median nasal process and RT/LF maxillary processes

Palate forms week 5-12 Failure of components to fuse during these periods results in cleft lip,

palate or both. Unilateral or bilateral Fusion of globular process with the LF/RT palatal shelves Separates the stomodeum into an upper (nasal) and lower (oral) cavity

Tongue forms weeks 4-8 Body from tuberculum impar and lateral tissues, and base from copula

form and fuse at the sulcus terminalis Post 1/3 and hyoid bone develops from the 2nd and 3rd brachial arches Know the nerve and blood supplies for the tongue, other oral soft tissues,

facial skeleton, teeth

NBQ

The buccopharyngeal membrane at what week in development?

a. 2 weeksb. 3 weeksc. 4 weeksd. 6 weeks

NBQ

The buccopharyngeal membrane at what week in development?

a. 2 weeksb. 3 weeksc. 4 weeksd. 6 weeks

NBQ

A cleft lip occurs when maxillary process fails to fuse with the

a. Palatine processb. Globular processc. Lateral nasal processd. Mandibular processe. Opposing maxillary process

NBQ

A cleft lip occurs when maxillary process fails to fuse with the

a. Palatine processb. Globular processc. Lateral nasal processd. Mandibular processe. Opposing maxillary process

NBQ

Palatal closure occurs during which week in embryonic development?

a. 2b. 4c. 8-12d. 16

NBQ

Palatal closure occurs during which week in embryonic development?

a. 2b. 4c. 8-12d. 16

Head & Neck

Most structures of oral cavity develop from 2 embryonic processes Frontal process

Forehead, frontal bone Median nasal process: center and tip nose, nasal septum,

globular process (philtrum, premaxillary palate) Lateral nasal process: sides of nose, infraorbital area

1st brachial arch Maxillary process: lateral palatine processes (palatal

shelves), upper parts of cheek, sides of upper lip Mand process: lower jaw, lower parts of the face and

lower lip, ant 2/3 of tongue

Salivary Glands

Major and minor, serous and mucous components, major from 1st brachial arch

PAROTID: Stenson’s duct, serous saliva, most common site for tumors

SUBMANDIBULAR: Wharton’s duct, serous mucous

SUBLINGUAL: anterior floor of mouth, mucous, several ducts along sublingual folds

Question

The embryological origin of the face is largely from thea. Second brachial archb. Second and third brachial archesc. Frontal process and first brachial archd. Frontal process and second brachial arch

Answer

The embryological origin of the face is largely from thea. Second brachial archb. Second and third brachial archesc. Frontal process and first brachial archd. Frontal process and second brachial arch

Tongue Development

Pharyngeal Arches:1st forms the anterior (moveable)2nd , 3rd forms the immovable base

The tongue is innervated by the V, VII, IX, X, and XII Cranial nerves for various functions.

Tissues of the Tongue

3 Parts: Tuberculum impar (central) Both lateral lingual swellings (sides)

As they grow, a U-shaped sulcus forms around the anterior of the tongue to separate it from the jaw tissues

This allows free movement of the anterior tongue

The 3 parts fuse completely to form the tongue body

Tongue formation: 1st Pharyngeal Arch

Tongue Development

The body and the base of the tongue are separated by the terminal sulcus

Behind the terminal sulcus the lingual tonsil develops from the base on the dorsal side

Waldeyer’s Ring: (ring of tonsils in pharynx) Lingual tonsil Palatine tonsils Pharyngeal tonsils

Body and Base of the Tongue

Lateral lingual swellings and tuberculum impar have completely merged and fused to form the body and base of the tongue.

Question

What is the origin of “Rests of Malassez”? Junctional epithelium Reduced enamel epithelium Hertwig’s epithelial root sheath Cementoblasts in the PDL

Answer

What is the origin of “Rests of Malassez”? Junctional epithelium Reduced enamel epithelium Hertwig’s epithelial root sheath Cementoblasts in the PDL

Question

Rests of Malassez are composed of Calcified PDL Calcifications n the dental pulp Groups of epithelial cells attached t the enamel Groups of epithelial cells in the PDL

Answer

Rests of Malassez are composed of Calcified PDL Calcifications n the dental pulp Groups of epithelial cells attached t the enamel Groups of epithelial cells in the PDL

Question

Which structure marks the embryonic origin of the thyroid gland?a. Tonsillar pillarb. Stenson’s ductc. Foramen ovaled. Foramen cecum

Answer

Which structure marks the embryonic origin of the thyroid gland?a. Tonsillar pillarb. Stenson’s ductc. Foramen ovaled. Foramen cecum

NBQ

What anatomic feature separates the root and the body of the tongue?

a. The lingual frenumb. The fungifofrm papillaec. The median grooved. The third brachial arche. The circumvallate papillae

NBQ

What anatomic feature separates the root and the body of the tongue?

a. The lingual frenumb. The fungifofrm papillaec. The median grooved. The third brachial arche. The circumvallate papillae

NBQ

Remnants of Hertwig’s epithelial root sheath sound in the PDL of a functional tooth are called:

a. Enamel pearlsb. Denticlesc. Rests of Malassezd. Cementiclese. Intermediate plexus

NBQ

Remnants of Hertwig’s epithelial root sheath sound in the PDL of a functional tooth are called:

a. Enamel pearlsb. Denticlesc. Rests of Malassezd. Cementiclese. Intermediate plexus

HISTOLOGY

Histology

Cells parts reviewed during A&P lectureTissues

Epithelium Connective Tissue Muscle Nervous Tissue

Histology: Epithelium Tissues

Simple and stratified (layered)Named by cell shapeAvascularBasement membrane separates from

underlying connective tissueReview locations of different typesStratified squamous epithelium lines oral

cavity

Histology: Connective Tissues

Collagen fibersLoose and denseCalcified and non-calcifiedCartilage: hyaline remodels into boneElastic is flexibleFibrous lines boney surfacesBone: form skeletal systemBlasts: buildClasts: consumeCytes: just hang around different hard CT

Histology: Muscle Tissues

Skeletal (voluntary)Smooth(GI and blood vessels)Cardiac (heart muscle)

Histology: Nervous Tissues

Ectodermal originCentral: brain and spinal cordPeripheral componentsAfferent (sensory) signals to CNSEfferent (motor) signals from CNS to muscle and

glandsSomatic system carries signals to voluntary musclesAutonomic system carries signals from CNS to

involuntary muscles and glands Sympathetic: causes activity, fight-or-flight Parasympathetic: maintain status quo, decrease activity

Tooth Development

Begins 7th weeks of embryonic life with 20 primary teeth

Continue development until late teensEnamel forms from ectoderm lining the

sotmoduemDentin/pulp form from ectomesenchyme

(derived from embryonic ectoderm adjacent to the underlying mesenchymal tissue

Each tooth is product of 2 tissues 1. Mesenchymal: derived from neural crest cells2. Epithelium: oral epithelium derived from ectoderm

NBQ

What type of primitive tissue gives rise to the enamel of a tooth?

a. Ectodermb. Mesodermc. Endodermd. None of the above

NBQ

What type of primitive tissue gives rise to the enamel of a tooth?

a. Ectodermb. Mesodermc. Endodermd. None of the above

NBQ

The embryonic origin of all connective tissue is

a. Mesenchymeb. Endodermc. Fasciad. Ectoderm

e. Epithelium

NBQ

The embryonic origin of all connective tissue is

a. Mesenchymeb. Endodermc. Fasciad. Ectoderm

e. Epithelium

NBQ

Rathke’s pouch if the embryonic origin of thea. Thyroid glandb. Palatec. Globular processd. Pituitary glande. Nasal septum

NBQ

Rathke’s pouch if the embryonic origin of thea. Thyroid glandb. Palatec. Globular processd. Pituitary glande. Nasal septum

Tooth Development: 2 Events

Morphodifferentiation Shaping of teeth Stages: Bud, Cap, Bell, Apposition

Cytodifferentiation Epithelial

Outer Inner Stratum Stellate reticulum

Mesenchymal Dental sac: alveolar bone, PDL, Cementum Dental papilla: odontoblasts Pulp

Tooth Development

1. Initiation (Bud) stage Dental lamina (ectodermal thickening) grows into the

underlying mesenchymal (conncective) tissue at 20 places to form the primary teetj

2. Proliferation (Cap) Stage Enamel organ develops from the dental lamina, and

will produce enamel Dental papilla arises and produces pulp/dentin The dental sac surrounds the developing tooth, and

becomes cementum, the PDL and alveolar bone

Tooth Development

3. Differentiation (Bell) Stage Enamel organ develops 4 distinct layers

1) Outer enamel epithelium 2) Stellate reticulum3) Stratum intermedium4) Inner enamel epithelium: becomes enamel.

IEE becomes amelobasts which produce enamel, odontoblasts from the dental papillae produce dentin

Tooth Development

Tooth structure is produced layer by layer (appositional growth)

Tooth matrix is initially soft, then mineralizes (hydroxyapatite is crystalized calcium phosphate)

Root formation begins after the crown if complete, and ends 1-4yrs after eruption

Enamel organ layers condense to form the reduced enamel epithelium

Hertwig’s epithelial root sheath (HERS), which develops from the internal and external enamel epithelium, helps determine outline of the root and dissolves

Remnants of HERS (knows as rests of Malassez) have the potential to form cysts

Remnants of the dental lamina are known as Rests of Serres

Teeth: Enamel

96% mineralized (hydroxyapatite)Composed of enamel rods perpendicular to surfaceEctodermal origin from inner enamel epitheliumSecreted by ameloblasts after dentin formation

beginsInner and outer enamel epithelial areas combine to

form the Reduced Enamel Epithelium as enamel formation is completed

Hertwig’s root sheath formsREE combines with surface epithelium at eruption

and cervical area becomes junctional epitheliumAmeloblasts have disappeared as formative cells

appear

Teeth: Dentin

70% mineralized Composed of dentinal tubules extending from DEJ to

pulp chamberMesodermal origin and formed by odontoblasts

(precedes enamel formation initially) Odontoblasts remain viable and capable of forming

dentin after tooth formation is completedPrimary dentition forms before completion of the root

apexSecondary dentin forms after apex is completedTertiary (reparative) dentin forms in response to

injury or some irritations

Teeth: Dentin

Peritubular dentin forms tubule wallsIntertubular dentin forms between tubulesOuterdentinal layer nearest DEJ formed 1st and is

called mantle dentinCicrumpulpal dentin forms inner dentinal layer

nearest pulp chamberTubules narrow with age

NBQ

The layer of dentin found adjacent to the pulp in young teeth is called

a. Tome’s granular layerb. Predentinc. Interglobular dentind. Dead tractse. Sclerotic dentin

NBQ

The layer of dentin found adjacent to the pulp in young teeth is called

a. Tome’s granular layerb. Predentinc. Interglobular dentind. Dead tractse. Sclerotic dentin

The last visible layer in Nonkeratinized stratified squamous epithelium is the

a. Basal cell layerb. Prickle cell layerc. Granular layerd. Corneum layer

The last visible layer in Nonkeratinized stratified squamous epithelium is the

a. Basal cell layerb. Prickle cell layerc. Granular layerd. Corneum layer

NBQ

Dentin is the product ofa. Dental laminab. Dental organc. Dental papillad. Dental cuticlee. Dental sac

NBQ

Dentin is the product ofa. Dental laminab. Dental organc. Dental papillad. Dental cuticlee. Dental sac

Teeth: Cementum

Cementicles Calcified ovoid or round nodule found in the PDL May be found in grps or near the surface of the

cementum More prevalent along the root in an aging person May be found at the site of trauma

Teeth: Cementum

Mature Cementum: 3 grps fibers1. Grp I: collagen fibers produced by

cementoblasts, parallel to long axis of root

2. Grp II: fibers from cells of dental sac, form fibers PDL

3. Grp III (external): coarser than internal, Sharpey’s fibers

Teeth: Pulp

Vascular tissue within pulp chamberContains connective tissue, nerves, blood

vessels, odontoblasts at peripheryNerves only respond with pain to stimulationDerived from dental papilla

Pulp & Dentin Comparisons

Closely related developmentally and functionally

Pulp = loose, non-calcified ct, vascularDentin=calcified ct, avascularDevelopment

Odontobasts = form dentin Dental papilla = form pulp

Bone: Alveolar

Formed during development & eruption of teeth

Located in boney crypts of jaw boneSame histology as other bones in bodyAnatomy

Each tooth in own alveolus (socket), inner cortical plate, spongiosa

Each socket has 3 parts: Outer cortical plate Alveolar bone proper: part of bone facing root of

tooth, follows outline of roots, sometimes called cribiform plate/lamina dura

Question

The cells that produce enamel derive from the

a. Stellate recticulumb. Junctional epitheliumc. Inner enamel epitheliumd. Outer enamel epithelium

Answer

The cells that produce enamel derive from the

a. Stellate recticulumb. Junctional epitheliumc. Inner enamel epitheliumd. Outer enamel epithelium

Question

Which of the following is a likely reaction to destruction of a focal area of odontoblasts by injury?

a. New odontoblasts will differentiate from epithelial rests of Malassez

b. New odontoblasts will form by division of vital odontoblasts adjacent to the zone of injury

c. New odontoblasts will form by differentiation from cells in the cell rich layer of the pulp

d. None of the above

Answer

Which of the following is a likely reaction to destruction of a focal area of odontoblasts by injury?

a. New odontoblasts will differentiate from epithelial rests of Malassez

b. New odontoblasts will form by division of vital odontoblasts adjacent to the zone of injury

c. New odontoblasts will form by differentiation from cells in the cell rich layer of the pulp

d. None of the above

PDL

Specialized form of ctDerived from dental sacMade of fiber bundles

1. Gingival: dentogingival, dentoperiosteal, transeptal, circumfrential

2. Principal: alveolar crest, horizontal, oblique, apical, interradicular

Fast turnover rateFibrous Matrix

Fibers are collagen & oxytalan with few elastic fibers assoc with blood vessels

Sharepy’s Fibers: terminal portion of PDL that is embedded in bone

PDL

Rich blood supply2 types nerves

1. Autonomic2. Afferent sensory

2 types nerve endings1. Free, un-myelinated2. Encapsulated

Width varies Wider in younger adults than older Greater near cervical/apical areas Greatest movements occur apical/cervical Related to amt of function

Oral Mucosa

Composed of stratified squamous epithelial layer and a ct lamina propria, separated by a basement membrane

It includes the masticatory, lining, and specialized mucosal tissues

Masticatory mucosal tissue is keratinized and protects the gingiva and hard palate. The keratinization of the attached gingiva ends at the free gingival margin

Lining mucosa is not keratinized and includes the alveolar, vestibular and buccal mucosa, floor of the mouth

Specialized mucosa refers to the papillae of the tongue

NBQ

In the oral cavity, one way in which lining mucosa differs from masticatory mucosa is that

a. Lining mucosa contains more muscle fibersb. Masticatory mucosa contains glandsc. Lining mucosa has no submucosa

d. Lining mucosa is not keratinized

NBQ

In the oral cavity, one way in which lining mucosa differs from masticatory mucosa is that

a. Lining mucosa contains more muscle fibersb. Masticatory mucosa contains glandsc. Lining mucosa has no submucosa

d. Lining mucosa is not keratinized

Anatomy of Gingiva

Stratified squamous epithelium with a basement membrane between the epithelium and connective tissue

Stratum corneum outside layerKeratinized=no nuclei, tough

Attached GingivaNon-Keratinized=have nuclei, more flexible,

lining mucosa Sulcular & Junctional Epithelium

Anatomy of Gingiva

No blood vesselsNutrients from connective tissue vasculatureDesmosomes connect epithelial cells to each otherHemidesmosomes connect epithelial cells to

connective tissueGingival Fibers: 9 groups based on orientation,

insertions, structures, involvedGingival connective tissue

Lots collagen matrix Few cells: fibroblasts, macrophages, lymphocytes,

neutrophils

3 Gingival Epithelium Areas

1. Oral Epithelium Outer surface of free and attached gingiva

from gingival margin to mucogingival junction

Keratinized or partially keratinized Orthokeratinized= thicker granular layer

Rete pegs connect to connective tissue inside2. Sulcular Epithelium

Lining of gingival sulcus Nonkeratinized=allows for crevicular fluid in

and out No Rete pegs, just smooth interface

3 Gingival Epithelium Areas

3. Junctional Epithelium Seals and protects Forms base of sulcus and attaches to tooth

surface 0.75-1.35mm long Nonkeratinized Attached by hemidesmosomes to enamel or an

implant surface in health, dentin or cementum in disease

Oral Epithelium

MelanocytesLangerhans cellsMerkle cellsInflammatory cellsStratified squamous (3 types)

1. Orthokeratinizeda. Less commonb. Cell layers: Basal (deepest), Prickle, Granular, Keratinized

outer layer

2. Nonkeratinizeda. Cell layers: Basal, prickle, nonker. outer layer

3. Parakeratinized: between #1&2a. Cell layers: Basal, prickle, keratinized outer layers

Oral Epithelium

Connective Tissues: Lamina Propria Layers: Papillary & Reticular

Submucosa: between lamina propria & musclesInterface

Area between oral epithelium & ct Rete Pegs: epithelial extension into lamina propria

Basement Membrane 2 layers: Basal lamina (densa) & Reticular lamina

(lucida) Epithelial cells for hemidesmosome attachments to basal

lamina

Question

Where are Von Ebner’s glands located? In submucosa of the pharynx In the submucosa of the cheek Beneath the floor of the mouth Beneath circumvallate papillae in the tongue

Answer

Where are Von Ebner’s glands located? In submucosa of the pharynx In the submucosa of the cheek Beneath the floor of the mouth Beneath circumvallate papillae in the tongue

Question

During which time of fetal development will cleft palate form?a. Second trimesterb. Week 1-3c. Weeks 6-11d. Early in the 3rd trimester

Answer

During which time of fetal development will cleft palate form?a. Second trimesterb. Week 1-3c. Weeks 6-11d. Early in the 3rd trimester