DH227 Board Review Oral Histology & Embryology

DH227 Board Review Oral Histology & Embryology
Lisa Mayo, RDH, BSDH Concorde Career College

General Embryology 23 chromosomes in each germ cell (haploid)
46 chromosomes after fertilization (diploid) Zygote: mitotic divisions Morula Blastocele Blastocyst 3 periods of development Period of ovum (1st week) Embryonic Period (2-8 weeks): most congenital malformations occur 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 mesoderm Cartilage rod: 1st brachial arch Muscular component: 2nd, facial muscles Vasculature component Nerve component: 1st, trigeminal nerve Internal brachial arches – corresponding pharyngeal pouches that give rise to External auditory meatus Pharyngotympanic tube Palatine tonsils Parathyroid glands

5 Brachial Arches 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).

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? Bone
Nervous tissue Dentin and pulp Chewing muscles

Answer Which of the following tissues derive from ectoderm? Bone
Nervous tissue Dentin and pulp Chewing muscles

NBQ The first brachial arch gives rise to the mandible, and it innervated by the trigeminal nerve Both statement are TRUE Both statements are FALSE The first statement is TRUE, the second statement is FALSE 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 Lower lip Lower border of the cheeks Anterior portion of the hard palate Base of tongue Base of the nasal septum

Pharyngeal Grooves and Pharyngeal Pouches

Development of Pharyngeal Arches
Each arch is separated Internally by Pharyngeal pouches Externally 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. External auditory canal-ear canal Middle ear and Eustachian tube-air filled cavity Tympanic membrane-eardrum(vibrates in response to sound)

Pharyngeal Grooves & Pharyngeal Pouches
2’nd Pharyngeal Pouch Becomes Palatine Tonsils 3’rd Pharyngeal Pouch Becomes Parathyroid Glands Thymus 4’th Pharyngeal Pouch Becomes Ultimobranchial Body

Prenatal Development Pre-implantation: 1-7 days Embryonic: 2-8 weeks
Fetal: weeks Major developmental malformation occur in the embryonic period

NBQ The olfactory (nasal) pits appear on the lateral sides of these
Maxillary process Olfactory process Mandibular process Frontal process Globular process

Prenatal Development 3 primitive tissue precursors form
Ectoderm: Form outer covering of body. Lining of oral cavity. epithelium, salivary glands, nervous system, ameloblasts (enamel) Endoderm: Epithelial linings of internal organs: GI tract, resp system, urinary tract Mesoderm: connective tissues of skeletal, vascular, muscle, dermis, dental pulp, periodontal attachment, cementum, dentin

Derivatives of Ectoderm, Mesoderm, and Endoderm layers

Ectoderm 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

Mesoderm 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.

Endoderm 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.

Further development of GI tract

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

Neural 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? 2 weeks

NBQ A cleft lip occurs when maxillary process fails to fuse with the
Palatine process Globular process Lateral nasal process Mandibular process Opposing maxillary process

NBQ Palatal closure occurs during which week in embryonic development?
2 4 8-12 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 the
Second brachial arch Second and third brachial arches Frontal process and first brachial arch Frontal process and second brachial arch

Answer The embryological origin of the face is largely from the
Second brachial arch Second and third brachial arches Frontal process and first brachial arch 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? Tonsillar pillar Stenson’s duct Foramen ovale Foramen cecum

Answer Which structure marks the embryonic origin of the thyroid gland? Tonsillar pillar Stenson’s duct Foramen ovale Foramen cecum

NBQ What anatomic feature separates the root and the body of the tongue? The lingual frenum The fungifofrm papillae The median groove The third brachial arch The circumvallate papillae

NBQ Remnants of Hertwig’s epithelial root sheath sound in the PDL of a functional tooth are called: Enamel pearls Denticles Rests of Malassez Cementicles Intermediate plexus

HISTOLOGY

Histology Cells parts reviewed during A&P lecture Tissues Epithelium
Connective Tissue Muscle Nervous Tissue

Histology: Epithelium Tissues
Simple and stratified (layered) Named by cell shape Avascular Basement membrane separates from underlying connective tissue Review locations of different types Stratified squamous epithelium lines oral cavity

Histology: Connective Tissues
Collagen fibers Loose and dense Calcified and non-calcified Cartilage: hyaline remodels into bone Elastic is flexible Fibrous lines boney surfaces Bone: form skeletal system Blasts: build Clasts: consume Cytes: just hang around different hard CT

Histology: Muscle Tissues
Skeletal (voluntary) Smooth(GI and blood vessels) Cardiac (heart muscle)

Histology: Nervous Tissues
Ectodermal origin Central: brain and spinal cord Peripheral components Afferent (sensory) signals to CNS Efferent (motor) signals from CNS to muscle and glands Somatic system carries signals to voluntary muscles Autonomic 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 teens Enamel forms from ectoderm lining the sotmoduem Dentin/pulp form from ectomesenchyme (derived from embryonic ectoderm adjacent to the underlying mesenchymal tissue Each tooth is product of 2 tissues Mesenchymal: derived from neural crest cells Epithelium: oral epithelium derived from ectoderm

NBQ What type of primitive tissue gives rise to the enamel of a tooth?
Ectoderm Mesoderm Endoderm None of the above

NBQ The embryonic origin of all connective tissue is Epithelium
Mesenchyme Endoderm Fascia Ectoderm Epithelium

NBQ Rathke’s pouch if the embryonic origin of the Thyroid gland Palate
Globular process Pituitary gland 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 Initiation (Bud) stage Proliferation (Cap) Stage
Dental lamina (ectodermal thickening) grows into the underlying mesenchymal (conncective) tissue at 20 places to form the primary teetj 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 Differentiation (Bell) Stage
Enamel organ develops 4 distinct layers Outer enamel epithelium Stellate reticulum Stratum intermedium 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 surface Ectodermal origin from inner enamel epithelium Secreted by ameloblasts after dentin formation begins Inner and outer enamel epithelial areas combine to form the Reduced Enamel Epithelium as enamel formation is completed Hertwig’s root sheath forms REE combines with surface epithelium at eruption and cervical area becomes junctional epithelium Ameloblasts have disappeared as formative cells appear

Teeth: Dentin 70% mineralized
Composed of dentinal tubules extending from DEJ to pulp chamber Mesodermal origin and formed by odontoblasts (precedes enamel formation initially) Odontoblasts remain viable and capable of forming dentin after tooth formation is completed Primary dentition forms before completion of the root apex Secondary dentin forms after apex is completed Tertiary (reparative) dentin forms in response to injury or some irritations

Teeth: Dentin Peritubular dentin forms tubule walls
Intertubular dentin forms between tubules Outerdentinal layer nearest DEJ formed 1st and is called mantle dentin Cicrumpulpal dentin forms inner dentinal layer nearest pulp chamber Tubules narrow with age

NBQ The layer of dentin found adjacent to the pulp in young teeth is called Tome’s granular layer Predentin Interglobular dentin Dead tracts Sclerotic dentin

The last visible layer in Nonkeratinized stratified squamous epithelium is the
Basal cell layer Prickle cell layer Granular layer Corneum layer

NBQ Dentin is the product of Dental lamina Dental organ Dental papilla
Dental cuticle 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 fibers
Grp I: collagen fibers produced by cementoblasts, parallel to long axis of root Grp II: fibers from cells of dental sac, form fibers PDL Grp III (external): coarser than internal, Sharpey’s fibers

Teeth: Pulp Vascular tissue within pulp chamber
Contains connective tissue, nerves, blood vessels, odontoblasts at periphery Nerves only respond with pain to stimulation Derived from dental papilla

Pulp & Dentin Comparisons
Closely related developmentally and functionally Pulp = loose, non-calcified ct, vascular Dentin=calcified ct, avascular Development Odontobasts = form dentin Dental papilla = form pulp

Bone: Alveolar Formed during development & eruption of teeth
Located in boney crypts of jaw bone Same histology as other bones in body Anatomy 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
Stellate recticulum Junctional epithelium Inner enamel epithelium Outer enamel epithelium

Answer The cells that produce enamel derive from the
Stellate recticulum Junctional epithelium Inner enamel epithelium Outer enamel epithelium

Question Which of the following is a likely reaction to destruction of a focal area of odontoblasts by injury? New odontoblasts will differentiate from epithelial rests of Malassez New odontoblasts will form by division of vital odontoblasts adjacent to the zone of injury New odontoblasts will form by differentiation from cells in the cell rich layer of the pulp None of the above

Answer Which of the following is a likely reaction to destruction of a focal area of odontoblasts by injury? New odontoblasts will differentiate from epithelial rests of Malassez New odontoblasts will form by division of vital odontoblasts adjacent to the zone of injury New odontoblasts will form by differentiation from cells in the cell rich layer of the pulp None of the above

PDL Specialized form of ct Derived from dental sac
Made of fiber bundles Gingival: dentogingival, dentoperiosteal, transeptal, circumfrential Principal: alveolar crest, horizontal, oblique, apical, interradicular Fast turnover rate Fibrous 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 supply 2 types nerves 2 types nerve endings
Autonomic Afferent sensory 2 types nerve endings Free, un-myelinated 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 Lining mucosa contains more muscle fibers Masticatory mucosa contains glands Lining mucosa has no submucosa Lining mucosa is not keratinized

Anatomy of Gingiva Stratified squamous epithelium with a basement membrane between the epithelium and connective tissue Stratum corneum outside layer Keratinized=no nuclei, tough Attached Gingiva Non-Keratinized=have nuclei, more flexible, lining mucosa Sulcular & Junctional Epithelium

Anatomy of Gingiva No blood vessels
Nutrients from connective tissue vasculature Desmosomes connect epithelial cells to each other Hemidesmosomes connect epithelial cells to connective tissue Gingival Fibers: 9 groups based on orientation, insertions, structures, involved Gingival connective tissue Lots collagen matrix Few cells: fibroblasts, macrophages, lymphocytes, neutrophils

3 Gingival Epithelium Areas
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 inside Sulcular Epithelium Lining of gingival sulcus Nonkeratinized=allows for crevicular fluid in and out No Rete pegs, just smooth interface

3 Gingival Epithelium Areas
Junctional Epithelium Seals and protects Forms base of sulcus and attaches to tooth surface mm long Nonkeratinized Attached by hemidesmosomes to enamel or an implant surface in health, dentin or cementum in disease

Oral Epithelium Melanocytes Langerhans cells Merkle cells
Inflammatory cells Stratified squamous (3 types) Orthokeratinized Less common Cell layers: Basal (deepest), Prickle, Granular, Keratinized outer layer Nonkeratinized Cell layers: Basal, prickle, nonker. outer layer Parakeratinized: between #1&2 Cell layers: Basal, prickle, keratinized outer layers

Oral Epithelium Connective Tissues: Lamina Propria
Layers: Papillary & Reticular Submucosa: between lamina propria & muscles Interface 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? Second trimester Week 1-3 Weeks 6-11 Early in the 3rd trimester

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

DH227 Board Review Oral Histology & Embryology

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