oral anatomy and embryology EXAM 2

chapters 3, 4, 5, 6, 12, 13, and 14

embryology

the study of prenatal development

primordium

earliest recognizable structure during stages of development of organ or tissue during prenatal development

karotype

oraganized profile of an individual’s chromosomes

phenotype

an observable characteristic or trait (thin/thick gingival phenotype)

endometrium

innermost lining of the uterus on its posterior wall

trophoblast layer

layer of peripheral cells — involved in forming prenatal support tissue

embryoblast layer

small inner mass of embryonic cells — involved in forming embryo during embryonic period

stomodeum

promotive mouth of future embryo, beginning of digestive tract

preimplantation period

1st week after fertilization (females ovum penetrated by and united with males sperm which then forms the zygote (fertilized egg))

second week of prenatal development during the embryonic period

• blastocyst has been implanted (trophoblast and embryoblast layers)

• proliferation, differentiation, and morphogenesis are all occuring

• embryonic cell layers form within blastocyst

• bilaminar embryonic disc has 2 layers:

  • superior epiblast layer - composed of high columnar cells

  • inferior hypoblast layer - composed of small cuboidal cells

third week of prenatal development during the embryonic period

• primitive streak is formed and mesoderm is created between epiblast layer and endoderm

• bilaminar disc becomes trilaminar disc

• top of epiblast layer becomes ectoderm —> skin epidermis, central nervous system and other structures

• mesoderm is created between endoderm and ectoderm —> formation of connective tissue like cartilage, bone, blood, and muscle

• bottom of epiblast layer becomes endoderm

• head (cephalic end) and tail (caudal end) are not visible

fourth week of prenatal development during the embryonic period

• trilaminar disc undergoes cephalic embryonic folding — places tissues into correct position/location for further development

• endoderm ends up inside ectoderm with mesoderm between most areas — creates a tubular embryo

• inner tube is lined by endoderm

• tube divides into:

  • foregut - anterior portion of tube-forms primitive throat

  • midgut and hindgut - eventually develops into the rest of the digestive system

• face and neck begin to develop and primitive eyes, ears, nose, oral cavity, jaw areas become present

main events that occur during neck development

• neck development begins 4th week and completed during fetal period

• neck forms from primitive pharynx and pharyngeal apparatus

• primitive pharynx formed by hollow tube of embryo derived from anterior part of foregut

cleft palate

failure of fusion of palatal shelves with primary palate and/or with each other

cleft uvula

least complicated type of cleft palate

palatal development

• starts 5th week of development — formed from the primary palate and secondary palate

• begins as intermaxillary segment — formed as result of fusion of 2 medial nasal processes internally within embryo

  • primary palate forms from this moving posteriorly, stopping where incisive foramen will be

• secondary palate forms 6th week of prenatal development — will form posterior 2/3 of hard palate, soft palate, uvula, and contain maxillary canines and premolars

• palate completion - primary and secondary palates fuse

• final palate includes hard and soft palate and separates nasal cavity from oral cavity and process is completed by 12th week

main events that occur during nasal cavity and nasal septum development

• nasal cavity and septum begin forming at same time as palate (5th to 12th week)

• tissues that form nasal septum grow inferiorly and deep to the median nasal proccesses

main events that occur during tongue development

• tongue develops 4th-8th week

• body of tongue - develops from 1st pharyngeal arch

  • begins with proliferation in 1st pharyngeal arch forming tuberculum impar

  • 2 lateral lingual swellings form and fuse together forming the body of the tongue

• base of tongue - develops from 2nd, 3rd, and 4th pharyngeal arches

  • 1st swelling - copula - forms between 2nd and 3rd pharyngeal arch

  • 2nd swelling - hypopharyngeal eminence - forms from the 3rd pharyngeal arch, overgrows copula — eventually forms mature base of tongue

  • 3rd welling - epiglottic swelling — forms from the 4th pharyngeal arch, forms the epiglottis

• lingual papilla begins to appear 8th week

odontogenesis

process of tooth development

dentition

natural teeth in jaws

primary dentition

20 teeth, develop during embryonic and fetal periods

permanent dentition

32 teeth, develop mostly during fetal period

adontia (hypodontia)

absence of a tooth or teeth — caused by a failure of induction within dental lamina at this stage

supernumerary teeth (hyperdontia)

development of 1 or more extra teeth — caused by extra teeth being initiated

microdontia

atypical finding of small tooth — peg laterals or peg molars

macrodontia

atypical finding of large teeth — caused by disturbance in proliferation process

enamel organ

leads to enamel

dental papilla

leads to dentin and pulp

dental sac

leads to periodontium (cementum, periodontal ligament, alveolar process)

enamel knot

will form first cusp and signal formation of secondary enamel knots

dens en dente

enamel organ may mistakenly undergo invagination by growth into dental papilla — tooth within a tooth

gemination

single tooth germ tries to divide into 2 tooth germs — 1 pulp, 1 root, but 2 crowns

fusion

union of 2 adjacent tooth germs during cap stage — 2 separate and distinct pulp cavities and united enamel, dentin, and pulp

tubercles

small round enamel extensions forming extra cusp — could be from enamel knots or enamel organ

outer enamel epithelium (OEE)

serves as protective barrier and nutritional supply for rest of enamel organ during enamel production

inner enamel epithelium (IEE)

differentiate by phases into ameloblasts (enamel-secreting cells)

dental core

area between OEE and IEE that supports future enamel matrix production — contains stellate reticulum (star shaped cells) and stratum intermedium (flat cuboidal cells)

enamel hypoplasia

caused by reduction in QUANTITY of enamel matrix production

enamel hypocalcification

caused by reduction in QUALITY of enamel matrix production — teeth appear more opaque, yellower, or browner within because of intrinsic staining of enamel

amelogenesis imperfecta

abnormal formation of dentin — because of lack of supportive structure, enamel is weaker, more brittle

cervical loop

most cervical part of the enamel organ — responsible for root development

hertig epithelial root sheath (HERS)

determines the number of roots and all the characteristics of them like size and shape

cementogenesis

appositional growth of cementum in the root area

cementoblasts

at dentin areas producing cementoid (cementum matrix)

cementocytes

mature cementoblasts that have become embedded in cementum they produced

dentinocemental junction (DCJ)

junction between dentin and cementum formed during root formation

concrescence

excessive cementum produced causing 2 or more teeth to be joined by the cementum only

taurodontism

teeth that have larger pulp chambers

enamel pearl

misplaced ameloblasts migrate to root surface causing enamel to grown on cemental root surface — pretty common and visible during x-rays

dilaceration

either distorted roots or severe associated crown angulation in formed tooth

periodontal ligament (PDL)

fibrous joint that anchors the root of the tooth to the alveolar bone socket

alveolar process

tooth-bearing part of each jaw containing alveoli

sharpey’s fibers

ends of these collagen fibers that insert into cementum and alveolar bone

reduced enamel epithelium (REE)

layers of enamel organ become compressed

osteoclasts

cells that resorb or breakdown bone

fibroclasts

cells that resorb or breakdown collagen fibers

odontoclasts

cells that resorb or breakdown dentin and cementum

stages of tooth development

initiation, bud, cap, bell

initiation stage of tooth development

odontogenesis of primary dentition begins 6-7th week of development; oral epithelium consists of 2 horseshoe-shaped bands of tissue (1 for each future arch) and is induced to produce a dental lamina

bud stage of tooth development

8th week of development for primary dentition; extensive proliferation is occurring at site of each dental placode creating oval masses (buds) — 10 buds on each arch and each bud develops into a tooth germ

cap stage of tooth development

9-10th week of development — morphogenesis is the main process at this stage — earliest forms of tooth tissues form; primordium of tooth forms at this stage

bell stage of tooth development

11-12th week of development for primary dentition; process of proliferation, differentiation, morphogenesis are ongoing — outer cells of dental papilla become odontoblasts and central cells of dental papilla become primordium of pulp

process of root development

• occurs long after crown development and beginning of eruption

• cervical loops grows deeper into dental sac, elongating and moving away from crown forming heritage epithelial root sheath (HERS)

• dental papilla cells are induced to become odontoblasts which then begin producing predentin

• HERS disintegrate allowing undifferentiated cells in dental sac to contact dentin induced those cells to become cementoblasts

periodontal ligament and alveolar process development

dental sac cells have differentiated into: collagen fibers to form PDL and osteoblasts to form alveoli (alveolar process forming tooth sockets)

events that occur during tooth eruption

• eruption occurs in chronological order in both dentitions

• formation of REE indicates primary tooth is ready to begin eruption

• active eruption begins where enzymes are related from REE and the REE fuses with oral epithelium for oral epithelium begins to disintegrate

• then coronal fused epithelial tissue peels back from crown, leaving primary junctional epithelium

• when root formation is complete, primary JE is replaced by definitive JE

amelogenesis

enamel production

dental fluorosis

hypo mineralization due to excessive systemic fluoride levels

neonatal line

line of retizus that marks trauma to ameloblasts at time of birth

attrition

wear due to tooth to tooth contact, seen as wear facets (grinding)

abrasion

wear due to friction (toothbrushing)

abfraction

flexing of tooth structure due to compressive and tensile forces causes enamel to chip away from dentin beginning at cervical area (clenching)

erosion

wear due to chemical acids not involving cariogenic bacteria (bulimia and sucking on acidic foods like lemons)

caries

breakdown of enamel due to cariogenic bacteria that causes demineralization eventually leading to a cavitated lesion

enamel properties

• hardest material tissue in the body — 96% inorganic or mineralized material and 1% organic material and 3% water

• mature enamel consists of mostly calcium hydroxyapatite

• protects tooth from physical, thermal, and chemical forces — can withstand 20-30 lbs of pressure per tooth

enamel production

• ameloblasts secrete initial enamel matrix through Tomes Process

• initial enamel matrix made up of proteins, carbohydrates, and only small amount of calcium hydroxyapatite crystals

• begins on masticatory surface of future crown (incisal or occlusal) — appositional growth continues, forming DEJ, moving cervical to CEJ

• process of enamel completing mineralization from initial enamel matrix (30%) to full mineralization level (96%)

histology of enamel

• enamel rod (enamel prism) - crystalline structural unit of enamel — each rod is made up of ribbons of crystals and lie perpendicular to denitn

• lines of Retzius - incremental lines that seen to transverse the enamel rods — associated with imbrication lines (raised bumps) and perikymata (grooves)

systemic remineralization

water fluoridation, supplements — impact teeth that are going to erupt

topical remineralization

water fluoridation, dental fluoride treatment — impact only erupted teeth

globular dentin

areas where both primary and secondary mineralization have occurred — more mineralized = harder

interglobular dentin

areas where only primary mineralization has occurred — less mineralized = softer

dentinal tubules

long tubes in dentin that extend from DEJ in crown area or DCJ in root area to outer wall of the pulp = only sensation is to pain / not to cold or heat just pain

what do dentinal tubules contain

cell bodies of odontoblasts that remain in the pulp after maturation and odontoblastic processes

resorption

inflammation and loss of dentin structure within the tooth

internal resorption

resorption starting from the inside out

external resorption

resorption starts from the outside

dentin hypersensitivity

exposed dentin tubules lead to pain sensation

dentin-pulp complex

not clinically visible if tooth and supporting periodontium are health

• dentin = 70% inorganic or mineralized material, 20% organic material, 10% water

mature dentin consists of mostly calcium hydroxyapatite and determines tooth shade

dentinoenamel junction (DEJ)

junction between dentin and enamel tissues — formed by the contact of predentin and the enamel matrix

dentinogenesis

production of dentin, begins before production of enamel

apposition and maturation of dentin

• odontoblasts begin appositional growth of predentin (dental matrix)

• ameloblasts are lost after eruption

• odontoblasts are not and will continue to produce dentin

• mineralization of predentin begins shortly after appositional growth and occurs in 2 phases

primary mineralization

calcium hydroxyapatite crystals forms as globules in predentin

secondary mineralization

another layer of crystals form, layered on the first, but don’t fuse everywhere

peritubular dentin

dentin that creates a wall around dentinal the tubule — highly mineralized after dentin maturation

intertubular dentin

dentin found between tubules — high level of mineralization

mantel dentin

first predentin produced found along dentinoenamel junction (DEJ) below enamel — creates CEJ

circumpulpal dentin

forms deep to mantle dentin and surrounds pulp, making up most of the dentin in the tooth — produces and matures after mantle dentin

primary dentin

produced within the tooth BEFORE completion of apical foramen of the root — most dentin is produced during this time

secondary dentin

formed AFTER completion of apical foramen — continues to be produced throughout life of the tooth and produced more slowly than primary dentin

tertiary dentin

forms in response to localized injury to exposed dentin, produced quickly in local regions

reactionary tertiary dentin

produced by existing odontoblasts