Oral Histology and Embryology

___ is an extra tooth that develops

supernumerary

___ is a type of supernumerary tooth that develops in the midline of the upper jaw, between two central incisors

mesiodens

___ is an abnormally small tooth located between the maxillary central incisors and maxillary canine

peg lateral

___ staining is a permanent intrinsic discoloration of teeth caused by taking __ antibiotics during tooth development from 2nd trimester of pregnancy to age 8

tetracycline

ectodermal dysplasia

Prenatal Development

begins with the start of pregnancy and continues until birth

3 periods of prenatal development

1) Pre-Implantation

2) Embryonic

3) Fetal

Primordium

the earliest recognizable structure during the stages of development of an organ or tissue during the prenatal development *observed in the face, neck, and oral cavity

Congenital malformation

aka. developmental disturbance or an anomaly, can occur during 1st trimester (preimplantation + embryonic period)

Amniocentesis

an amniotic fluid test (AFT) that uses some amniotic fluid to detect chromosomal abnormalities late in pregnancy

Noninvasive prenatal testing (NIPT)

involves a simple blood draw, less risk, can be performed early in pregnancy to determine if there are any genetic abnormalities

Teratogens

Drugs (alcohol, tetracycline, etc), chemicals, infections (syphilis, herpes, rubella), radiation

Why should a dental professional understand embryonic development?

Must understand the development of an individual's orofacial region, including its sequential process to later understand any associated developmental disturbance present

Preimplantation Period

First week, involves the zygote (fertilized egg) turning into a blastocyst and becoming embedded in the endometrium

During fertilization, __ occurs which allows for the correct number of chromosomes

the final stages of meiosis (join the ovum's chromosomes with the sperm's chromosomes)

After fertilization, ___ occurs which transforms the zygote to a ____, which becomes a ____ after numerous cell divisions

mitosis; morula; blastocyst

By the end of the first week, the blastocyst travels through the fallopian tubes to undergo _, to become embedded in the endometrium

implantation

After a week of cleavage, the blastocyst consists of peripheral cells, the __ layer, and a small inner mass of embryonic cells called the __ layer

trophoblast; embryoblast

Down Syndrome (Trisomy 21)

extra chromosome on number 21 present after meiotic division (characterized by flat broad face, epicanthic folds, groover lower lip, tongue fissures, lingual papillae hypertrophy, arched palate, microdontia)

Embryonic Period

Weeks 2 to 8, involves the processes of induction, proliferation, differentiation, morphogenesis, and maturation. These processes allow the implanted blastocyst to develop into an embryo

The first developmental process involved during prenatal development is the process of __ which is __

induction; the action of one group of cells on another that leads to the establishment of the developmental pathway in the responding tissue

Proliferation

known as the dramatic process, is controlled levels of cellular growth which may be appositional, interstitial, or as a result of cellular byproducts

Appositional growth

tissue enlarges by the addition of layers on the outside of a structure. Hard tissue e.g. mature bone and hard dental tissue is appositional

Interstitial growth

occurs from deep within a tissue or organ. Soft tissue e.g. gingival tissue increases by interstitial growth

Differentiation

change in embryonic cells which start genetically identical, become distinct structurally and functionally to become specialized cells

Cytodifferentiation

development of different cell types

Histodifferentiation

development of different tissues

Morphodifferentiation

The development of the differing structure or shape or morphology for each organ or system

Morphogenesis

process of development of specific overall tissue structure or chape, occurs due to the migration or proliferation of embryonic cells which is followed by inductive interactions between those cells

Maturation

Begins during the embryonic period and continues during the fetal period; tissue types and organs become fully developed

Week 2

Increased number of embryonic cells form the embryonic cell layers or germ layers within blastocyst. Bilaminar disc forms from blastocyst and appears as a flattened circular plate

Bilaminar embryonic disc

Inner cell mass divided into two sheets: epiblast layer and hypoblast layer

Epiblast layer

-superior layer in bilaminar disc

-composed of high columnar cells

Hypoblast layer

-inferior layer in bilaminar disc

-composed of small cuboidal cells

Bilaminar embryonic disc

is suspended in the endometrium lining of the uterus between the amniotic cavity which faces the epiblast layer and yolk sac which faces the hypoblast layer

Week 3

The primitive steak forms within the bilaminar embryonic disc, which allows for bilateral symmetry.

Cells from epiblast layer migrate toward the hypoblast layer in area of primitive streak

Primitive streak

rod-shaped grooves thickening in the midline of the disc that results in an increased proliferation of cells

Migratory cells from the epiblast layer become located between the layers are thus considered _

mesoderm, an embryonic connective tissue now adjoining embryonic ectoderm (epiblast layer) and endoderm (hypoblast layer)

Trilaminar embryonic disc

is formed when three embryonic layers are present (ectoderm, mesoderm, endoderm)

Ectoderm

involved in formation of epidermis and the CNS

Mesoderm

involved in formation of connective tissue; such as, skin dermis, cartilage, bone, blood, muscle, tissue producing cells such as fibroblasts, chondroblasts, and osteoblasts

Endoderm

involved in formation of respiratory epithelium and cells of glands

Cephalic end

-the beginning of the GI tract of trilaminar disc

-the oropharyngeal membrane forms, consisting of only ectoderm and endoderm without any intermediate mesoderm

-this membrane is the future primitive mouth or stomodeum

Caudal end

tail end of trilaminar disc, cloacal membrane forms the ending of the GI tract

Third Week: CNS Development

First, specialized cells from ectoderm differentiate into neuroectoderm which are localized on the neural plate. Secondly, the neural plate thickens from growth and invaginates to form the neural groove. Near the end of the third week, the neural groove deepens further and is surrounded by neural folds.

Neural crest cells (NCCs)

cells developed from neuroectoderm which migrate from the crests of the neural folds and join the mesoderm to form mesenchyme

Mesenchyme

involved in development of many face and neck structures such as pharyngeal or brachial arches

Somites

mesoderm differentiates and begins to divide on each side of the neural tube into 38 paired cuboidal segments forming the somites

Somatomeres

mesoderm extends cranially from first somite alongside the neural tube in a series of seven paired condensations known as somatomeres

Somites and somatomeres are both involved in ____

development of most skeletal structures of the head, neck, and trunk and the associated striated muscles of the face, jaws, pharynx, and dermis of the dorsal skin

Fourth Week: CNS development

As further growth of the neuroectoderm occurs, the neural tube is formed by the neural folds undergoing fusion at the most superior part. The neural tube forms the future spinal cord and other neural tissues of CNS

Week 4: Cephalic embryonic folding

-The folding places developing tissue types into their correct positions for further embryonic development and produces a tubular embryo

-folding occurs at cephalic and caudal ends, and laterally

-forms future digestive tract

The tube formed by embryonic folding is separated into three major regions:

foregut, midgut, and hindgut

Foregut

anterior part of tub, which forms the primitive pharynx and includes part of the primitive yolk sac as it becomes enclosed with folding

Midgut and Hindgut

form the rest of the mature pharynx as well as the remainder of the digestive tract

Face and neck begin to develop in the ___ week

fourth

The __ period is considered the most critical period of prenatal development

embryonic

Ectodermal dysplasia

syndrome involving abnormal development of one or more ectodermal structures such as the teeth, skin, hair, nails, eyes, facial structure and glands

-may be partial or complete anodontia

Treacher Collins Syndrome

Mandibulofacial dysostosis develops in the embryo resulting in failure of certain orofacial development, presenting with downward slanting eyes, underdeveloped zygomatic bone, hearing loss/ abnormal or absent ears

-dental developmental disturbances anodontia, enamel dysplasia, micrognathia with small lower jaw

Treponema pallidum (syphilis)

produces dental developmental disturbances resulting in Hutchinson's incisor with a screwdriver shape and mulberry molar, as well as blindness, deafness, and paralysis if not treated

Fetal Alcohol Syndrome (FAS)

a group of alcohol-related birth defects that include physical and mental problems

oral changes such as crowding, mouth breathing, anterior open bite, and associated gingivitis may occur because of an increased finger sucking habit

Radiation during pregnancy

may injure embryonic cells resulting in cell death, chromosome injury, and delay of mental and physical growth

- xrays should not be given to pregnant women unless an emergency requiring it arrises

Fetal Period

Begins at 3 months and continues to the 9th month, embryo enlarges and becomes fetus, maturation of tissue and organs allow organs to begin to function

The fetal heartbeat and movements are present by __

the end of the fourth month