Ch 18 (dental anatomy/embryology

Embryologic Stages

1. Period of ovum 2. Period of embryo 3. Period of fetus

Period of the ovum

fertilization to 2 weeks

Period of embryo

weeks 3-8 of gestation

Period of fetus

weeks 9-36 gestation

By the time the embryo is 3 weeks old it's length measures approximately—-

3 to 4 mm - from the top of the head to the tail

Pharyngeal arches

three ridges of tissue bulge laterally from the throat area that develop into a number of structures "U" shaped bars of tissue

The open end of the "U" faces posteriorly and surrounds the upper end of the ___

foregut and part of the primitive oral cavity

The fifth arch (of the pharyngeal arches) will ___

degenerate and form nothing of any consequence

The fourth sixth arch (of the pharyngeal arches) are ___

poorly developed and are not readily seen on the emryonic surface

The ones closest to the head are the largest and those farther down are

smaller in size (tail is smaller than head)

The longitudinal section through the embryo of the pharyngeal arches is divided into ___

halves

The body is relatively hollow with the exception of a tube closed at its upper and lower ends and running through the middle of the body cavity, the lining of which developed from—

the endoderm

Foregut

Upper part ; digestive tube from the throat region to the duodenum

Midgut

Middle ; *rest of small intestines as well as the cecum, ascending colon, and most of the transverse colon

Hindgut

Lower ; *descending colon, sigmoid colon, and rectum of large intestine

Where the foregut region and the stomodeum share a common wall found in the location that will become the region between palatine tonsils and an area about 2/3 of the way back from the tip of the tongue

buccopharyngeal membrane

When the buccopharyngeal membrane breaks down at about 4 1/2 weeks?

the connection between the oral cavity and the digestive tract are established

frontal prominence

in the anterior (frontal) view of a 3 week embryo ; forehead area the stomodeum (primitive oral cavity) & the mandibular processes of the mandibular arch

During the ___ embryonic week some changes can be seen

4th

First two small depressions from low on the frontal prominence ; these are the

nasal pits, the beginning of the nasal cavities

The areas on either side of these nasal pits begin to form a ridge and become the

medial nasal process and the lateral nasal process

By the 6th week two medial nasal processes have fused together and along with the two maxillary process, have formed the

upper lip

The lateral nasal process takes no part in forming the upper lip. It gets pushed up and out of the way. True or False?

True

Also at about 6 weeks the nasal pits deepen until they open into the

primitive oral cavity

Mandibular symphysis

formed by the fusion of the mandibular processes at about the seventh week

The ___ and ___ begin to fuse at their lower end and that connection then starts to form perforations in it.

medial nasal ; maxillary processes

Connective tissue flows into the groove and begins to fill in the area that lies between these perforations ; Increase in connective tissue of the upper lip in the area of the groove and the groove fills in and slowly disappears

Migration

If migration fails the tissues will be stretched and will break down as development continues, resulting in separation between the medial nasal process and the maxillary process

Cleft lip

Cleft lip occurs

about the 6th embryonic week

The result of a midline cleft of the upper lip

If two medial nasal processes do not fuse together

The formation of the palate or roof of the mouth involve these processes

Right and left maxillary processes the medial nasal process

Primary palate /or/ premaxilla

The medial nasal processes form a block of tissue that includes the area of the maxillary central and lateral incisors as well as a small "V" shaped wedge of tissue lingual to these teeth back to the incisive foramen

The medial nasal processes also help to form the ___ the wall that divides the nasal cavity into right and left halves

nasal septum (septum = separate into right & left halves)

If a cleft palate is going to develop it will begin somewhere between — If it occurs early the entire palate will be — If it happens near week 11 only the ___ or the ___ will be affected

• weeks 7 & 11

• Open or cleft

• Soft palate; ovula

A combined cleft lip and palate occurs in about ____ births among whites in the United States

1 in 700

For African Americans clefts rate about

1 in 2000

Clefts are more frequent in Asians at about

3 in 2000

Clefts involving only the palate and not the lip, the ratio is about the same for all races, at about

1 in 2500

___ tend to have a higher incidence of cleft lip, or cleft lip with cleft palate, whereas have more isolated incidence of cleft palate

Males ; females

Involves lack of connective tissue migration between both maxillary processes and the fused medial nasal processes

Bilateral cleft lip

External bulges in the future neck region

Pharyngeal arches

Depressions on the neck surface

Pharyngeal grooves

Depressions on the inside

Pharyngeal pouches

Trigeminal nerve

Cranial nerve of the first arch ; fifth cranial nerve

Facial nerve

Cranial nerve of the second arch ; seventh cranial nerve

Small depression in the middle of the posterior tongue This is the point where the thyroid gland begins to develop and then migrates downward eventually lying in the lower front neck region

Foramen cecum

The thyroid gland starts out as a ___ then becomes a ___, and ___ with the glandular tissue developing at the deep end of the tube

cord of cells — tube — grows downward

If for some reason the tube does not grow downward the patients thyroid gland forms into a big red lump at the back of the tongue

Lingual thyroid

Upward growth - forms the anterior part of the pituitary gland and what is known as the pars intermedia or the intermediate part of the gland hormones

Rathke's pouch

Microglossia

the tongue is too small for the mouth ; can cause eating and speech problems

Macroglossia

the tongue is too large for the mouth ; can cause difficulties with speech eating, breathing, and many require surgery and speech therapy

Ankyloglossia

being tongue tied ; too short of a lingual frenum which limits the movement of the tongue