Anatomy - Outcome 4

Question 1

what does odontogenesis means?

Answer 1

The Beginning of Tooth Development

Question 2

Development of teeth in Utero

Answer 2

Not all teeth begin developing at the same time:

-tooth development begins in mandibular midline area at 5th – 6th week in utero
-tooth development continues in the anterior maxillary midline area
-tooth development progresses posteriorly in both jaws

Question 3

What tissues do the teeth arise from?

Answer 3

A tooth arises from epithelial and connective tissue (mesenchyme)

both are derivatives of ectodermal germ layer

Question 4

Tooth germ has 3 parts -

Answer 4

1. Enamel Organ
2. Dental Papilla
3. Dental Sac

Question 5

Enamel Organ - description

Answer 5

→ originates from the dental lamina

→ thickening of epithelium

→ ectodermal germ layer

→ will form enamel

Question 6

Dental Papilla Description

Answer 6

→ connective tissue under enamel organ

→ originates from mesenchyme

→ ectodermal germ layer

→ will form dentin and pulp

Question 7

Dental Sac Description

Answer 7

→ fibrous cell layer

→ originates from mesenchyme

→ ectodermal germ layer

→ will form periodontal ligament, lamina dura, and cementum

Question 8

Summary of Development and Life Cycle of a tooth

Answer 8

Stratified/Squamous/Oral Epithelium → Thickened → Dental Lamina → Enamel Organ → Tooth Germ

Question 9

Tooth Germ: Bud Stage

Answer 9

Primary Dental Lamina (beginning of 8th week)
-thickened oral epithelium, a proliferation of the cells of the dental lamina
-formation of 10 buds on the maxilla and 10 on the mandible
-grow into underlying mesenchyme (connective tissue)
-forms enamel organ

Question 10

Tooth Germ: Cap Stage

Answer 10

(9th -10th Weeks)

-mesenchyme cells differentiate and grow under the enamel organ
-unequal growth in different parts of the tooth bud, leading to the formation of a cap shape attached to the dental lamina.
-a primordium of the tooth develops with a specific form: the tooth germ.
-A depression results in the deepest part of each tooth bud of the dental lamina and forms a cap or enamel organ
-A part of the mesenchyme deep to the buds condenses into a mass within the concavity of the cap of the enamel organ.
-This inner mass of ectomesenchyme is called the dental papilla.
-The dental papilla will produce the future dentin and pulp for the inner part of the tooth.
A basement membrane still exists between the enamel organ and the dental papilla and is the site of the future dentinoenamel junction (DEJ).

Question 11

What will dental papilla produce?

Answer 11

The dental papilla will produce the future dentin and pulp for the inner part of the tooth.

Question 12

Tooth Germ: Bell Stage

Answer 12

(11th - 12th weeks)

Four layers distinguishable in the enamel organ -

1. Outer Enamel Epithelium
2. Inner Enamel Epithelium
3. Stellate Reticulum
4. Stratum intermedium

Question 13

What is Outer Enamel Epithelium? (OEE)

Answer 13

cuboidal cells
protective layer

Question 14

What is Inner Enamel Epithelium? (EE)

Answer 14

-a single layer of cuboidal cells
-lines inside (concave area)
-future ameloblasts
-separated from dental papilla by the -basement membrane

Question 15

What is Stellate Reticulum? (SR)

Answer 15

inside OEE (Outer Enamel Epithelium)
protection/cushion
transport nourishment to IEE (Inner Enamel Epithelium)
composed of a loose network of star-shaped epithelial cells

Question 16

What is Stratum intermedium? (SI)

Answer 16

inside SR (Stellate Reticulum)
between SR and IEE (Stellate Reticulum & Inner Enamel Epithelium)
flat cells
directly nourishes IEE (Inner Enamel Epithelium)

Question 17

What is Basement Membrane?

Answer 17

between dental papilla and IEE
fixed and determines the final shape of a tooth
further cell differentiation and growth occurs around basement membrane (BM)
IEE → ameloblasts – top of BM
Dental papillae → odontoblast – below BM
future DEJ

Question 18

Secondary Dental Lamina

Answer 18

before enamel and dentin formation begins
primary dental lamina breaks from oral epithelium
formation of secondary dental lamina → permanent or succedaneous tooth

Question 19

What is dentinogenesis?

Answer 19

Dentin Formation

Question 20

Dentin Formation

Answer 20

1st mineralized layer of any developing tooth
Dentin is first formed at the incisal/cusp area of a tooth and progresses in a rootward direction
odontoblast
“attached” to basement membrane (DEJ)
create narrow extensions as they grow → tubules surround the cell
the nucleus continues moving away from DEJ in narrow extensions
odontoblastic process remains in tubule
also cork secured collagen fibers
mineralization begins at DEJ and moves downward (pulpal)

Question 21

What is Amelogenesis?

Answer 21

Enamel Formation

Question 22

Enamel Formation

Answer 22

-product of the enamel organ
-begins after dentin begins, at the dentin surface of the cusp/incisal edge
-ameloblasts move upward and outward leaving an organic enamel matrix
-enamel rods and inter-rod substance (enamel matrix)
-crystal formation – 96% mineralized

NOTE: IEE cells become ameloblast cells

Question 23

Primary Enamel Cuticle

Answer 23

produced by ameloblasts after enamel formation complete
smooth coating over enamel

Question 24

Ameloblasts are…

Answer 24

Ameloblasts are cells which secrete the enamel proteins enamelin and amelogenin

Question 25

Remaining Original Layers - what happens?

Answer 25

stellate reticulum, stratum intermedium, outer enamel epithelium, and ameloblast cells
reduced to few layers of cells known as the reduced enamel epithelium
reduced enamel epithelium (REE) which produces secondary enamel cuticle
part of the REE attaches to the oral epithelium as the tooth erupts
future junctional epithelium

Question 26

Secondary Enamel Cuticle

Answer 26

protects tooth until eruption
non-mineralized

Question 27

When does Root Formation take place?

Answer 27

The process of root development takes place after the crown is completely shaped and the tooth is starting to erupt into the oral cavity.

Question 28

Root formation process

Answer 28

-continues after enamel complete
-dentin surrounds pulp chamber
-continues as tooth develops
-complete 1-4 years after eruption
-The structure responsible for root development is the cervical loop. The cervical loop is the most cervical part of the enamel organ, a bilayer rim that consists of only IEE and OEE.
-It begins to grow deeper into the surrounding mesenchyme of the dental sac, elongating and moving away from the newly completed crown area to enclose more of the dental papilla tissue and form Hertwig epithelial root sheath (HERS).
-This sheath or membrane shapes the root(s) and induces dentin formation in the root area, so that it is continuous with coronal dentin.

Question 29

What is cervical loop?

Answer 29

The cervical loop is the most cervical part of the enamel organ, a bilayer rim that consists of only IEE and OEE.

Question 30

Periodontal Ligament & Cementum

Answer 30

-dental sac cells surround developing dentin (root)
-the circularly arranged fibers of the dental sac become the Periodontal Ligament (PDL) around the tooth root
the PDL produces the cementum that covers the root dentin and the lamina dura of the tooth socket
-fibers of the PDL become trapped in their substance (as it forms cementum and lamina dura)
-the eventual attachment of the PDL fiber in the cementum and lamina dura holds the tooth in the socket

Question 31

Tooth Eruption Defined

Answer 31

• the process by which developing teeth emerge through bone and soft tissue of the jaws and the overlying oral mucosa to enter the oral cavity, contact teeth of the opposing arch, and function in mastication.

-is often thought of as the emerging of the crown into the oral cavity.

-but it also refers to the total life span of the tooth, from the beginning of crown development until the tooth is lost (and this is because there is always tooth movement occurring)

Question 32

Process of Tooth Eruption

Answer 32

-the occlusal movement of the tooth is brought about by the lengthening of the root and the development of additional bone beneath the root
-the apical end of the developed root is relatively fixed
-as the developing root lengthens, its growing apical end maintains its position
-the crown moves occlusally
-with the exception of the permanent molars, the enamel organ of each permanent tooth develops from the dental lamina lingual to its primary predecessor
-as the root gets longer, the tooth begins to move occlusally. REMEMBER the crown of the tooth is surrounded by the reduced enamel epithelium (REE)
-as the tooth moves occlusally the REE moves with it
-after the tooth emerges into the mouth the REE becomes known as the junctional epithelium
-the tooth comes into occlusion during root formation
-this occlusal movement does not stop when the root is completed, it continues until the tooth is lost or death occurs;

Question 33

Passive Eruption

Answer 33

as teeth wear down at the “incisal edges” or “cusp tips” due to mastication, the teeth erupt slightly to compensate for this wear; if this did not occur, the relationship of the jaws would change and the patient’s lips would eventually appear more compressed (this can still happen!)

Question 34

Supra-eruption

Answer 34

this occurs when there is a loss of an opposing tooth; this condition allows the tooth or teeth to erupt farther than normal into the space; this can mean serious problems in replacement of missing teeth with a partial denture or fixed bridge

Question 35

The Process of Primary Tooth Shedding (Resorption & Exfoliation)

Answer 35

-the shedding of primary teeth takes place because of the gradual resorption (disintegrating or eating away of organic material) of their roots and loss of periodontal ligament attachment
-the developing permanent tooth located lingual to or beneath the root of the primary tooth creates sufficient pressure because of it’s increasing crown size to cause resorption of the primary tooth root and of the bone surrounding this primary tooth root
-as the root resorbs, the tooth loosens
-eventually all the periodontal ligament of the primary tooth is lost and the rootless primary crown literally falls off the jaw (exfoliate means to fall out)

Question 36

How long does resorption of a primary tooth take?

Answer 36

“resorption” of a primary tooth takes place for about one year prior to “exfoliation”

Question 37

What promotes osteoclasts to form?

Answer 37

regardless of its position, the fact that the permanent tooth crown is present and that its root is developing, causes the permanent tooth crown to move occlusally toward the surface of the oral cavity. This creates pressure on the root of the primary tooth. It is believed that this pressure promotes “osteoclasts” to form and begin resorbing the primary tooth root (also dentinoclast and cementoclast)

Question 38

In some cases, the permanent tooth bud fails to develop. In these instances:

Answer 38

roots of the primary tooth may resorb even though there is no permanent tooth bud, or
the primary tooth may retain its roots and continue to function in the mouth for many years.

Question 39

What is a submerged tooth?

Answer 39

Teeth are considered “submerged” when eruption is prevented because of crowding or tipping of the adjacent teeth into the space created by a missing tooth.

Question 40

“alternate loosening and tightening of a primary tooth before it sheds”

Answer 40

-one day a child says his tooth is loose and several days later, the tooth seems to be firmly attached.
-tightening is caused by the fact that the pressure of the developing permanent tooth is sometimes relieved but a slight “tension” seems to be induced on the adjacent periodontal ligament of a primary tooth.
-this slight tension stimulates the periodontal ligament around the resorbing 1° root end to new cementum and new bone around the root.
this results in attachment of new periodontal ligament fibers and the primary tooth tightens in the jaw.
-then further development of the permanent tooth and more resorption of bone and root.
-loosening and re-attachment may alternate several times with eventual shedding

Question 41

Why a primary tooth may need to be extracted?

Answer 41

Sometimes the relative positions of primary teeth and developing permanent teeth are such that the primary tooth root is not subjected to pressure that would allow it to resorb. Thus, the primary tooth will not be loose enough to fall out on its’ own. Extracting the retained primary tooth may have to be considered

Question 42

What is Akylosis?

Answer 42

-the term “ankylosis” refers to the union of 2 similar or dissimilar hard tissues
previously detached but beside each other

-frequently seen in primary teeth
-the cementum of a primary tooth fuses at the cervical line with adjacent bone
-the tooth which would normally be loose is “firm as a rock”
-secondary tooth unable to erupt until the ankylosed tooth is removed or until the permanent tooth deviates from its path of eruption and emerges (erupts) out of alignment
-commonly occurs with the primary 2nd molars which are to be replaced by the permanent 2nd premolars
-assuming an accurate diagnosis, treatment would indicate extracting the ankylosed primary tooth

Question 43

What are ectopic teeth?

Answer 43

“ectopic” defined: out of place arising or produced at an abnormal site

Question 44

Primary cause of ectopic eruption

Answer 44

-the primary cause of “ECTOPIC ERUPTION” is lack of harmony in the rate of jaw growth, eruption time, and sizes of teeth (we need to remember that different organs and tissues grow at different rates and at different times)

upon accurate diagnosis, treatment will involve:
exposing an x-ray to confirm suspicions
orthodontics with gingival surgery
remove primary tooth to make room
use spacer elastics to make space