Tooth Development

Question 1

Fetus

Answer 1

: from 9th week till birth.

Question 2

Oral ectoderm layers

Answer 2

Basal layer of columnar cells and sup of flat cells

Question 3

Break down of bycci pharyngeal membrane is at

Answer 3

4th week iul

Question 4

Neural crest cells

Answer 4

They are group of cells coming from neuroectoderm they separate from lateral aspect of neural plate. Neural crest cells migrate beneath the epithelium along the entire free margin of the jaw.

Question 5

Histological stages of tooth development

Answer 5

1-Initiation • 2-Proliferation • 3-Histodifferentiation • 4-Morphodifferentiation • 5-Apposition

Question 6

Origin and time of formation of the dental and vestibular lamina

Answer 6

❖By the 7th week the primary epithelial bands divides into two laminae, a facially located vestibular lamina and a lingually situated dental lamina.

Question 7

Mechanism of formation of dental bud and its depth

Answer 7

❖The tooth buds of deciduous teeth develop by cell division of dental lamina on its labial side by the influence of neural crest cells.
❖The cell division at this area is more rapid than the adjacent cells to form round or ovoid swellings (bud shape) of epithelial structure called Dental (enamel) organ
The dental lamina is shallow and microscopic sections often show the buds close to the oral epithelium.

Question 8

Outer e epi cell shape

Answer 8

Cuboidal deeply stained rounded nucleus

Question 9

How inner cells turn stallate

Answer 9

❖The increasing fluid increases the volume of the extracellular compartment of the enamel organ, so that the cells of the organ are forced apart

Question 10

Desmosomes in cap stage found between

Answer 10

Found between stallate ret cells and outer and inner ee

Question 11

Cellular activity in dental papilla in cap stage

Answer 11

❖The cells of dental papilla show division and become condensed with active budding of capillaries &mitotic figures

Question 12

Fibers of sac in cap stage

Answer 12

❖In this zone, gradually a denser and more fibrous layer develops.

Question 13

Knob of knot and in which teeth group Is knot found

Answer 13

❖This knot projects in part toward the underlying dental papilla showing knob like
enlargement, which
disappears in the bell stage by apoptosis

sections of molar cap stage tooth germ

Question 14

When do Enamel knot and cored disappear

Answer 14

Before enamel formation

Question 15

How e nich is formed

Answer 15

Cutting through a curved lateral lamina so that the mesenchyme appear to be surrounded by dental epithelium

Question 16

OEE in early bell

Answer 16

The cells of outer enamel epithelium decrease in height and become low cuboidal. This to facilitates entrance of nutrients to enamel organ

Question 17

IEE in early bell

Answer 17

These cells show elongation reaching 40 microns in length. Most of this elongation is towards the dental papilla resulting in the disappearance of the cell free zone. As the inner dental epithelial cells get in contact with the peripheral connective tissue cells of the dental papilla. They exert an organizing influence on the undifferentiated mesenchymal cells to differentiate into odontoblasts; this process is known as induction. Also the inner dental epithelium shows alteration in their functional polarity by migration of the nucleus and mitochondria to the proximal end of the cell, while the Golgi bodies and centrioles migrate to the distal end(reversed polarity). At this stage the inner dental epithelium begins to be arranged on the basement membrane of future amelodentinal junction (ADJ).

Question 18

Cervical loop appear at what stage

Answer 18

Early bell

Question 19

Origin of stratum intermedium

Answer 19

❖This layer is derived from the cells inside the enamel organ perhaps from the inner dental epithelium or from the enamel knot, which insinuated themselves in this place.

Question 20

Function of stratum intermedium

Answer 20

Alkaline phosphatase enzymes
High metabolic activity
well developed cytoplasmic organelles, acid mucopolysacharides and glycogen deposits indicate a high degree of metabolic activity.
❖The stratum intermedium may show mitotic division and attached to the inner dental epithelium and stellate reticulum by desmosomes.

Question 21

Dental sac layers in early bell stage and its fiber shape and continuity

Answer 21

❖Close to the end of the early bell stage the dental sac shows a circular arrangement of its fibers resembling a capsular structure.
❖Its inner layer is more vascular and shows a plexus of nerve fibers and lies close to the outer dental epithelium and dental papilla.
❖The outer layer of the dental sac lies against the wall of the bony crypt. ❖The fibers of this capsule may merge with fibers of the lamina propria of the gingiva.

Question 22

Membrane preformativa

Answer 22

❖The basement membrane that separates the enamel organ and dental papilla just prior to dentin formation is called membrana preformativa

Question 23

Early odontoblast shape

Answer 23

Cuboidal the col.

Question 24

Outer EE changes in late bell

Answer 24

1. O.E.E become flattened. They become low cuboidal with high nuclear/cytoplasmic ratio (little cytoplasm).
2. Folding of the smooth surface of outer enamel epithelium to increase its surface area.
3. At the region of these folds the dental sac sends many capillary loops, to provide a rich nutritional supply.
4. O.E.E develop microvilli, cytoplasmic vesicles and increased number of mitochondria at the end facing the capillary loops for active transport of materials.

Question 25

Ameloblasts shape and dimensions

Answer 25

4 – 5 microns in diameter 40 microns in length in cross section they are
hexagonal.

Question 26

Changes of stallate reticulum in late bell

Answer 26

❖The space needed for the developing enamel will be gained from:
➢ The shrinkage of the stellate reticulum by the loss of the intercellular fluid.
❖Becomes hardly distinguished from the stratum intermedium. ❖The shrinkage begins at the height of the cusp or the incisal edge and progresses cervically.

Question 27

Root formation what you forget

Answer 27

❖ At the first the epithelial root sheath bends at the future cemento enamel junction into horizontal
plane known as diaphragm.The proliferation of the cells of the epithelial diaphragm is accompanied by proliferation of the cells of connective tissue of the pulp, which occurs in the area adjacent to the diaphragm.

❖After dentine deposition
the connective tissue of the dental sac proliferates and invades the Hertwig epithelial root sheath dividing it into a network of epithelial strands.he cells of the inner enamel epithelium forming the sheath of Hertwig remain short and induce

❖The wide apical foreman is reduced first to the width of the diaphragmatic opening and later is further narrowed by apposition of dentine and cementum at the apex of the root.The epithelial strands may undergo degeneration; remnants may persist in the periodontal ligament in the form of network or isolated islands known as epithelial rests of Malassez

Question 28

Multirooted root formation

Answer 28

The odontoblasts differentiate along the diaphragm, and the pulpal surface of the extended epithelial bridges form dentin, and on the periphery of each opening, root development follows in the same way as described for single rooted teeth.

Question 29

The effect of enamel pearl in primary school

Answer 29

Enamel pearl in deciduous teeth may cause delayed exfoliation of primary teeth because of slower process of enamel resorption. This may lead to deviation of erupting permanent molars.

Question 30

Intermediate cementum

Answer 30

: ❖ If the continuity of the Hertwig’s root sheath is broken after odontoblastic differentiation and before dentine formation, intermediate cementum is developed.
❖ It occurs at apical 2/3 of premolars and molars roots and rare in incisors and deciduous teeth

Question 31

Reasons of development of accessory canal

Answer 31

• Disturbance in the fusion of the tongue like extension of the diaphragm causes defects in the pulpal floor.
• large bv
• loss of continuity of ERSH before od differentiate

Question 32

1. Initiation

What structure is responsible and what are the abnormalities

Answer 32

The dental lamina and tooth buds represent that part of the oral epithelium that has powers for tooth formation.
Absence of either single tooth or multiple teeth (partial anodontia) most frequently, upper 2, upper and lower 8,due to lack of initiation
Complete lack of teeth
(anodontia) as in Ectodermal Dysplasia syndrome.
Abnormal initiation may result in development of single or multiple supernumerary teeth.

Question 33

Proliferation stage and it’s abnormalities

Answer 33

Proliferative activity is found in dental lamina, bud, cap, early bell stage and late bell stage where the dental matrices are not yet deposited. The unequal growth by mitotic division causes regular changes in size and proportions of the growing tooth germ.
Any disturbance in this stage causes dental problems ranging from; absence of teeth, disturbed tooth formation, or giving supernumerary teeth

Question 34

Histodifferentiation

Answer 34

This phase reaches its highest development in the bell stage just before the beginning of matrix formation. So the differentiation of ameloblasts and stratum intermedium is essential for enamel formation, also the differentiation of odontoblasts is important for the producing of dentine.
In case of vitamin A deficiency, ameloblasts fail to differentiate properly so their organizing influence is disturbed and atypical dentin called osteodentin is formed.

Question 35

Morphodifferentiation

Answer 35

The morphologic pattern and relative size of the future tooth is started at the early bell stage when the inner enamel epithelium arranges them on the basement membrane. At late bell stage the morphodifferentiation is established by outlining the future amelodentinal
junction and
amelocemental junction. The morphology of the tooth is performed at this stage by differential growth of the formative cells just prior to matrix deposition.In Morphodifferentiation stage, endocrine disturbances affect size or form of teeth without affecting ameloblasts and odontoblasts functions resulted in underdeveloped or extra structures in the tooth. Also delayed eruption in hypopituitarism and hypothyroidism causes small clinical crown mistaken as small anatomical crown.

Question 36

Function of outer EE

Answer 36

1. It limits the boundary of the enamel organ. 2. Active transport of materials specially, after hard dental tissue formation as it becomes folded to facilitate the passage of nutrient material to the enamel organ.
2. It picks up the calcium salts from the dental sac to either the stellate reticulum or stratum intermedium.
3. It forms with the inner dental epithelium the epithelial root sheath of Hertwig which is responsible for root formation.

Question 37

Stallate reticulum function

Answer 37

Acts as a buffer against physical forces that may distort the configuration of the developing amelodentinal junction giving rise to gross morphologic changes, so maintains tooth shape

2. It seems to permit only a limited flow of nutritional elements from the outlying blood vessels to the formative cells, so it acts as a store house for the nutritive materials.
3. It keeps room for the developing enamel and supports its production as they shrink and lose their intercellular fluid to bring the ameloblasts close to the blood vessels situated outside the outer enamel epithelium.

Question 38

Time of initiation for primary teeth permanent centrals

5s 6s and 7s

Answer 38

Primary ----2m iul 
1s -----5m iul
5s -----10m old
6s------4m iul
7s ----- 12m old

Question 39

Function of IEE

Answer 39

Morphodifferentiation function as it determines the form and size of the crown and root portions of the tooth
2. Organizing function as it exerts an organizing influence induction on the undifferentiated cells of the dental papilla to differentiate into odontoblasts.
3. Formative functions as it differentiated into ameloblasts (by reciprocal induction) that lays down enamel matrix and helps in its mineralization.
4. This layer is arranged in a pattern to determine the future morphology of the amelodentinal junction (A.D.J) and the crown.
5. It forms with the outer dental epithelium the epithelial root sheath of Hertwig which is responsible for root formation.
6. Nutritive function as it shares in the transport of the nutritive materials from the dental papilla to the enamel organ before dental hard tissue formation.7. Protective function as after the full enamel thickness is deposited it secretes an organic layer called primary enamel cuticle.
➢A protective covering to enamel of unerupted tooth against resorption and preventing precipitation of cementum.
7. Protective function also as it forms with the other layers of the dental organ
the reduced enamel
epithelium which protects the enamel surface until the tooth
erupts.
8. Contribute to the formation of the dentogingival junction of erupted teeth.