Odontogenesis

Question 1

What are the 3 phases of tooth development?

Answer 1

Initiation (Sites of future teeth are established by tooth germs which are formed from invaginations of the oral epithelium called dental lamina)

Morphogenesis (The shape of the crown is established)

Histogenesis (The formation of enamel and dentin as well as dental pulp and periodontium)

Question 2

What is the embryological origin of the teeth and vestibule of the mouth?

Answer 2

Ectomesenchymal tissue from the neural crest forms the dental papilla

Ectoderm forms the enamelitself

Question 3

What are the 2 types of lamina formed in the oral cavity? What do they form?

Answer 3

Dental lamina which form the teeth.

Vestibular lamina which form the gums and the rest of the oral cavity.

Question 4

Which side of the mouth does the vestibular lamina form?

Answer 4

Buccally

Question 5

Which side of the mouth does the dental lamina form?

Answer 5

Lingually

Question 6

How are the laminae formed?

Answer 6

First there is a thickening of mesenchyme in the oral epithelium which thickens

by the 6th week the oral epithelium thickens and invaginates into the oral mesenchyme to form a primary epithelial band.

By the 7th week the primary epithelial band divides into 2 processes, a buccally located vestibular lamina and a lingually located dental lamina.

Question 7

What are the stages of formation of the teeth from tooth germs?

Answer 7

Bud stage

Cap stage

Bell stage

They are differentiated based on themorphodifferentiation and histodifferentiation of their enamel organs (epithelial components)

Question 8

What happens during the bud stage?

Answer 8

The enamel organ in the bud stage is a simple, spherical or ovoid, epithelial condensation that is poorly morphodifferentiated and histodifferentiated. It is surrounded by mesenchyme.

*The cells of the tooth bud have a higher RNA content than those of the overlying oral epithelium, a lower glycogen content and increased oxidative enzyme
activity.

Question 9

What happens during the cap stage?

Answer 9

During the cap stage there is morphodifferentiation of the enamel organ to form a cap shaped structure.

Internal and external enamel epithelia are formed from peripheral cells (columnar cells) and a central portion is formed which consists of rounded cells (cuboidal cells).

In the 12th week the stellate reticulum starts to form from the central rounded cells. Intercellular spaces contain lots of glycosaminoglycans

Question 10

What happens during the early bell stage?

Answer 10

Further morphodifferentiation and histodifferentiation takes place.

A high degree of histodifferentiation is achieved in the early bell stage. The enamel organ shows four distinct layers: external enamel epithelium, stellate reticulum, stratum intermedium and internal enamel
epithelium.

Question 11

What week does the cap stage begin?

Answer 11

11th week of development

Question 12

When does the early bell stage begin?

Answer 12

14th week of development

Question 13

How would bone resorption issues affect the bell stage?

Answer 13

They would interfere with mitoses that take place leading to altered occlusal margins in the tooth. (increased internal epithelial folding is common)

Question 14

What does the external enamel epithelium do during the bell stage?

Answer 14

The external enamel epithelium is thought to be involved in the maintenance of the shape of the enamel organ and in the exchange of substances between the enamel organ and the environment.

The point at which the external and internal enamel epithelium meet is the cervical loop

Question 15

What happens in the stellate reticulum during the bell stage?

Answer 15

In addition to glycosaminoglycans, the cells also contain
alkaline phosphatase but have only small amounts of RNA and glycogen. The mesenchyme-like features of the stellate reticulum include the synthesis of collagens in the tissue.

The main function ascribed to the stellate reticulum is a mechanical one. This relates to the protection of the underlying dental tissues against physical disturbance and to the maintenance of tooth shape. It has been
suggested that the hydrostatic pressure generated within the stellate reticulum is in equilibrium with that of the dental papilla, allowing the proliferative pattern of the intervening internal enamel epithelium to determine
crown morphogenesis.

Question 16

What does the ennermost cell layer do in the enamel organ?

Answer 16

The innermost cell layer of the enamel organ, the internal enamel epithelium, deposits and later modifies the enamel. The other components of the enamel organ, the stratum intermedium, the stellate reticulum and the external enamel epithelium, play important supportive roles.

Question 17

What does the dental papilla seen in the cap stage mature into?

Answer 17

The Dentin and the pulp

Question 18

What does the dental follicle seen in the cap stage develop into?

Answer 18

The cementum, the periodontal ligament, and the alveolar bone

Question 19

Which structure from the cap stage eventually forms the enamel?

Answer 19

The enamel organ; the inner epithelium forms ameloblasts which elongate to form enamel.

Question 20

Which structure from the cap stage forms the dentin?

Answer 20

The dental papilla cells differentiate into odontoblasts which form the dentin in the opposite direction to the enamel.

Question 21

Why are cells of the stellate reticulum shaped like stars?

Answer 21

Cells within the stellate reticulum produce glycosaminoglycans which increase the osmolarity of the central chamber and these cells are connected to each other by gap junctions. So when water enters the central chamber it expands pulling the cells apart.

Question 22

When are cervical roots formed?

Answer 22

During the bell stage

Question 23

What structures form the cervical loops?

Answer 23

They are formed by the junction between internal and external enamel epithelium which extends to form the cervical sheath and then the root of the tooth.

Question 24

What is morphodifferentiation during the bell stage? what happens simultaneously to this stage?

Answer 24

The establishment of the shape of the crown

Histodifferentiation occurs simultaneously.

Question 25

What happens during histodifferentiation?

Answer 25

The Odontoblasts are formed from the dental papilla and the ameloblasts are formed from the enamel organ's inner epithelium.

Question 26

When happens to the dental lamina during the late bell stage?

Answer 26

It disintegrates and degenerates. Separating the tooth germ from the oral epithelium.

Question 27

What adverse outcome could arise from the disintegrated dental lamina?

Answer 27

The remaining cells can form odontogenic cysts and tumours The cells can also form extra teeth

Question 28

What tooth development stage do we see mineralization of the matrix? What else happens during this stage?

Answer 28

Advanced bell stage. During this stage the tooth is mineralized while organic material is also degraded. Ameloblasts eventually also fuse with the outer enamel epithelium and form the reduced enamel epithelium.

Question 29

What structure is formed by the fusion of the internal and external enamel epithelia? What does this become?

Answer 29

Hertwig's root sheath which becomes the tooth's root. Inner layer of root sheath cells become odontoblasts which secrete dentin. The root sheath disintegrates and cells from the follicle interact with the newly formed dentin and these cells form cementum and the periodontal ligaments. Some cells remain and become the epithelial rests of malassez

Question 30

What triggers differentiation of dental papillary cells into odontoblasts?

Answer 30

Differentiation of dental papillary cells into odontoblasts is a result of signalling from the differentiating inner enamel epithelium.

Question 31

How is the formation of dentin related to the formation of enamel?

Answer 31

The establishment of a layer of dentin is necessary for the production of enamel matrix and thus inner enamel epithelium stimulates dental papilla cells to differentiate into a layer of dentin and then the layer of dentin triggers inner enamel epithelial cells to form enamel.

Question 32

Which phase of amelogenesis is the Tomes' process produced?

Answer 32

During the secretory phase

Question 33

What happens during the 3 phases of amelogenesis?

Answer 33

Presecretory: Ameloblasts are formed from inner enamel epithelium Secretory: Ameloblasts produce extracellular matrix proteins Maturation: The enamel becomes mineralized by producing inorganic hydroxyapatite and breaking down the organic material

Question 34

How does the Tomes' process allow for the production of enamel?

Answer 34

It is responsible for the release of extracellular matrix proteins into the enamel. Initial layer produced is then mineralized immediately (this layer is made up of mantle dentin and this layer does not contain enamel rods.) The Tomes' process extends distally after the formation of the initial layer. The distal part of the Tomes' process produces the rods and the proximal part produces inter rod enamel. Enamel sheath is produced between the rod and inter rod enamel groupings. Finally, the distal portion of the Tomes' process disappears and a layer of rodless enamel is formed creating a sandwich of enamel with rods between to layers of rodless enamel.

Question 35

What are the stages of the maturation phase of enamel formation? What happens during these phases?

Answer 35

Transitional phase: Ameloblasts decrease in size and undergo apoptosis. The layer of ameloblasts is reduced. Maturation proper phase: Inorganic material replaces organic material. A ruffled border is formed by the reduced ameoblasts in a cyclical way (creation, loss, recreation of this border). Ruffle ended ameloblasts have tight junctions on apical border, whereas smooth ended ameloblasts have leaky junctions. Tight junctioned ameloblasts produce lysosymes, serine proteases and metalloproteinases which break down the proteins in the enamel matrix. These broken down proteins then diffuse into the smooth ended ameloblasts. Calcium binding proteins and calcium ATPases help increase calcium levels in the enamel matrix thus mineralizing it. This occurs in waves travelling from the least mature part of the crown to the most mature.

Question 36

When do periodontal tissues start to develop?

Answer 36

After the tooth's root has calcified

Question 37

When does the initiation stage of tooth development begin?

Answer 37

in the 6th to 7th week of gestation

Question 38

When does the bud stage of tooth development occur?

Answer 38

In the 8th week

Question 39

When does the cap stage of tooth development occur

Answer 39

in the 9th to 10th weeks

Question 40

When does the bell stage take place?

Answer 40

in the 11th to 12 weeks

Question 41

What 3 stages are there for tooth development besides the bud, cap, and bell stages?

Answer 41

Before the 3 stages is the initiation stage After the bell stage is the apposition stage.

Question 42

When do the first signs of tooth formation occur?

Answer 42

Day 11 in the 1st brachial arch (thickening of epithelium)

Question 43

What are the earliest mesenchymal markers for tooth formation?

Answer 43

Lim-homeobox genes (Lhx-6 and Lhx-7)

Question 44

What signals control position of the teeth early in development?

Answer 44

FGF-8 andd Pax-9 these determine the position of the tooth germs.

Question 45

How many genes approximately have been identified to be responsible for odontogenesis?

Answer 45

More than 300

Question 46

How is the primary epithelial band formed?

Answer 46

By the 6th week the oral epithelium thickens and invaginates into the mesenchyme to form a primary epithelial band.

Question 47

What does the primary epithelial band form?

Answer 47

It divides into vestibular and dental lamina

Question 48

How are tooth germs classified into their respective stages (bud, cap, or bell)?

Answer 48

According to degree of morphodifferentiation and histodifferentiation of their epithelial components (enamel organ).

Question 49

What happens during the bud stage?

Answer 49

Epithelial incursion into the mesenchyme and proliferation as well as growth of the dental lamina forming a bud within the mesenchyme. Buds + mesenchyme develop into a tooth germ.

Question 50

How are cells of the tooth bud different to the rest of the overlying oral epithelium biochemically?

Answer 50

Cells of the tooth bud have a higher RNA content than those of the overlying epithelium Lower glycogen content Increased oxidative enzyme activity.

Question 51

What happens during the cap stage?

Answer 51

By the 11th week morphogenesis has progressed to the deeper surfaces of the enamel organ invaginating to form a cap shaped structure. At this stage the differentiation is relatively poor. However, a greater distinction develops between rounded cells in central part of the enamel organ and the peripheral cells which are becoming arranged to form internal and external epithelia. by the 12th week the central cells of the enlarging enamel organ have become separated and glycosaminoglycans are produced which results in the stellate reticulum. Cells of the external enamel epithelium remain cuboidal whereas those of the internal enamel epithelium become columnar.

Question 52

What happens during the bell stage?

Answer 52

Continued histo and morphodifferentiation. Cap shape becomes more like a bell with 4 cell types: Inner and outer enamel epithelium, stellate reticulum, and stratum intermedium. Dental lamina separates from the dental organ. Dental papilla undergoes differentiation and produces 2 types of cells, outer cells of the dental papilla which produce dentin (odontoblasts) and central cells (form the primordium of the pulp) Dental sac increases its collagen content and differentiates at a later stage.

Question 53

Which layer of the differentiated enamel organ produces ameloblasts?

Answer 53

The inner enamel epithelium

Question 54

Which layer of the differentiated enamel has high levels of alkaline phosphatase?

Answer 54

Stratum intermedium.

Question 55

How is the crown formed?

Answer 55

During the bell stage, dental papilla is separated from the enamel organ by a basement membrane. Below the basement membrane is a region called the acellular zone. Here enamel proteins are produced forming epithelial pearls which separates oral epithelium from the developing tooth. The IEE completes its folding and the future crown shaped pattern will form.

Question 56

What happens during the appositional stage?

Answer 56

Enamel, dentin, and cementum are secreted. Tissues are initially secreted as a matrix that is partially calcified which serves as a framework for later calcification.

Question 57

What are the 2 steps of amelogenesis?

Answer 57

First step produces mineralized enamel. (~30% mineralized) Second step involves influx of additional mineral content as well as removal of the organic material and water. Influx of mineral results in growth of the crystals in width and thickness.

Question 58

What enamel proteins are produced during amelogenesis?

Answer 58

Amelogenins (bulk of the proteins) Tuftelin Enamelin Amelins/Ameloblastins

Question 59

What does amelogenin do?

Answer 59

Accumulate during the secretory stage which undergo minor short-term and major long-term processing to form smaller fragments. These fragments form the bulk of the final organic matrix of maturing enamel. Amelogenin prevents crystals from fusing during their formation it must be removed to permit crystal growth They also form aggregates called nanospheres that surround the enamel crystals along their long axis

Question 60

Where is amelogenin most common?

Answer 60

Least concentrated in positions where enamel is growing (i.e site where interrod sites and rods grow)

Question 61

What is the function of enamalin?

Answer 61

Enamalin is important for crystal nucleation and growth

Question 62

What is the function of tuftelin?

Answer 62

Localizes specifically at the Dentin Enamel junction and participates in its establishment.

Question 63

What is the function of ameloblastin?

Answer 63

Ameloblastin is important for mineral formation and crystal elongation. (aka amelin and sheathlin) highest concentration found near enamel growth sites. Secreted together with amelogenins.

Question 64

What enzymes act during amelogenesis?

Answer 64

Metalloproteinasis such as MMP20 or enamelysin for short term breakdown. Serine proteinases for bulk degradation Phosphatases

Question 65

What occurs during the secretory stage?

Answer 65

Cells acquire intense synthetic and secretory activity. Enamel proteins are translated by RER packed into secretory granules and secreted immediately. Contents of the secretory granules are released against the newly formed dentin along the surface of the Tome's process. Secretion of enamel is immediately followed by mineralization. Ameloblasts then migrate away from the dentin layer and develop a distal and proximal tome's process. Proximal TP extends from distal junctional complex to the surface of the enamel layer and interdigitates with the enamel beyond the initial layer. Distal TP produces enamel proteins at 2 defined sites.

Question 66

What are the functional stages in the life cycle of an ameloblast?

Answer 66

Morphodifferentiation Histodifferentiation Secretory before Tomes' Process formation Secretory after Tomes' process formation Maturation (ruffle-ended) Maturation (smooth-ended) Protective

Question 67

What is the structure of dentin like?

Answer 67

Similar to osteoid in that it is principally collagen and noncollagenous compounds. First deposited as a layer of pre-dentin (unmineralized) and is elastic, this elasticity provides flexibility and prevents fracture of the overlying more brittle enamel. Gradually it mineralizes to form dentin while the non-collagenous proteins are incorporated at the mineralization front. Inorganic material is hydroxyapatite in the form of small plates. The organic components include type 1, 3, and 5 collagen with small amounts of lipids and noncollagenous matrix proteins. Mature dentin is composed of 70% inorganic, 20% organic and 10% water matter by weight.

Question 68

What are the types of dentin? Where are they located?

Answer 68

Primary dentin: Forms most of the tooth, outlines the pulp chamber. (Mantle dentin is an example of primary dentin) Seconday dentin: Develops after root formation has been completed and represents the continuous deposition of dentin by odontoblasts. (deposited much more slowly and on the roof (between the horns) and floor of the root) Tertiary dentin: Produced rapidly in response to stimuli (such as atresia) the quality of this is dependent on duration and quality of dentin produced. Tertiary dentin may have tubules – sparse in numbers and irregularly arranged

Question 69

How is primary dentin different to secondary dentin?

Answer 69

Secondary dentin has a tubular structure that is continuous with primary dentin, line between primary and secondary dentins. Dentinall tubules are less organized than the primary dentin. Some regions may have absent tubules and others have thicker tubules. However, ratio of mineral to organic component is equal in primary, secondary, and tertiary dentin, but it isn't deposited evenly along the periphery of the pulp chamber.

Question 70

Where is the mantle dentin located?

Answer 70

It is the outer layer of dentin in the coronal portion only

Question 71

What are the different types of tertiary dentin and how are they produced?

Answer 71

Reactionary dentin is produced by pre-existing odontoblasts, Reparative dentin is produced by newly differentiated odontoblasts.

Question 72

When does dentin formation begin?

Answer 72

At the bell stage. Root dentin forms slightly later – require the formation of Hertwig’s rooth sheath from the Cervical Loop It is produced in the papillary tissue adjacent to the folded IDE – spreads down the cusp slope as far as the cervical loop of the enamel/dental organ

Question 73

How do odontoblasts form? What occurs after they form and activate?

Answer 73

Differentiation of the mesenchyme within the dental papilla. And this occurs after the pre ameloblasts begins. Pre-ABs induce differentation of mesenchymal cells (odontoblasts) and they repolarize in the opposite way of the pre-ABs. After differentiation the odontoblasts start dentinogenesis and this triggers ameloblast differentiation and enamel formation after the start of enamel formation.

Question 74

How does mantle dentin form?

Answer 74

After odontoblast differentiation the dental matrix forms. Odontoblasts differentiate in the pre-existing ground substance of the dental papilla and the first collagens are deposited in the dental papilla (korff's fibers) Fibers extend towards the inner dental epithlium and fan out below this epithelium. As the odontoblasts increase in size and mature they start producing collagen 1 fibrils which are parallel to the future dentin-enamel junction. As CNs are being made the plasma membrane of the ODs adjacent to the IDE extends stubby processes into the forming ECM in the dental papilla – some of these extensions project up into the IDE – will form the enamel spindle The ODs also bud off matrix vesicles that lie next to the membrane between the IDE and DP Also develops a process = Tome’s fiber – left behind in the forming dentin matrix as the OD moves away from the BM toward the forming pulp *Become fenestrated – permits increased exchange

Question 75

What is the vascular supply of dentin?

Answer 75

When the mantle dentin forms, capillaries beneath the newly differentiated OD layer. As circumpulpal dentin forms the capillaries migrate between the odontoblasts. The endothelium of these capillaries become fenestrated to permit exchange.

Question 76

How is mineralization controlled?

Answer 76

The mineral phase first appears within the matrix vesicles next to the basement membrane as single crystals Crystals grow rapidly and rupture from the confines of the vesicles and spread as clusters of crystallites that fuse with adjacent ones. Deposition lags behind the formation of organic matrix so that organic pre-dentin is always found between the odontoblast and the mineralization front and the crystals spread and fuse. Control is exerted probably through the secretion of matrix proteins

Question 77

What is the function of the basement membrane during amelogenesis?

Answer 77

After the odontoblasts differentiate. DIrect contact is necessary for the completion of pre-ameloblast differentiation to mature ameloblasts and thus amelogenesis. Ameloblasts then begin amelogenesis after forming Tome's Processes. Upon contact of the enamel matrix with dentin the disintegrating basement membrane starts mineralizing and forms the dentinoenamel junction. Odontoblasts form dentinal tubules. Mineralization of the developing dentin and enamel is distinct for each type of tissue.

Question 78

What happens to odontoblasts and ameloblasts following amelogenesis?

Answer 78

The cell bodies of the odontoblasts remain in the pulp tissue The cell bodies of the ameloblasts participate in tooth eruption and disappear shortly after.

Question 79

How is the crown formed?

Answer 79

Crown growth starts at the cusp tips and both dentin and enamel are laid down incrementally.

Question 80

How is the root formed?

Answer 80

Development of the root begins after the enamel and dentin formation has reached the future cementoenamel junction. Epithelial cells of the inner and outer dental epithelium proliferate from the cervical loop of the enamel organ to form the Hertwig's epithelial root sheath. This sheath determines the shape and number of roots. The rim of the sheath is called the epithelial diaphragm and encloses the developing primary alveolar foramen. This sheath lacks a stellate reticulum and stratum intermedium and is only capable of differentiating into odontoblasts, no ameloblasts. Dentin is thus formed above the root sheath.

Question 81

What are the epithelial cell rests of malassez?

Answer 81

The root sheath fragments to form several discrete clusters of epithelial cells these are the epithelial cell rests of malassez and they persist into adulthood within the periodontal ligament.

Question 82

How is root dentin formed?

Answer 82

It is compositionally different from coronal dentin in that collagen fibers are arranged differently and less dentin is deposited in the root. Similarly to crown area the dental papilla outer cells are induced to differentiate into odontoblasts which is influenced by the internal enamel epithelium of Hertwig's root sheath. The odontoblasts then undergo dentinogenesis and secrete predentin. After dentin is formed the basement membrane disintegrates along with Hertwig's sheath.

Question 83

What is the root composed of?

Answer 83

Dentin and cementum

Question 84

How is cementum formed?

Answer 84

Cementogenesis in the root area occurs upon degradation of hertwig's root sheath. This degradation allows contact of the dental sac cells with the dentin surface. This induces formation of cementoblast cells. The cementoblasts cover the root dentin and undergo cementogenesis laying down cementoid. When the cementoid is mineralized it is called cementum.

Question 85

What are cementocytes?

Answer 85

Cementoblasts do not leave cellular processes within the cementum, instead many cementoblasts are entrapped in the forming cementum and these entrapped cementoblasts become cementocytes.

Question 86

What is the site of contact between cementum and root dentin called?

Answer 86

The dentinocemental junction

Question 87

Which cells form the pulp? When does this take place?

Answer 87

The central cells of the dental papilla. These form while the cementum is forming

Question 88

How does the periodontal ligament form?

Answer 88

Surrounding tissues of the tooth also develop as the crown and root are forming. The mesenchyme of the dental sac condenses to form the periodontal ligament adjacently to the new cementum. This involves synthesis of collagen and bundling into fibers. The ends of these fibers insert into the outer layer of cementum and surrounding alveolar bone. Cells of hertwig's root sheath that is disintegrating at this stage form discrete islands of epithelial cells which become the cell rests of malassez

Question 89

What common issues are associated with the cell rests of malassez?

Answer 89

Radicular cysts.

Question 90

How are multiple roots formed on a single tooth?

Answer 90

Anterior teeth, premolars and molars all begin as a single root. Root of the posterior teeth divides from the trunk into the correct number of root branches and differential growth of the H. root sheath results in the devision of the root trunk into multiple roots.

Question 91

When does tooth eruption take place relative to development of supporting structures?

Answer 91

Soon after root formation begins the tooth begins to erupt until it reaches its final position. While roots are forming the supporting structures are also developing. (periodontal ligament and cementum)

Question 92

How do supporting structures develop?

Answer 92

As the root sheath fragments the dental follicle cells will penetrate between epithelial cells and lie close to the newly formed dentin. These cells will differentiate into cementoblasts which will make cementum.

Question 93

What are the clinical causes of defective tooth development with Enamel hypoplasia?

Answer 93

Enamel hypoplasia caused by: Amelogenesis Imperfecta Febrile illness or Vitamin deficiency Local infection or trauma (Turner's tooth) Fluoride ingestion (dental fluorosis) Congenital syphilis (hutchinson's incisors) Birth injury such as that caused by premature birth or idiopathic factors. Enamel hypocalcification

Question 94

What are the clinical causes of defective tooth development related to dentin formation dysfunction?

Answer 94

Dentinogenesis imperfecta Dentin dysplasia Regional odontodysplasia

Question 95

What are the types of amelogenesis imperfecta?

Answer 95

Type 1: Hypoplastic Type 2: Hypomaturation Type 3: Hypocalcified Type 4: Hypomaturation-hypoplastic with taurodontism

Question 96

What are the types of dentinogenesis imperfecta?

Answer 96

Type 1: Occurs with osteogenesis imperfecta Type 2: Hereditary opalescent dentin Type 3: Bradywine type (Shell-like appearance and multiple pulp exposures)