Odontogensis

Question 1

What two cells do teeth develop from?

Answer 1

Oral epithelial cells: ectoderm origin Mesenchyman cells: ectomesenchymal origin

Question 2

What is the first stage of tooth development?

Answer 2

Initiation/ 6-7th week. Induction: Ectoderm lining stomodeum gives rise to oral epithelium and then to dental lamina; adjacent to deeper ectomesenchyme, which is influenced by the neural crest cells. Both tissue types are separated by a basement membrane

Question 3

what is the second stage of tooth development?

Answer 3

Bud stage 8th week. Proliferation; Growth of dental lamina into bud shape that penetrates growing ectomesenchyme

Question 4

What is the third stage of tooth development ?

Answer 4

CAP STAGE 9th-10th week: Prolifferation, differentiation, morphogensis. Formation of tooth germ as enamel organ, that forms into cap shape that surrounds inside mass of dental papilla, with an outside mass of dental sac, both from ectomesenchyme

Question 5

What is the fourth stage of tooth development?

Answer 5

BELL STAGE. 11th-12th week; proliferation, differentiation morphogenesis. Differentiation of enamel organ into bell shape with 4 cell types dental papilla into 2 cell types

Question 6

What is the fifth stage of tooth development?

Answer 6

Apposition; induction, proliferation. Dental tissue types secreted in successive layers as matrix

Question 7

What is the sixth stage of tooth development?

Answer 7

Maturation, dental tissue fully mineralise to mature form

Question 8

Describe initiation of tooth development

Answer 8

Thickened band of epithelium forms primitive jaws called the primary epithelial band, each band quickly gives rise to 2 sub divisions: vestibular lamina & dental lamina

Question 9

PICDescribe dental lamina

Answer 9

Epithelial outgrows at the sites corresponding to the future deciduous teeth

Question 10

What orientation do succesional dental lamina move in bud stage?

Answer 10

Lingual, or palatal

Question 11

Describe the cap stage

Answer 11

Commencement of cell proliferation and the beginning of cell differenciation.

Enamel organ: future enamel.

Formation of the tooth bud in a cap shape with a deep central depression,

Dental papilla: condenses mass of ectomesenchyme within the concavity of enamel organ (future dentin & pulp)

Dental sac/follicle: ectomesenchyme surrounding the outside of the enamel organ (forms future cemntum, PDL, alveolar bone

Question 12

Describe the bell stage

Answer 12

Further proliferation & histogensis. External enamel epithelium cubodial, stellate reticulum, strattim intermedium, internal enamel epithelum. Outer and central cells of dental lamina. Dental lamina break down

Question 13

Describe the apposition and maturation stage of tooth development

Answer 13

During the apposition stage enamel dentine and cementum are initally secreted as a matrix in layer. Maturation is mineralisation of this matrix

Question 14

Define apposition

Answer 14

Cells of the inner enamel epithelium differentitate into preameloblasts and undergo repolarisation. This stimulates the differentiation of odontoblasts from the mesenchyma cells of dental papilla. The enamel organ looses connection with oral epithelium due to the break down on the dental lamina, odontoblasts begin dentinogenesis secreting predentine

Question 15

PICWhat is the process of Apposition?

Answer 15

Basement membrane between the preameloblasts and the odontoblast disintegrates, preameloblasts come into contact with newly formed predentine → triggering preameloblasts to differentiate into ameloblasts and commence amelogenesis → tomes process = mineralisation of the disintegrating basement membrane forms the DEJ

Question 16

Describe crown maturation

Answer 16

Dentinogensis forms the foundation that proceeds amelogenesis. Bulk of crown is formed by dentinogenesis & amelogensis

Question 17

Describe dentinogenesis

Answer 17

Process develops at proximal end of odontoblast, as cell secretes matrix in increments it moves pulpward this odontoblastic process elongates and is left in dentine.

Question 18

Describe Amelogensis

Answer 18

Process starts at cusps, ameloblasts retreat & lay down incremental deposition of enamel matrix stretching from ameloblasts to the surface. Calcium phosphate crystals are deposited and matrix begins to mineralise. Resulting in maturation

Question 19

Describe root formation

Answer 19

Occurs after crown completion, and eruption commencement. The cervical loop elongates moving away from the crown to enclose more of the dental papilla tissue and form Hertwig root sheath

Question 20

PICDescribe Cementum Formation

Answer 20

Outer root sheath cells form acellular cementum covering dentine, on completion these cells disperse to form epithelial rests in the future PDL space. Ectomesenchymal cells of dental follicle differentiate into cementoblasts and secrete cementoid over the acellular cementum which later calcifies into cellular cementum.

Question 21

How does periodontal ligament formation form?

Answer 21

Dental follicle cells differentiate into fibroblasts who form collagen fibers. → Fibers embed in cementum and other end embeds in alveolar bone, →Fibers bundles increase in density as teeth erupt into functional occlusion

Question 22

What are the three phases of tooth eruption?

Answer 22

Pre-eruptive phase Prefunctional eruptive phase Functional eruptive phase

Question 23

Describe what happens in Pre-eruptive phase?

Answer 23

Movements related to tooth eruption begin during crown formation. Phase is finished with early root formation.

Question 24

Describe the prefunctional eruptive phase (root formation)

Answer 24

Root formation: Proliferation of epithelial root sheath that cause initiation of root dentin and pulp formation.

Question 25

Describe the prefunctional eruptive phase (movement)

Answer 25

Occurs occlusally through bony crypt of jaws to reach oral mucosa.

Question 26

Describe the prefunctional eruptive phase (Penetration)

Answer 26

Of tooth’s crown tip through the fused epithelial layers allowing entrance of crown to oral cavity

Question 27

Describe the prefunctional eruptive phase - Intraoral insical/occlusal movement

Answer 27

Eruptive tooth continues until clinical contact with opposing crowns

Question 28

Describe the prefunctional eruptive phase - tissues overlying the teeth

Answer 28

Tissues overlying the teeth: Degenerate resulting in eruption pathway. Gubernacular cord directed to mucosa. Osteoblastic and osteoclastic function to remodel bone as teeth enlarge and move. Resorption of roots of deciduous teeth, similar to the process of bone resorption for their eruprion

Question 29

What are the elements of Prefunctional Eruptive phase?

Answer 29

Root formation Movement Penetration Intraoral incisal/occlusal movement Tissues overlying the teeth Tissue underlying the teeth

Question 30

Describe the prefunctional eruptive phase - tissues underlying the teeth

Answer 30

As crown erupts more space is made to accomodate rooth lengthening. Root dentine and cementum development. Fine trabeculae form in fundic area fist, and gradually bone becomes denser until functional occlusion is reached

Question 31

Describe Functional Eruptive Phase

Answer 31

Takes place after teeth are functioning and continues as long as teeth are present. During this period of root completion, height of alveolar process undergoes a compensating increase The fundic alveolar plates resorb to adjust for formation of the root tip apex. Increased mineral density of bone.

Question 32

What is Anodontia?

Answer 32

Absence of teeth

Question 33

What is Hypodontia?

Answer 33

Absence of 6 or fewer teeth?

Question 34

What is hyperdontia?

Answer 34

Supernumerary teeth and supplemental teeth

Question 35

What is the variation in tooth size?

Answer 35

Macrodontia, microdontia

Question 36

What is Den Evaginatus?

Answer 36

Extra cusp due to effects on enamek organ (talon)

Question 37

What is germination?

Answer 37

Occurs in a single tooth germ, tried to unsuccessfully to divide into two tooth germs

Question 38

What is fusion?

Answer 38

Results form the union of two adjacent

Question 39

What is Enamel Dysplasia?

Answer 39

Faulty development of enamel - hypoplasia, hypomineralisation, dentine dysplasia

Question 40

What are some variations in root formation?

Answer 40

Enamel pearl, dilaceration. Cementun formation

Question 41

When do the early stages of tooth development commence?

Answer 41

6th week in utero