Tooth Development

Question 1

Ectoderm

Answer 1

epithelium

• one of the three basic germ layers that forms skin, central nervous system, tooth enamel and many other structures.
• has folded/proliferated into the embryo as the anterior aspect of oral cavity
• no blood supply

Question 2

Endoderm

Answer 2

epithelium

one of the three basic germ layers that forms the gut tube and its derivatives

Question 3

Mesoderm

Answer 3

one of the three basic germ layers that forms blood vessels, bone, connective tissue and other structures

Question 4

Neural crest cells

Answer 4

cells of the neuroepithelium that form at the tips (crest) of the neural folds and then migrate to form many structures including spinal ganglia, head and neck connective tissue, dentin, support tissues of the tooth and many other structures

Question 5

Ectomesenchyme

Answer 5

embryonic connective tissue (mesenchyme) that is derived from neural crest cells (will form dentin, cementum, periodontal ligament, alveolar bone)

Question 6

Day 37 of development

Answer 6

o Formation of the primary epithelial band (proliferated epithelium at the site of the future dental arches)

Question 7

Day 42-48 of development

Answer 7

2 subdivisions form: dental lamina and vestibular lamina

Question 8

Dental lamina

Answer 8

horseshoe shaped thickening of epithelium were the developing teeth are

Question 9

vestibular lamina

Answer 9

cells enlarge and then degenerate to form the vestibule of the oral cavity

Question 10

Steps of tooth development

Answer 10

1) sites established
2) shape of tooth determined
3) cells differentiate to give rise to dental tissues
(steps 2 and 3 overlap)

• cell signalling occurs throughout
• each stage describes the morphology of the tooth: budstage, capstage, bellstage

Question 11

Enamel organ (enamel)

Answer 11

epithelial ingrowth

Question 12

condensed ectomesenchyme

Answer 12

• makes dental papilla (dentin in adult))
• surrounding enamel organ and dental papilla is dental follicle/sac (gives rise to cementum and periodontal ligament, alveolar bone)

Question 13

bud stage

Answer 13

Stage 1

• tooth buds grow in to underlying ectomesenchyme
• These are the buds for the deciduous teeth (“shed” during childhood)
• Cells only proliferate…no change in function at this time

Question 14

cap stage

Answer 14

• deep surface of the bud invaginates and becomes cap shaped
• Peripheral cells: become cuboidal or columnar shape
• As development continues in the enamel organ, the matrix has increasing amounts of glycoaminoglycans
• Center area becomes hydrated, cells pulled apart and maintain contact via desmosomes (Stallate reticulum: hydration and desmosomes become star shaped)
• Layer adjacent to the dental papilla is called the inner enamel epithelium which give rise to the ameloblast which secrete enamel

Question 15

Stratum intermedium

Answer 15

does not secrete enamel but important in producing enamel synergistically with inner enamel epithelium

Question 16

Bell stage

Answer 16

-developing tooth becomes bell shaped as the undersurface of the enamel cap deepens to form four regions: outer enamel epithelium, stellate reticulum, stratum intermedium, inner dental epithelium

Question 17

Outer enamel epithelium

Answer 17

thick basement membrane separates it from ectomesenchyme. Will not produce enamel

Question 18

Stellate reticulum

Answer 18

mechanical role. Protects dental tissues and produces signalling molecules

Question 19

stratum intermedium

Answer 19

flattened cells overlying inner dental epithelium, role in producing proteins and transporting them to inner dental epithelium

Question 20

Inner dental epithelium

Answer 20

columnar shape cells, elongate prior to producing enamel and (functionally) change polarity to secrete adjacent to the basement membrane. Give rise to ameloblasts.

Question 21

Cervical loop

Answer 21

• inner and outer enamel epithelium are continuous at the cervical loop
• this is where outer epithelium bends to meet the inner epithelium
• gives rise to epithelium that will signal root development

Question 22

Early events of bell stage (late cap stage)

Answer 22

• dental lamina and lateral lamina around tooth germ begin to degenerate
• developing tooth has lost connection with oral cavity
• tooth will continue to develop in the underlying tissues of the oral cavity
• cells of dental/lateral lamina usually completely degenerate
• persistence of these cells may form small cysts (filled with keratin) over the developing tooth and could interfere with tooth eruption
• tooth crown assumes final shape

Question 23

Development of blood vessels in dental papilla

Answer 23

during cap stage and continue to increase through development.

Dental sac/follicle also well vascularized (but blood vessels never penetrate stellate reticulum)

Question 24

Hard tissue formation

Answer 24

• late cap stage though bell stage significant for histodifferentiation.
• cells of inner dental epithelium differentiate into ameloblasts
• cells of dental papilla differentiate into odontoblasts

Question 25

histodiferentiation

Answer 25

cells transforming into morphologically and functinally distinct components

Question 26

Reciprocal induction

Answer 26

development of dentin and enamel requires the ameloblasts and odontoblasts signal each other. Lack of this causes abnormal tooth development. differentiation of odontoblasts initiated by an organizing influence from the cells of the inner enamel epithelium. dentin formation always precedes enamel formation

Question 27

Inner enamel epithelium

Answer 27

- mitotic activity of the inner enamel epithelium ceases at the site where dentin will first appear - under inductive influence of developing ameloblasts (pre ameloblasts) some of the ectomesenchymal cells become columnar and differentiate into odontoblasts

Question 28

odontoblasts

Answer 28

- differentiated from dental papilla induced by pre-ameloblasts - begin to secrete predentin that eventually calcify as dentin - as predentin calcifies, odontoblasts move towards papilla - long apical processes of odontoblasts reside in dentinal tubules (canaliculi) that extend the full thickness of the dentin

Question 29

ameloblasts

Answer 29

- differentiated from inner enamel epithelial cells - contact with dintin induces ameloblasts to begin secretion of enamel matrix - enamel becomes mineralized almost immediately - ameloblasts moving away from the odontoblasts and from their own blood supply - when enamel is full thickness ameloblasts enter maturation stage

Question 30

Nourishment of enamel organ

Answer 30

Early in development: enamel gets nourishment from blood vessels of dental papilla, and blood vessels surrounding the enamel organ Later in development: layer of dentin interferes with diffusion from papilla, stellate reticulum collapses as compensation and brings peripheral blood vessels closer to the new active ameloblast layer

Question 31

papillary layer

Answer 31

- formed from reorganized cells of statum intermedium, stellate reticulum, and outer enamel epithelium - ameloblast layer and papillary layer form the reduced dental/enamel epithelium

Question 32

Dental follicle

Answer 32

- formed from supporting tissues of tooth | - some cells differentiate into cementoblasts and form cementum (poor regenerative capacity)

Question 33

Periodontal ligament

Answer 33

- derived from dental follicle (ectomesenchyme) - located between cementum and alveolar bone of tooth socket - CT with thick collagen fibers (mostly type I) - different than other ligaments of body (cellular, vascularized, highly innervated) - high rate of collagen turnover (vulnerable with nutritional deficiencies) - CT of gingiva continuous with CT of periodontal ligament

Question 34

Tooth eruption

Answer 34

- tooth covered by reduced enamel epithelium - bone overlying tooth resorbed - CT over the tooth breaks down - Reduced enamel epithelium and oral epithelium fuse: central epithelial cells degenerate and dentogingival junction formed which gives rise to junctional epithelium of gingiva.