Histology - Teeth

Front 1

Developmental stages of tooth

Back 1

1. primary epithelium band, 5wks: initiation
2. bud stage, 6-8wks: ingrowth
3. cap, 8-12wks: morphogenesis
4. bell, 12-16wks: differentiation
5. crown, 18wks: mineral forms

Front 2

Bud stage of tooth development

Back 2

1. epithelial cells move into the underlying ectomesenchyme
2. ectomesenchyme cells pack closer together, around the bud

Front 3

tooth germ

Back 3

dental organ, dental papilla, dental follicle

Front 4

Cap stage of tooth development

Back 4

1. the bud splits into a cap-like structure due to proliferation
2. the epithelium forms the enamel organ
3. ectomesenchymal cells aggregate beneath the enamel organ in a process called condensation, to form the dental papilla
4. the dental follicle (sac) forms

Front 5

Describe enamel knot

Back 5

The enamel knot is a group of closely oriented cells within the enamel organ. This structure signals the formation of cusps. After providing the signal, enamel knot cells die by apoptosis.

Front 6

Fgf-4

Back 6

gene expressed at the enamel know, induce cusp development

Front 7

Describe bell stage tooth development

Back 7

1. during bell stage, the undersurface of the enamel organ deepens, and cellular histo-differentiation begins. The inner dental epithelium folds according to tooth type
2. dental lamina disintegrates into small islands
3. epithelial cells assume different appearance in preparation for formation of the hard tissue (enamel). stellate reticulum is reduced in thickness at location of mineral formation.

Front 8

4 epithelial cell types observed during bell stage are

Back 8

outer dental epithelium: cuboidal cells
stellate reticulum: star-shaped cells
stratum intermedium: several flattened layers
inner dental epithelium: short columnar

Front 9

Describe the interaction between the IDE and DP cells

Back 9

1. cells of IDE and DP communicate with each other though the BM.
2. IDE and DP stops proliferating. Reversal of polarity: nuclei move opposite direction from the BM and become taller.
3. preameloblast send signals below and the cells of DP become odontoblasts. Predentin forms when mineral is secreted to the ECM. The undifferentiated pre-odontoblast sit below the the odontoblasts.
4. Presence of dentin signals the preameloblast to make enamel and becomes ameloblasts

Ameoblasts make enamal and odontoblast make dentin, DEJ = dental enamal junction

Front 10

permanent teeth

Back 10

permanent molar tooth germs (w/o precursors) begin to develop as the dental lamina burrows back from the second premolar.

Front 11

reciprocal interaction

Back 11

important in determining the location at which teeth will develop

Front 12

BMP4 + FGF8 ->
FGF8 -> Pax9 ->

Back 12

BMP4 + FGF8 -> no tooth development
FGF8 -> Pax9 -> tooth development

Hint 12

some of the epithelium cells begin to secret Fgf8 and the protein go down to ectomesenchyme and induce expression of Pax9.

Below. When BMP4 and Fgf8 are expressed, teeth do not develop

Front 13

3 mechanisms of signaling

Back 13

1. single signal
2. combined signals resulting in antagonism
3. combined signals resulting in synergism

Hint 13

antagonism (FGF and BMP in tooth undevelopment)
synergism (FGF and BMP work together in heart development)

Front 14

Late bell, early crown stage

Back 14

1. Mineralized dentin and enamel have begun to form
2. First odontoblasts differentiate at the tip of the cusp or incisal edge
3. Subsequently, ameloblasts begin to differentiate at the same location.
4. Both cell types progressively differentiate down the slopes of the cusp, with odontoblasts always earlier.

Front 15

reduced dental epithelium

Back 15

reduction in thickness of the enamel organ where dentin and enamel have been secreted.

Front 16

Is inner dental epithelial cells involved in root dentin formation?

Back 16

No, inner dental epithelial cells are not involved in root dentin formation, they are only found in the crown

Front 17

Root Formation

Back 17

1. Internal and external dental epithelial cell layer grows downward from the cervical loop to form HERS
2. The inner layer of cells secrete some enamel related proteins, but don't become ameloblasts
3. HERS cells induce dental papilla cells to differentiate into odontoblasts to produce root dentin.
4. HERS then breaks away to form epithelial rests of Malassez
5. Dental follicle cells migrate inward (green arrow) and become cementoblasts and starts to secrete cementum

Hint 17

HERS: Hertwig's epithelial root sheath

Front 18

cementoblasts

Back 18

-precursors are in the dental follicle.
-cementocytes are found w/i mineralized cementum, and have cytoplasmic processes in canaliculi, oriented toward the vascularized PDL.
-cementum forms continually and thickens with age.

Hint 18

PDL: periodontal ligament

Front 19

epithelial cell rests of Malassez

Back 19

found in the periodontal ligament, residue of HERS that didn't completely disappear

Front 20

Dental follicle produces 3 cell types

Back 20

cementoblasts, periodontal ligament fibroblasts and alveolar bone osteoblasts

Front 21

percent of minerals in these tissues:
enamel
dentin
cementum
bone

Back 21

95% mineral
70%
50-61%
45-47%

Front 22

Events during tooth eruption

Back 22

1. bone remodeling: create a pathway thru bone
2. root growth
3. mucosal penetration: penetrate the oral mucosa
4. preocclusal eruption: until the occlusal plane is reached
5. PDL remodeling: to permit movement

Front 23

odontoclasts

Back 23

bone resorption

Front 24

2 required structures in regulation of tooth eruption

Back 24

1. dental follicle 2. reduced dental epithelium

Front 25

mechanisms of tooth eruption

Back 25

RDE = reduced dental epithelium generate TGF-beta, which is received by the dental follicle and secrete CSF-1, which brings in osteoclast, teeth erupt. another signal produced at the root promote bone formation

Front 26

reciprocal interactions: epithelial-mesenchyme relationships

Back 26

mesenchyme determines the fate of the epithelium

Front 27

Mandibular central incisor erupts first

Back 27

Ture

Front 28

diphyodont dentition
monophyodont dentition

Back 28

diphyodont: 2 sets of teeth
monophyodont: 1 set of teeth

Front 29

Andontia

Back 29

congenitally missing teeth, complete or partial. 3rd molar, maxillary lateral incisors and MD second premolars are most commonly affected.
(oligodontia, hypodontia)

Front 30

Oligodontia

Back 30

congenital absence of many but not all teeth

Front 31

Hypodontia

Back 31

only a few teeth are missing

Front 32

Rod Sheath

Back 32

Rod sheath is a space created by crystal orientation at right angels. Small amounts of protein remains here (sheathlin). The rod sheath separates enamel rods/prisms.