Root Development & Tooth Eruption

Question 1

What is the cervical loop?

Answer 1

Region where the inner and outer enamel epithelia meet with no stellate reticulum in between

Question 2

What does the HERS do? (3)

Answer 2

Maps out root shape

Induce odontoblast differentiation

Initiates cementum and PDL formation

Question 3

What type of odontoblasts are formed during the growth of HERS?

Answer 3

Root odontoblasts

Question 4

When does the HERS disintegrate?

Answer 4

When root odontoblasts lay down predentin

Question 5

How does the HERS induce cementum and PDL formation?

Answer 5

HERS disintegrates; root odontoblast predentin becomes mineralised

Dental follicle mesenchymal cells contact root dentin triggering differentiation into cementoblasts

Cementoblasts secrete cementum

Fibroblasts will secrete collagen = PDL

Question 6

What are the two types of cementum and where are they found?

Answer 6

Acellular cementum - coronal two-thirds of root

Cellular cementum - apical third of root

Question 7

Contrast the basic structures of cellular and acellular cementum.

Answer 7

Cellular - thicker with cementocytes

Acellular - thin layer

Question 8

What are the cell rests of Malassez?

Answer 8

Persisting clusters of epithelial cells remaining from HERS disintegration

Question 9

What complications could arise from the cell rests of Malassez?

Answer 9

Odontomas

Cysts

Question 10

Describe the formation of the root apex.

Answer 10

At a certain horizontal level, the HERS will change orientation and grow at right angles until they meet and fuse in the centre - epithelial diaphragm

A small gap is left - apical foramen

Question 11

When does the PDL start to develop?

Answer 11

Tooth eruption

Question 12

What cells secrete the collagen for the PDL?

Answer 12

Dental follicle fibroblasts

Question 13

What do the epithelial layers fuse to become before eruption?

Answer 13

Reduced enamel epithelium

Question 14

*What happens as the tooth makes its way to the oral cavity?

Answer 14

Alveolar bone resorbed to form the epithelial canal

REE fuses with oral epithelium

Question 15

Is there any bleeding when teeth erupt and why?

Answer 15

No

Tooth erupts through the epithelial canal

Question 16

Why is decay of enamel more problematic after tooth eruption?

Answer 16

No ameloblasts available to replace enamel

Question 17

What epithelia form the dento-gingival junction?

Answer 17

Oral epithelium

Reduced enamel epithelium

Question 18

What is the Gubernacular cord?

Answer 18

Dental lamina which connects the teeth to the oral epithelium from within the bony crypt

Question 19

Where does bone resorption start for tooth eruption?

Answer 19

Gubernacular cord

Question 20

Why are the roots of deciduous teeth resorbed?

Answer 20

No more anchoring so it can fall out and allow permanent teeth to erupt

Question 21

What are the three proposed mechanisms of tooth eruption?

Answer 21

Pulling by the PDL

Pushing by root growth

Pushing by alveolar bone remodelling

Question 22

What is the most likely mechanism of tooth eruption?

Answer 22

Pushing by alveolar bone remodelling

Question 23

How is bone remodelled during tooth eruption?

Answer 23

Resorbed above tooth by osteoclasts

Deposited below tooth by osteoblasts

Question 24

What part of the dental follicle is osteogenic?

Answer 24

Basal/apical half

Question 25

What part of the dental follicle is osteoclastic?

Answer 25

Coronal half

Question 26

What factor does the osteogenic half of the dental follicle release and what does it do?

Answer 26

BMP2 Promotes osteoblast differentiation

Question 27

What tissue controls alveolar bone metabolism?

Answer 27

Dental follicle

Question 28

What factors does the osteoclastic half of the dental follicle release and what do they do?

Answer 28

M-CSF1 (macrophage colony stimulating factor 1) RANKL (receptor activator of nuclear factor Kappaβ ligand) MCP1 (monocyte chemotactic protein 1) Promote osteoclast differentiation

Question 29

Where is NF1-C expressed and where do defects occur?

Answer 29

Crown and root odontoblasts In root odontoblasts

Question 30

What is the function of NF1-C?

Answer 30

Promotes odontoblast differentiation (in root)

Question 31

What is characteristic of NF1-C mutant mice?

Answer 31

Rootless teeth

Question 32

What two disorders result in short roots?

Answer 32

Dentin dysplasia type 1 Sponastrime dysplasia

Question 33

Which gene is affected in dentin dysplasia type 1?

Answer 33

DSPP/dentin sialophosphoprotein gene

Question 34

What is the difference between sponastrime dysplasia and dentin dysplasia type 1?

Answer 34

Sponastrime dysplasia also results in short limbs/dwarfism and spinal and facial bone abnormalities

Question 35

What syndrome results in abnormally long roots?

Answer 35

OFCD oculo-facio-cardio-dental syndrome

Question 36

What does BCOR usually do?

Answer 36

Inhibit methylation of H3K4 and H3K36 to promote odontoblast differentiation

Question 37

What does a mutation in BCOR result in?

Answer 37

Methylation of H3K4 and H3K36 Mesenchymal cells do not differentiate so roots keep growing and have an open apex (OFCD syndrome)

Question 38

What is taurodontism?

Answer 38

Failure of HERS to invaginate at the proper horizontal level (epithelial diaphragm forms too late)

Question 39

What syndrome results in taurodontism?

Answer 39

Tricho-dento-osseous

Question 40

What are the three types of taurodonts?

Answer 40

Hypotaurodont Mesotaurodont Hypertaurodont

Question 41

What is different about the teeth in taurodontism? (3)

Answer 41

Enlarged pulp chamber Apical displacement of pulp floor No constriction at cementoenamel junction

Question 42

What type of mice will have variable root numbers?

Answer 42

EDA+/-

Question 43

The loss of what gene would result in single rooted molars?

Answer 43

Ezh2 in dental mesenchyme

Question 44

What can mutations in the ectodysplasin pathway result in?

Answer 44

Taurodontism Variable root (and cusp) number

Question 45

What does Ezh2 code for?

Answer 45

Histone methyl transferase which methylates H3K27

Question 46

Which pathway determines cusp number?

Answer 46

Ectodysplasin pathway

Question 47

Why does the osteoclastic half of the dental follicle secrete chemokines?

Answer 47

To recruit monocytic precursors and macrophages to produce osteoclasts