Tooth Tissue & Formation

Question 0

What cells form dentin?

Answer 0

Odontoblasts

Question 1

What cells form enamel?

Answer 1

Ameloblasts

Question 2

What is gnarled enamel?

Answer 2

When the regular orientation of the rods has been altered due to crowding of ameloblasts during enamel formation.

Question 3

Where do you most often find gnarled enamel?

Answer 3

Inter-cuspal regions

Only on teeth with more than one cusp

Question 4

What are the problems caused by gnarled enamel?

Answer 4

Enamel is weaker

Tooth more prone to caries

Question 5

What is essential for enamel rod formation?

Answer 5

Tomes process

Question 6

What are enamelins and amelogenins?

Answer 6

Glycoproteins found in developing enamel

Question 7

What are the defect lines found in enamel and dentine known as?

Answer 7

Enamel - Striae of Retzius

Dentine - Contour Lines of Owen

Question 8

What stage does enamel synthesis begin?

Answer 8

Late bell stage (cytodifferentiation)

Question 9

What are the five stages of tooth formation?

Answer 9

Initiation
Morphogenesis
Cytodifferentiation
Matrix secretion
Root formation

Question 10

What is the reduced enamel epithelium?

Answer 10

The several layers of the enamel organ remaining on the enamel surface after formation of enamel is completed. It acts as a protective layer.

Question 11

Where on a formed tooth is enamel the thinnest?

Answer 11

The cervix (neck) of the tooth

Question 12

Where does enamel formation start and end?

Answer 12

Starts at the cusp of the tooth and ends at the cervical region of the tooth.

Question 13

What are enamel lamella?

Answer 13

Hypomineralised defects in the enamel that extend from the surface to the ADJ and provide access to organisms and toxins directly to the dentine.

Question 14

What is an enamel tuft?

Answer 14

Hypomineralised defect, like an enamel lamellae, but only extending 1/3 into the enamel.

Question 15

What are enamel spindles?

Answer 15

Small portions of odontoblast tubules that become trapped in the first layer of enamel that is formed. Found at the ADJ.

Question 16

What are Hunter-Schreger bands?

Answer 16

alternating light and dark lines seen in enamel of the tooth that begin at the ADJ and end before they reach the enamel surface; they may represent areas of enamel rods cut in cross-sections dispersed between areas of rods cut longitudinally.

Question 17

How does the bone of the maxilla mature?

Answer 17

Intramembranous ossification - where bone forms from within

Question 18

How does the bone of the mandible mature?

Answer 18

Endochondral ossification - cartilage precursor is replaced with bone

Question 19

What embryonic layer do teeth & their supporting structures arise from?

Answer 19

Ectoderm - tooth enamel

Ectomesenchyme - all other parts of teeth & supporting structures

Question 20

What are the three embryonic layers?

Answer 20

Ectoderm, mesoderm, endoderm

Question 21

What is the neural crest?

Answer 21

A fourth cell type that forms between the ectoderm and the neural tube. It is a.k.a ectomesenchyme. Neural crest tissue migrates into the developing face and jaws.

Question 22

What is mandibulofacial dysostosis?

Answer 22

Failure of the ectomesenchymal cells to migrate. Can get severe & mild forms. A.k.a. treacher collins syndrome.
Signs - down slanting eyes, malformed ears, large interpupilar distance, small lower jaw

Question 23

What happens during the initiation stage of tooth formation?

Answer 23

Primary epithelial band develops at approx 6wks IUL
- appears as a thickening in epithelium of embryonic mouth (stomodaeum)
- forms from proliferation of the oral epithelium at the basal lamina
Cell proliferation forms the dental lamina and vestibular lamina from the PEB at approx 7 weeks
- vestibular lamina will form buccal sulcus
- dental lamina forms the enamel organ (enamel & dentine)

Question 24

What happens during the morphogenesis stage of tooth formation?

Answer 24

Approx 8-10wks IUL
Dental lamina thickens into ‘bud’ stage (enamel organ)
Dental papilla (cells surrounding the enamel organ) appear
Approx 11wks IUL
Enamel organ forms a ‘cap’ over the papilla
EEE & IEE meet at the cervical loop

Question 25

What is hypohidrotic ectodermal dysplasia?

Answer 25

Abnormal development of skin, teeth, nails, hair and sweat glands before birth. Due to a problem with EDA gene.

Question 26

What happens in the cytodifferentiation stage of tooth development?

Answer 26

Approx 14wks IUL.
More cell layers differentiated - stellate reticulum, stratum intermedium, IEE, EEE.
Tooth shape is being defined.

Question 27

When do permanent teeth begin to form?

Answer 27

week 12 - dental lamina for permanent teeth begins to form

week 16 - FPM germ develops as a backwards extension of the dental lamina

Question 28

What happens during the matrix secretion stage of tooth formation?

Answer 28

Approx 18wks IUL
Crown shape is well defined - crown formation is complete before root formation begins
Apposition of enamel and dentine begins
- dentinogenesis occurs first
- amelogenesis

Question 29

What are the stages of amelogenesis?

Answer 29

1. Protein matrix deposited by ameloblasts. Matrix is partially mineralised and does not contain collagen.
2. Once the framework is established, the organic part is removed and mineralisation is complete.
   * The ameloblasts change form and function several times during amelogenesis.

Question 30

What are the stages of dentinogenesis?

Answer 30

Odontoblast differentiation from IEE
Deposition of dentine matrix (mainly collagen).
This unmineralised dentine is predentine.
Mineralisation of dentine (hydroxyapatite).

Question 31

What are the phases of ameloblast differentiation?

Answer 31

Differentiation - IEE cells to ameloblasts
Secretory Phase - synthesis & secretion of enamel matrix proteins
Maturation Phase - most matrix proteins removed, mineral content of enamel increased
Protection Phase - ameloblasts regress to form REE

Question 32

What is amelogenesis imperfecta?

Answer 32

Disorder of tooth development causing teeth to be unusually small, discoloured, pitted or grooves and prone to rapid wear & breakage.
Due to problems with MMP20 gene.
Enamel appears yellow & rough, premolars not completely formed, enamel is not mineralised, serious & mild forms exist.

Question 33

What is dentinogenesis imperfecta?

Answer 33

Change in colour of dentine - blue/grey or yellow/grey & translucent.
Enamel is formed normally but dentine isn’t.

Question 34

What happens during the root formation stage of tooth development?

Answer 34

Hertwig’s Epithelial Root Sheath (a 2-cell-layered structure, previously the cervical loop) induces formation of root dentine. Once the initial layer is formed HERS breaks up and its remains persist as Debris of Malassez.
Mesenchymal cells from the follicle contact the dentine and differentiate into cementoblasts which form cementum.
Fibres from the developing PDL are embedded in the cementum.

Question 35

What are the different tooth germs and what do they form?

Answer 35

Enamel organ - enamel
Dental papilla - dentine, pulp
Dental follicle - cementum, PDL, alveolar bone

Question 36

What is gemination?

Answer 36

When two teeth are developed from one tooth bud. Results in a tooth with one main crown with a cleft in it, that looks like it is two teeth at the cervix, but it is not. The number of teeth in the arch will be normal.

Question 37

What is concresence?

Answer 37

When the cementum overlying the roots of at least two teeth joins together. Caused by trauma or crowding of teeth. Surgical separation of the teeth may be necessary if one is to be extracted.