Week 10 (dentin)

Question 1

What is dentine?
What is the dentin covered by in the crown and in the root?
What are two major features that distinguish dentin from enamel?

Answer 1

Dentine is mineralised tissue that forms the bulk of the tooth.
crown: enamel
Root: cementum
Two major properties distinguish
dentine from enamel.
1. Firstly, dentine is sensitive.
2. Secondly, dentine is formed
throughout life, increasing in
thickness at the expense of the dental
pulp

Question 2

Explain Dentinogenesis

Answer 2

Dentinogenesis commences with the formation of pre dentin by odontoblasts
Dentin consists of a large number of
small parallel tubules (Dentinal tubules)
in a mineralised collagen matrix.
* The odontoblast cytoplasmic processes
extend only 25–50% of the full length of
the dentinal tubule.
* The odontoblast process occupies most
of the space within the tubule and
coordinates the formation of
peritubular dentin.

Question 3

What are the physical properties of dentine?

Answer 3

Fresh dentine is pale yellow in colour.
* Dentine is harder than bone and cementum but softer than enamel.
* Higher fracture toughness- Dentine is much more resistant to the
propagation of cracks than enamel.
* Dentine is permeable, the permeability depending on the size and
patency of the tubules.
* By X-Ray: more radiolucent (darker) than enamel and more radioopaque (lighter) than cementum.

Question 4

What is the chemical composition of dentin

Answer 4

➢70% inorganic
➢20% organic, and
➢10% water.

(The inorganic component is in the form of (impure) calcium hydroxyapatite crystallites that give it its hardness.
* The organic component of dentine consists of collagen fibrils (type I
collagen) embedded in an amorphous ground substance.)

Question 5

What is the life cycle of odontoblasts

Answer 5

1. Preodontoblasts
   * Small, ovoid Cells
   * High nucleus/ cytoplasmic ratio
2. Secretory Odontoblasts
   * Formed of a cell body & odontoblastic
   process
   * Large plump cell, open-face nucleus
3. Resting Odontoblasts
   * The cell enter quiescent state after
   dentin formation and mineralisation is
   completed

Question 6

Dentinogenesis

Answer 6

Matrix Formation
After the differentiation of
odontoblasts, it secretes the initial
organic matrix, the predentin. This
matrix is composed of
➢small collagen fibrils (nearly all
type I)
➢characteristic ground substance.

Maturation (Mineralization)
* Maturation of dentin or
mineralization of predentin occurs
soon after its appositional growth.
* Formation of calcium
hydroxyapatite crystals- form as
globules or calcospherules in the
collagen fibers of the predentin

Question 7

What are the two types of mineralization

Answer 7

• Globular
  -linear calcification

Question 8

What are the types of dentin

Answer 8

peritubular dentin
intertubular dentin
Mantle dentin
Circumpulpal dentin
Primary dentin
Secondary dentin
tertiary dentin

Question 9

Peritubular dentin
Location:
Histological features:

Answer 9

Wall of tubules
Highly mineralized

Question 10

Intertubular dentin
location:
Histological Features:

Answer 10

Between tubules
Highly mineralized

Question 11

Mantle dentin
Location and Chronology:
Histologic Features:

Answer 11

Outermost layer near dentinoenamel
junction underneath enamel
First dentin formed

Question 12

Circumpulpal dentin
Location and Chronology:
Histologic Features:

Answer 12

Layer around outer pulpal wall
Dentin formed after mantle dentin

Question 13

Primary dentin
Location and Chronology:
Histologic Features:

Question 14

Location and Chronology:
Histologic Features:

Question 15

Location and Chronology:
Histologic Features: