Craig’s the Oral Environment

Question 1

Dentin and cementum are mainly comprised of ___ matrix reinforced with the calcium phosphate mineral called ___.

Dentin forms the bulk of the tooth and is joined to the enamel at the ___

Dentin is covered by ___ that provides connection of the tooth to the ___ via the ___.

Answer 1

1. Collagen type 1
2. Apatite
3. Dentin-enamel junction (DEJ)
4. Cementum
5. Alveolar bone
6. PDL

Question 2

Enamel is formed by ___ starting at the DEj. They exchange signals with ___ located on the other side of the DEJ and move away from each other.

The structural arrangement of enamel forms keyhole-shaped structures known as ___ that are ~__ µm across.

Answer 2

1. Ameloblasts
2. Odontoblasts
3. Enamel prisms
4. 5 µm

Question 3

Why is dentin more soluble/susceptible to acid than enamel? (Aka rapid spread of caries once it penetrates the DEJ) (Four reasons)

Answer 3

1. Different carbonate content (3% for enamel to 5% for dentin) for their calcium-deficient carbonate-rich hydroxyapatite.
2. Dentin apatite crystals are smaller than enamel crystals (more surface area to attacking acids)
3. Dentin mineral occupies only 50% of dentin structure, so not as much apatite compared to enamel (85%)
4. The dentin tubules provide a pathway for acid dissolution.

Question 4

Dentin - percent volume composition?

Answer 4

50 vol% carbonate-rich, calcium-deficient apatite
30 vol% organic matter (mostly type 1 collagen)
20 vol% fluid

Question 5

Dentin tubules represent the tracks taken by the ___ cells from the DEJ or cementum to the pulp chamber. Tubule density is lowest at the ___ and highest near the ___, where ___ cells in a close-packed array.

How does this affect dentin bonding?

Answer 5

1. Odontoblastic cells
2. DEJ
3. Pulp chamber
4. Odontoblastic cells
5. Deep dentin has a higher density of tubules per unit area which means more moisture when deep dentin is cut. A wetter surface means possible interference with bonding procedures.

Question 6

Why is the dentin-pulp complex considered vital tissue?

What’s differentiates primary from secondary dentin? How about from tertiary dentin?

Answer 6

1. The odontoblasts rest inside the dentin and line the walls of the pulp chamber.
2. Secondary dentin forms over time and has a change in orientation of the dentin tubules.
3. Tertiary is in response to insults such as caries or tooth preparation and is less organized than either 1 or 2.

Question 7

Why is bonding to dentin difficult? (Four reasons)

Answer 7

1. Dentin collagen matrix is wetter than enamel.
2. Cutting dentin results in smear layer formation. (Plugs up dental tubules)
3. Dentin may be altered by caries (tertiary dentin) which may result in loss of mineral
4. Lower mineral content

Question 8

Why is the DEJ considered a crack-arresting interface?

Answer 8

Enamel is brittle and is not as tough as dentin. Dentin is needed to support and redistribute stresses to resist crack propagation from enamel to dentin. The gradual transition from dentin to enamel prevents an abrupt transition in mechanical properties which would lead to high stress at the junction.

Question 9

Enamel - Percent volume composition?

How does that compare to most bones?

Answer 9

95% vol Hydroxyapatite (mineral)
4-5% vol Water
1% vol Organic material

Most bones are 70% vol minerals and contains collagen (think bone marrow dishes)

Question 10

At what pH does enamel start to dissolve?

How does this compare to stomach acid?
Soda?
Sparkling water?

Answer 10

Critical pH of 5.5

Stomach acid: 1.5 to 2
Soda: 2.5 to 3.5
Sparkling water: 3 to 6