1 - Fundamentals of Dental Materials

Question 1

1. 10 What are the two structural units of enamel?

- What mineral do both of these structural units have?

Answer 1

Cylindrical enamel rods and interrod enamel

Both have hydroxyapatite crystals

Question 2

1. 10 Between the cylindrical enamel rods and the interrod enamel is a narrow space - what do you call this space?
   - What shape is this space?

Answer 2

Narrow space around 3/4 of each rod is called Rod sheath

It is a keyhole shape

Question 3

1.14 What are the two structural units of dentin?

Answer 3

Intertubular dentin

Peritubular dentin

Question 4

1.14 Describe intertubular dentin

Answer 4

Structural component of the hydroxyapatite-embedded collagen matrix - bulk of the dentin

Question 5

1.14 Describe peritubular dentin

Answer 5

Limited to the lining of the tubular walls - little organic matrix densely packed with apatite crystals

Question 6

1.20 What is the strongest and simple of the primary chemical bonds?

Answer 6

Covalent bond - electrons are shared by atoms so that each achieves an inert struture

Question 7

1.32 What are some of the biological concerns when dealing with the properties of materials?

Answer 7

The possibility of toxicity and sensitivity reactions that occur locally or systemically within associated tissues

Question 8

1.33 Describe the “surface energy” property of materials.

(Describe how a low surface energy liquid will interact with a high energy surface energy substrate)

Answer 8

A low surface energy liquid will readily spread over a high surface energy substrate.

(I think of it as gravitational pulls and that whatever object with the stronger gravitational pull will pull the other object towards in. In the case of the liquid, if the liquid is weaker, then it will spread. If the liquid is stronger, then it will not spread.)

Question 9

1.33 Describe the “wetability” property of materials.

Answer 9

The measure of the affinity of a liquid for a solid as indicated by the spreading of a drop

(Think of it as a droplet of water on cotton vs on vinyl - the water will absorb deeply into the cotton, but it will remain a bead on the vinyl.)

Question 10

1.35 What is adsorption?

Answer 10

Dissimilar substances in intimate contact with the surfaces of a solid = adhere

High energy surfaces will adsorb molecules more readily than low energy surfaces

From Wiki: the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.

Question 11

1.40 What is the best but most expensive bio-compatibility test?

Answer 11

Usage test (clinical trials) - material is placed in a situation identical to its intended clinical use - in animals or humans

Question 12

1.44 What is microleakage?

Answer 12

When a material does not bond with significant strength to resist contraction on polymerization, wear, or thermal cycling.

This results in an influx of materials through the gap between a tooth and its restoration that may irritate the pulp.

Question 13

1.46 What is the most important factor in whether an acid (which is used to remove the smear layer in dentin tubules) will be a source of irritation to the pulp?

Answer 13

The remaining dentinal thickness (RDT) - 0.5mm minimum.

If, after removing the smear layer in the tubule, the dentin is at least 0.55 mm thick, then there will be minimal pulp irritation.

Remaining dentinal thickness is the best pulp protector