Week 4 PP

Question 1

5 Types of Gypsum

Answer 1

1. Impression Plaster
2. Model Plaster
3. Dental Stone
4. Die-Stone
5. High-Strength Stone

As an assisant, you will work with 1-3. (less crystals) Not working with 4 & 5 in dental office. (more crystals)

Question 2

Crystals in Gypsum?

Answer 2

Hemihydrate crystals are within gypsym (1/2 part water & 1 part of calcium sulfate)

More crystals = more strength

The only difference between the five are the size, shape, and porosity of the hemihydrate crystals.

Question 3

Impression Plaster & Model Plaster

Answer 3

-commonly called plaster of Paris
-White in colour
-used primarily for pouring preliminary impressions
-model plaster is the weakest (greatest quantity of water)

Question 4

Dental Stone

Answer 4

• Usually yellow in colour
  -Used when a more durable diagnostic cast is required such as for a retainer
  -The result is a study model that is much stronger and denser than one made from plaster

Question 5

Die Stone

Answer 5

• known as densite or improved dental stone
  -the crystals in high-strength stone are smooth and very dense
  -Used to replicate the exact portion of the tooth known as die
  -Used by the dental laboratory technician (production of crowns, bridges, and indirect restorations)

Question 6

High-Strength Stone

Answer 6

-Strongest, least expansion!
-The crystals in high-strength stone are smooth and very dense
-Use by the dental laboratory technician
-Require the least water

Question 7

Stone setting reactions

Answer 7

Follow manufacturers instructions
Mixed with cool water
Too much water = voids and bubbles = missing anatomy = weak & brittle
Not enough water = dry mix = short working time

Question 8

Storage Methods for Gypsum Products

Answer 8

-Dry & Cool Place
-Humidity not advised

Question 9

Gypsum Pouring Methods

Answer 9

1. Double-pour method
2. Box-and-pour method (not used for study models)
3. Inverted-pour method

Question 10

What is the Double Pour Method?

Answer 10

-Anatomic portion (teeth) is poured first
-A Second mix is prepared for the art portion (base)
-Base former can be used

Question 11

What is the Boxing Wax Pour Method?

Answer 11

Used for whitening trays, sports guards
-Both portions are poured at once using one batch of mixed stone

Question 12

What is the Inverted Pour Method?

Answer 12

• One large mix
  -The anatomical portion is poured first
  -Base is poured second

This is the method used at SAIT