Alginate

Question 1

What are the key properties of impression materials?

Answer 1

• Flow = ability to replicate the intraoral surface details.
• Dimensional Stability = ability to retain its absolute dimensional size over time.
• Tear Resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.

Question 2

What are desirable properties of impression materials?

Answer 2

1. Adequate shelf life
2. Acceptable odor and taste.
3. Biologically acceptable: No toxic or irritant constituents
4. Easily manipulated: Easy to use with the minimum of equipment
5. Setting characteristics that meet clinical requirements:
6. Properties of the set material:
7. Economically commensurate with the results obtained

Question 3

What factors affect the accuracy of impression materials?

Answer 3

• Must be in Fluid Or Plastic State on insertion
• Dimensional changes on setting -> neglible
• Must be ELASTIC on removal from the mouth
• Adhere to the tray.
• Dimensional Stability on Storage.
• Compatible with Model & Dies.

Question 4

What are the classifications of impression materials?

Answer 4

1) Method of setting
a. Hardening by chemical reaction:
- Plaster of Paris, Alginates, and Rubber impression materials.
b. Softening and hardening by heat:
- These are thermoplastic substances.
- e.g. Impression compounds.

2) Behaviour after setting
a. Non-elastic impression materials:
- They are used only when no undercuts exist.
- e.g. Plaster of Paris, and Zinc oxide Eugenol.
b. Elastic impression materials:
- They can be used when undercuts exist.
- e.g. Hydrocolloids, and Rubber impression materials.

3) Viscosity
a. Mucodisplacive impression materials:
- e.g. Impression compound, high viscosity alginates, and high viscosity elastomers.
b. Mucostatic impression materials:
- e.g. Plaster, zinc oxide Eugenol, and low viscosity alginate

Question 5

List some non-elastic and elastic impression materials.

Answer 5

1) Non-elastic impression materials
- wax
- Impression plaster (plaster of Paris)
- Impression compound
- Zinc-oxide-Eugenol impression material

2) Elastic impression materials
- alginate
- agar

Question 6

What are the advantages and disadvantages of alginate?

Answer 6

1) Advantages
- Easy of mixing and manipulation.
- Minimum equipment.
- Flexible.
- Accuracy.
- Low cost.

2) Disadvantages
- Restrict the model & die material to only gypsum.
- Not accurate in reproducing fine details.

Question 7

What is sol-gel transformation?

Answer 7

• Particles are suspended in the solution. The consistency of solution changes, when the environment changes, ie. Temp, pressure or chemical stimulus
• The molecules agglomerate and form a gel like structure.
• for agar to change consistency -> need reduction in temp
• for alginate to change consistency -> need chemical reaction.

Question 8

What is the composition of alginate?

Answer 8

• Sodium Potassium Alginate.
• Calcium Sulfate.
• Sodium Sulfate.
• Diatomaceous Earth.
• Potassium Sulfate or Fluoride.
• Glycol (in dustless alginates)

Question 9

What are the properties of alginate?

Answer 9

1. Permanent deformation:
   - It should be less than 3% according to ADA specification.
2. Strength:
   - Compressive strength
   - Tear strength

Question 10

What factors affect strength of alginate?

Answer 10

• W/P ratio.
• Proper spatulation.
• Rate of deformation.
• Thickness of impression material.