Dental Material Properties

What are ideal properties of Impression Materials?

• Non-toxic

• Non-irritant

• Acceptability to the Patient

  • Setting time, taste, consistency

• Accuracy

  • Surface reproducibility

  • Dimensional stability

• Use of Material

  • Ease of mixing, working time, setting time, handling of materials

• Compatible with model materials

• Inexpensive

  • Long shelf life

• Ideally long working time and fast setting

Inelastic materials are?

Rigid materials with a low maximum flexibility

What transforms from a hard material to a soft, moldable material simply by increasing the temperature?

Impression Compound (thermoplastic)

Impression compound has what level of thermal expansion and thermal conductivity?

• High coefficient of thermal expansion

• Low thermal conductivity

What category of material is used for edentulous arches and bite restorations?

Inelastic materials

What are the 3 types of Inelastic materials?

1. Impression compound (thermoplastic)

2. Zinc Oxide Eugenol (ZOE) paste

3. Impression Plaster

Change is PURELY PHYSICAL in which inelastic material?

Impression Compound

Exposure to moisture and heat will accelerate the reaction in what inelastic material?

ZOE

Impression Plaster is based on __ __ __, which reacts with water to form calcium sulfate dihydrate.

Calcium Sulfate hemihydrate

Does Impression Plaster have an endothermic or exothermic setting reaction?

Exothermic setting reaction

Elastic materials are divided in 2 groups:

1. Hydrocolloids 

2. Elastomers

What is syneresis?

Lose water to contract

What is imbibition?

Absorb water to expand

Name the 2 kinds of Hydrocolloids and their examples.

1. Irreversible: Alginate

2. Reversible: Agar

What inorganic compound in Potassium alginate retards the ration to provide adequate working time?

Sodium Phosphate

Does Alginate go through syneresis or imbibition?

Syneresis, so pour it up ASAP

What is the only material that is easily torn?

Agar, it has poor tear resistance

Melting and gelling at different temperatures is called?

Hysteresis

What material is able to be changed from a liquid to a gel by raising or lowering the temperature?

Agar

Which subgroup of Elastic materials have a 2 paste system of a base and a catalyst?

Elastomers

What are the 3 viscosities of Elastomers?

1. Light body: register finest details

2. Heavy body: fill tray and provide support for the less viscous material

3. Medium body: combines both light and heavy properties

The setting reaction of Elastomers is inhibited when it comes in contact with what?

Latex

What are the disadvantages of lead dioxide in Polysulfide?

• may have some toxic effects

• stains clothes

• smells, tastes bad

• needs custom tray

What is vulcanization?

cross links the polymers through condensation reaction

Which 2 elastomers are hydrophobic?

1. Condensation Silicone

2. Addition Silicone (polyvinyl siloxane)

Which elastomer can be poured up later, is very elastic, and alcohol byproduct instead of water?

Condensation Silicone

__ __ enhances polymerization and cross-linking of polymer chains to make a very rigid polyether material

Sulfonic ester

Which elastomer is very stiff and is the least % flexibility?

Polyether

__ __ has excellent surface detail, most accurate, % elastic recovery.

Addition Silicone

Addition silicone is also known as?

Polyvinyl siloxane

What gas is released during setting of addition silicone and should not be poured for at least 45-60 mins?

Hydrogen gas

What are the anatomical landmarks for a MAX impression?

• Frena

• Tuberosity

• Vestibule

• Rugae

What are the anatomical landmarks for a MAND impression?

• Frena

• Retromolar area

• Vestibule

• Floor of the mouth