Impression Materials (2)

Question 1

What are the categories of impression material types? Which are we focused on?

Answer 1

Rigid or Brittle
Plastic
*Elastic - but really viscoelastic

Question 2

What are the different types of hydrocolloids?

Answer 2

Reversible (agar)

Irreversible (Alginate)

Question 3

What are the basic categories of polymers

Answer 3

Thermoplastic

Termoset

Question 4

Termoplastic polymers

Answer 4

No cross-linking

Physical state is reversibly controlled by temperature - fluid when heated, and harder when cooled

Question 5

Thermoset polymers

Answer 5

Transformation from monomer to polymer involves irreversible cross-linking

Question 6

Synthetic elastomers

Answer 6

Oligomers polymerize into elastomers

Question 7

What are the physical phenomena that occur during polymerization

Answer 7

Advantageous final properties are increased
Inherent density increase, causing a volumetric contraction
Heat of reaction causes material to heat up
There is a contraction on cooling

Question 8

Polysulfide

Answer 8

Low molecular weight oligomers

Conform well to a prepped tooth, resulting in good surface detail

Question 9

What oxidizes polysulfide?

Answer 9

Lead dioxide or copper hydroxide to form a polysulfide rubebr

Question 10

What helps a polysulfide impression be accurate?

Answer 10

Rigid custom tray for minimal thickness of impression material

Question 11

Silicones are inherently ____________

Answer 11

Hydrophobic

Question 12

What type of silicones can be made hydrophilic? How?

Answer 12

The addition type.
By the simple addition of surfactant or
Chemical incorporation of hydrophilic moieties to the silicone backbone

Question 13

What is the contact angle important for?

Answer 13

Unset impression material over wet structures

Unset gypsum-water mix into set impression

Question 14

What are the requirements of Ideal impression materials

Answer 14

Low cost
Long shelf life
Biocompatibility
Pleasant to the patient

Question 15

What properties of an impression are ideal before setting

Answer 15

Ease of manipulation
Control over working time
Good wetting on moist oral structures

Question 16

What properties of an impression are ideal during setting

Answer 16

No dimesnsional change

Short setting time

Question 17

What properties of an impression are ideal after setting

Answer 17

High flexibility
High tear strength
No dimensional changes
Compatibility with disinfectants
Compatibility with die and cast materials