Impression materials and digital impressions

Question 1

What is an impression

Answer 1

Negative record of the tissues of the mouth
It is used to reproduce the from of the teeth and surrounding tissues

Question 2

Mode of setting elastic materials

Answer 2

Alginate, polysulfide, polyether, silicone

Chemical reaction (irreversible)

Question 3

Mode of setting non elastic materials chemical

Answer 3

Impression plaster, zinc oxide Eugenol

Chemical reaction (irreversible)

Question 4

Mode of setting elastic materials physical

Answer 4

Agar

Question 5

Mode of setting non elastic physical

Answer 5

Impression compounds, impression waxes

Question 6

Why does hydrophilicity matter for impression materials

Answer 6

Allows impression materials to capture accurate details in a moist environment, ensuring better adaptation to wet oral tissues and reducing the risk of voids or bubbles in the impression

Question 7

Alginate dimensional stability

Answer 7

Short term stability, ideal for quick impressions

Water sensitive, can swell if exposed to water or shrink if allowed to dry out

Question 8

What is dimensional stability

Answer 8

Ability of an impression material to maintain its shape and size over time after setting
Without experiencing distortion, shrinkage or expansion

Question 9

Alginate tear strength

Answer 9

Moderate tear strength
Typically lower compared to elastomeric materials, which can make them less ideal for highly detailed impressions

Question 10

Handling of alginate

Answer 10

Careful technique is required during removal to prevent tearing

Use a gentle rocking motion, to reduce stress on the material

Question 11

What is tear strength

Answer 11

Ability of an impression material to resist tearing or rupture WHEN it is removed from the mouth

Question 12

What is Alginate less suitable for

Answer 12

Precise restorations like crowns and bridges

Question 13

Agar setting reaction

Answer 13

Cooling at 37-45
Heating at 70-100

Question 14

Agar dimensional stability short term

Answer 14

High initial accuracy, excellent at fine details due to its low viscosity in the sol state

Question 15

Agar dimensional stability long term

Answer 15

Poor
Syneresis: loss of water from the gel leadin to shrinkage

Inhibition: uptake of water causing expansion

Question 16

Agar tear strength

Answer 16

Careful handling to prevent tearing

Question 17

Agar elasticity

Answer 17

Good, can stretch and recover shape without permanent deformation