Hydrocolloids

Question 1

What is a solution?

Answer 1

Liquid consisting of homogenous mixture of solute and solvent e.g. saline

Question 2

What is a suspension?

Answer 2

Liquid continuous phase with solid discrete phase (2 phases exist) e.g. flour in water (they will eventually separate)

Question 3

What is a composite?

Answer 3

At least 2 distinct phases which can be individually recognised e.g. resin composite = glass particles and resin visible microscopically

Question 4

What is a colloid?

Answer 4

Somewhere between a suspension and a solution - particles dispersed in another material (continuous phase) but form a homogenous solution. The particles do not settle out like suspensions

Question 5

What is a hydrocolloid?

Answer 5

Colloid - particles dispersed in another material (when the material is water)

Question 6

List 4 types of colloid solutions?

Answer 6

Aerosols
Emulsion
Sols
Gel

Question 7

What is an aerosol?

Answer 7

Solid or liquid dispersed in gas

Question 8

What is an emulsion?

Answer 8

liquid dispersed in liquid

Question 9

What is a sol?

Answer 9

Solid dispersed in liquid

Question 10

What is a gel?

Answer 10

Liquid dispersed in solid

Question 11

What type of hydrocolloids are used for impression materials?

Answer 11

Sols and gels

Question 12

What process does impression taking using hydrocolloids use during setting?

Answer 12

Transition from sol to gel

Question 13

Difference in strutcure of sol and gel

Answer 13

Sol = random arrangement of fibrils
Gel = cross links between fibrils

Question 14

Difference between reversible or irreversible hydrocolloids?

Answer 14

How easy it is to break cross links

Question 15

Name a reversible hydrocolloid

Answer 15

Agar

Question 16

Properties of agar

a) interaction with water
b) stiffness
c) elasticity
d) strength
e) dimensional stability

Answer 16

a) hydrophilic = doesn’t require dry field
b) flexible - can move past undercuts
c) visco-elastic - will eventually return to original dimensions
d) low tear resistance
e) poor dimensional stability

Question 17

Why is agar technique sensitive?

Answer 17

Good technique means to is close to elastic rather than visco-elastic
- remove in rapid motion
Ensure fully set

Question 18

Describe agar dimensional stability, how to avoid?

Answer 18

Has high water content so can lose water over time

Pour cast quickly or store in soaked tissue

Question 19

Name an irreversible hydrocolloid?

Answer 19

Alginate

Question 20

effect of temperature of water in setting of alginate?

Answer 20

Hot water = faster setting

Cold water = slower setting

Question 21

Mixing alginate powder and water forms what type of hydrocolloid?

Answer 21

Sol

Sets into gel

Question 22

Properties fo alginate

a) water reactions
b) rigidity
c) elasticity
d) strength
e) dimensional stability

Answer 22

a) hydrophilic
b) flexible = undercuts
c) elastic/viscoelastic - allow to fully set
d) low strength = tears easily
e) poor dimensional stability - water evaporates