D2 - hydrocolloid Impression Materials and Disinfection and Alternatives to Impressions

Question 1

what are the requirements for impression materials?

Answer 1

• surface detail reproduction
• dimensional accuracy and stability
• no changes when exposed to disinfectants
• no interaction with model/die materials
• non toxic
• easily manipulated
• palatable taste
• realistic working/setting time

Question 2

Name for when moist surfaces repel?

Answer 2

Hydrophobicity

Question 3

What does a high viscosity do to impression material?

Answer 3

Less detail but can displace soft tissues

Question 4

What does a low viscosity do to impression material?

Answer 4

More detail but tray won’t contain

Question 5

what are the two classifications of impression materials?

Answer 5

• non elastic

- elastic

Question 6

Give two example of a non elastic impression material

Answer 6

• Zinc Oxide and Eugenol pastes

- impression plaster

Question 7

Give two examples of elastic impression materials

Answer 7

• hydrocolloids

- synthetic elastomers

Question 8

Name a reversible hydrocolloid

Answer 8

agar

Question 9

Name a irreversible hydrocolloid

Answer 9

alginate

Question 10

what two forms do hydrocolloids exist in and what are their characteristic?

Answer 10

sol - fluid, low viscosity, random chain arrangement

gel - increases viscosity, parallel chain arrangement, elastic

Question 11

How can a sol change into a gel?

Answer 11

By a temperature or chemical reaction

Question 12

How can a gel change into a sol?

Answer 12

temperature

Question 13

What is agar supplied in gel with?

Answer 13

• borax (to give more body)

- potassium sulphate (to counteract retardant effect of borax upon dental plaster (gypsum))

Question 14

What does agar require?

Answer 14

Water bath conditioning. In clinical use it requires water cooled trays

Question 15

What are the advantages of agar? (2)

Answer 15

• take up moisture

- re use

Question 16

What are the disadvantages of agar? (5)

Answer 16

• special equipment
• cost
• cross infection concerns of reuse
• low tear strength
• dimensionally unstable due to water content

Question 17

What is the name for the loss of water from squeezed chains?

Answer 17

Syneresis

Question 18

What is the name for uptake of water? It causes swelling due to chain separation

Answer 18

Imbibition

Question 19

What can agar be used for clinically?

Answer 19

partial dentures
crowns
bridges

Question 20

How can agar be used in the laboratory?

Answer 20

duplicating material

Question 21

what are the properties of alginate?

Answer 21

• low viscosity
• adequate working time
• rapid set
• elastic
• must use no less than 3-5mm thick to prevent distortion on removal
• susceptible to syneresis and imbibition

Question 22

how is alginate supplied?

Answer 22

powder mixed with water

Question 23

What is a variant to alginate which offers marginally better detail reproduction and tear resistance? It has poor dimensional stability and is supplied as two pastes

Answer 23

Modified alginate with silicone polymers

Question 24

Give 2 alternatives to impressions

Answer 24

CAD CAM

intraoral scanner

Question 25

what is immersio disinfection?

Answer 25

• solution freshly made
• follow manufactures instructions
• time immersion
• rinse with water

Question 26

How do you make up Actichlor tablets?

Answer 26

• 10 tabs in 1000ml water. Each tablet weighs 1.7g
• effervescent chlorine releasing tablets
• 1000ppm= 1% available chlorine
• rinse
• immerse for 2 mins