01: Dr Moon Alginate Lecture

Question 1

Rigid Impression Material

Answer 1

Not for Undercuts

Question 2

Elastic Impression Material

Answer 2

Limited Undercuts

Question 3

Irreversible Alginate

Answer 3

Not for Crown and Bridge

Question 4

Reversible Agar

Answer 4

For crown and Bridge

Question 5

Elastomeric rubber

Answer 5

For crown and bridge

Question 6

What does accurate mean

Answer 6

+/- 0.2% dimensional change after 15 mins

Question 7

What does stable mean

Answer 7

+/- 0.2% dimensional change at specific times like 1 hour, 1 day, 3 days, 1 week, etc.

Question 8

How to keep alginate accurate?

Answer 8

Do not let it tear upon removal
Keep it bonded to tray
Do not distory

Question 9

Is alginate expected to be stable?

Answer 9

No.

Question 10

Why can’t we use alginate for crown and bridge prep

Answer 10

It doesn’t produce fine detail. It often permanently distorts when removed from preps

Question 11

What are two reversible strains

Answer 11

elastic: stretches instantly and snaps back
viscoelastic: (soft tissue) stretches slowly on laoding and rebounds back slowly

Question 12

Irreversible strains

Answer 12

Viscous strain: Strain begins and increases as long as load is applied as molecule flow in a solid
Plastic: Permanent strain in metals as stress exceeds yield strength of ductile metals

Question 13

what would a tight watch on your skin be in terms of a strain

Answer 13

viscoelastic (reversible) retarded stretch and rebound

Question 14

If you left a crayon or candle on its side for a year what type of strain would occur?

Answer 14

viscous (irreversible) strain. Continues as long as stress is still being applied

Question 15

what type of strain happens to a rubber ball as it impacts the ground?

Answer 15

elastic (reversible) instantaneous strain and rebound

Question 16

What percent of the population is allergic to alginate?

Answer 16

1%

Question 17

How could you describe the chemical nature of alginate impression material

Answer 17

Irreversible hydrocolloid

Question 18

What is alginate made from

Answer 18

brown seaweed

Question 19

How does the alginate set

Answer 19

chemical reaction b/w Ca++ with COO-

Question 20

What is a hydrocolloid

Answer 20

mixture of water and particles (less that .5 microns)

Question 21

What is a sol thixotropic paste

Answer 21

Its a paste that mixes better the more you mix it

Question 22

How long do you have before it sets

Answer 22

45 seconds

Question 23

What happens upon setting

Answer 23

A gel forms with water and glass filler trapped in weak alginate fibrils

Question 24

Is alginate stretchy

Answer 24

not really, less than 10%

Question 25

Why do you have to be careful taking the impression out of the mouth

Answer 25

because a distorted impression will result in inaccurate occlusion

Question 26

What is an alginate retarder?

Answer 26

Sodium phosphate powder

The calcium reacts with the phosphate first and forms calcium phosphate

Question 27

What will accelerate the reaction

Answer 27

warm and hot water

Question 28

What temp water should we use?

Answer 28

Room temp ~70 degrees

Question 29

What provides dimensional accuracy?

Answer 29

Impression not moved while setting
Impression completely set before removal
Prevent tearing by waiting 1 minute after set
Prevent tearing by removing with "snap"
Prevent tearing by "Smooth Creamy Mix"
Prevent tearing by eliminating air bubbles with good mixing
provide 3-5mm between tray and teeth
impression bonded securely to tray

Question 30

What spatula should we use to mix alginate

Answer 30

The thin flexible spatula

Question 31

How long to mix alginate

Answer 31

1 min/45 s

Question 32

load tray time

Answer 32

2 mins/1min

Question 33

Seat tray

Answer 33

2.24 min/1.25 min

Question 34

Initial gelation

Answer 34

2.75 min/1.75 min

Question 35

revome tray

Answer 35

4.75 min/3 min

Question 36

Rinse well

Answer 36

30 seconds

Question 37

Disinfect

Answer 37

10-15 mins

Question 38

Pour

Answer 38

asap

Question 39

Separate impression from cast

Answer 39

under 30 mins and after 1 hour

Question 40

Sources of dimensional instability

Answer 40

Water evaporation
Imbibition
Syneresis (exposure to humidity)

Question 41

Steps to Dispense and Mix Alginate

Answer 41

1. Tumble container to fluff powder
2. Be sure bowl and spatula are clean and dry
3. Fill scoops w/o packing
4. Level scoops w/o packing
5. Place powder in bowl
6. Measure room temp H2O: 1 ring per scoop
7. Don’t put powder in bowl if there is any water in bowl
8. Reassure patient
9. Wet powder gingerly and then mix vigorously in thin layer 1/2 around the bowl back and forth to eliminate air bubbles for .75 minutes
10. Form a smooth creamy mix

Question 42

Why do we make mandibular impression first

Answer 42

To reduce chances of gagging

Question 43

How should the tray be put in the mouth

Answer 43

Sideways
Rotate and align
Seat posteriors first

Question 44

How much alginate should remain between tray and teeth upon seating

Answer 44

3-5mm

Question 45

Who should hold tray

Answer 45

You, not the patient

Question 46

Criteria for a good cast

Answer 46

Complete dentition
Min blebs/roughness
No voids on teeth
Base about 1/2 inch thick