01: Dr Moon Alginate Lecture Flashcards

1
Q

Rigid Impression Material

A

Not for Undercuts

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2
Q

Elastic Impression Material

A

Limited Undercuts

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3
Q

Irreversible Alginate

A

Not for Crown and Bridge

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4
Q

Reversible Agar

A

For crown and Bridge

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5
Q

Elastomeric rubber

A

For crown and bridge

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6
Q

What does accurate mean

A

+/- 0.2% dimensional change after 15 mins

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7
Q

What does stable mean

A

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

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8
Q

How to keep alginate accurate?

A

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

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9
Q

Is alginate expected to be stable?

A

No.

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10
Q

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

A

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

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11
Q

What are two reversible strains

A

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

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12
Q

Irreversible strains

A

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

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13
Q

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

A

viscoelastic (reversible) retarded stretch and rebound

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14
Q

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

A

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

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15
Q

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

A

elastic (reversible) instantaneous strain and rebound

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16
Q

What percent of the population is allergic to alginate?

A

1%

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17
Q

How could you describe the chemical nature of alginate impression material

A

Irreversible hydrocolloid

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18
Q

What is alginate made from

A

brown seaweed

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19
Q

How does the alginate set

A

chemical reaction b/w Ca++ with COO-

20
Q

What is a hydrocolloid

A

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

21
Q

What is a sol thixotropic paste

A

Its a paste that mixes better the more you mix it

22
Q

How long do you have before it sets

A

45 seconds

23
Q

What happens upon setting

A

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

24
Q

Is alginate stretchy

A

not really, less than 10%

25
Why do you have to be careful taking the impression out of the mouth
because a distorted impression will result in inaccurate occlusion
26
What is an alginate retarder?
Sodium phosphate powder | The calcium reacts with the phosphate first and forms calcium phosphate
27
What will accelerate the reaction
warm and hot water
28
What temp water should we use?
Room temp ~70 degrees
29
What provides dimensional accuracy?
``` 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 ```
30
What spatula should we use to mix alginate
The thin flexible spatula
31
How long to mix alginate
1 min/45 s
32
load tray time
2 mins/1min
33
Seat tray
2.24 min/1.25 min
34
Initial gelation
2.75 min/1.75 min
35
revome tray
4.75 min/3 min
36
Rinse well
30 seconds
37
Disinfect
10-15 mins
38
Pour
asap
39
Separate impression from cast
under 30 mins and after 1 hour
40
Sources of dimensional instability
Water evaporation Imbibition Syneresis (exposure to humidity)
41
Steps to Dispense and Mix Alginate
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
42
Why do we make mandibular impression first
To reduce chances of gagging
43
How should the tray be put in the mouth
Sideways Rotate and align Seat posteriors first
44
How much alginate should remain between tray and teeth upon seating
3-5mm
45
Who should hold tray
You, not the patient
46
Criteria for a good cast
Complete dentition Min blebs/roughness No voids on teeth Base about 1/2 inch thick