2. Gypsum Flashcards

1
Q
Desirable Properties
• \_\_\_\_
• Dimensional stability 
• \_\_\_\_
• Abrasion resistance
A

accuracy

strength

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2
Q

Gypsum or Epoxy?
• Different ____
• Epoxy > some labs use epoxy; but most of dentistry is gypsum

A

properties

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3
Q

What Is Gypsum?
• Naturally occurring mineral that formed as the result of evaporating ____ in massive prehistoric basins
• Chemically, it is ____
• Primary ingredient in ____ and ____

• Two parts \_\_\_\_
A
sea water
hydrous calcium sulfate (CaSO4-2H2O)
wallboard
plaster
water
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4
Q

Food Grade Gypsum
• Necessary in the manufacture of ____ and ____
• Used in the food, beverage and pharmaceutical industries as an ____
source of supplemental calcium.

A

tofu
beer
economical

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5
Q

Types of Gypsum Products
• ____ plaster - used to mount models on articulators
• All these products are ____ identical, but difference is how they’re ____

A

mount
chemically
manufactured

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6
Q

Die Stone
• Used to pour up dies for ____, removable PD
• ____

A

crown/bridges

velmix

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7
Q

Manufacture of Gypsum Products

CaSO4.2H2O + heat CaSO4.1⁄2H2O + 11⁄2H2O

calcium sulfate ____ calcium sulfate ____

Effect of Heating Environment Open air — ____
Steam autoclave — ____
Salt bath — ____

* Mined out of earth, in a heating process water is driven out
* Calcium sulfate hemihydrate (\_\_\_\_ in wet lab)
A

dihydrate
hemihydrate

beta hemihydrate
alpha hemihydrate
alpha hemihydrate
powder

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8
Q

Types of Gypsum Products • Impression Plaster
– Calcium sulfate ____ hemihydrate: Type ____

• Model Plaster
– Calcium sulfate ____ hemihydrate: Type ____
– ____ casts
– Orthodontic casts

• Dental Stone
– Calcium sulfate ____ hemihydrate: Type ____ – ____ casts

* Used in edentulous patients; simple oral anatomy (can be taken out in pieces though)
* Dental stone > harder model
A

beta
I

beta
II
diagnostic

alpha
III
denture

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9
Q

Types of Gypsum Products

• High-Strength Dental Stone: Type ____ (____)
– ____ stone
– Hard surface resistant to abrasion
– ____ hardening solutions

• High Strength/High expansion: Type ____ (____)
– ____ casting

• Synthetic Gypsum
– By-product of ____ manufacture

A
IV alpha
die
gypsum
V
alpha
basemetal
phosphoric acid
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10
Q

Types of Gypsum Products

Type I/II
\_\_\_\_, porous
Irregular
\_\_\_\_ volume of water
\_\_\_\_ hemihydrate

Type III/IV/V
____ & Regular shapes, ____ vol. of water
____ hemihydrate

A

spongy
high
beta

prismatic
lower
alpha

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11
Q

Setting Reaction

11⁄2H2O + CaSO4.1⁄2H2O CaSO4.2H2O

Calcium sulfate hemihydrate calcium sulfate ____

Model plaster — ____ ml
Dental stone — ____ ml
High-strength dental stone — ____ ml

A

dihydrate
45
30
19-24

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12
Q

Manipulation of Gypsum
• Add water ____ then weighed powder
• Mix ____ to a smooth mix
• Mechanical mixing ____

• Mix on vacuum that \_\_\_\_ the air out - much better mix
A

first
vigorously
recommended
pulls

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13
Q

The Setting of Gypsum
• ____ formation
• ____ formation
• ____ Expansion

11/2H2O + CaSO4+1/2H2 —> CaSO4*2H2O

• Have model set in more water - \_\_\_\_ setting conditions
• Add powder to the water (best way)
• Initial crystal growth > \_\_\_\_ contact > expansion > termination
• Allow to set in more water, then you much more \_\_\_\_
	○ In presence of water, less \_\_\_\_ > can expand a whole lot more
A
nuclei
crystal
setting
hydroscopic
solid phase
expansion
surface tension
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14
Q

Properties of Gypsum
Products
• Mixing time
– Mechanical - ____ sec – Hand spatulation - ____ min
• Working time – ____ min
• Setting time
– From start of mixing to hardened material – Measured with a ____ test

A

20-23
1
3
penetration

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15
Q
Methods of Determining Setting Time
• \_\_\_\_ needle
– Initial and final setting time
• Vicat needle
– Initial \_\_\_\_ time
• Loss of Gloss
– Few minutes before \_\_\_\_
setting time
• Temperature rise
• Penetration test
• By putting amount of \_\_\_\_ as sets > determines when it reaches a full set
	○ Or, loss of gloss, leave it alone until it undergoes a full set
A

gillmore
setting
vicat needle
pressure

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16
Q

Determination of Setting Time
A ____ Needle for measuring setting time of gypsum
B ____ Needles

A

Vicat

Gillmore

17
Q
Control of Properties 
• Setting Time
– \_\_\_\_ eg. Gypsum 
– Fineness
– \_\_\_\_
– Mixing time

– Temperature
• Below 50 ̊C (122 ̊F)- ____ effect
• Above 50 ̊C (122 ̊F)- ____
– Accelerators & Retarders

* W/P ratio is important
* Add \_\_\_\_ water > speed up the reaction
A
impurities
W/P ratio
no
retardation
warm
18
Q
Accelerators and Retarders
• Prolonged setting of
\_\_\_\_ product
• \_\_\_\_ reduces working time
• Accelerator Plus retarder restores \_\_\_\_ time
• Dotted line is naturally set; add accelerator to speed up the step, or add retarder/accelator so it's more conducive for the office…
A

natural
accelerator
working

19
Q
Control of Properties
• Setting Time
– Accelerators - shorten \_\_\_\_ time
– Act as \_\_\_\_ sites for dihydrate crystal growth
• Potassium sulfate
• Terraalba-set gypsum
– no effect on setting \_\_\_\_
• Sodium chloride - \_\_\_\_ conc.
• Sodium sulfate - \_\_\_\_ conc.
* Nucleating sites > allows for rxn to occur more quickly
* Slurry off model trimmer > terra alba; used it as the water for a mix, the model would set much more quickly
A
setting
nucleating
expansion
low
low
20
Q
Control of Properties
• Retarders - lengthen \_\_\_\_ time by interfering with dihydrate \_\_\_\_ formation
– \_\_\_\_- 'poison 'nuclei
• (dried blood), alginate, agar, saliva
– Borax
– Sodium chloride- \_\_\_\_ conc. >2%
– Sodium sulfate - \_\_\_\_ conc. >3.4%
– Citrates, acetates, and borates
A
setting
crystal
colloids
high
high
21
Q

Snap Stone
Working time ____ seconds
Setting time ____ minutes

A

60-90

2

22
Q

Setting Expansion
• Expansion occurs due to adjacent crystals pushing each other ____
• Setting expansion= ____%

• Similar to the way \_\_\_\_ forms
A

apart

0.06-0.5

23
Q

Setting Expansion

• Clinical Significance
- Slightly larger models are important 
- Crowns, bridges & dentures are not
fabricated too tightly
- Compensate for casting metal \_\_\_\_ upon cooling

• Controlled by
– ____ time (increased)
– W/P ratio (more water less ____)
– Addition of chemicals (____)

* Casting metals > shrinking of metals
* Make the model and put it into water > \_\_\_\_ expansion
A
shrinkage
mixing
expansion
reduced
hydroscopic
24
Q

Compressive Strength

• It's better in \_\_\_\_, and a lot less in plasters (\_\_\_\_) bc need to add more water to the plasters to get the materials to set
A

Type V

Type I

25
Q

Control of Properties

Strength
• Wet strength vs Dry strength
• \_\_\_\_ ratio
• \_\_\_\_ (mixing) time
– Over and \_\_\_\_

• ____ & Retarders

A

W/P
spatulation
under mixing
accelerators

26
Q

Strength and Surface Hardness

• Increased by
– Low ____ ratio
– Increased ____ time
– ____ hardening solutions

• Decreased by
– High ____ ratio
– Addition of ____ and
____ by reduced inter- crystalline ____

• Spatulation > mixing time
A

W/P
spatulation
gypsum

W/P
accelerators
retarders
cohesion

27
Q
Infection Control
• Disinfecting solutions 
- \_\_\_\_
- Iodophor
- \_\_\_\_
- Ethylene Oxide

• Disinfecting the ____ rather than the model is preferable

A

glutaraldehyde
sodium hypochlorite
impression

28
Q
Epoxy Products
• Two-component system, \_\_\_\_ & \_\_\_\_
• Similar to commercial systems
• \_\_\_\_ - monomer
• \_\_\_\_ - polyamine
• Linking process called \_\_\_\_
A
resin
hardener
resin
hardener
polymerization
29
Q

Advantages
• Superior ____ & ____
• Necessary with certain laboratory techniques

A

compressive strength

abrasion resistance

30
Q
Disadvantages
• Shrinkage \_\_\_\_% to \_\_\_\_%
• Viscous when poured creating \_\_\_\_
• Sets slowly up to \_\_\_\_ hours
• Not compatible with \_\_\_\_
• \_\_\_\_ sensitivity & allergy
• Gypsum product will expand a little, metal shrinks etc
• Here, with epoxy, the dies shrink
	○ Have a tooth > pour in epoxy, and shrinkage, then the die is slightly smaller than the patient's tooth
• Epoxy more \_\_\_\_ to work with
A

0.03
0.3
porosity
16
alginate
chemical
difficult