2. Gypsum Flashcards Preview

Dental Materials, Module II > 2. Gypsum > Flashcards

Flashcards in 2. Gypsum Deck (30):
1

Desirable Properties
• ____
• Dimensional stability
• ____
• Abrasion resistance

accuracy
strength

2

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

properties

3

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 ____

sea water
hydrous calcium sulfate (CaSO4-2H2O)
wallboard
plaster
water

4

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

tofu
beer
economical

5

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

mount
chemically
manufactured

6

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

crown/bridges
velmix

7

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)

dihydrate
hemihydrate

beta hemihydrate
alpha hemihydrate
alpha hemihydrate
powder

8

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

beta
I

beta
II
diagnostic

alpha
III
denture

9

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

IV alpha
die
gypsum
V
alpha
basemetal
phosphoric acid

10

Types of Gypsum Products

Type I/II
____, porous
Irregular
____ volume of water
____ hemihydrate

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

spongy
high
beta

prismatic
lower
alpha

11

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

dihydrate
45
30
19-24

12

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

first
vigorously
recommended
pulls

13

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


nuclei
crystal
setting
hydroscopic
solid phase
expansion
surface tension

14

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

20-23
1
3
penetration

15

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

gillmore
setting
vicat needle
pressure

16

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

Vicat
Gillmore

17

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

impurities
W/P ratio
no
retardation
warm

18

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…

natural
accelerator
working

19

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

setting
nucleating
expansion
low
low

20

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

setting
crystal
colloids
high
high

21

Snap Stone
Working time ____ seconds
Setting time ____ minutes

60-90
2

22

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

• Similar to the way ____ forms

apart
0.06-0.5

23

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

shrinkage
mixing
expansion
reduced
hydroscopic

24

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

Type V
Type I

25

Control of Properties

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

• ____ & Retarders

W/P
spatulation
under mixing
accelerators

26

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

W/P
spatulation
gypsum

W/P
accelerators
retarders
cohesion

27

Infection Control
• Disinfecting solutions
- ____
- Iodophor
- ____
- Ethylene Oxide

• Disinfecting the ____ rather than the model is preferable

glutaraldehyde
sodium hypochlorite
impression

28

Epoxy Products
• Two-component system, ____ & ____
• Similar to commercial systems
• ____ - monomer
• ____ - polyamine
• Linking process called ____

resin
hardener
resin
hardener
polymerization

29

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

compressive strength
abrasion resistance

30

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

0.03
0.3
porosity
16
alginate
chemical
difficult