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Gypsum Products Flashcards

(79 cards)

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0
Q

Rocks or solid particles which were ground to powder form and the heated

A

Gypsum

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1
Q

Example of gypsum products

A
  1. Orthoplaster
  2. Dental stone
  3. Plaster of paris
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2
Q

Gypsum produced for dental applications

A

Calcium sulfate dihydrate

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3
Q

Process of heating gypsum

A

Calcination

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4
Q

Heating is done in a kettle or an open bath

A

Open calcination

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5
Q

Stirring in open calcination

A

110 degrees celcius to 120 degrees celsius or

230 degrees farenheit to 250 degrees fahrenheit

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6
Q

Product of open calcination

A

Beta hemihydrate or plaster of paris

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7
Q

Beta hemihydrate is also known as

A

Plaster of paris

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8
Q

Consists of large, irregularly shaped orthorombic crystal particles with capillary pores

A

Plaster of paris

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9
Q

Spongy and irregular in shape

A

Crystals

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10
Q

Done in an autoclave and there’s a pressure involved

A

Closed calcination

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11
Q

Pressure and temperature of closed calcination

A

16 psi

120 degrees celcius to 130 degrees celcius

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12
Q

Product of closed calcination

A

Alpha hemihydrate or dental stone

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13
Q

Alpha hemihydrate is also known as

A

Dental stone

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14
Q

Consists of smaller, regularly shaped crystalline particles in the form of rods or prisms

A

Dental stone

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15
Q

Crystals are prismatic and more regular in shape

A

Dental stone

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16
Q

Used to take impression

A

Impression/ soluble plaster

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17
Q

Used to make study cast or model for records purposes

A

Plaster of paris

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18
Q

Stronger than plaster of paris

A

Dental stone ( class 1 )

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19
Q

Used as working cast that can withstand forces applied

A

Dental stone (class 1)

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20
Q

Stronger than class 1 dental stone

A

Dental stone high strength or class 2 dental stone

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21
Q

Used as working die for crown restoration and other treatments needing accurate measurements

A

Dental stone high strength (class 2 dental stone)

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22
Q

Refers to single tooth or several teeth

A

Die material

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23
Q

Used as inventing medium to compensate the high shrinkage of metals such as chrome cobalt ion

A

Dental stone high strength high expansion

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24
Other uses of gypsum products:
1. Used for ceramics 2. Used for medical purposes: cast for broken bones 3. Used to stabilize articulation between upper and lower cast
25
Addition of powder to water until the mixing time is completed
Mixing time
26
Time of mechanical mixing
20 to 30 seconds
27
It requires atleast a minute to obtain a smooth mix
Hand spatulation
28
Time available to use a workable mix
Working time
29
Maintained to perform one or more tasks
Uniform consistency
30
Measured from the time of mixing to the point where the consistency is no longer acceptable for the product's intended purpose
Working time
31
Time adequate for working time
3 minutes
32
Time that elapses from the beginning of mixing until the material hardens
Setting time
33
Measured by penetration tests
Setting time
34
Types of penetration test
1. Vicat needle | 2. Gilmore needle
35
Measure initial setting time (1/4 lb)
Vicat needle
36
Measures final setting time 1/4 and 1 lb
Gilmore needle
37
Measured from the start of mixing until the 2nd increase of temperature
Initial setting time
38
Time for initial setting time
7-13 minutes
39
Measured from the start of mixing until the 2nd decrease of temperature
Final setting time
40
Time for final setting time
20 minutes
41
Significance of finding initial setting time
1. Time to trim off extra plaster or stone that overflowed | 2. To prevent the breakage of the cast
42
Significance of finding final setting time
1. To prevent premature separation | 2. To prevent powdery casts
43
Manipulation of gupsum products:
✔️ know the WP ratio ✔️ put the water first then the powder in the bowl ✔️ let them settle for 30 seconds to remove air ✔️ mix it using rotatory motion at 120 rpm for 1 1/2 minutes ✔️ tap the mixture to released entrapped air
44
Theoretical factors affecting setting time
1. Number of nuclei 2. Solubility of the hemihydrate 3. Rate of crystal growth
45
Number of nuclei crystallization
Greater number of nuclei, decrease ST, the shorter | Lesser number of nuclei, increase ST, the longer
46
Solubility of the hemihydrate
More soluble, the faster the ST
47
Rate of crystal growth
Faster rate of crystallization, faster ST
48
Practical factors affecting setting time
1. Presence of impurities 2. Fineness 3. WP ratio 4. Mixing time 5. Temperature 6. Accelerators and retarders
49
Decrease ST =
Faster setting
50
Particle size and shape of crystals
Fineness
51
Smaller crystals, more soluble, faster
Fineness
52
Too thin
Prone to air bubbles
53
Too thick
Not all powder will be mixed with water
54
WP ratio
More water, less powder, longer setting time | Less water, more powder, shorter setting time
55
Mixing time
2 minutes
56
Longer time, faster mixing rpm, faster setting time
Mixing time
57
Up to 50 degrees celcius
Accelerator
58
Above 50 degrees celcius
Retarder
59
Most practical way for a clinician to control setting time
Altering temperature
60
Tend to remove the surface coating of crystals making them more soluble to water
Accelerators
61
Best accelerator regardless of concentration
K2SO4
62
Tend to create surface coating of crystals making them less soluble to water
Retarders
63
Examples of retarder
1. Borax 2. Nitrates 3. Citrates 4. Higher conc of NaCl and Na2SO4
64
Plaster impression WP ratio: Psi: Setting expansion:
.50-.75 290-870 0-.15 %
65
Plaster of paris WP ratio: Psi: Setting expansion
.45-.50 1300 0-.30%
66
Dental stone WP ratio: Psi: Setting expansion
.28-.30 3000 0-.20%
67
Die stone WP ratio: Psi: Setting expansion
.22-.24 5000 0-.10%
68
Dental stone high strength hig expansion WP ratio: Psi: Setting expansion
.18-.22 7000 .10-30%
69
Why is that the WP ratio for plaster impression is high?
So that it can flow more because it's for impression taking
70
Factors affecting compressive strength
1. Shape and size of the particles 2. WP ratio 3. Mixing technique 4. Use of chemical modifiers
71
Factors affecting setting expansion
1. WP ratio - increase water, decrease setting expansion - increase powder, increase setting expansion 2. Addition of chemical modifiers - potassium sulfate
72
Accelerators
ST: - SE: - S : -
73
Retarders
ST: + SE: - S: -
74
Particle size
ST: + SE: + S: +
75
WP ratio
ST: + SE: - S: -
76
Spatulation
ST: - SE: + S: -
77
Temperature
ST: - SE: 0 S: 0
78
Care for gypsum products
1. Put it in a cool dry place | 2. Place it in air tight container

Dental Materials (2 decks)

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