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Dental materials 2 > model and die materials > Flashcards

model and die materials Flashcards

1
Q

In dentistry, what is the purpose of replicas of hard and soft tissues

A

diagnosis and treatment of oral disease

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2
Q

what are the 3 types of repicas

A
  1. study models
  2. casts
  3. dies
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3
Q

what are study models used for, give an example

A

they are used for the observation of the patients oral stucture
eg; orthodontists use study models to evaluate the crowding of teeth or progress of correction of that crowding

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4
Q

what are two usages of casts

A
  1. they are used to make orthodontic retainers

2. cast of the remaining ridges in edentulous patients are used to make dentures for that patient

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5
Q

what are dies and what are they generally used for

A

are highly accurate replicase of a single tooth and are used for metal crowns or inlays

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6
Q

What are two factors on which the accuracy of replicas depend on

A
  1. the accuracy of the impression

2. materials used to pour the impression

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7
Q

what are 6 desirable qualities required of materials to be used for making models, casts, and dies

A
  1. accuracy
  2. dimensional stability
  3. reproduction of fine detail
  4. strength and resistance to abrasion
  5. ease of adaption to the impression
  6. color and safety
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8
Q

what do desirable qualities of model materials depend on , give an example.

A

they depend on dental application
eg: dentist do not require the same dimensional accuracy for a study model as for a die ( die must be more dimensionally accurate)

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9
Q

what are two common materials used to pour impressions and what is more prominently used and why

A
  1. gypsum materials
  2. epoxy materials

Gypsum materials because they can be poured into almost all impression materials used in practice today

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10
Q

what stands as an issue for epoxy materials

A

model material-impression compatibility, ghey are compatible with most eLASTOMERIC IMPRESSION materials but cannot be used with the alginates or agar impression materials

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11
Q

what are the 5 types of gypsum products

A

1.impression plaster
2model plaster
3dental stone
4die stone ( high strength-low expansion dental stone)
5high strength-high expansion dental stone )

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12
Q

what are model plasters used for

A

study models that doe not require abrasion resistance

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13
Q

what is orthodontic plaster

A

mixture of model plaster and dental stone

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14
Q

what is an IMPRESSION plaster used for

A

mounting casts on an articulator

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15
Q

what does an impression plaster differ from a model plaster

A

in impression plasters, setting time has been shortened and dimensional change on setting has been reduced to 0.06%.

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16
Q

what type of gypsum material is used for casts that need abrasion resistance

A

dental stones

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17
Q

what differs in plasters, dental stones, and high-strength dental stones, chemical or physical nature

A

all of the mentioned materials differ in their physical forms, their chemical makeup however is the same, they are all made up of the same chemical ; calcium sulfate hemihydrate

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18
Q

name 4 disadvantages of using excess water in the gypsum mix

A
  1. increases setting time
  2. reduces hardness of set gypsum
  3. reduces strength
  4. reduces expansion
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19
Q

all from of gypsum materials are manufactured from what

A

gypsum mineral; calcium sulfate dihydrate

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20
Q

what is the only difference between the model materials and the gypsum

A

the amount of water in the crystal, during the manufacture of model materials, etc. ,water is driven out of the dihydrate gypsum to form the hemihydrate

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21
Q

what are the three types of hemihydrate

A
  1. plaster hemihydrate
    2.dental stone ‘’ ‘’
    3,high-strength dental stone ‘’ ‘’
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22
Q

how is beta-calcium sulfate hemihydrate produced

A

also known as plaster hemihydrate, it is produced in an open kettle at about 115 C

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23
Q

how is alpha-calcium sulfate hemihydrate produced

A

aka dental stone hemihydrate, high pressure steam 125 C

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24
Q

WHAT hemihydrate is produced by boiling the gypsum in a 30 % solution of calcium chloride

A

high-strength dental stones

25
Q

the hemihydrate produced in this case is the least porous, most regular and largest of all hemihydrates

A

high-strength dental stones

26
Q

to produce a workable mass , which material requires the most excess water and whcih requires the least , consecutively and why

A

plaster, has small porous crystals

high-strength stone requires the least excess water because of its large dense crystals

27
Q

Basically, what is the rule when adding excess water to hemihydrates

A

the larger and more dense the crystal size of the hemihydrate, the less excess water needed to get a workable mass

28
Q

what chemical when added, reduces setting time from 10 to 4 minutes

A

an accelerator eg ; potassium sulfate

29
Q

what chemical when added extends setting time to several hours

A

A RETARDER ;borax BORING

30
Q

what is the mechanism of an accelerator

A

it makes the dihydrate less soluble than the hemihydrate so the rxn is moved towards the dihydrate because the dihyrate assumes its solid form more rapidly

31
Q

what does this fractton mean

0.45 or 45/100

A

water_powder ratio meaning 45 ml of water is added to 100 g of powder

32
Q

which respectively has the lowest and highest water powder ratio of the gypsum materials

A

lowest: high strength stones
highest: plaster

33
Q

Gypsum materials are hygroscopic what does that mean

A

ut means that they absorb water from the air to some extent, so if they are left in an open conatiner the surface of the particles will convert to dihydrate this subsequently will result in an increases setting time

34
Q

to avoid changes in the rate of setting reaction, how should gypsum materials be stored

A

in closed container to protect them form humidity

35
Q

name 5 properties of gypsum materials

A
  1. reproduction of detail
  2. dimensional accuracy
  3. strength
  4. hardness and abrasion resistence
  5. setting time
36
Q

the total setting time for gypsum materials can be divided into two psrts, nsme them

A
  1. initial setting time

2. final setting time

37
Q

define the initial setting time

A

the interval between the time the water and powder are mixed and the time that the mix can no longer be poured into an impression

38
Q

the initial setting time is identical to what

A

working time of the material, 8-16 min

39
Q

definethe final setting time

A

the time at which the conversion of the hemihydrate to the dihydrate is essentially complete

40
Q

BY DEFINITION, HOW CAN WE KNOW THAT THE MATERIAL HAS REACHED FINAL SET

A

when gilmore needle cannot penetrate into set mass

41
Q

to capture the most detail, the die material must fulfill two conditions, name them

A
  1. the die material must be chemically compatible with the impression
  2. and it must also wet the impression material readily
42
Q

what does wetting mean

A

the die material must flow into the details of the impression and must not bead up or resist onto the impression material

43
Q

is gypsum water or oil based

A

gypsum is water-based

44
Q

name water-based impression materials

A

alginates, agars

45
Q

name oil-based impression materials

A

polyethers, addition silicone

46
Q

what happens when gypsum is poured into water-based impressions

A

good wetting occurs

reduvtion in the number of bubbles and improves rep of details

47
Q

what happens when gypsum is poured into polyether impressions, how can it be solved

A

wetting is reduced rsylting in a limited ability of the gypsum to flow into all the details of the impression

this can be solved by adding a surfactant

48
Q

define a surfactant

A

a chemical that acts like a soap

49
Q

define strength

A

is the indicative of the ability of the material to resist fracture

50
Q

whichof the gypsum materials have the least compressive strength and why

A

plasters, beacause of the amount of excess water present

51
Q

which gypsum material is almost 4 times as strong in compression

A

high-strength dental stones

52
Q

a proper manipulation of gypsum materials consists of 4 phases name them

A
  1. the measurement and combination of powder and liquid
  2. spatulation
  3. pouring ( sets in 45-60 min)
  4. disinfection if necessary
53
Q

what is the proper method of comnbination of gypsum powders with water

A

proper water-powder ratio is critical
water is added first, then powder is sprinkled into the water slowly over a period of 30 sec
do not add powder to water all at once or bubbles will form during the final mix

54
Q

what is the time needed for the gypsum model to set

A

45 to 60 min

55
Q

which is preferred, the disinfection of impressions or models

A

impressions

56
Q

why is the disinfection of impressions preferred more than that of models

A
  1. easier
  2. more effective
  3. limits the inroduction of contaminated items into the labratoy area
57
Q

epoxy materials set by a chem rxn name it

A

polymerization

58
Q

WHAT PRECAUTION must be known before handling an epoxy material

A

the hardener is toxic and allergenic, and must not come into contact with the skin during the manipulation of the unset material

59
Q

an edentulous patient who has undergone radiation which led to xerstomia, what material is best for making an impression

a. polusulfide
b. polyether
c. zoe
d. irreversible hydrocolloids( algenates)

A

Becasue the patient has undergone radiation all hydrophillic impressions cannot be used
so we rule out d. zoe can adhere to tissure and may cause ulcers upon removal so we rule that out too

so it is a)

Dental materials 2 (3 decks)

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