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Dental Materials Mrs. Walker > Materials Chapter 8 > Flashcards

Materials Chapter 8 Flashcards

1
Q

What is the purpose of impression materials?

A

used to make replicas of the teeth and other tissues

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2
Q

What is a study model?

A

a physical model of the oral tissues for study

used in diagnosis and treatment planning

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3
Q

What is a cast?

A

exact replication of the size and shape of a preparation for the construction of a restoration appliance

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4
Q

What is a die?

A

replica of a single tooth

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5
Q

What is the purpose of an impression tray?

A

used to carry the impression material into the mouth

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6
Q

What are stock trays?

A

“off the shelf” trays that come in a variety of materials, shapes, and sizes

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7
Q

Why are there different-shaped trays?

A

different shaped trays are designed to take impressions of different oral conditions: partially and fully edentulous mouths, as well as mouths with a full complement of teeth

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8
Q

What are custom trays?

A

these are trays or appliances made on a model of the patients arch with arcylic or other resin

produces the most accurate impressions

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9
Q

How many impressions are necessary when a custom tray is used?

A

two

  1. a preliminary impression is taken;
    a gypsum product is poured into the impression to construct the custom tray
  2. the custom tray is used to make the final impression
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10
Q

What are some of the different dental devices that require the use of a custom tray?

A

full dentures, inlays, crowns, bridges, some RPD

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11
Q

What is the purpose of a bite registration?

A

records the occlusal surfaces of both arches; done to relate the upper and lower cast together

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12
Q

When is a triple tray used?

A

used with the dual-arch or closed mouth impression technique

this tray is a quadrant tray with a “J” shape that curls around the posterior of the most distal molars

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13
Q

What is awesome about a triple tray?

A

It records the prepared tooth, the patients bite registration and the opposing teeth all at the same time

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14
Q

What are impression materials that set by chemical reaction to form elastic rubber materials are called?

A

thermoset

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15
Q

What do chemical reactions involve?

A

chain lengthening, cross-lengthening or both

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16
Q

What are impression materials that undergo physical change when they cool or solidify are called?

A

thermoplastic

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17
Q

Which materials are more stable? thermoplastic or thermoset?

A

thermoset

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18
Q

What are the differences between elastic and inelastic impression materials and in what cases would one be preferred over the other?

A

dentulous mouths require elastic material because there are a lot of nooks and crannies present.

edentulous impressions may use elastic or inelastic impression materials

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19
Q

Which type of impression material sets hard and rigid and would “lock” around teeth of a dentulous patient if used?

A

inelastic

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20
Q

Define viscosity

A

a liquids ability to flow

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21
Q

When is retraction cord used?

A

placed in the gingival sulcus to facilitate crown and bridge impressions

use of retraction cord allows the low viscosity material to flow and thus reproduce areas of ta prep that are hard to reach

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22
Q

What are the 3 types of inelastic impression material?

A
  1. plaster
  2. wax and impression compound
  3. zinc oxide-eugenol (ZOE)
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23
Q

What are the 2 types of aqueous elastomeric impression materials?

A
  1. alginate (irreversible hydrocolloid)

2. Agar (reversible hydrocolloid)

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24
Q

What are the 4 types of nonaqueous elastomeric impression materials?

A
  1. polysulfides
  2. condensation silicones
  3. polyethers
  4. addition silicones
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25
Q

What was the first impression material used in dentistry?

A

wax

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26
Q

Wax used for taking impressions is solid at ____ temperature but is moldable at a temperature that is tolerated by oral tissues.

A

mouth

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27
Q

Wax is a _________ (undergoes physical change) material and can be thought of as a low molecular weight polymer.

A

thermoplastic

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28
Q

What is an impression compound?

A

a wax with added filler to improve handling and stability

it is stronger and more brittle and when softened, flows much less compared with wax

Is softened in hot liquid

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29
Q

What is Zinc oxide-eugenol (ZOE)

A

Come as two pastes; one contains eugenol and inert fillers and the other is formed by using zinc oxide powder and vegetable oil

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30
Q

What is ZOE used for?

A

use limited to impressions for edentulous ridges for removable dentures

not commonly used today

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31
Q

What factors determine whether or not an impression material is considered to be a hydrocolloid?

A

major component is water

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32
Q

What is a gel as it relates to dental materials?

A

consists of 2 phases:

1) a solid carbohydrate polymer network, like the soap used to create a foam.
2) water trapped in very small pockets of the material, like the air trapped in the of foam formed by soap.

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33
Q

What are irreversible hydrocolloids

(alginate)?

A

these are not as accurate as hydrocolloid materials, but they are easier to use

set by a chemical reaction that cross-link carbs

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34
Q

Why are alginates termed “irreversible impression materials”?

A

because they will not reverse to the sol state once they react and become a gel

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35
Q

What are some of the advantages of reversible (Agar) and irreversible (alginate) hydrocolloid materials?

A
  1. will wet a tooth surface that is contaminated by other fluids
  2. fewer air bubbles
  3. will absorb a limited amount of oral fluid
  4. pouring the impression with gypsum products is easier than with elastomeric impression materials
  5. hydrophilic
36
Q

What are some of the disadvantages of reversible and irreversible hydrocolloid materials?

A
  1. water evaporates from the surface of the impression when left exposed to air causing shrinkage
  2. materials contract slightly after setting and exude water
  3. will absorb water and distort impression
37
Q

What is syneresis?

A

the process of materials contracting slightly after setting and extruding water;

this occurs slowly with hydrocolloid materials

38
Q

What is imbibition?

A

the process of materials absorbing water, swelling and distorting

this can happen when disinfecting a hydrocolloid material

39
Q

What are some characteristics of reversible hydrocolloids (Agar)?

A
  • requires special equipment
  • dimensionally unstable, distorts easily
  • produces really accurate impressions
  • come in a tube or carpule
40
Q

What are some of the advantages of agar?

A
  • works well in wet environment

- attains great detail

41
Q

What are some disadvantages of agar?

A

requires special equipment
dimensionally unstable (pour within 30 mins)
-poor tear strength

42
Q

What are Nonaqueous Elastomeric Impression Materials?

A
  • Polysulfides
  • Condensation Silicones
  • Polyethers
  • Addition Silicones

Also called rubber base materials and elastomers

43
Q

Polysulfide rubber

A

-1st impression material, often called “rubber base”

Polymerization creates condensation of water and other by-products

STINKS like a perm (from the sulfur)

44
Q

What are some of the advantages of polysulfide (rubber base)

A

Very accurate

Long working time- 4-6 minutes

45
Q

What are some of the disadvantages of polysulfide?

A

Stink and stain clothing

Set time is very long- up to 15 minutes

46
Q

What are condensation silicones impression materials ?

A
  • these are impression materials that are based on silicone rubber
  • hydrophobic and the setting process is the result of condensation reaction
  • this material sets by condensation polymerization: alcohol is main by-product
47
Q

Characteristics of Polyethers

A
  • Not popular
  • Taste and smell bad
  • Very accurate
  • Easy to pour
  • Now are being designed to work like VPS
48
Q

Characteristics of Addition Silicones

A

-Polyvinylsiloxane / Vinyl Polysiloxane (PVS/VPS interchangeable)

MOST POPULAR

  • Polymerization occurs by addition polymerization (free radicals linking)
  • Good dimensional stability
  • Impression can be shipped to lab without pouring
49
Q

Alginate impression material is:

a) Expensive compared with other impression materials
b) Easy to use
c) Not affected by gain or loss of water
d) Well known for its long-term stability

A

b) Easy to use

A major advantage of alginate impression material is the ease of use. It is also fairly inexpensive. It is very much affected by the gain or loss of water. It should be poured as soon as possible because of its lack of stability.

50
Q

Impression materials that have mechanical properties permitting considerable elastic deformation but that return to their original form are classified as:

a) Thermoplastic
b) Elastomeric
c) Inelastic
d) Resins

A

b) Elastomeric

Elastomeric impression materials, or elastomers, are flexible and may be deformed and then return to their original shape. Thermoplastic impression materials may be elastic or inelastic. They set by a physical change when cooled. Inelastic materials cannot be stretched; they also are rigid. Resins, by definition, are rigid polymers.

51
Q

Dr. Jones requested that you mix alginate and take an impression. “While measuring the water, you got involved in conversation and did not notice how warm it was. This oversight will:

a) Make the mix unusable
b) Lengthen the gelation time
c) Not affect the gelation time
d) Shorten the gelation timed

A

d) Shorten the gelation time

An increase in the water temperature will increase the rate of setting or shorten the gelation time. The mix is usable regardless of water temperature as long as there is adequate working time.

52
Q

Which of the following dental materials is an example of an aqueous elastomeric?

a) Impression compound
b) ZOE impression paste
c) Polysulfide
d) Irreversible hydrocolloid
e) Addition siliconed)

A

d) Irreversible hydrocolloid

“Aqueous” refers to water. Therefore, the impression material must be water-based. In dentistry, there are two such materials: reversible and irreversible hydrocolloid. Irreversible is the only water-based choice. Polysulfides and addition silicones are elastomers. Impression compound is much like wax. ZOE impression material is an inelastic material and contains no water in its composition.

53
Q

The brown paste used in rubber base IS called the:

a) Polymer
b) Accelerator
c) Base
d) Filler

A

b) Accelerator

The brown paste in polysulfide impression material is the accelerator; the white paste is the base. Retarders are chemicals added to materials to decrease the setting rate. Fillers are added to the pastes to control the viscosity.

54
Q

Dental impression compound is known as a/an

a) Chemoplastic material
b) Irreversible material
c) Hydroelastic material
d) Thermoplastic material

A

d) Thermoplastic material

Dental impression compound is a thermoplastic material. It can be heated and softened repeatedly. Alginate is an example of an irreversible material. Once it has set, it cannot be resoftened. The other terms, chemoplastic and hydroelastic, are not used to describe impression materials.

55
Q

Which of the following is an example of an inelastic impression material?

a) Polysulfide
b) ZOE impression paste
c) Alginate
d) Addition silicone

A

b) ZOE impression paste

ZOE impression paste sets into a hard, brittle mass. This makes it inelastic (or not elastic). Polysulfide and addition silicone are elastomers (they are elastic and will flex). Alginate also sets into an elastic material.

56
Q

The term used for the setting of hydrocolloid impression materials is:

a) Crystallization
b) Polymerization
c) Curing
d) Gelation

A

d) Gelation

The hydrocolloids, alginate and agar, set by changing from a sol to a gel. This setting process is called gelation. Gypsum products (see Gypsum Materials) set by a crystallization process, and elastomeric impression materials set by polymerization. In dentistry, curing is another term for polymerization.

57
Q

The popularity of agar impression material is limited by the:

a) High cost
b) Need for special equipment
c) Poor reproduction of detail
d) Difficulty in pouring the impression

A

b) Need for special equipment

The use of agar impression material does require special equipment, but the impression material is very reasonably priced. The detail reproduction is excellent, and the impression is easy to pour compared to elastomeric impression material.

58
Q

When an agar impression slightly contracts and exudes water, it is termed:

a) Imbibition
b) Gelation
c) Syneresis
d) Hysteresis

A

c) Syneresis

The shrinkage and exudation of water is syneresis. Imbibition occurs when the impression
absorbs water, such as during long exposure to disinfecting solutions. Gelation is the term given to the setting process of hydrocolloid material. Hysteresis refers to a material’s characteristic of having a melting temperature different from its gelling temperature.

59
Q

Addition silicones are the most popular type of rubber impression materials. The reason for this IS cost.

a) The first statement is true; the second statement is false.
b) The first statement is false; the second statement is true.
c) Both statements are true.
d) Both statements are false.

A

a) The first statement is true; the second statement is false.

Addition silicones are the most popular of the elastomeric impression materials, but cost is not the reason. They are expensive. The ease of use and the excellent characteristics and properties account for their popularity.

60
Q

Custom impression trays are made on a model of the patient’s arch. Therefore, to make a custom tray, an alginate impression IS also needed.

a) The first statement is true; the second statement is false.
b) The first statement IS false; the second statement is true.
c) Both statements are true.
d) Both statements are false.

A

c) Both statements are true.

The accurate fit of the custom tray to the patient’s oral tissues requires an existing model. Therefore, an alginate impression is usually taken and poured with a gypsum product (stone or plaster), and the custom tray is then made on the study model.

61
Q

Mrs. Smith has not been to the dentist for several years. It was found that she needed extensive restorative treatment, to which she agreed. You were asked to take impressions as the first step of her care. The impression material of choice would be:

a) Agar
b) Alginate
c) Dental impression compound
d) Addition silicone

A

b) Alginate

Alginate would be the impression material of choice for these impressions. They are poured in dental stone and used for diagnosis and treatment planning. The accuracy of alginate is adequate for this purpose, but not for final impressions. Agar and elastomeric impression materials are final impression materials, which means that casts and dies are made from these impressions on which restorations are fabricated. Dental impression compound is used for the fabrication of dentures.

62
Q

The impression tray that is used to record the prepared tooth, a bite registration, and an impression of the opposing teeth is a:

a) Stock tray
b) Custom tray
c) Triple tray
d) Bite registration tray

A

c) Triple tray

With a triple tray, three “records” can be obtained: the prepared tooth, the bite registration, and the impression of the opposing tooth. It is considered a special use tray. A custom tray is made on a model of the patient’s arch with an acrylic resin. It is custommade by a dental professional. A stock tray is an “off the shelf” tray and can be purchased in a variety of
shapes, sizes, and materials. Bite registration trays, another special use tray, record the occlusal surfaces of both arches.

63
Q

Which of the following impression materials set by physical means?

a) Agar
b) ZOE
c) Alginate
d) Addition silicone

A

a) Agar

ZOE, alginate, and addition silicone impression materials all set by a chemical reaction. Wax used as an impression material, agar, and impression compound set by a physical change, and will solidify or gel when cooled. These are said to be thermoplastic materials.

64
Q

Alginate impression material is:

a) Expensive compared with other impression materials
b) Easy to use
c) Not affected by gain or loss of water
d) Well known for its long-term stability

A

b) Easy to use

A major advantage of alginate impression material is the ease of use. It is also fairly inexpensive. It is very much affected by the gain or loss of water. It should be poured as soon as possible because of its lack of stability.

65
Q

Impression materials that have mechanical properties permitting considerable elastic deformation but that return to their original form are classified as:

a) Thermoplastic
b) Elastomeric
c) Inelastic
d) Resins

A

b) Elastomeric

Elastomeric impression materials, or elastomers, are flexible and may be deformed and then return to their original shape. Thermoplastic impression materials may be elastic or inelastic. They set by a physical change when cooled. Inelastic materials cannot be stretched; they also are rigid. Resins, by definition, are rigid polymers.

66
Q

Dr. Jones requested that you mix alginate and take an impression. “While measuring the water, you got involved in conversation and did not notice how warm it was. This oversight will:

a) Make the mix unusable
b) Lengthen the gelation time
c) Not affect the gelation time
d) Shorten the gelation timed

A

d) Shorten the gelation time

An increase in the water temperature will increase the rate of setting or shorten the gelation time. The mix is usable regardless of water temperature as long as there is adequate working time.

67
Q

Which of the following dental materials is an example of an aqueous elastomeric?

a) Impression compound
b) ZOE impression paste
c) Polysulfide
d) Irreversible hydrocolloid
e) Addition siliconed)

A

d) Irreversible hydrocolloid

“Aqueous” refers to water. Therefore, the impression material must be water-based. In dentistry, there are two such materials: reversible and irreversible hydrocolloid. Irreversible is the only water-based choice. Polysulfides and addition silicones are elastomers. Impression compound is much like wax. ZOE impression material is an inelastic material and contains no water in its composition.

68
Q

The brown paste used in rubber base IS called the:

a) Polymer
b) Accelerator
c) Base
d) Filler

A

b) Accelerator

The brown paste in polysulfide impression material is the accelerator; the white paste is the base. Retarders are chemicals added to materials to decrease the setting rate. Fillers are added to the pastes to control the viscosity.

69
Q

Dental impression compound is known as a/an

a) Chemoplastic material
b) Irreversible material
c) Hydroelastic material
d) Thermoplastic material

A

d) Thermoplastic material

Dental impression compound is a thermoplastic material. It can be heated and softened repeatedly. Alginate is an example of an irreversible material. Once it has set, it cannot be resoftened. The other terms, chemoplastic and hydroelastic, are not used to describe impression materials.

70
Q

Which of the following is an example of an inelastic impression material?

a) Polysulfide
b) ZOE impression paste
c) Alginate
d) Addition silicone

A

b) ZOE impression paste

ZOE impression paste sets into a hard, brittle mass. This makes it inelastic (or not elastic). Polysulfide and addition silicone are elastomers (they are elastic and will flex). Alginate also sets into an elastic material.

71
Q

The term used for the setting of hydrocolloid impression materials is:

a) Crystallization
b) Polymerization
c) Curing
d) Gelation

A

d) Gelation

The hydrocolloids, alginate and agar, set by changing from a sol to a gel. This setting process is called gelation. Gypsum products (see Gypsum Materials) set by a crystallization process, and elastomeric impression materials set by polymerization. In dentistry, curing is another term for polymerization.

72
Q

The popularity of agar impression material is limited by the:

a) High cost
b) Need for special equipment
c) Poor reproduction of detail
d) Difficulty in pouring the impression

A

b) Need for special equipment

The use of agar impression material does require special equipment, but the impression material is very reasonably priced. The detail reproduction is excellent, and the impression is easy to pour compared to elastomeric impression material.

73
Q

When an agar impression slightly contracts and exudes water, it is termed:

a) Imbibition
b) Gelation
c) Syneresis
d) Hysteresis

A

c) Syneresis

The shrinkage and exudation of water is syneresis. Imbibition occurs when the impression
absorbs water, such as during long exposure to disinfecting solutions. Gelation is the term given to the setting process of hydrocolloid material. Hysteresis refers to a material’s characteristic of having a melting temperature different from its gelling temperature.

74
Q

Addition silicones are the most popular type of rubber impression materials. The reason for this IS cost.

a) The first statement is true; the second statement is false.
b) The first statement is false; the second statement is true.
c) Both statements are true.
d) Both statements are false.

A

a) The first statement is true; the second statement is false.

Addition silicones are the most popular of the elastomeric impression materials, but cost is not the reason. They are expensive. The ease of use and the excellent characteristics and properties account for their popularity.

75
Q

Custom impression trays are made on a model of the patient’s arch. Therefore, to make a custom tray, an alginate impression IS also needed.

a) The first statement is true; the second statement is false.
b) The first statement IS false; the second statement is true.
c) Both statements are true.
d) Both statements are false.

A

c) Both statements are true.

The accurate fit of the custom tray to the patient’s oral tissues requires an existing model. Therefore, an alginate impression is usually taken and poured with a gypsum product (stone or plaster), and the custom tray is then made on the study model.

76
Q

Mrs. Smith has not been to the dentist for several years. It was found that she needed extensive restorative treatment, to which she agreed. You were asked to take impressions as the first step of her care. The impression material of choice would be:

a) Agar
b) Alginate
c) Dental impression compound
d) Addition silicone

A

b) Alginate

Alginate would be the impression material of choice for these impressions. They are poured in dental stone and used for diagnosis and treatment planning. The accuracy of alginate is adequate for this purpose, but not for final impressions. Agar and elastomeric impression materials are final impression materials, which means that casts and dies are made from these impressions on which restorations are fabricated. Dental impression compound is used for the fabrication of dentures.

77
Q

The impression tray that is used to record the prepared tooth, a bite registration, and an impression of the opposing teeth is a:

a) Stock tray
b) Custom tray
c) Triple tray
d) Bite registration tray

A

c) Triple tray

With a triple tray, three “records” can be obtained: the prepared tooth, the bite registration, and the impression of the opposing tooth. It is considered a special use tray. A custom tray is made on a model of the patient’s arch with an acrylic resin. It is custommade by a dental professional. A stock tray is an “off the shelf” tray and can be purchased in a variety of
shapes, sizes, and materials. Bite registration trays, another special use tray, record the occlusal surfaces of both arches.

78
Q

Which of the following impression materials set by physical means?

a) Agar
b) ZOE
c) Alginate
d) Addition silicone

A

a) Agar

ZOE, alginate, and addition silicone impression materials all set by a chemical reaction. Wax used as an impression material, agar, and impression compound set by a physical change, and will solidify or gel when cooled. These are said to be thermoplastic materials.

79
Q

What is the composition of an irreversible hydrocolloid (alginate)?

A
  • potassium alginate: carbohydrate polymer that dissolves in water
  • silica: a filler that gives the mixed material “body” for handling
  • calcium sulfate: reactor for cross-linking reaction
  • sodium phosphate: acts as a retarder for working time
80
Q

How do alginate materials set?

A

by a chemical reaction that cross-links a carbohydrate polymer

81
Q

What happens during the setting reaction of alginate?

A
  1. powder is mixed with water
  2. alginate powder, sodium phosphate and calcium sulfate dissolve
  3. After the phosphate ions have reacted, the calcium ions react with the dissolved alginate
  4. This reaction cross-links the polymer chains and gelatin occurs
  5. The set material is a hydrogel that is composed mainly of water
82
Q

What is the purpose of the sulfate compound in agar (reversible hydrocolloid)?

A

it improves the hardness of the gypsum material that is poured into the impression

83
Q

What is a hydrocolloid conditioner?

A

special equipment used to prepare agar.

it has 3 compartments: the first boils the agar, the second stores the material at 150 degrees until needed, and the third compartment is used to temper the impression material before several minutes before it is used (110 degrees)

84
Q

Define Hysteresis

A

the melting and gelling of a reversible hydrocolloid at different temperatures

85
Q

How do non-aqueous elastomeric (rubber) impression materials set?

A

via polymerization reactions

they are more stable than hydrocolloid materials but are also more expensive

86
Q

What is one very important difference between the different types of elastomeric impression materials?

A

the adhesive that is used to bond the impression material to a non-perforated tray is different for each type

87
Q

How are non-aqueous elastomeric impression materials named?

A

based on their polymerization chemistry

Dental Materials Mrs. Walker (3 decks)

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