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DMD2 sem 2 > Impression Materials > Flashcards

Impression Materials Flashcards

1
Q

What are impression materials and how are they used?

A

Impression materials are materials designed to take the “negative” shape of teeth materials and surrounding structures when the impression material is in a more plastic unset condition and then it hardens and is used as a mold for a positive replication of tooth structure in die or another suitable model.

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2
Q

What are the key properties of impression materials?

A

Flow = ability to replicate intraoral surface details

Dimensional stability = Ability to retain absolute dimensional size over time

Tear resistance = Ability to resist tearing in thin sections (such as through the feather edged material within the gingival sulcus)

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3
Q

What are the desirable properties for impression materials?

A

Adequate shelf life

Acceptable odor and taste

Biologically acceptable: No toxic or irritant constituents

Easily manipulated: Easy to use with the minimum of equipment

Setting characteristics suitable for the purpose

Good set material properties

Can handle addition and correction

Satisfactory consistency and texture

Readily disinfected without loss of accuracy

Compatiblity with cast and die materials

Economically commensurate with the results obtained

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4
Q

What are the setting characteristics that meet clinical requirements?

A

Suitable working time

Suitable setting time

Readily wets oral tissues

Not affected by oral fluids

Does no release gas during setting

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5
Q

What are the characteristics of set material that make them ideal for clinic?

A

Sufficient mechanical strength to handle resistance to tear on removal from the mouth

Elastic properties with no permanent deformation after strain

Good dimensional accuracy

Dimensional stability over temperature and humidity ranges met in clinic and lab

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6
Q

Can any impression material fulfill all the desirable characteristics?

A

No, selection of material should be best suited for a particular clinical situation. The technique depends on the dentist.

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7
Q

What factors affect the accuracy of impression materials?

A

Must be in fluid or plastic state on insertion

Dimensional changes on setting are negligible

Must be elastic on removal from the mouth

Must adhere to the tray

Must have dimensional stability with storage

Must be compatible with model and dies

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8
Q

How are impression materials classified by method of setting?

A

Hardening by chemical reaction (eg alginates)

Softening and hardening by heat (eg impression compounds)

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9
Q

How are impression materials classified by behaviour after setting?

A

Non-elastic impression materials: Used with no undercuts exist (eg plaster of paris)

Elastic impression materials: Can be used when undercuts exist. (eg hydrocolloids)

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10
Q

How are impression materials classified?

A

By method of setting

Behavior after setting

According to viscosity

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11
Q

How are impression materials classified by viscosity?

A

Mucodisplasive impression materials (eg high viscosity alginates, impression compound)

Mucostatic impression materials (eg Plaster)

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12
Q

What are the types of non-elastic impression materials?

A

Wax

Impression plaster (Plaster of Paris)

Impression compound

Zinc oxide-Eugenol impression material

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13
Q

What limits the use of wax for occlusal records?

A

It is distorted upon removal

Release of internal stresses

High flow properties

Large dimensional changes upon cooling

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14
Q

What is the application for plaster of paris?

A

Application: Used to make impression for edentulous patients

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15
Q

How is Plaster of Paris mixed?

A

Powder and water are mixed

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16
Q

What is the composition of plaster of paris?

A

CaSO4.1/2 H2O

Modifiers: Chemicals used to control setting time and setting expansion.

4% K2SO4

1% borax

Natural gums

Flavoring agents

Colouring agents

Potato starch

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17
Q

What are the types of elastic impression materials?

A

Hydrocolloid: Alginate, agar, and agar/alginate

Rubber base: Polysulfide, polyether, and silicone (Condensation polyer and addition polymer)

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18
Q

How is gypsum produced?

A

By heating the plaster to 110 - 130 degrees

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19
Q

What is formed from plaster if it is heated?

A

Gypsum = 110 - 130 degrees celsius

Platic or stone = 110 - 130 degrees celsius

Hexagonal anhydrite = 130 - 200 degrees celsius

Orthorhombic anhydrite = 200 - 1000 degrees celsius

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20
Q

What is the purpose of using chemical modifiers in plaster of paris?

A

They control the setting time and setting expansion

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21
Q

What are the types of modifiers used in plaster of paris?

A

K2SO4 (4%)

Borax (1%)

Natural gums

Flavouring agents

Colouring agents

Potato starch

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22
Q

What is the setting reaction for plaster of paris?

A

CaSO4.1/2H2O + 1.5 H2O -> CaSO4.2H2O + heat

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23
Q

What are the advantages to using plaster of paris?

A

Accuracy:

High flowy

Minimum linear setting expansion (+0.06%)

It fractures into clean clear cut fragments so it can be reassembled with great accuracy

Dimensional stability

It is easily manipulated, cheap and has a good shelf life

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24
Q

What are the disadvantages to using plaster of paris impression material?

A

Its taste and consistency are usually unpleasant to the patient and dehydrates the soft tissues

Does not accept additions or corrections

Not elastic

A separating medium should be used

Cannot be electroplated

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25
Q

What is impression compound?

A

It is one of the oldest impression materials in dentistry

It is a thermoplastic material

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26
Q

What is the application of impression compound?

A

Impression for edentulous patients

As an impression tray

Peripheral seal material

Single impression with copper band

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27
Q

How is impression compound presentation?

A

In the form of:

Sheets

Sticks

Cones

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28
Q

What is the composition of impression compound?

A

40% resins

7% waxes

Plasticizers (3% organic acids)

50% fillers: Talc powder, chalk or iron oxide

Colouring agents

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29
Q

What are the classifications of impression compounds?

A

Type 1 “lower fusing materials”

Type 2 “Higher fusing materials”

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30
Q

How is impression compound manipulated and how does it set?

A

Impression compounds are thermoplastic materials

They are hard at 37 degrees and are soft at 45 degrees. Cooling must continue until the entire mass is rigid to reduce plastic flow on removal from the mouth.

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31
Q

What is the accuracy like for impression compound?

A

Dimensional accuracy: They are not sufficiently fluid to record all the fine details.

Dimensional stability: They have a high coefficient of thermal expansion. Cooling shrinkage is 0.3 - 0.4%

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32
Q

How can the poor dimensional stability be overcome?

A

By making a secondary impression or spray cold water on the metal tray.

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33
Q

What are the disadvantages of using impression compound?

A

Not very fluid

High coefficient of thermal expansion meaning they experience cooling shrinkage

The material is non-elastic, most serious drawback of this material

Internal stresses are relieved leading to warpage or distortion. (can also be caused by premature removal before it hardens and cools)

Poor thermal conductivity

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34
Q

What are the advantages to using impression compound?

A

Accepts addition and correction

Does not need a separating medium

Non-toxic and non-irritant

Hardens in a reasonable time in the mouth

Has adequate shelf life

Can be electroplated with copper

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35
Q

How is zinc oxide-eugenol impression material applied?

A

Full mouth edentulous impressions

Largely replaced by light bodied rubber impression materials

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36
Q

How is zinc oxide-eugenol impression material presented?

A

Soft or hard set types usually in the form of 2 pastes in collapsible tubes

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37
Q

What is the composition of zinc oxide-eugenol impression material?

A

One paste is called the base paste contains:

Zinc oxide 80% (powder)

Inert oil 15% (forms a paste)

Hydrogenated resin

The other paste is called the accelerator and contains:

Eugenol or oil of cloves (12 - 15%)

Filler talc powder

Gum rosin and oils (65%)

MgCl2 or zinc acetate

Inert oils

Moisture

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38
Q

What is the setting mechanism for zinc oxide-eugenol?

A

Chelation reaction:

ZnO + eugenol undergoes a chelation reaction to form zinc eugenolate + ZnO

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39
Q

How is the setting time of zinc oxide-eugenol controlled?

A

Setting time can be accelerated by:

Heat

Ethyl alcohol

High humidity

Setting time can be retarded by glycerin

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40
Q

What are the disadvantages of using zinc-oxide eugenol?

A

Must have adequate adhesion to the tray

Eugenol can be irritant

Eugenol can adhere to tissues

It cannot be electroplated

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41
Q

What are the advantages of zinc oxide-eugenol?

A

Has satisfactory working and setting time

Has satisfactory shelf life

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42
Q

What are the types of elastic impression materials?

A

Hydrocolloids (Such as agar and alginate)

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43
Q

How do hydrocolloids set? (setting reaction)

A

Via a sol - gel transformation:

Sol -> Agglomeration of molecules of dispersed phase -> Fibrils (micelles) -> Network pattern enclosing dispersion phase particles by adhesion/capillary attraction

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44
Q

What is the difference between alginate and agar impression material?

A

Reduction in temperature -> Agar impression material

Chemical reaction -> Alginate impression material

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45
Q

What affects dimensional stability of hydrocolloids?

A

Syneresis (the contraction of a gel accompanied by the separating out of liquid) -> Loss of water -> Shrinkage

Imbibition -> Absorption of water -> Expansion

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46
Q

What are the advantages of using alginate?

A

Ease of mixing and manipulation

Minimum equipment

Flexible

Accuracy

Low cost

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47
Q

What are the disadvantages of alginate impression material?

A

Restrict the model and die material to only gypsum

Not accurate in reproducing fine details

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48
Q

What is alginate used for?

A

Preparing study cast

Preparing gypsum models

Removable partial denture

Athletic mouth protector

NOT RECOMMENDED FOR IMPRESSION OF CAVITY PREPARATIONS

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49
Q

What is the composition of alginate impression material?

A

Sodium potassium alginate

Calcium sulfate

Sodium sulfate

Diatomaceous earth

Potassium sulfate or fluoride

Glycol (in dustless alginates)

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50
Q

What is the setting reaction for sodium alginate?

A

Water + powder mixing plastic mass

Retarding Reaction (gives use working time): Na2PO4 + CaSO4 -> Na2SO4 + CaPO4

Setting reaction: Sodium alginate + CaSO4 -> Ca++alginate + Na2SO4

THIS REACTION IS IRREVERSIBLE

51
Q

What are the properties of alginate impression material?

A

Permanent deformation <3% (ADA specification)

Strength: Compressive and tear strength are affected by W/P ratio, proper spatulation, rate of deformation, and thickness of impression material.

Storage: Should be stored in 100% relative humidity to avoid syneresis/imbibition and thus avoid shrinkage and expansion.

52
Q

What equipment is required for alginate material manipulation?

A

Equipment needed includes:

Powder-dispensing cup

Water-dispensing cup

Rubber mixing bowl

A spatula

53
Q

What are the steps in alginate material manipulation?

A

Dispensing

Mixing

Loading the tray

Making the impression

Removal of the impression

Pouring the impression

Storage

54
Q

What are the advantages to using agar?

A

It is highly accurate

Elastic

55
Q

What are the disadvantages to using agar?

A

Difficult to manipulate

No method for obtaining model die

Dimensionally unstable

Patient discomfort of thermal shock

56
Q

What is the composition of agar impression materials?

A

Agar 12.5%

Potassium sulfate: 1.7%

Borax 0.2%

Alkyl benzoate 0.1%

Water 85.5%

Colour and flavours (trace)

57
Q

What are the types of agar material and how are they different?

A

Tray type which is stiffer

Syringe type which has less agar

58
Q

What is the setting reaction for agar?

A

Sol is cooled to form the gel and heated to form sol. (37 degrees = setting temp; 45 degrees = sol)

59
Q

What is the elastic recovery requirement for agar impression material?

A

ANSI/ADA specification requires elasstic recovery greater than 96.5%. it depends on time under compression and rate of loading.

60
Q

How flexibly is agar impression material?

A

Flexibility requirement by ANSI/ADA is 4 - 5%

61
Q

What is the strength of agar impression material?

A
  1. 8MPa for compressive strength

0. 8 - 0.9 N/mm tear strength

62
Q

How is dimensional stability maintained in agar?

A

Storage should be in 100% relative humidity to avoid synersis / imbibition which in turn avoid shrinkage / expansion. Immediate pouring the cast is recommended

63
Q

How is agar manipulated in the tray?

A

Material liquefaction takes place in boiling water for 8 to 12 minutes

Tube is then immersed in water at 43 degrees celsius to 49 degrees celsius and manipulated to ensure even cooling

The tray is filled and then tempered for a minimum of 2 minutes in water at 46+/- 1 degrees celsius

64
Q

How is the syringe manipulated for agar use?

A

The syringe, loaded with a cylinder, is placed in boiling water for 10 minutes

No tempering is required before use

The agar is then injected directly into the tooth preparation

After removal, the impression is rinsed, disinfected, superficially dried and then poured

65
Q

How is agar manipulated for impression taking?

A

It is heated in water at 100 degrees celsius for 8 - 12 minutes

Stored in water at 65 degrees celsius

Placed in the tray at 65 degrees celsius

Tempered in 45 degrees in water for 2 - 3 minutes

Impression is taken and cooler (20 degree) water is circulated through the impression mould until gelation takes place

66
Q

What is the laminate technique?

A

It is a combined alginate/agar technique where the hydrocolloid in the tray is replaced with a mix of chilled alginate that bonds with the agar from the syringe and the agar sets in the cool alginate rather than the water circulating through the tray.

67
Q

What are the advantages of the laminate technique?

A

Maximum details are reproduced

Lower equipment cost and less preparation time

Most cost effective way of producing an impression with adequate details

68
Q

What are the disadvantages of the laminate technique?

A

The bond between agar and alginate is not always sound

The alginate has a higher viscosity displacing the agar hydrocolloid during setting

The dimensional inaccuracy of the alginate hydrocolloid limits its use to single units

69
Q

Additional applications of using hydrocolloids:

A

Duplicating materials

Construction of prosthetic appliances and orthodontic models

70
Q

How is the hydrocolloid material of duplicating material different to that of impression material?

A

It has a higher water content

Agar and alginate content is lower which affects compressive strength and percent permanent set.

71
Q

What are the types of modified alginates?

A

Traditional = 2 component system consisting of water and a powder

Recent = 2 component system consisting of alginate sol and Ca++ reactor

72
Q

What is the biocompatibility of hydrocolloids like?

A

No known chemical or allergic reactions associated with hydrocolloid impressions

Most likely side effect is thermal injury from reversible agar hydrocolloid as a result of improper tempering or faulty equipment during impression

Inhalation of fine airborne particles from alginate material can cause silicosis and pulmonary hypersensitivity. Dustless alginate is preferred

73
Q

How are hydrocolloids disinfected?

A

Since the hydrocolloid impression must be poured within a short time after removal from the mouth disinfection should be relatively rapid to prevent dimensional change

Most manufacturers recommend disinfectants such as iodophor, bleach or glutaraldehyde

74
Q

Are all hydrocolloids compatible with gypsum?

A

No, agar hydrocolloid materials are more compatible with gypsum than alginates.

Impression should be washed of saliva and any traces of blood will retard the setting of gypsum.

If the agar impression was stored it should be rinsed with cool water to remove any exudate formed from syneresis from puring up the gypsum model

75
Q

What are the effects that could arise from mishandling hydrocolloids?

A

Grainy material

Separation of tray and syringe materials

External bubbles

Irregularly shaped voids

Rough or chalky stone model

Distortion

76
Q

What are rubber base impression materials?

A

Non aqueous elastomeric impression materials, that are rubber-like, and are made-up from long chain coiled molecules

77
Q

What are the advantages to elastomers?

A

High accuracy

More dimensional stability than agar and alginate

Ease of manipulation

Can be used with undercuts

Can be electroplated

78
Q

What are the consistencies of elastomeric impressions?

A

Low (Syringe/wash)

Medium (regular)

High (tray)

Extra high (Putty)

79
Q

How can rubber based impressions be mixed?

A

3 types of mixing:

Hand mixing

Auto-mixing

Dynamic mechanical mixing

80
Q

What are the types of elastomeric impression techniques?

A

Simultaneous dual viscosity technique

Single viscosity (mono-phase technique)

Putty wash technique

81
Q

What are the types of elastomeric impression materials?

A

Polysulfides

Silicone (condensation and addition polymers)

Polyether

82
Q

What is the composition of polysulfide rubber impression material?

A

2 pastes: A base and a catalyst.

Base consists of 80% low molecular weight organic polymer with reactive mercaptan group and 20% reinforcing agents such as titanium dioxide, zinc sulfate, copper carbonate and silica

Catalyst consists of lead dioxide and copper hydroxide

83
Q

What is the setting reaction for polysulfide rubber impression material?

A

Mercaptan + lead dioxide -> Polysulfide + H2O

THIS REACTION IS SENSITIVE TO MOISTURE AND TEMPERATURE

84
Q

What is the working time for polysulfide rubber impression material?

A

5 - 7 minutes final setting time is 8 - 12 minutes

85
Q

What is the permanent deformation rate of polysulfide rubber impression material?

A

2 - 3%

86
Q

What is the dimensional accuracy and stability of polysulfide rubber impression material like?

A

Dimensional accuracy: Highly accurate

Dimensional stability: Polymerization shrinkage of 0.25% takes place within the 1st 24 hours

87
Q

What is the flow of polysulfide rubber based impression material?

A

An average flow of 0.3 - 0.9% occurs within the 1st 15 minutes

88
Q

What is the flexibility, elasticity, and tear resistance of polysulfide rubber based impression material like?

A

Most flexible of all rubbers

Viscoelastic with elastic recovery of 98%

It is also highly tear resistant

89
Q

How compatible is polysulfide rubber based impression material with die materials?

A

Compatible

It can also be disinfected by most disinfectants

90
Q

What are the advantages of polysulfide rubber impression material?

A

High dimensional stability

High strength and resistance to tear

Can be electroplated

91
Q

What are the disadvantages of polysulfide rubber impression material?

A

Can be distorted

Hydrophobic

Bad odor (sulfide odor)

Staining of clothes

Relatively long setting time

92
Q

What are condensation silicone rubber impression materials made of?

A

A base and a catalyst

Base: Paste of low molecular weight silicone liquid with reinforcing agents as silica.

Catalyst: Paste or liquid of tin organic ester (Tin octoate) and alkyl silicate.

93
Q

What is the condensation setting reaction of silicone rubber impression materials?

A

Dimethyl siloxane + Ortho-ethyl silicate + tin octoate -> Silicone rubber + ethyl alcohol

EVAPORATION OF ETHYL ALCOHOL LEADS TO INCREASE IN SHRINKAGE WITHIN THE 1ST 24 HOURS

94
Q

What is the composition of addition silicone rubber impression material?

A

2 pastes:

1: Low molecular weight silicone with terminal vinyl group, chloroplaticic acid catalyst, and reinforcing fillers.
2: Paste or liquid of low molecular weight silicone with silane hydrogens. reinforcing fillers

95
Q

What is the addition setting reaction of silicone rubber impression materials?

A

Silane - containing siloxane + vinyl terminal siloxane + Chloroplatinic acid -> Silicone rubber

96
Q

What is the accuracy of addition silicone like?

A

Highly accurate

97
Q

What is the flow like in addition silicone?

A

Low flow

98
Q

Which is more dimensionally stable condensation or addition silicone?

A

Addition silicone

99
Q

How is flexibility and elasticity different between silicone and polysulfide impression materials?

A

Silicone is less flexible and more elastic than polysulfides.

100
Q

Is silicone compatible with die materials?

A

Silicone is highly compatible with die materials

101
Q

What is tear strength like in silicone?

A

Relatively low but rapid rate of removal gives high tear strength

102
Q

What are the advantages of silicone based rubber impression materials?

A

Highly accurate

Elastic

Campatible with most die materials

Can be electroplated

Can be disinfected by most disinfectants

103
Q

What is the composition of polyether impression material?

A

Present only in medium consistency as base and catalyst:

Base contains moderately low molecular weight polyether with ethyline imime terminal group

Catalyst contains aromatic sulfonic acid ester

104
Q

What is the setting reaction for polyether impression materials?

A

Polyether with ethylene imine groups + sulfonic acid ester -> Cross linked high molecular weight polyether rubber

105
Q

What are the advantages of using polyether impression materials?

A

Highly accurate

Very compatible with die materials

Good tear strength

Can be disinfected by various antimicrobials

Better mechanical properties than polysulfides

Less dimensional changes than condensation silicone

106
Q

What is the dimensional stability like in polyether impression material?

A

Polymerization shrinkage of 0.25% within 24 hours

107
Q

What is the flexibility of polyether impression material like?

A

Least flexibility of all rubbers

108
Q

What is the elasticity of polyether like?

A

Viscoelastic with elastic recovery 98.9%

109
Q

What is the tear strength of polyether like?

A

Better than silicone less than polysulfide

110
Q

What are the disadvantages to using polyether impression materials?

A

Increased working time

High stiffness

High cost

111
Q

What are the most recent advances in impression materials?

A

Light curing impression materials (polyether urethane dimethacrylate impression material)

Addition silicone

Soft polyether impression material

Optical impression

Alginate substitute

Automatic mixing devices

112
Q

What are the advantages and disadvantages to using light curing impression materials?

A

Adv:

Allows operator to work for a longer time

Extraordinary tear resistance compared to other impression materials

Strain in compression is higher than that of condensation silicone but lower than that of addition silicones

Disadv:

Expansion rate of light-curing material about 0.07% one day after curing whereas other impression materials have negative dimensional changes after 24 hours mixing.

The surface material that set against teeth and gums was tacky (moisture inhibits setting)

113
Q

What are the features of addition silicone?

A

Most accurate of elastomeric impression materials

Supplied in different viscosities: Extra-light, light, medium, mono-phase, heave and putty

It is modification of original condensation silicones

It is hydrophilic impression material

114
Q

What is the reaction for addition silicone?

A

Base material: Polymethyl hydrogen siloxane copolymer which is moderately low molecular mass polymer with silane terminal group

Accelerator material: Vinyl-terminated polydimethyl siloxane. On mixing addition reaction occurs between silane adn vinyl group

115
Q

What are the benefits to using additional silicone?

A

Minimal dimensional change during polymerization reaction and no by-products

No longer necessary to wait 1 hour before pouring. (addition silicone has least viscoelastic qualities thus requiring least time for recovery from viscoelastic deformation)

Addition silicone is not susceptible to changes in humidity and doesn’t undergo any further chemical reactions or release byproducts

Low dimensional change on setting

High tear strength

Hydrophilic (excellent wetting of oral tissues and isn’t affected by moisture and doesn’t form bubbles or voids)

Ability to repour impression without loss of accuracy (opposite to polyether)

Very accurate with great detail reproduction

Flexible and elastic so easily removed from the mouth when set

Elastic recovery; impression returns to its original dimensions upon removal from undercut areas in the mouth without distortion.

Colourized thermo-chromic impression material can allow dentist to know when it has set

High tear strength

116
Q

How are hydrogen gas bubbles removed from surface of addition silicone when pouring gypsum dies?

A

Palladium is added which absorbs hydrogens

117
Q

Why is addition silicone able to recover elastically so well?

A

Due to highly cross-linked structure of addition silicone

118
Q

What are the disadvantages of using addition silicone?

A

Setting time can be longer than other materials

Hydrogen gas released can lead to bubbles in gypsum

Expensive

Gloves containing sulfur inhibit setting

119
Q

What are the advantages to using soft polyether impression material?

A

Excellent wettability

Good dimensional stability

Excellent detail reproduction without distortion

120
Q

What are the disadvantages to using soft polyether impression material?

A

Impression cannot be repoured

Some products are rigid

Poor taste and colour

121
Q

What are the advantages and disadvantages to an optical impression?

A

Advantages:

No need for impression material or trays

Impression can be transmitted and stored electronically

No mess

3D, 360 degree view of preparation that can be moved and turned every angle

Adjustments can be made to the virtual impression

No disinfection required

Disadvantages:

Expensive start up cost

Technique sensitive

More equipment needed

122
Q

What is the alginate substitute?

A

Alginate modified by adding silicone polymers without hand mixing

123
Q

What are the advantages and disadvantages to using alginate substitute?

A

Advantages:

Good hydrophilic properties

Shorter setting time

Easy removal from the mouth

Excellent detail reproduction, elastic recovery and dimensional stability can be stored and reused

Dust-free and compatible with gypsum die materials

Higher patient acceptance than traditional alginate

No hand mixing or powder/liquid mix

Disadvantages:

Much more expensive than traditional alginate.

The material sets very hard & can be a challenge to separate from the model

124
Q

What are the advantages and disadvantages to automixing device?

A

Advantages:

Consistent, homogeneously mixed material.

Less waste dispenses, only the amount of material needed.

The mix obtained is free of voids.

Automatic mixing decrease the strain for dental assistants.

Allow the dentist to use quick setting material.

Higher viscosity materials extrude quickly.

Disadvantages:

Takes up counter space.

Not all impression materials are available in poly-bags.

DMD2 sem 2 (97 decks)

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