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Dental Materials > Auxiliary Materials > Flashcards

Auxiliary Materials Flashcards

1
Q

Six major steps to use elastomeric impression materials to fabricate gypsum models, casts etc

A
  1. Preparing a tray
  2. Managing tissues
    3.Preparing impression materials
  3. Making an impression
    5.Removing of impression material
  4. Preparing stone casts and dies
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2
Q

Use of custom tray

A

To reduce the quantity of material required to make an impression

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3
Q

Why is tissue management necessary

A

To ensure access for tooth preparation and for making an impression

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4
Q

How is tissue managed

A

Use of gingival retraction cord.

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5
Q

Objective of retraction cord

A

To displace the gingival tissue laterally away from the margin of the preparation.
One or two gingival retraction cords are placed under the margin around the tooth for atleast 5 min before making impressions.

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6
Q

When is double cord technique used

A

When the gingival margin is close to gingival attachment.

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7
Q

Manipulation of impression materials are done by?

A
  1. Hand mixing
  2. Static mixing
  3. Dynamic mixing
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8
Q

What is static mixing

A

A technique to turn two fluids into homogeneous mixture without mechanical mixing.

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9
Q

In static mixing the mixing top is made of?

A

Helical mixer elements in cylindrical housing.

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10
Q

What is flow division

A

The leading edge of the first element split the material entering the mixer into two streams.
The stream flow in either side of the helix will make 180° turn.when they reach the second element.
Both streams are split by the leading edge of the second element and two substream combine to new streams entering the second element.

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11
Q

Common mixing tips have how many elements and striations

A

11-16 elements and 2048-4069 striations

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12
Q

Dynamic mechanical mixing

A

Uses a motor to drive parallel plungers, forcing Materials into mixing top and out into an impression tray or syringe.

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13
Q

The use of the motor driven impeller in dynamic mixing

A

To nic the materials as they are passing through, not propel the material.

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14
Q

Which materials are used to mix in dynamic mixing

A

Higher viscosity materials

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15
Q

What are the techniques used to make an impression

A

1.multiple mix technique
2. Monophase technique
3. Putty wash technique

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16
Q

Multiple mix technique

A

Syringe material and tray material are used.
The syringe material is put around the tooth preparation. The filled tray is then inserted in the mouth seated over the syringe material.
The tray material will force the lighter material to adapt to the prepared tissues.

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17
Q

How to repair an impression in multiple mix technique

A

By cutting away the interproximal and gingival areas of the impression.
Impression materials surface must be roughened enough to ensure the new material bond to the set impression

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18
Q

Monophase technique is also

A

Single viscosity technique

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19
Q

Which impression materials are used in monophase technique

A

Addition silicone and medium bodied polyether

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20
Q

Success of monophase depends on

A

Pseudoplastic property of material

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21
Q

Putty wash technique was originally developed for which impression material

A

Condensation silicone

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22
Q

Putty wash technique

A

Thick putty is placed on a stock tray and made a preliminary impression is made.
Then The light bodied wash is provided in the tray during Preliminary impression making.
A thin consistency wash material is placed into the putty impression and repeated into the mouth to make a final impression

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23
Q

Six main causes of impression inaccuracies

A
  1. Polymerization shrinkage
    2 loss of condensation reaction byproduct
  2. Thermal contraction from oral temperature to room temperature
  3. Absorption of water or disinfectant over a period of time
  4. Incomplete recovery from deformation because of viscoelastic behaviour
  5. Incomplete recovery because of plastic deformation
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24
Q

How to know when to remove the impression material from the mouth

A

Inject some of the syringe material onto a space that is not field of operation before inserting the impression tray
Thie material can be probed with a blunt instrument from time to time.

When it’s firm and returns completely to its original contour the material is sufficiently elastic to be removed.

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25
Q

What are the mechanics of removing the impression materials

A
  1. Breaking the physical adhesion between material and tissue.
  2. Stretching of the material enough to pass under the height of contour of hard tissue
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26
Q

Which has the lowest viscosity and the least stiff elastomeric impression material

A

Polysulfide

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27
Q

Advantage and disadvantage of Hydrophobic characteristic of silicone impression

A

Advantage:- makes them suitable for pouring of epoxy resin to produce dies.

Disadvantage::- makes pouring with gypsum products challenging. Because it increases risks of voids in gypsum and casts

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28
Q

How is Hydrophobicity overcome to make gypsum products

A

Use of debubblizers.
Use of surfactant sprays.
Use of dilute solution of soap

An alternative to the use of surfactant is to select hydrophilized addition silicone

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29
Q

Which material do not need the aid of surfactant

A

Polyether and polysulfide

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30
Q

Who is it not advisable to alter the base/catalyst ratio as means of controlling working or setting time?

A

Working and setting time decreases as the filler content in material increases.
Altering the base or catalyst will change the curing rate of the material.
Since accelerator paste contains retarder as well as reactor, increasing it may not produce a predictable change

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31
Q

What are two categories of shear-thinning phenomenon

A
  1. Thixotropy
  2. Pseudoplasticity
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32
Q

What is pseudoplastic material

A

It displays decreasing viscosity with increasing shear stress and recovers it’s viscosity immediately upon decrease in shear stress

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33
Q

What is thixotropic material

A

It does not flower until sufficient energy in the form of impact force or vibration force is applied to overcome the yield stress of the material.
At rest , it takes specific time to regain previous viscous state

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34
Q

Permanent deformation in compression following strain induced in impression materials increases as:-

A

1.Addition Silicone
2. Condensation silicone
3. Polyether
4. Polysulfide

35
Q

The stiffness (elastic modulus) of impression materials of similar viscosity increased in order of:-

A

Polysulfide
condensation silicone
Addition
Polyether

36
Q

What is tear strength

A

The amount of force needed to tear a specified test specimen divided by thickness of specimen

37
Q

Trea strength from higher to lower:

A

Silicones (Addition and condensation)
Polyether
Polysulfide

38
Q

Tear energy

A

Dividing force needed to crack propagating divided by t/(1+lambda). Where t is thickness of specimen and lambda is extension ratio.

Extension ratio is extended portion of length ∆l divided by orginal length l

39
Q

Which material has highest resistance to tearing

A

Polysulfide

40
Q

Why are hydrophilic materials potentially more susceptible to distortion prior to being poured with a gypsum forming products

A

Because long immersion time may cause the surfactant in hydrophilic polyvinyl siloxane to leach out and render impression less hydrophilic

41
Q

How does surfactant added to hydrophilized PVS affect contact angle of water droplets during setting and pouring of casts with gypsum

A

The water droplets may absorb a sufficient quantity of surfactant sprays and become a liquid of lower surface tension.
Lowering of surface tension makes water droplets spread wider on surface of PVS yielding lower contact angles.

42
Q

Which impression material has highest and lowest cytotoxicity

A

Highest :- Polyether

lowest :- Polysulfide

43
Q

What is colloid

A

A substance that is microscopically dispersed uniformly throughout another substance

44
Q

What is hydrocolloid

A

Colloids have two phase:- dispersed and dispersion phase
When the colloid’s dispersion phase is water, it is hydrocolloid

45
Q

Physical change of Agar

A

Reversible.

The sol turns to gel in cooler temperature. This is also called gelation temperature (37-50°C).

The gel turns to sol in warm temperatures. Also called liquefaction temperature (70-100°C)

46
Q

Composition of Agar

A

Main component:- polysaccharide extracted from certain seaweed
And water.
Filler:- Borax
Accelerator:- potassium sulphate to counteract borax’s Retarder effect.

Thymol and glycerine added as a bactericidal and plasticizer

47
Q

The three compartment conditioning unit of Agar making

A
  1. Liquefaction (100°C) for 10 mins
  2. Storage bath (65°C)
  3. Tempering (45°C)
48
Q

The Agar syringe material is

A

Not tempered, as the material should be in a fluid state to enhance tissue adaptation

49
Q

Gelation of the Agar impression in mouth is accelerated by

A

Circulation of cool water (18°-21°C) through tray for 3-5 mins

50
Q

If the Agar material is held rigidly in tray then?

A

The impression material will shrink towards the centre of its mass thereby creating larger dies

51
Q

How Alginate sets

A

By crosslinking of algic acid with calcium ions

52
Q

Describe making of Agar impression

A

Requires three compartment conditioning.
1. To allow liquifaction of hydrocolloid in boiling water of 100°C for minimum 10mins
2. Then placed into storage bath of 65°C to retain Sol condition until needed
3. For immediate preparation,the impression tray is filled with the storage bath material and a guaze is place over it and the tray is placed in water-filled tempering compartment at 45°C .

53
Q

Composition of Alginate

A

Brown seaweed extraction which is a linear copolymer of beta-D-mannuronic acid and alpha-L-glucouronic acid.
For impression making alginate is richer is mannuronic acid.

Main component -sodium/potassium or triethanolamine alginate.
Filler-Diatomaceous earth, zinc oxide
Reactor- Calcium sulfate dihydrate
Accelerator - potassium titanium fluoride

54
Q

Types of Alginate

A
  1. Dustless
  2. Disinfectant alginate
  3. Chromatic Alginate
    4.siliconed Alginate
55
Q

How does the retarder optimise the working time of alginate

A

The process of production of calcium alginate is so rapid that it does not allow sufficient working time.
A water soluble phosphate salt is added to composition as a retarder.
Calciums ions will react with the phosphate and thus, the rapid reaction between calcium and soluble alginate is deferred until phosphate ions from trisodium phosphate are exhausted.

56
Q

Setting time for fast setting and normal setting alginate

A

Fast setting - 1.5-3 mins
Normal setting - 3-4.5 mins

57
Q

How can clinicians control the setting time of Alginate

A

By altering the temperature of Water .
Higher the temperature, shorter is setting time

58
Q

Why is it important to add water to a rubber mixing bowl before adding powder when mixing fast setting alginate

A

If the powder is placed first in the bowl, penetration of the water to the bottom of the bowl is inhibited and a longer mixing time may be required to ensure homogeneous mix

59
Q

How much should be the thickness between impression and Tissue in Alginate

A

3mm

60
Q

Results of insufficient Spatulation of alginate

A

Failure of the ingredients to dissolve sufficiently so that chemical reactions can proceed uniformly throughout the mass

61
Q

Result of Overmixing of Alginate

A

Breaks up the formation of calcium alginate network and reduces it’s strength

62
Q

Two major factors that affect shelf life of Alginate

A

1.Storage Temperature
2.Moisture contamination from ambient air

63
Q

How can distortion of hydrocolloid impression material be minimised during storage

A

2% potassium sulphate solution or 100% relative humidity in the storage chamber to reduce dimensional change of Agar impression

64
Q

Why do agar and alginate include a gypsum hardener and how does it function

A

Agar includes borax which is Retarder.
In Alginates, it produces not only insoluble calcium alginate but also sodium sulfate which is Accelerater at low concentrations but in High it acts as a retarder.

To overcome the gypsum setting it is done by:-
1. Immersing of Agar in a solution of 2% potassium sulphate prior to pouring impression with gypsum
2. By incorporating gypsum Hardener in material such as sulfate in Agar and Potassium titanium fluoride in Alginate

65
Q

Optimal method for disinfecting hydrocolloid impression material without causing distortion or degradation

A
  1. To use household bleach, iodophors, synthetic phenols.
  2. Immersion of material But should not exceed 10 mins
66
Q

What is the principal that makes Laminate technique (agar-alginate Technique) effective?

A

Agar in the tray is replaced with a mix of chilled alginate that bonds to Agar expressed from syringe.
Alginate gels by chemical reaction whereas,
agar gels by contact with cool alginate rather than water circulation through tray.

Since Agar is the one that contacts the prepared teeth, maximal detail is reproduced. Because only syringe material needs to be heated, equipment cost is lower and less time preparation

67
Q

Main disadvantage of Laminate technique

A
  1. Bond between Agar and Alginate is not always sound
  2. Viscosity of Alginate displaces the Agar during seating
  3. Dimensional inaccuracies of alginat limits it’s use to single units
68
Q

How is The Bonding Issue in the Laminate technique adressed

A

It requires that the bond between the two materials under Tensile strength should be in excess of 50kPa

69
Q

Impression plaster is

A

Beta-calcium sulfate hemihydrate.

70
Q

Why is Impression plaster suitable for taking impressions of soft tissues

A

Because of its Fluidity, it has Mucostatic characteristic.

71
Q

Composition of Impression plaster

A

Potassium sulfate -antisetting expansion agent
Borax- retarder

72
Q

Which pigment is added to make a clear distinction between impression and the model after the casting of nodel

A

Alizarin Red

73
Q

What is beading. What does it provide?

A

Long, narrow strips of wax can be adapted around the periphery of impression.

It provides a clear indication of where the impression ends which prevents from over trimming and Overextension

74
Q

Disinfection of impression plaster

A

10 min soak in sodium hypochlorite solution

75
Q

Impression compound is

A

Also called as modeling plastic.
It’s a thermoplastic material

76
Q

Types of impression compound

A

Type 1- low fusing Material for making impressions in oral cavity

Type 2- higher fusing also called tray compound. Used for forming trays to be used in oral cavity

77
Q

What is the other common application of Impression compound

A

Border molding of Acrylic custom tray during fitting of the tray

78
Q

Composition of Impression Compound

A

Mixture of waxes, thermoplastic resins, filler and a coloring agent.

Shellac, stearic acid, Gutta percha are added to improve plasticity

79
Q

Disinfectant of impression compound

A

2% alkaline glutaraldehyde solution

80
Q

Composition of ZOE

A

Base - zinc Oxide
Fixed vegetable or mineral oil

Accelerator:- oil of cloves or Eugenol
Gum or polymerized rosin
Filler
Lanolin
Resinous balsam
Accelerator solution (CaCl2) and color

81
Q

Chief Disadvantage of ZOE

A

Possible stinging or burning sensation caused by Eugenol as it leaches out and contacts soft tissues

82
Q

How can the clinician shorten time of setting of ZOE

A

By adding a small amount of zinc acetate or a drop of water in paste before mixing.
The use of cool spatula and mixing slab is also effective in prolonging the setting time

83
Q

Disinfectant of ZOE

A

2% alkaline glutaraldehyde solution

84
Q

Other applications of ZOE

A

Bite registration paste.
Surgical dressing
Temporary filling material
Root canal filling material
Cementing medium
Temporary reclining material

Dental Materials (4 decks)

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