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Fixed Pros I > Impression Materials and Techniques > Flashcards

Impression Materials and Techniques Flashcards

1
Q

what is an analogue impression

A
  • a negative likeness or copy in reverse of the surface of an object
  • an imprint of the teeth and adjacent structures for use in dentistry
  • made from soft semi fluid material allowed to set
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2
Q

what is an impression technique

A

a method and manner used in making a negative likeness

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3
Q

what is an impression tray

A

a device that is used to carry, confine, and control impression material while making an impression

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4
Q

what is the ideal impression material

A
  • easy to mix and handle
  • suitable working time
  • suitable setting time
  • compatible with die and stone materials
  • not toxic or allergic to the patient
  • dimensionally stable
  • accurate to record the fine details
  • acceptable odor and taste
  • adequate stretch
  • adequate shelf life
  • ready to be disinfected without loss of accuracy
  • fluid or plastic when inserted into the mouth
  • it must be an exact record of all the aspects
  • economic
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5
Q

what is impression criteria

A
  • exact dupliction of the prepared teeth
  • including uncut tooth structure beyond finish line
  • accurate reproduction of the other teeth and tissues, permit cast articulation and restoration contouring
  • free of air bubbles especially in the finish line and occlusal surfaces
  • extended enough to capture the vestibule, tuberosities and retromolar pad
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6
Q

what is wettability

A

ability of liquid to flow over a solid surface

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7
Q

what is wettability related to

A

surface energy of the solid and surface tension of the liquid

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8
Q

what is the contact angle of wettability

A
  • hydrophobic: contact angle >90 degrees, surface not wetted
  • hydrophilic: contact angle <90 degrees, surface wetted
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9
Q

what is viscosity and what is it related to

A
  • resistance of liquid to flow
  • reverse of fluidity
  • related to unset, liquid material
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10
Q

what are liquid and viscosity categorized as

A
  • newtonian
  • none-newtonian
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11
Q

what is newtonian

A

a fluid viscosity is not affected by shear rate
- viscosity is constant

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12
Q

what is a none- newtonian

A

a fluid that does not follow
- viscosity can be changed

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13
Q

what is pseudoplasticity

A
  • shear thinning
  • reduce viscosity with increase share
  • material does not flow until under pressure
  • less viscous with increased share
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14
Q

what is viscoelasticity

A
  • characteristic of solid that behaves as an elastic solid and a viscous fluid
  • related to the set impression
  • mechanical properties depending on loading rate
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14
Q

what are the mechanical properties depending on loading rate in viscoelasticity

A
  • associated with viscus nature
  • as increased load rate, properties improved
  • increased tear strength and elastic limit
  • quick removal, decreased distrortion
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15
Q

what is accuracy

A

ability to replicate the intra oral surface details

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16
Q

what is dimensional stability

A

ability to retain its absolute dimensional size over time

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17
Q

what is tear resistance

A

ability to resist tearing in thin sections, such as through the feather edge material within the gingival sulcus

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18
Q

describe nonelastic impression materials

A
  • rigid, cannot be removed from undercuts
  • edentulous impressions
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19
Q

describe elastic impression materials

A

-can be removed from undercuts without distortion
- dentate impressions

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20
Q

what are the two types of impression materials

A
  • nonelastic
  • elastic
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21
Q

what are the types of nonelastic impression materials

A
  • plaster
  • impression compound
  • zinc oxide eugenol
  • impression waxes
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22
Q

what are the types of elastic impression materials

A
  • hydrocolloids
  • non aqueous elastomers
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23
Q

what are the non aqueous elastomers

A

-condensation silicone
- polysulfides
- polyethers
- addition silicone

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24
Q

what are the types of hydrocolloids

A
  • agar reversible
  • alginate irreversible
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25
Q

what are the nonelastic/rigid impression materials popular in previous century

A

-plaster of paris
- impression plaster
- gutta percha
- modeling compound
- ZOE
- various waxes

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26
Q

the first nonelastic/rigid impression materials were popular in the previous century and arent used now with the exception of:

A

recording atrophic edentulous ridges or flappy ridges

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27
Q

what are the elastic impression materials and the year

A
  • reversible hydrocolloid - first impression material 1925
  • irreversible hydrocolloid 1940
  • polysulfide rubber 1950
  • vinyl poly siloxanes 1970
  • polyether 1975
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28
Q

describe aqueous elastomeric hydrocolloids

A
  • water is the major component
  • hydrocolloid
  • reversible and irreversible
  • reversible is not commonly used today
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29
Q

describe none- aqueous elastomeric polymers

A
  • polysulfide
  • vinyl polysiloxane
  • polyether
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30
Q

describe reversible hydrocolloid

A
  • softens under heat and solidifies when cooled
  • secondary bonds
  • no chemical change
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31
Q

describe irreversible hydrocolloid

A
  • chemical reaction that cannot revert to preset state
  • primary bonds
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32
Q

describe aqueous elastomeric - hydrocolloids

A
  • colloidal materials, agar, or alginate dissolved in water
  • sol to gel
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33
Q

describe sol to gel reaction in agar and alginate

A
  • agar: reversible due to temperature change
  • alginate: irreversible chemical reaction
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34
Q

what are the properties related to gel network in aqueous elastomeric hydrocolloids

A
  • evaporation (shrinkage)
  • syneresis: gel relaxation; water extruded from gel - shrinkage
  • inhibition: absorption of water causing expansion
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35
Q

what consistencies do elastic polymers come in

A

light, medium, heavy and putty

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36
Q

what are the types of elastic polymers

A
  • polysulfide or rubber base PS
  • vinvyl polysiloxane VPS
  • polyether PE
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37
Q

what is the chemical setting reaction in none aqueous elastomeric

A
  • condensation polymerization: by product is H2O or -OH
  • addition polymerization: no by product
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38
Q

what is the tray selection criteria

A
  • feel comfortable to the patient
  • extended slightly beyond the facial/buccal surfaces of the teeth
  • extend approximately 2-3mm beyond the 3rd molar, retromolar, or tuberosity
  • sufficiently deep to allow 2-3mm of material between the tray and the occlusal/incisal edges
  • sufficiently rigid
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39
Q

the impression tray must be sufficiently rigid to:

A
  • carry the impression material into the oral cavity
  • hold the material in close proximity to the teeth
  • avoid breaking during removal
  • prevent wrapping of the completed impression
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40
Q

what are the types of impression trays

A
  • stock trays
  • custom trays
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41
Q

describe stock trays

A
  • plastic or metal; perforated or rimmed
  • complete arch, quadrant, or dual arch
  • dentate or edentulous arch
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42
Q

describe custom trays

A
  • made 24 hours in advance
  • light cured, auto cured, thermoformed
  • better fit
  • less material waste
  • controlled thickness of mateiral
  • increased accuracy
43
Q

what is impression tray retention and adhesion for

A

to prevent impression distortion due to material pulling away from tray

44
Q

what gives retention and adhesion in impression trays

A
  • mechanism perforations or rims
  • chemical adhesion
45
Q

what are the adhesive materials for retention and adhesion in impression trays

A
  • specific for each material; including alginate
  • should always be used
  • apply and dry
46
Q

what is the goal of preliminary impressions

A

a fully or overextended impression of the arch, with all anatomical landmarks

47
Q

what is the purpose of preliminary impressions

A
  • evaluate arch form
  • anatomical landmarks
  • musculature
  • hard and soft tissue anomalies
  • restorative space
  • diagnostic wax up
  • fabrication of custom tray
48
Q

what is the final impression material selected based on

A

the type of impression required for the procedure

49
Q

what is tissue retraction

A

in the final impression single or double cord technique; cord/s removed right before impression making

50
Q

where is the light bodied consistency dispensed in the final impression

A

into the sulcus, over and around the prepared teeth and onto the surrounding tissue

51
Q

describe the final impression with the custom tray

A
  • the custom tray with dried adhesive loaded with medium or heavy bodied consistency and tray is seated with no downward pressure approximately 4-6 minutes
  • once set remove as quickly and straight as possible
  • the impression is disinfected, inspected for accuracy, placed in a biohazard bag, labeled and ready for the lab tech
52
Q

what is the purpose of tissue manipulation for gingival retraction

A

to atraumatically displace gingival tissue to allow access for impression material to record the finish line and provide sufficient thickness of the impression

53
Q

what are the techniques for tissue manipulation for gingival retraction

A
  • mechanical
  • chemo- mechanical
  • surgical
  • surgical not widely used
54
Q

what is an example of chemo mechanical tissue manipulation for gingival retention

A

impregnated cords

55
Q

what are examples of surgical techniques for tissue manipulation and gingival retraction

A
  • electrosurgery
  • rotary curettage
  • laser
56
Q

what are the classifications of retraction cords dependent on and describe each

A
  • configuration: twisted, knitted, plain
  • surface finish: waxed, unwaxed
57
Q

what is the chemo mechanical technique

A
  • pack the retraction cord, soaked in hemostatic agent then dried using cord packing instrument
  • double vs single cord technique
  • remove cord/s after 4 minutes
  • impression material injected into the sulcus
58
Q

what is the double vs single cord technique

A
  • two knitted cords with different diameters are used
  • smaller diameter will be deep into the sulcus
59
Q

what was irreversible hydrocolloid/alginate developed for and where is it from

A

a substitute for agar impressino material when its supply became scarce during WWII
- based on a nature substance extracted from brown seaweed

60
Q

when irreversible hydrocolloid/alginates are mixed with water what do they form

A

a sol gel

61
Q

is alginate hydrophobic or hydrophilic

A

hydrophilic

62
Q

what is the composition of alginate

A
  • soluble alginates
  • calcium sulphate: reactor, insoluble calcium alginate
  • zinc oxide: filler
  • potassium titanium fluoride: accelerator
  • diatomaceous earth: filler, provides strength and stiffness
  • sodium phosphate: retarder
  • coloring and flavouring agent
63
Q

describe the chemical reaction in alginate

A

Na alginate + CaSO4 -> Ca alginate + Na2SO4

64
Q

alginate is a powder which contains the following reacting ingredients:

A
  • potassium or sodium alginate (15-20%): reacts with calcium ions
  • calcium sulphate dihydrate (14-20%) reacts with potassium alginate to form a dihydrate insoluble alginate gel
65
Q

what is the technique using alginate

A
  • powder: liquid ratio
  • add water first
  • avoid incorporating air into the mix
  • mixing time is 45-60 seconds, based on fast set or regular set
  • contaminants such as gypsum may accelerate the set
  • thickness of alginate should be 3mm
66
Q

what is the recommended technique for alginate impression disinfectin

A

-1:10 dilution of household bleach
- impression then wrapped immediately in soaked paper towel and sealed bag

67
Q

how long should the stone cast set after pouring the alginate impression

A

60 minutes

68
Q

what are the 2 major factors that affect the shelf life of the impression

A

storage temperature and moisture

69
Q

how should the diagnostic cast be cleaned up after taken out of impression

A
  • small nodules and projections on the impression surface should be removed
  • casts should be trimmed and mounted
70
Q

what are dimensional changes in the impression caused by

A

delay in pouring the impression

71
Q

what is distortion caused by

A

moving the tray during setting, premature removal of tray, not removing with a snap , delay pouring cast

72
Q

what can tearing be caused by

A

impression removed before it sets, slow rate of removal, thin mix used, deep undercuts, not enough material in tray

72
Q

what is loss of detail from

A

premature tray removal from mouth

73
Q

how is non aqueous elastic material distinguished from hydrocolloids

A

hydrocolloids are aqueous

74
Q

what are elastomeric impression materials made of

A

synthetic rubber

75
Q

what problems do elastomeric impression materials solve with hydrocolloids

A
  • poor tear resistance
  • poor dimensional stability
76
Q

describe polysulfide

A
  • AKA mercaptan or simply rubber
  • provided as two tubes as base and accelerator
  • requires a custom tray
  • longer setting time, malodor, stain clothes
77
Q

what is the composition of polysulfide

A
  • base: polysulfide polymer mixed with inert fillers
  • catalyst: lead dioxide mixed with small amounts of sulfur and act as oxidation initiator
78
Q

describe vinyl polysiloxane

A
  • limited shelf life
  • requires special tray adhesive
  • provided as auto mix unit, syringe, and mixing tips
  • no syneresis, or imbition however respond with shrinkage over time
  • more flexible, so there is more chance for distortion during removal
  • best dimensional stability among impression materials
79
Q

what is the impression technique with vinyl polysiloxane

A
  • wait 20-30 minutes before pouring for stress relaxation. it can be delayed up to 7-10 days
  • stiffness makes removal of tray more difficult
80
Q

what is the composition of addition silicon in vinyl polysiloxane

A
  • base: poly dimethyl siloxane
  • catalyst: polyvinyl siloxane- platinum salt
  • cross linking agent: alkyl ortho silicate or organo hydrogen siloxane
  • filler: silica
81
Q

what is the manipulation and technique of vinyl polysiloxane

A
  • addition reaction, no by product
  • automix: uniform mixing, less air, less mixing time
    -sulfur inhibit the polymerization: latex gloves retards the setting
  • hydrophobic: dry field needed, surfactant added: improves wettability and less cast bubbles
  • elastic recovery from undercuts
82
Q

describe the H2 release in vinyl polysiloxane manipulation and technique

A
  • secondary reaction not a byproduct
  • 15-30 min delay in pouring
  • platinum act as H2 scavengers
83
Q

what effects the dimensional stability of vinyl polysiloxane

A

multiple pours
- delayed pouring

84
Q

describe polyether

A
  • hydrophilic
  • high elastic recovery
  • provided as hand, auto mix unit or electronic mixing
  • light, medium and heavy body consistencies
  • difficult removal from mouth or cast
85
Q

why is it difficult to remove polyether from mouth or cast

A
  • undercut block out
  • less stiff than VPS
  • material stiffness and harder removal are not correlated
86
Q

how should you prevent tearing in polyether

A

break the seal and rock slightly

87
Q

how do water, saliva and blood affect polyether material

A

increase the marginal discrepancy

88
Q

when does increased water absorption occur in polyether

A

if a thinning agent is used

89
Q

what is the composition of polyether

A
  • base: polyether
  • catalyst: glycol based plasticizers
  • cross linking agent: sulfate
  • filler: silica
90
Q

describe polyether manipulation and technique

A
  • addition reaction, no by product
  • short setting time
  • excellent accuracy and dimensional stability
  • dimensional stability: affected by multiple pours and delayed pouring
91
Q

which are the tear strengths of PS? VPS? PE?

A

PS: highest
- VPS: adequate
- PE: adequate

92
Q

what tray do you use with PS? VPS? PE?

A
  • PS: custom
  • VPS: custom or stock
  • PE: custom or stock
93
Q

what is the working/setting time of PS? VPS? PE?

A
  • PS: 3-6/8-10
  • VPS: 2-4/4-6
  • PE: 3/6
94
Q

what is the pour time of PS? VPS? PE?

A
  • PS: 1 hour
  • VPS: 7 days
  • PE: 7 days
95
Q

what is the moisture toelrance/ pouring ease of PS? VPS?PE?

A
  • PS: acceptable
  • VPS: poor/adequate
  • PE: very good
96
Q

what is the cause of voids

A
  • lifting intra oral tip while syringing or presence of moisture
97
Q

what is the cause of tacky unset VPS material in the preparation area

A
  • early removal or sulfur contamination from gloves
98
Q

what are the effects of disinfectant soaked paper towel for 10 mins on eaach material

A
  • no adverse effect on VPS
  • potential expansion with increased exposure time for PS and PE
  • imbition and expasion for alginate
99
Q

it is better to ______ the impression than soaked paper towel

A

rinse and spray

100
Q

what are the acceptable disinfectants

A
  • glutaraldehyde
  • iodophors
  • sodium hypochlorite
  • synthetic phenols
  • dual or synergized quaternaries
  • sodium bromide
  • chlorine
101
Q

what is GPT-9

A

-a digital impression
- a digital scan
- intra oral scanners
- scan then send electronic file

102
Q

what is a digital scan

A

capturing the optimal image directly of the patients anatomy or indirectly of a definitive cast of the anatomy

103
Q

what is a digital impression

A
  • not a negative likeness or copy in reverse of the surface of an object
104
Q
A

Fixed Pros I (13 decks)

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