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FIXED > lecture 7- impression materials and tech > Flashcards

lecture 7- impression materials and tech Flashcards

1
Q

used to make initial impressions from mounted casts PRIOR to fixed proths work

A

alginate

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2
Q

alginate is ___based and

A

water based

irreversible when water is added

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3
Q

softens under heat and solidifies when cooled

A

reversable hydrocolloid

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4
Q

chemical reaction that cannot revert to preset state

A

irreversible hydrocolloid

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5
Q

There is no chemical change making the
changes permanent. Therefore, this is
reversible

A

reversable hydrocolloid

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6
Q

➢ Chemical change is permanent. Therefore,
this is non-reversible
➢ Alginate is in this category

A

irreversible hydrocolloid

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7
Q

Alginate is ____, so moist tissue surfaces are not a hindrance to the
impression unlike PVS materials.

A

hydrophilic

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8
Q

any substance consisting of particles
substantially larger than atoms or ordinary molecules but too small to be visible to the unaided eye
-agar or alginate dissolved in water

A

colloidal materials

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9
Q

a process that converts a colloidal solution into a gel-like network:

agar: reversible due to _______
alingate: irreversible due to:____-

A

sol to gel

agar: temp change
alginate: chemical rxn

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10
Q

3 properties related to gel network

A
  1. evaporation (shrinkage)
  2. syneresis: get relaxation; water extruded from gel (shrinkage)
  3. imbibition: absorption of water causing expansion
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11
Q

this reacts with calcium ions and is the powder

A

Na alginate (or potassium alginate)

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12
Q

reacts with Potassium Alginate to form a dihydrate insoluble alginate gel
-it is the gel

A

calcium alginate

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13
Q

powder to liquid rato is used. add what first?

avoid incorporating what into mix?

A

water first

avoid mixing in air

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14
Q

alginate is provided as a powder, which contains the following reacting ingredients:

A

Potassium or Sodium Alginate(15-20%)
and
Calcium Sulphate Dihydrate (14-20%):

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15
Q

what is alginate mixing time

A

45-60 seconds

based on fast set or regular set so dont be slow!

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16
Q

what is the thickness of alginate should be

A

3mm in tray

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17
Q

After pouring the impression, the stone cast
should not be separated for:
with yellow stone

A

60 mins with yellow stone

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18
Q

CDC recommend _____ dilution of household
bleach for disinfection

A

1:10 ratio

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19
Q

Impression placed in small what for transfer and so not dry out

A

Ziploc baggie
or head rest cover with a few drops of
water in the bottom of the baggie and
is sealed.

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20
Q

the
two major factors that affects the shelf
life of the impression

A

storage temp and moisture

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21
Q

If you remove your impression from the
mouth, rinse it off, and then wrap the
impression with a wet paper towel, what
will happen?

A

alginate absorbs more water as it continues to harden and the material swells

now anything made from that impression will NOT fit because the model has distorted as it absorbed water

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22
Q

placing in bag with 2-3 drop sof water sealed allows

A

alginate to not dehydrate as it sets, but does
not provide so much water as to cause further
absorption and distoration

(alginate is hydrophilic- water loving)

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23
Q

The diagnostic cast should be removed from the impression approximately
_______ after its final set.

A

one hour

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24
Q

What is a Dental Impression for
Fixed Prosthodontics?

A

analogue impression

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25
Q

-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

A

analogue impression

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26
Q

method and manner used in making a negative likeness

A

impression technique

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27
Q

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

A

impression tray

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28
Q

What do we look for in a dental impression?

A

-Exact duplication of the prepared teeth
-Includes uncut tooth structure beyond finish line
-Accurate reproduction of the other teeth and tissues
-Free of air bubbles specifically in the finish line and occlusal surfaces
-Extended enough to capture the vestibule,
tuberosities, and retromolar pad is ideal

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29
Q

Impression Tray Selection Criteria
1. Extended slightly beyond the _____ surfaces of the teeth
2. Extended approximately_____beyond the 3rd molar, retromolar, or tuberosity
3. Sufficiently deep to allow _____ of material between the tray and the occlusal/incisal
edges

A
  1. facial/buccal
  2. 2 -3 mm
  3. 2 -3 mm
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30
Q

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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31
Q
  • Plastic or metal; perforated or rimmed
  • Complete arch, quadrant, or dual arch
  • Dentate or edentulous arch
A

stock trays

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32
Q
  • Made in advance
  • Light cured, auto cured, or thermoformed
  • Better fit than stock trays
  • Less material waste
  • Controlled thickness of material
  • Increased accuracy
A

custom trays

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33
Q

used to prevent impression
distortion due to material pulling away from
tray

A

adhesive

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34
Q

provides chemical adhesion

A

adhesive

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35
Q

adhesive materials:
1
2
3

A
  • Specific for each material; including Alginate
  • Should always be used
  • Apply and dry
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36
Q

what is the goal of impression technique for single crown

A

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

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37
Q

what is the purpose (or what we want to see) for good impression technique for single crown

A
  • Evaluate arch form
  • Anatomical landmarks
  • Musculature
  • Hard and soft tissue anomalies
  • Restorative space
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38
Q

The material selected is dependent on the type of

A

impression required for the procedure

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39
Q

tissue retraction for impression technique of single crown

A

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

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40
Q

for single crown, the custom tray with dried adhesive is loaded with medium or heavy body material and seated with some downward pressure for how long

once set, it is remove quickly how

impression is than disinfected and inspected

A

4-6 mins

gently and straight as possible

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41
Q

what impression material is
1.rigid, cannot be removed from undercuts
2.best for edentulous impressions

A

nnonelastic

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42
Q

what impression material
1. can be removed from undercuts without distortion
2. best for dentate impressions

A

elastic

43
Q

The first impression materials were popular in the previous century
* Plaster of Paris
* Impression plaster
* Gutta percha
* Modeling compound
* Zinc Oxide Eugenol
* Various waxes
Less commonly used now with the exception of recording atrophic edentulous ridges or flappy ridges

A

nonelastic/rigid

44
Q

Elastic Materials examples

A

Reversible Hydrocolloid (AGAR) – Circa 1925
Irreversible Hydrocolloid (Alginate) – Circa 1940
Polysulfide Rubber – Circa 1950
Vinyl Poly Siloxanes – Circa 1970
Polyether – Circa 1975

45
Q
  • Water is the major component
  • Hydrocolloid
  • Reversable and irreversible
  • Reversable is not commonly used today
A

aqueous elastomeric (hydrocolloids)
(elastic)

46
Q
  • Polysulfide
  • Vinyl Polysiloxane (silicone)
  • Polyether
A

none-aqueous elastomeric (polymers)
(elastic)

47
Q

ability of liquid to flow over a solid surface

A

wettability

48
Q

wettability is related to surface energy of the ____ and surface tension of ____

A

energy= solid
tension= liquid

49
Q

contact angle of wetting:
1: hydrophobic:
2: hydrophilic:

A
  1. hydrophobic: contact angle >90 degrees [surface not wetted]
  2. hydrophilic: contact angle <90 degrees
    [surface wetted]
50
Q

non-aqueous elastomers provide:
1
2
3
4

A
  1. accuracy
  2. dimensional stability
  3. tear resistance
  4. viscoelasticity
51
Q

Ability to replicate the intra-oral surface details

A

accuracy

52
Q

Ability to retain its absolute dimensional size over time

A

dimensional stability

53
Q

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

A

tear resistance

54
Q

Characteristic of a solid that behaves as an elastic,
solid, and a viscous liquid
* This term relates to the set impression

A

viscoelasticity

55
Q

the mechanical properties for viscoelasticity depend on LOADING RATE:
1
2

A
  1. viscus nature improves tear strength and elastic limit
  2. quick removal, decreased distortion
56
Q

Elastic polymers: come into different consistencies;

A

light medium heavy and putty

57
Q

3 elastic polymers

A

PS- polysulfide or rubber base
VPS- vinyl polysiloxane
PE- polyether

58
Q

non-aqueous elastomers chemical setting reaction:

A
  1. condensation polymerization
    by product: H2O or OH
  2. addition polymerization
    no by product
59
Q

these materials are synethetic rubber and are distinguished from hydrocolloids which are water based (aqueous)

A

non aqueous elastomeric

60
Q

Non aqueous elastomeric materials offer potential solutions to the two main problems associated with hydrocolloids (alginate):

A

poor tear resistance and poor dimensional stability

61
Q

It is known also as Mercaptan or simply rubber base
and provided as two tubes of base and accelerator

A

polysulfide

62
Q

polysulfide requires this type of tray and negatives of it:

A

custom tray
longer setting time, smells and stains

63
Q

polysulfide base:

A

polysulfide polymer mixed with inert fillers

64
Q

polysulfide catalyst

A

lead dioxide mixed with small amounts of sulfur and act as oxidation initiator

65
Q

Elastomeric Impression material we use now

A

vinyl polysiloxane

66
Q

vinyl polysiloxane uses special what:

and provided as an _____unit, syringe, and mixing tips

A

special tray adhesive

auto-mix unit

67
Q

overtime this happens with vinyl polysiloxane

A

shrinkage

68
Q

vinyl polysiloxane is (more/less) flexible

A

more so more chance for distoration

69
Q

Best dimensional stability among impression materials (addition silicon)

A

vinyl polysiloxane

70
Q

Wait 20 – 30 min. before pouring for stress relaxation. It can be
delayed up to 7- 10 days

-Stiffness makes removal of the tray more difficult

A

vinyl polysiloxane

71
Q

vinyl polysiloxane composition of addition______

A

silicon

72
Q

base of vinyl polysiloxane:

A

Poly Dimethyl Siloxane

73
Q

catalyst of vinyl polysiloxane

A

Polyvinyl siloxane - Platinum salt

74
Q

Vinyl Polysiloxane: addition reaction, NO____

A

by-product

75
Q

vinyl polysiloxane auto-mix:

A

-uniform mixing
-less air
-less mixing time

76
Q

vinyl polysiloxane hydrophobic:

A

-dry field needed
-surfactant added; improve wettability and less cast bubbles

77
Q

in vinyl polysiloxane, sulfur inhibits the polymerization so

A

later gloves retards the setting

78
Q

this impression material is elastic and recovers from undercut- can flex and return to shape

A

vinyl polysiloxane

79
Q

this is released during setting as secondary rxn, NOT a by product

in vinyl polysiloxane

A

H2

80
Q
  • Hydrophilic
  • High elastic recovery
  • It is provided as hand, auto-mix unit, or electronic mixing
  • Light, medium, and heavy body consistencies
  • Difficult removal from mouth or cast
A

polyether

81
Q

Need to block out undercuts
more stiff than VPS

which elastomeric impression material

A

polyether

82
Q

this elastomeric impression material has
1. high elastic recovery
2. hydrophilic
3. hand, automix unit, or electronic mixing

A

polyether

83
Q

in polyether, when removing impression,

A

break the seal and rock slightly to prevent
tearing

84
Q

Water, saliva, and blood affects the material; increase the marginal
discrepancy
* Increased water absorption occurs if a thinning agent is used

what material?

A

polyether

85
Q

polyether composition
base
catalyst
cross-linking agent

A

Base: Polyether
Catalyst: Glycol based plasticizers
Cross-linking agent: Sulfate
Filler: Silica

86
Q

polyether is addition reaction (with/without) by product

A

without (no)

87
Q

this Elastomeric impression material has short setting time, excellent accurancy and dimensional stability (multiple pours and delayed pours)

A

polyether

88
Q

The preferred elastomeric impression materials on the market are

A

PVS and PE

89
Q

known for their hydrophilic properties and good flowability

A

polyethers

90
Q

are known for their excellent elasticity, high
tear strength and stability.

A

pvs

91
Q

have a high resistance to tearing but stretch and do
not recover completely elastically

A

PS

92
Q

lends itself to
taking final denture impressions or full-arch impressions of multiple crown
preparations more easily

A

PS

93
Q

voids unacceptable
caused by

A

lifting intra-oral tip while syringing or presence of moisture

94
Q

tacky unset VPS material in the rep area
cause:

A

early removal or Sulfur contamination from gloves

95
Q

Disinfectant soaked paper towel for 10 min.:
* No adverse effect on

A

VPS

better to rinse and spray impression

96
Q

Potential expansion with increased exposure time for

A

PS and PE

97
Q

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

A

tissue retraction

98
Q

tissue retraction techniques

A
  1. mechanical
  2. chemo-mechanical (impregnated cord)
  3. surgical (electrosurgery, rotary curettage handpiece, laser)
99
Q

classification of retraction cords

A
  1. depending on the configuration: twisted, knitted, plain
  2. depending on surface finish: waxed or unwaxed
100
Q

chemo-mechanical technique:

A

Pack the retraction cord, soaked in hemostatic agent, then lightly dried; use cord packing instrument to place

101
Q

double vs single cord technique

A

double: two knitted cords with different diameters are used. smaller is deeper

single: one cord

102
Q

remove cords after_____. impression material is injected into sulcus once cords are removed

A

4 mins

103
Q

capturing the optical image directly of
the patient’s anatomy or indirectly of a definitive
cast of the anatomy

A

digital scan

104
Q
A

FIXED (8 decks)

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