3. Impression Materials Flashcards Preview

Dental Materials, Module II > 3. Impression Materials > Flashcards

Flashcards in 3. Impression Materials Deck (33):
1

What is an Impression?
! A 3d ____ imprint/image of oral tissues used for making a ____ cast

negative
positive

2

Properties of an ideal impression material

Accuracy
! Reproduction of ____
! ____ stability

! ____
! Adherence to ____ tray
! Compatibility with ____ materials

1: Reaction continues and shrinks over time (poor dimensional stability); elasticity - must be elastic in order to recover from any ____ experienced upon removal

detail
dimensional

elasticity
impression
die

deformations

3

Accuracy of Impression Materials

2: standardization of materials - ways to measure accuracy according to ____ standards

left: metal mold, measure dimensions across ____ and ____, and then impression of standard die and make a cast, and measure them and compare to the standard; right: ADA requires for an accurate impression, the impression material should be able to record a line that is ____um thick; the 3 pictures show diff materials and how well they record the lines; most detailed is the ____ picture

ADA
arch
tooth heights
bottom

4

Elastic Recovery of Hydrocolloid Impressions

3: cross-section of impression surround a tooth; once set, remove and it becomes deformed (____ once removed); then, it is the finished materials, aglinate and agar > more perm deformation for ____ than ____

10%
alginate
agar

5

Application of Tray Adhesive

! Use right adhesive for impression material
! Inadequate adhesion= ____ and ____

4: within a ____ solvent, impression sticks to the adhesive and doesn't come undone from the tray; diff classes of impression materials have diff ____ - they are ____

dislodgment
distortion
volatile
adhesives
matching

6

Adhesives in Impression Tray

! Adhesives improve ____ of impressions

1: rim-lock on stock tray, can take impression w/o adhesive and it won't come out, however, once it sets it shrinks ____ the tooth; with an adhesive, it shrinks ____ from the tooth, you get a slightly larger space resulting in a slightly ____ die (this is preferable! You don't want shrinkage towards the tooth, the indirect restorations will fit better)

accuracy
toward
away
larger

7

Ideal Properties

Handling Characteristics

- ____ time
- ____ time
- ____ life

1. The 2 materials put together and you start ____ (working time begins). Once you finish the viscosity ____ and eventually is too ____ for you to record any impression (working time ends). We want a working time that is reasonable, not too long. Usually 2-3 min is good enough

2. “Beginning of mix until the material is ____.” This is anywhere from 5-8 min sometimes 9 min. Don’t want this to be too long bc it can be uncomfortable for the pt with that thing sitting in their mouth

3. Refers to how long you can keep the material before using it. Whereas ____ refers to the stability after you have taken the impression and storing it.

We can also have mixing time: from the beginning of ____ until ____. Typically 1 min

working
setting
shelf

mixing
increases
viscous

set

dimensional stability

mixing
complete

8

Ideal Properties
Biologic Properties
! ____ and discomfort

! Disinfection
– 1% ____
– 2% Glutaraldehyde
– ____

____ Considerations
! Initial cost of equipment
! Cost of materials

toxicity
sodium hypochlorite
iodophors
economic

9

Classification of impression material
1. Based on the ____ state of the ____ material
! ____
! Non- ____ or rigid

physical
set
elastic
elastic

10

Elastic /Non-Elastic Materials

Elastic
Elastomers
- ____
- non-____

Non-elastic
____ plaster
Impression compound
____
Impression waxes

aqueous
aqueous
impression
zinc oxide-eugenol

11

Elastic Impression Materials

! ____ Elastomers

! Hydrocolloids
– ____
– ____

! Non Aqueous Elastomers – Addition ____
– Condensation ____
– ____
– ____

aqueous
alginates
agar-agar
silicones
silicones
polyethers
polysulfides

12

2. Mechanism of setting
! Reversible physical change
! Irreversible chemical reaction

! Reversible
– ____, Wax, ____

! Irreversible
– Alginate ____
– Elastomers- ____, Silicones, ____
– Impression ____
– Zinc Oxide-Eugenol

3: impression compound is a ____-based material

compound
agar hydrocolloid

hydocolloid
polysulfide
polyether
plaster
wax

13

3. According to their use in dentistry
! Impression materials for edentulous patients
– All ____

! Materials for dentate patients
– ____ materials

Technically there are no ____ for edentulous pt and all impression materials can be used for them. You cant always assume though that you can use a ____ impression material for them

materials
elastic
undercuts

14

Agar-Agar Reversible Hydrocolloid

! Organic ____ colloid from ____

hydrophilic
sea weed

15

Agar-agar
Reversible hydrocolloid

Components
Agar: ____, ____
Borax: ____, ____
K2SO4: ____, ____
Alkyl Benzoate: ____, ____
Dyes and Flavor: ____, ____
Water: ____, ____

The picture shows that its gel-like when its set so its rather fragile and needs the ____ for strength

Potassium sulfate - manufacturers put it in and allows it to ____ well

____ is the majority of the material (85%) dont get caught up with the agar its still much more water

12.5
dispersed phase
0.2
strength
1.7
accelerator (die)
0.1
inhibits mould
trace
appearance and taste
85.5
continuous phase

borax
set
water

16

Agar-agar

Agar sol >>>> Agar Gel (____oC)

Agar gel >>>>> Agar sol (____oC)

Gelation temperature

Hysteresis: The difference of temperature between ____ and ____

43
100
liquefaction
gelation

17

Presentation and Manipulation

Heating - ____oC
Storage - ____oC (after ____)
Tempering - ____oC (when ____ arrives)

100
65
liquified
46
patient

18

Armamentarium for Agar Impression

! Water- cooled trays ____oC

! Snap removal

Water chennales that run around tray, once loaded, turn on water and you can cool it

snap removal - all impression materials are ____ > if you put a force on it > it recovers better than if you do it ____, if you're removing an impression it's better to remove with a ____ > recovers quickly/sharply/better than if you do it slowly

13
viscoelastic
force
slowly
snap

19

Handling for Agar
! Working time ____ min ! Setting time ____min(variable)

1. This working time doesnt correspond to what we talked about bc you’re just squeezing the liquified tube into the tray and that its well covered
2. Depends on how well your ____ channels are connected to the tray for it to set properly

7-15
5

water

20

Biological Properties

Agar-Agar

! non ____
! non ____
! ____ shock
! ____

toxic
irritant
thermal
disinfection

21

Storage of Impressions
____ Rel. humidity by wrapping in moist ____

No more than ____ mins

100%
paper towels
30

22

Economic Considerations

Agar-Agar

Need for ____ equipment -High ____ investment

special
intitial

23

Alginate Composition

Source: ____ from Seaweed
____ Acid

Sodium, potassium & Ammonium salts are soluble in ____

Weve all taken alginate impressions. Its also obtained from seaweed, but has a different ____ formula

“Most of them are either ____ or ____

alginic acid
anhydro-B-mannuronic

water

chemical

sodium
potassium
mannuroate

24

Alginate Composition

Componnent:
K Alginate: ____, ____
Ca Sulfate: ____, ____
ZnO: ____, ____
K-Ti-Fluoride: ____, ____
Diatomaceous earth: ____, ____
Sodium phosphate: ____, ____

K-Ti-Fluoride is imilar to ____ of the agar-agar as a stone hardener

ZnO/K-Ti-Fluoride: filler particles that ____ material

K Alginate/Ca Sulfate: when you add water these two react to form ____ (fast)

Sodium Phosphate: this 1st reacts with ____ until the NaP is all gone then the Ca sulfate and K alginate rxn begins

15
soluble alginate
16
reactor
4
filler
3
stone hardener
60
filler particle
2
retarder

K2SO4
strengthen
Ca sulfate

25

ALGINATE
Setting Reactions:
2Na3PO4 + 3CaSO4 ---> Ca3(PO4)2 + 3Na2SO4

Na.nAlg + n/2CaSO4 ---> n/2Na2SO4 + Ca.n/2Alg sol

This first rxn takes place until all ____ is consumed then the 2nd rxn begins to make the ____. An IMPORTANT rxn to remember

Sodium or potassium or ammonium alginate reacts with CaSO4 to make the CaAlg gel that’s the set material. When you mix water first you have a ____

Na3PO4
gel

sol

26

Alginates- Presentation
! Bulk - in ____ container
! ____ pouches
! Regular and Fast set
– obtained by adjusting concentration of ____
! Hard set vrs soft set
• Concentration of ____ - ____ forms available

metal
predispensed
sodium phosphate
filler
injection

27

Alginates- Presentation
! Bulk - in ____ container
! ____ pouches
! Regular and Fast set
– obtained by adjusting concentration of ____
! Hard set vrs soft set
• Concentration of ____ - ____ forms available

metal
predispensed
sodium phosphate
filler
injection

28

Alginates-Properties
Accuracy

! Detail reproduction - ____ um
! Elastic recovery - ____%
! Dimensional stability
- ____
- imbibition
! Compressive /tear strength – ____ ratio
– Rate of ____
! Permanent deformation - ____

Alginate is not as accurate as agar bc it cant do ____ microns. Elastic recovery is also lower, and it has the same problems with dimensional stability if stored in a dry or moist environment

IMPORTANT point about these aqueous elastomers that has very low strength, the strength that is appropriate here is ____ strength. If there are deep undercuts and it has low strength it will tear and leave remnants of the material in the pt sulcus.

Why do we still use alginate so much then? It is ____ and we only use it for ____ impressions to make study casts

75
97.3
syneresis
W/P
deformation
high

25
tear
cheap/convenient
preliminary

29

PROPERTIES
Handling

! Powder Dust/Segregation
! Proportioning (W/P ratio)
! Mixing time (____ min)
! Working time ____ min
! Setting time ____ min
! Effect of temperature (____oC)

If the powder is ruffled and you continue to inhale this dust you can get fibrogenesis of the lungs. You want to use a certain ____ material. The different particles can also segregate after settling for a long time so you have to stir it.

IMPORTANT point: as the room or water temp is INCREASED the reaction is ____ aka you setting time and working time is ____

1
2.5
3.5
18-24

dustless

accelerated
decreased

30

Alginates - Properties
Handling
! Effect of ____ ratio
! Effect of water ____

! Environmental temp
! Retardation of die stone

Too much ____ is weak impression material. Use the right measuring cylinder for the right properties.

____ is a colloid material and will affect the setting of the gypsum

water/powder
temperature
water
alginate

31

Biological Properties

! Dust from alginate
– ____ and carcinogenesis
– Use dustless alginate coated with ____
– Disinfection (same as ____)

fibrogenesis
glycol
agar-agar

32

Properties of Hydrocolloids

These tear strength values are very ____ compared to other impression materials

Reproduction limit
Agar: ____
Algin: ____

low
25
75

33

Storage of Impressions
____% Rel. humidity No more than ____ mins

Same as ____

100
30
agar-agar