lecture 7- impression materials and tech Flashcards by Madyson Flax

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

alginate

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alginate is ___based and

water based

irreversible when water is added

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softens under heat and solidifies when cooled

reversable hydrocolloid

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chemical reaction that cannot revert to preset state

irreversible hydrocolloid

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

reversable hydrocolloid

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

irreversible hydrocolloid

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

hydrophilic

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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

colloidal materials

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

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

sol to gel

agar: temp change
alginate: chemical rxn

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3 properties related to gel network

evaporation (shrinkage)
syneresis: get relaxation; water extruded from gel (shrinkage)
imbibition: absorption of water causing expansion

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this reacts with calcium ions and is the powder

Na alginate (or potassium alginate)

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

calcium alginate

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powder to liquid rato is used. add what first?

avoid incorporating what into mix?

water first

avoid mixing in air

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

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

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what is alginate mixing time

45-60 seconds

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

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what is the thickness of alginate should be

3mm in tray

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

60 mins with yellow stone

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CDC recommend _____ dilution of household
bleach for disinfection

1:10 ratio

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

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

storage temp and moisture

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

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

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

one hour

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What is a Dental Impression for
Fixed Prosthodontics?

analogue impression

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-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

analogue impression

method and manner used in making a negative likeness

impression technique

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

impression tray

What do we look for in a dental impression?

-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

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

1. facial/buccal 2. 2 -3 mm 3. 2 -3 mm

Tray must be sufficiently rigid to:

* 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

* Plastic or metal; perforated or rimmed * Complete arch, quadrant, or dual arch * Dentate or edentulous arch

stock trays

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

custom trays

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

adhesive

provides chemical adhesion

adhesive

adhesive materials: 1 2 3

* Specific for each material; including Alginate * Should always be used * Apply and dry

what is the goal of impression technique for single crown

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

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

* Evaluate arch form * Anatomical landmarks * Musculature * Hard and soft tissue anomalies * Restorative space

The material selected is dependent on the type of

impression required for the procedure

tissue retraction for impression technique of single crown

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

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

4-6 mins gently and straight as possible

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

nnonelastic

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

elastic

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

nonelastic/rigid

Elastic Materials examples

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

* Water is the major component * Hydrocolloid * Reversable and irreversible * Reversable is not commonly used today

aqueous elastomeric (hydrocolloids) (elastic)

* Polysulfide * Vinyl Polysiloxane (silicone) * Polyether

none-aqueous elastomeric (polymers) (elastic)

ability of liquid to flow over a solid surface

wettability

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

energy= solid tension= liquid

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

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

non-aqueous elastomers provide: 1 2 3 4

1. accuracy 2. dimensional stability 3. tear resistance 4. viscoelasticity

Ability to replicate the intra-oral surface details

accuracy

Ability to retain its absolute dimensional size over time

dimensional stability

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

tear resistance

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

viscoelasticity

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

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

Elastic polymers: come into different consistencies;

light medium heavy and putty

3 elastic polymers

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

non-aqueous elastomers chemical setting reaction:

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

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

non aqueous elastomeric

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

poor tear resistance and poor dimensional stability

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

polysulfide

polysulfide requires this type of tray and negatives of it:

custom tray longer setting time, smells and stains

polysulfide base:

polysulfide polymer mixed with inert fillers

polysulfide catalyst

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

Elastomeric Impression material we use now

vinyl polysiloxane

vinyl polysiloxane uses special what: and provided as an _____unit, syringe, and mixing tips

special tray adhesive auto-mix unit

overtime this happens with vinyl polysiloxane

shrinkage

vinyl polysiloxane is (more/less) flexible

more so more chance for distoration

Best dimensional stability among impression materials (addition silicon)

vinyl polysiloxane

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

vinyl polysiloxane

vinyl polysiloxane composition of addition______

silicon

base of vinyl polysiloxane:

Poly Dimethyl Siloxane

catalyst of vinyl polysiloxane

Polyvinyl siloxane - Platinum salt

Vinyl Polysiloxane: addition reaction, NO____

by-product

vinyl polysiloxane auto-mix:

-uniform mixing -less air -less mixing time

vinyl polysiloxane hydrophobic:

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

in vinyl polysiloxane, sulfur inhibits the polymerization so

later gloves retards the setting

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

vinyl polysiloxane

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

* 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

polyether

Need to block out undercuts more stiff than VPS which elastomeric impression material

polyether

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

polyether

in polyether, when removing impression,

break the seal and rock slightly to prevent tearing

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

polyether

polyether composition base catalyst cross-linking agent

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

polyether is addition reaction (with/without) by product

without (no)

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

polyether

The preferred elastomeric impression materials on the market are

PVS and PE

known for their hydrophilic properties and good flowability

polyethers

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

pvs

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

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

voids unacceptable caused by

lifting intra-oral tip while syringing or presence of moisture

tacky unset VPS material in the rep area cause:

early removal or Sulfur contamination from gloves

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

VPS better to rinse and spray impression

Potential expansion with increased exposure time for

PS and PE

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

tissue retraction

tissue retraction techniques

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

classification of retraction cords

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

chemo-mechanical technique:

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

double vs single cord technique

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

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

4 mins

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

digital scan